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Sample records for magnetic anisotropy induced

  1. Origin of magnetization-induced anisotropy of magnetic films

    Institute of Scientific and Technical Information of China (English)

    Jin Han-Min; Chong-Oh Kim; Taek-Dong Lee; Hyo-Jin Kim

    2007-01-01

    It is proposed that the magnetization-induced anisotropy of magnetic films of cubic crystal structure originates from the anisotropy of atomic pair ordering, shape anisotropy, and strain anisotropy resulting from the constraint of the magnetostriction strain imposed on the film by the substrate. Calculated are the three anisotropy constants and their sum K vs temperature for Ni, Fe, and 55%Ni-Fe films; the room temperature (RT) constants vs the substrate temperature Tt during deposition or annealing after deposition for Ni and 50%Ni-Co films; the RT constants vs composition fraction for Fe-Ni films with Tt = RT, 250℃ and 450℃, Co-Ni films at Tt = RT, 100℃ and 320℃, and Fe-Co films with Tt = RT and 300℃; the spread of RT K vs composition fraction for Fe-Ni films; and RT △K/K vs composition fraction for Fe-Ni and Co-Ni films, where △K denotes the variation of K of the film that is detached from its substrate. The calculated curves well accord with the measurements. The irrelevancy of K to the substrate material and the fast kinetics of the annealing in a field applied in the direction of the hard axis are explained reasonably.The anisotropies of Fe and Ni films originate mainly from the shape anisotropy and the strain anisotropy, respectively. The major anisotropy component in many cases depends not only on composition fraction but also on Tt . For example, the RT anisotropy of 40-70%Ni-Fe films, when Tt is RT, mostly comes from the anisotropy of atomic pair ordering while it stems mostly from the shape anisotropy when Tt is 450 ℃. The most important cause of the spread in values of K is the spread of the intrinsic anisotropic stresses superimposed on the intrinsic isotropic planar stress. It is suggested that the field cooling induced magnetic anisotropy originating from the induced crystal texture observed in the bulk alloys is also a major origin for Co and Co-rich alloy films of hexagonal crystal structure.

  2. Growth Induced Magnetic Anisotropy in Crystalline and Amorphous Thin Films

    Energy Technology Data Exchange (ETDEWEB)

    Hellman, Frances

    1998-10-03

    OAK B204 Growth Induced Magnetic Anisotropy in Crystalline and Amorphous Thin Films. The work in the past 6 months has involved three areas of magnetic thin films: (1) amorphous rare earth-transition metal alloys, (2) epitaxial Co-Pt and hTi-Pt alloy thin films, and (3) collaborative work on heat capacity measurements of magnetic thin films, including nanoparticles and CMR materials.

  3. Selective-resputtering-induced perpendicular magnetic anisotropy in amorphous TbFe films.

    Science.gov (United States)

    Harris, V G; Pokhil, T

    2001-08-06

    Perpendicular magnetic anisotropy energy in rf magnetron sputtered amorphous TbFe films is measured to increase exponentially with pair-order anisotropy induced by the selective resputtering of surface adatoms during film growth.

  4. Anisotropy of magnetic susceptibility of rocks induced by experimental deformation

    Directory of Open Access Journals (Sweden)

    J. Zhou

    1997-06-01

    Full Text Available In the present paper, the influence of the rheological process on the Anisotropy of Magnetic Susceptibility (AMS of rocks is studied experimentally. The cylindrical samples of quartz-magnetite rock undergo a process under the confining stress of 300 MPa, temperature of 500-800 °C and strain rate of 5 ´ 10-5 - 1 ´ 10-4/s. The residual deformation after the above process ranges 9-42%, depending on the experimental condition. It is found that the magnetic susceptibilities and the shapes of magnetic grains in these samples are almost isotropic before deformation. After being deformed, these samples show certain amounts of anisotropy of magnetic susceptibility and the axes of maximum principal susceptibilities deviate from the original ones more or less. Furthermore, the grains become oblate-ellipsoidal and a certain preferred orientation occurs. The grain shape anisotropy seems to be the main reason for AMS formation. It appears that there is a limitation of the piezomagnetic theory in explaining some tectonomagnetic phenomena. The results obtained in this study imply that ductile deformation at high temperature and pressure in depth during a long time-process may result in another kind of response in rock magnetism, which could be a new mechanism of tectonomagnetic variation.

  5. Magnetic anisotropy in Fe-25Cr-12Co-1Si alloy induced by external magnetic field

    Institute of Scientific and Technical Information of China (English)

    ZHEN Liang; SUN Xue-yin; XU Cheng-yan; GAO Run-sheng; XU Ren-gen; QIN Lu-chang

    2007-01-01

    Structural and magnetic properties of Fe-25Cr-12Co-1Si alloy thermo-magnetically treated under different external magnetic field conditions were investigated. Orientation and morphology of the ferromagnetic α1 phase embedded in α2 phase matrix before and after step ageing are characterized by transmission electron microscope(TEM). The results show that the ellipsoidal particles of ferromagnetic α1 phase are aligned along the direction of external magnetic field during isothermal magnetic ageing. Approximately 28% of the total coercivity can be attributed to the shape anisotropy of α1 phase particles induced by external magnetic field for Fe-25Cr-12Co-1Si alloy thermo-magnetically treated with a parallel magnetic field.

  6. Cap-Induced Magnetic Anisotropy in Ultra-thin Fe/MgO(001) Films

    Science.gov (United States)

    Brown-Heft, Tobias; Pendharkar, Mihir; Lee, Elizabeth; Palmstrom, Chris

    Magnetic anisotropy plays an important role in the design of spintronic devices. Perpendicular magnetic anisotropy (PMA) is preferred for magnetic tunnel junctions because the resulting energy barrier between magnetization states can be very high and this allows enhanced device scalability suitable for magnetic random access memory applications. Interface induced anisotropy is often used to control magnetic easy axes. For example, the Fe/MgO(001) system has been predicted to exhibit PMA in the ultrathin Fe limit. We have used in-situ magneto optic Kerr effect and ex-situ SQUID to study the changes in anisotropy constants between bare Fe/MgO(001) films and those capped with MgO, Pt, and Ta. In some cases in-plane anisotropy terms reverse sign after capping. We also observe transitions from superparamagnetic to ferromagnetic behavior induced by capping layers. Perpendicular anisotropy is observed for Pt/Fe/MgO(001) films after annealing to 300°C. These effects are characterized and incorporated into a magnetic simulation that accurately reproduces the behavior of the films. This work was supported in part by the Semiconductor Research Corporation programs (1) MSR-Intel, and (2) C-SPIN.

  7. Controlling the induced anisotropy in soft magnetic films for high-frequency applications

    NARCIS (Netherlands)

    Chezan, A.R.; Craus, C.B.; Chechenin, N.G.; Vystavel, T.; Hosson, J.Th.M. De; Niesen, L.; Boerma, D.O.

    2002-01-01

    Nanocrystalline soft magnetic Fe–Zr–N films were successfully deposited by dc magnetron reactive sputtering. The nitrogen content was controlled by varying the Ar/N2 ratio and/or the substrate temperature. The films have saturation magnetization and induced uniaxial anisotropy values in the range 17

  8. Texture induced magnetic anisotropy in Fe3O4 films

    Science.gov (United States)

    Liu, Er; Huang, Zhaocong; Zheng, Jian-Guo; Yue, Jinjin; Chen, Leyi; Wu, Xiumei; Sui, Yunxia; Zhai, Ya; Tang, Shaolong; Du, Jun; Zhai, Hongru

    2015-10-01

    This letter reports a free energy density model for textured films in which the related physical concept and expression of magneto-texture anisotropy energy are presented. The structural characterization and out-of-plane angular dependence ferromagnetic resonance of strongly textured Fe3O4 films were systematically investigated. We found that the typical free energy density model for polycrystalline film cannot be applied to the textured films. With the introduction of magneto-texture anisotropy energy in the free energy density model for thin films, we simulated and quantitatively determined the competing anisotropies in (111)-textured Fe3O4 films.

  9. AFM research on the mechanism of Fe-based alloy stress annealed inducing magnetic anisotropy

    Institute of Scientific and Technical Information of China (English)

    FANG YunZhang; ZHENG JinJu; SHI FangYe; WU FengMin; SUN HuaiJun; LIN GenJin; YANG XiaoHong; MAN QiKui; YE FangMin

    2008-01-01

    The cross-section of the Fe-based alloy (Fe73.5Cu1Nb3Si13.5B9) ribbon annealed at 540℃ under various tensile stress was investigated with atomic force microscope (AFM). The stress effect mechanism in Fe-based alloy ribbon tensile stress an- nealed inducing transverse magnetic anisotropy field was studied using the X-ray diffraction spectra and longitudinal drive giant magneto-impedance effect curves, and the model of direction dominant in encapsulated grain agglomeration was es- tablished. The relationship between the direction dominant in encapsulated grain agglomeration and magnetic anisotropy field was disclosed.

  10. AFM research on the mechanism of Fe-based alloy stress annealed inducing magnetic anisotropy

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The cross-section of the Fe-based alloy (Fe73.5Cu1Nb3Si13.5B9) ribbon annealed at 540℃ under various tensile stress was investigated with atomic force microscope (AFM). The stress effect mechanism in Fe-based alloy ribbon tensile stress an-nealed inducing transverse magnetic anisotropy field was studied using the X-ray diffraction spectra and longitudinal drive giant magneto-impedance effect curves, and the model of direction dominant in encapsulated grain agglomeration was es-tablished. The relationship between the direction dominant in encapsulated grain agglomeration and magnetic anisotropy field was disclosed.

  11. Photo-Induced Magnetic Anisotropy of Polymer Film Containing Azobenzene Organic Free Radical Group

    Institute of Scientific and Technical Information of China (English)

    徐则达; 张勇; 陈小芳; 范星河; 宛新华; 周其凤

    2003-01-01

    The forward degenerate four-wave mixing geometry was employed to induce microstructure in an organic free radical azobenzene polymer film. Before irradiated with Ar+ laser beams (λ = 514.5 nm), the azobenzene organic free radical polymer exhibits magnetic isotropic measured by superconducting quantum interference device. After photo-induced microstructure, the polymer film becomes magnetic anisotropy. When the applied magnetic field H = 50 Gauss, the magnetization along the normal direction of the polymer film is Mz = 5.5 × 10-5 emu/g,which is larger than Mx = 4.1 × 10-5 emu/g in the direction parallel to the polymer film.

  12. Modification of magnetic anisotropy induced by swift heavy ion irradiation in cobalt ferrite thin films

    Energy Technology Data Exchange (ETDEWEB)

    Nongjai, Razia [Department of Applied Physics, Zakir Hussain College of Engineering & Technology, A.M.U., Aligarh 202002 (India); Khan, Shakeel, E-mail: skhanapad@gmail.com [Department of Applied Physics, Zakir Hussain College of Engineering & Technology, A.M.U., Aligarh 202002 (India); Ahmed, Hilal; Khan, Imran [Department of Applied Physics, Zakir Hussain College of Engineering & Technology, A.M.U., Aligarh 202002 (India); Annapoorni, S. [Department of Physics and Astrophysics, University of Delhi, Delhi 110007 (India); Gautam, Sanjeev [Advanced Analysis Center, Korea Institute of Science and Technology (KIST), Seoul 136-791 (Korea, Republic of); Lin, Hong-Ji; Chang, Fan-Hsiu [National Synchrotron Radiation Research Center (NSRRC), Hsinchu 30076, Taiwan (China); Hwa Chae, Keun [Advanced Analysis Center, Korea Institute of Science and Technology (KIST), Seoul 136-791 (Korea, Republic of); Asokan, K. [Material Science Division, Inter University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110067 (India)

    2015-11-15

    The present study demonstrates the modification of magnetic anisotropy in cobalt ferrite (CoFe{sub 2}O{sub 4}) thin films induced by swift heavy ion irradiations of 200 MeV Ag-ion beams. The study reveals that both magnetizations and coercive field are sensitive to Ag-ions irradiation and to the fluences. The magnetic anisotropy enhanced at low fluence of Ag-ions due to domain wall pinning at defect sites created by ion bombardment and at high fluence, this magnetic anisotropy ceases and changes to isotropic behavior which is explained based on the significant structural and morphological changes. An X-ray absorption and x-ray magnetic circular dichroism studies confirms the inverse spinel structure of these compounds. - Highlights: • CoFe{sub 2}O{sub 4} thin films have been deposited on Silicon substrate by pulsed laser deposition technique. • Swift heavy ion irradiation of thin films at three different fluences. • Studied the structural and magnetic properties of the samples. • XRD and Raman studies indicate strain in the films. • Observed perpendicular magnetic anisotropy.

  13. Anisotropy of remanent and induced magnetization in hematite ore deformed in torsion

    Science.gov (United States)

    Machek, Matěj; Petrovský, Eduard; Roxerová, Zuzana; Kusbach, Vladimír; Siemes, Heinrich

    2016-04-01

    Induced and remanent magnetization measurements, e.g. shape of hysteresis loops, FORC diagrams and decomposition of isothermal remanent magnetization (IRM) acquisition curves, became routine tools in rock-magnetic measurements, interpreted mostly in terms of composition and grain-size distribution of iron oxides. It is assumed that the substances investigate are with respect to these measurements isotropic and single measurement of one sample is sufficient for interpretation. This assumption is valid for powdered samples, but solid rock samples in general behave anisotropically. In our contribution we report on magnetic measurements of hematite ore samples deformed in torsion, which show significant anisotropy of shape of hysteresis loops and IRM acquisition curves; the degree of anisotropy reflecting the degree of deformation. Samples, measured in different directions, showed different shape of hysteresis loop, from regular, which may be interpreted either as randomly oriented multi-domain grains, or with different degree of distortion (wasp-waistedness), reflecting different distribution of contrasting coercivities. Also decomposition of IRM acquisition curves, measured in different direction, yielded different interpretation in terms of relative contributions of components with different coercivities. The increasing strain is reflected in the strength and orientation of microstructure and crystallographic preferred orientation (CPO). The AMS in deformed samples is not controlled by hematite CPO. It is rather dominated by occurrence of magnetite grains along samples edges parallel to shear plane, probably due to the diffusion of Fe ions from iron jacket, even though samples were shielded by a silver (70)/palladium (30) sleeve of 0.5 mm thickness. We interpret this anisotropy as result of deformation, causing preferred orientation of basal planes of hematite. Moreover, the anisotropy is asymmetric. Our results suggest that, at least in deformed rocks containing

  14. Growth induced magnetic anisotropy in crystalline and amorphous thin films

    Energy Technology Data Exchange (ETDEWEB)

    Hellman, F.

    1998-07-20

    The work in the past 6 months has involved three areas of magnetic thin films: (1) amorphous rare earth-transition metal alloys, (2) epitaxial Co-Pt and Ni-Pt alloy thin films, and (3) collaborative work on heat capacity measurements of magnetic thin films, including nanoparticles and CMR materials. A brief summary of work done in each area is given.

  15. X-ray analysis of oxygen-induced perpendicular magnetic anisotropy in Pt/Co/AlO{sub x} trilayers

    Energy Technology Data Exchange (ETDEWEB)

    Manchon, A. [SPINTEC, URA 2512 CEA/CNRS, CEA/Grenoble, 38054 Grenoble Cedex 9 (France)], E-mail: aurelien.manchon@m4x.org; Pizzini, S.; Vogel, J.; Uhlir, V. [Institut Neel, CNRS/UJF, B.P. 166, 38042 Grenoble Cedex 9 (France); Lombard, L.; Ducruet, C.; Auffret, S.; Rodmacq, B.; Dieny, B. [SPINTEC, URA 2512 CEA/CNRS, CEA/Grenoble, 38054 Grenoble Cedex 9 (France); Hochstrasser, M. [Laboratory for Solid State Physics, ETH Zuerich, 8093 Zuerich (Switzerland); Panaccione, G. [Laboratory TASC, INFM-CNR, Area Science Park, S.S.14, Km 163.5, I-34012, Trieste (Italy)

    2008-07-15

    X-ray spectroscopy measurements have been performed on a series of Pt/Co/AlO{sub x} trilayers to investigate the role of Co oxidation in the perpendicular magnetic anisotropy of the Co/AlO{sub x} interface. It is observed that high temperature annealing modifies the magnetic properties of the Co layer, inducing an enhancement of the perpendicular magnetic anisotropy. The microscopic structural properties are analyzed via X-ray Absorption Spectroscopy, X-ray Magnetic Circular Dichroism and X-ray Photoelectron Spectroscopy measurements. It is shown that annealing enhances the amount of interfacial oxide, which may be at the origin of a strong perpendicular magnetic anisotropy.

  16. The anisotropy of the surface tension at the magnetic-field-induced phase transformations

    CERN Document Server

    Cebers, A

    2002-01-01

    The surface properties of the magnetic colloid phases arising at the magnetic-field-induced phase separation in the Hele-Shaw cell are considered. By the numerical resolution of the equation for the concentration distribution in the transition layer between the phases, the anisotropy of the surface tension is calculated. The anisotropic shapes of the droplets of the concentrated phase are found by the Wulff construction and are compared with that obtained by the numerical simulation of the kinetics of the magnetic colloid phase separation in the Hele-Shaw cell.

  17. Current induced domain wall motion in nanostripes with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Noh, Su Jung; Tan, Reasmey P.; Chun, Byong Sun [Department of Materials Science and Engineering, Korea University, Seoul 136-713 (Korea, Republic of); Kim, Young Keun, E-mail: ykim97@korea.ac.k [Department of Materials Science and Engineering, Korea University, Seoul 136-713 (Korea, Republic of)

    2010-11-15

    We report micromagnetic modeling results of current induced domain wall (DW) motion in magnetic devices with perpendicular magnetic anisotropy by solving the Landau-Lifschitz-Gilbert equation including adiabatic and non-adiabatic terms. A nanostripe model system with dimensions of 500 nm (L)x25 nm (W)x5 nm (H) was selected for calculating the DW motion and its width, as a function of various parameters such as non-adiabatic contribution, anisotropy constant (K{sub u}), saturation magnetization (M{sub s}), and temperature (T). The DW velocity was found to increase when the values of K{sub u} and T were increased and the M{sub s} value decreased. In addition, a reduction of the domain wall width could be achieved by increasing K{sub u} and lowering M{sub s} values regardless of the non-adiabatic constant value.

  18. Inducing magnetic anisotropy and optimized microstructure in rapidly solidified Nd-Fe-B based magnets by thermal gradient, magnetic field and hot deformation

    Science.gov (United States)

    Zhao, L. Z.; Li, W.; Wu, X. H.; Hussain, M.; Liu, Z. W.; Zhang, G. Q.; Greneche, J. M.

    2016-10-01

    Direct preparation of Nd-Fe-B alloys by rapid solidification of copper mold casting is a very simple and low cost process for mini-magnets, but these magnets are generally magnetically isotropic. In this work, high coercivity Nd24Co20Fe41B11Al4 rods were produced by injection casting. To induce magnetic anisotropy, temperature gradient, assisted magnetic field, and hot deformation (HD) procedures were employed. As-cast samples showed non-uniform microstructure due to the melt convection. The thermal gradient during solidification led to the formation of radially distributed acicular hard magnetic grains, which gives the magnetic anisotropy. The growth of the oriented grains was confirmed by phase field simulation. A magnetic field up to 1 T applied along the casting direction could not induce significant magnetic anisotropy, but it improved the magnetic properties by reducing the non-uniformity and forming a uniform microstructure. The annealed alloys exhibited high intrinsic coercivity but disappeared anisotropy. HD was demonstrated to be a good approach for inducing magnetic anisotropy and enhanced coercivity by deforming and refining the grains. This work provides an alternative approach for preparing fully dense Nd-rich anisotropic bulk Nd-Fe-B magnets.

  19. Ion irradiation induced enhancement of out-of-plane magnetic anisotropy in ultrathin Co films

    Energy Technology Data Exchange (ETDEWEB)

    Mazalski, P.; Kurant, Z.; Maziewski, A. [Faculty of Physics, University of Bialystok, Bialystok (Poland); Liedke, M. O.; Fassbender, J. [Helmholtz-Zentrum Dresden-Rossendorf, Dresden (Germany); Baczewski, L. T.; Wawro, A. [Institute of Physics, Polish Academy of Science, Warszawa (Poland)

    2013-05-07

    Ga{sup +} or He{sup +} irradiated MBE grown ultrathin films of sapphire/Pt/Co(d{sub Co})/Pt(d{sub Pt}) were studied using polar Kerr effect in wide ranges of both cobalt d{sub Co} and platinum d{sub Pt} thicknesses as well as ion fluences F. Two branches of increased magnetic anisotropy and enhanced Kerr rotation angle induced by Ga{sup +} or He{sup +} irradiation are clearly visible in two-dimensional (d{sub Co}, LogF) diagrams. Only Ga{sup +} irradiation induces two branches of out-of-plane magnetization state.

  20. Stress induced anisotropy in CoFeMn soft magnetic nanocomposites

    Energy Technology Data Exchange (ETDEWEB)

    Leary, A. M., E-mail: leary@cmu.edu; Keylin, V.; McHenry, M. E. [Materials Science and Engineering Department, Carnegie Mellon University, 5000 Forbes Ave., Pittsburgh, Pennsylvania 15213 (United States); Ohodnicki, P. R. [Functional Materials Development Division, National Energy Technology Laboratory (NETL), 626 Cochrans Mill Road, Pittsburgh, Pennsylvania 15236 (United States)

    2015-05-07

    The use of processing techniques to create magnetic anisotropy in soft magnetic materials is a well-known method to control permeability and losses. In nanocomposite materials, field annealing below the Curie temperature results in uniaxial anisotropy energies up to ∼2 kJ/m{sup 3}. Higher anisotropies up to ∼10 kJ/m{sup 3} result after annealing Fe-Si compositions under stress due to residual stress in the amorphous matrix acting on body centered cubic crystals. This work describes near zero magnetostriction Co{sub 80−x−y}Fe{sub x}Mn{sub y}Nb{sub 4}B{sub 14}Si{sub 2} soft magnetic nanocomposites, where x and y < 8 at.% with close packed crystalline grains that show stress induced anisotropies up to ∼50 kJ/m{sup 3} and improved mechanical properties with respect to Fe-Si compositions. Difference patterns measured using transmission X-ray diffraction show evidence of affine strain with respect to the stress axis.

  1. Stress induced anisotropy in CoFeMn soft magnetic nanocomposites

    Energy Technology Data Exchange (ETDEWEB)

    Leary, AM; Keylin, V; Ohodnicki, PR; McHenry, ME

    2015-05-07

    The use of processing techniques to create magnetic anisotropy in soft magnetic materials is a well-known method to control permeability and losses. In nanocomposite materials, field annealing below the Curie temperature results in uniaxial anisotropy energies up to similar to 2 kJ/m(3). Higher anisotropies up to similar to 10 kJ/m(3) result after annealing Fe-Si compositions under stress due to residual stress in the amorphous matrix acting on body centered cubic crystals. This work describes near zero magnetostriction Co80-x-yFexMnyNb4B14Si2 soft magnetic nanocomposites, where x and y < 8 at. % with close packed crystalline grains that show stress induced anisotropies up to similar to 50 kJ/m(3) and improved mechanical properties with respect to Fe-Si compositions. Difference patterns measured using transmission X-ray diffraction show evidence of affine strain with respect to the stress axis. (C) 2015 AIP Publishing LLC.

  2. Crucial role of interlayer distance for antiferromagnet-induced perpendicular magnetic anisotropy

    Science.gov (United States)

    Wang, Bo-Yao; Lin, Po-Han; Tsai, Ming-Shian; Shih, Chun-Wei; Lee, Meng-Ju; Huang, Chun-Wei; Jih, Nae-Yeou; Cheng, Pei-Yu; Wei, Der-Hsin

    2015-12-01

    Antiferromagnetic (AFM) thin films were recently proposed to be an alternative to conventional materials for achieving perpendicular magnetic anisotropy (PMA) in ferromagnetic thin films, because AFM thin films exhibit an advantage of flexible control. Here, we report that antiferromagnet-induced PMA is highly sensitive to interfacial moments of AFM thin films as well as the magnetic interaction of such moments with volume moments, determined according to the vertical interlayer distance. Magnetic hysteresis loops and x-ray magnetic domain imaging revealed the establishment of perpendicular magnetization on face-centered tetragonal (fct)-like Mn/Co/Ni films when covered with monolayered Mn films. A cover of Mn films that exhibit contracted fct- [vertical-to-in-plane lattice constant ratio (c /a )=0.95 ] and expanded fct-like (c /a =1.05 ) structures at different thickness levels induced in-plane magnetic anisotropy and PMA in Co/Ni films, respectively, confirming that the interlayer distance is a crucial parameter for establishing perpendicular magnetization.

  3. Binary information propagation in circular magnetic nanodot arrays using strain induced magnetic anisotropy

    Science.gov (United States)

    Salehi-Fashami, M.; Al-Rashid, M.; Sun, Wei-Yang; Nordeen, P.; Bandyopadhyay, S.; Chavez, A. C.; Carman, G. P.; Atulasimha, J.

    2016-10-01

    Nanomagnetic logic has emerged as a potential replacement for traditional Complementary Metal Oxide Semiconductor (CMOS) based logic because of superior energy-efficiency (Salahuddin and Datta 2007 Appl. Phys. Lett. 90 093503, Cowburn and Welland 2000 Science 287 1466-68). One implementation of nanomagnetic logic employs shape-anisotropic (e.g. elliptical) ferromagnets (with two stable magnetization orientations) as binary switches that rely on dipole-dipole interaction to communicate binary information (Cowburn and Welland 2000 Science 287 1466-8, Csaba et al 2002 IEEE Trans. Nanotechnol. 1 209-13, Carlton et al 2008 Nano Lett. 8 4173-8, Atulasimha and Bandyopadhyay 2010 Appl. Phys. Lett. 97 173105, Roy et al 2011 Appl. Phys. Lett. 99 063108, Fashami et al 2011 Nanotechnology 22 155201, Tiercelin et al 2011 Appl. Phys. Lett. 99 , Alam et al 2010 IEEE Trans. Nanotechnol. 9 348-51 and Bhowmik et al 2013 Nat. Nanotechnol. 9 59-63). Normally, circular nanomagnets are incompatible with this approach since they lack distinct stable in-plane magnetization orientations to encode bits. However, circular magnetoelastic nanomagnets can be made bi-stable with a voltage induced anisotropic strain, which provides two significant advantages for nanomagnetic logic applications. First, the shape-anisotropy energy barrier is eliminated which reduces the amount of energy required to reorient the magnetization. Second, the in-plane size can be reduced (˜20 nm) which was previously not possible due to thermal stability issues. In circular magnetoelastic nanomagnets, a voltage induced strain stabilizes the magnetization even at this size overcoming the thermal stability issue. In this paper, we analytically demonstrate the feasibility of a binary ‘logic wire’ implemented with an array of circular nanomagnets that are clocked with voltage-induced strain applied by an underlying piezoelectric substrate. This leads to an energy-efficient logic paradigm orders of magnitude superior to

  4. Current induced perpendicular-magnetic-anisotropy racetrack memory with magnetic field assistance

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Y.; Klein, J.-O.; Chappert, C.; Ravelosona, D. [IEF, University of Paris-Sud, Orsay 91405 (France); UMR8622, CNRS, Orsay 91405 (France); Zhao, W. S., E-mail: weisheng.zhao@u-psud.fr [IEF, University of Paris-Sud, Orsay 91405 (France); UMR8622, CNRS, Orsay 91405 (France); Electronics and Information Engineering School, University of Beihang, Beijing 100191 (China)

    2014-01-20

    High current density is indispensable to shift domain walls (DWs) in magnetic nanowires, which limits the using of racetrack memory (RM) for low power and high density purposes. In this paper, we present perpendicular-magnetic-anisotropy (PMA) Co/Ni RM with global magnetic field assistance, which lowers the current density for DW motion. By using a compact model of PMA RM and 40 nm design kit, we perform mixed simulation to validate the functionality of this structure and analyze its density potential. Stochastic DW motion behavior has been taken into account and statistical Monte-Carlo simulations are carried out to evaluate its reliability performance.

  5. Enhancement of electric-field-induced change of magnetic anisotropy by interface engineering of MgO magnetic tunnel junctions

    Science.gov (United States)

    Bonaedy, Taufik; Choi, Jun Woo; Jang, Chaun; Min, Byoung-Chul; Chang, Joonyeon

    2015-06-01

    Electric-field-induced modification of magnetic anisotropy is studied using tunnel magnetoresistance of the Co40Fe40B20/ MgO/ Co40Fe40B20 and Co40Fe40B20/ Hf (0.08 nm)/ MgO/ Co40Fe40B20 magnetic tunnel junctions. In both systems, the interfacial perpendicular magnetic anisotropy is increased with increasing electron density at the MgO interface. A quantitative comparison between the two systems reveals that the change of magnetic anisotropy energy with electric field is significantly enhanced in Co40Fe40B20/ Hf/ MgO/ Co40Fe40B20 compared to Co40Fe40B20/ MgO/ Co40Fe40B20. The sub-monolayer Hf insertion at the Co40Fe40B20/MgO interface turns out to be critical to the enhanced electric field control of the magnetic anisotropy, indicating the interface sensitive nature of the effect.

  6. Perpendicular Magnetic Anisotropy and Induced Magnetic Structures of Pt Layers in the Fe/Pt Multilayers Investigated by Resonant X-ray Magnetic Scattering

    Science.gov (United States)

    Lee, Mihee; Takechi, Ryota; Hosoito, Nobuyoshi

    2017-02-01

    Depth distribution of the magnetization induced in the paramagnetic Pt layers of Fe/Pt multilayers was investigated by resonant X-ray magnetic scattering (RXMS) near the Pt L3 absorption edge. Two samples with different perpendicular magnetic anisotropy (PMA) were chosen for RXMS measurements. The magnetic depth profile of the Pt layer was determined in the magnetic saturation state of the Fe magnetization with the sample of weak PMA. The magnetization process of the Pt layer was investigated with the sample of moderate PMA. It is found that the Pt atoms near the interface region have a perpendicular component of the induced magnetization even in the saturation state of the Fe magnetization, suggesting that the PMA of Fe/Pt multilayers originates from the Pt atoms near the interface region. Concerning the magnetization process, the induced Pt magnetization is not proportional to the Fe magnetization. This implies a complicated magnetizing mechanism of the Pt layer by the Fe magnetization.

  7. Growth-induced magnetic anisotropy and clustering in vapor-deposited Co-Pt alloy films

    Energy Technology Data Exchange (ETDEWEB)

    Shapiro, A.L.; Rooney, P.W.; Tran, M.Q.; Hellman, F. [Department of Physics, University of California--San Diego, La Jolla, California 92093 (United States); Ring, K.M.; Kavanagh, K.L. [Department of Electrical and Computer Engineering, University of California--San Diego, La Jolla, California 92093 (United States); Rellinghaus, B.; Weller, D. [IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120 (United States)

    1999-11-01

    Polycrystalline and epitaxial (100)-, (110)-, and (111)-oriented CoPt{sub 3} and Co{sub 0.35}Pt{sub 0.65} films were deposited at various growth rates and over a range of growth temperatures from {minus}50 to 800&hthinsp;{degree}C. Films grown at moderate temperatures (200{endash}400&hthinsp;{degree}C) exhibit remarkable growth-induced properties: perpendicular magnetic anisotropy and large coercivity, as well as enhanced Curie temperature and low-temperature saturation magnetization. Magnetic measurements indicate significant Co clustering in these epitaxial fcc films. These properties are independent of crystallographic orientation, increase with increasing growth temperature, and vanish with annealing. We propose that the correlation between magnetic inhomogeneity, magnetic anisotropy, and enhanced moment is explained by clustering of Co into thin platelets in a Pt-rich lattice. This clustering occurs at the growth surface and is trapped into the growing film by low bulk atomic mobility. {copyright} {ital 1999} {ital The American Physical Society}

  8. Uniaxial magnetic anisotropy induced low field anomalous anisotropic magnetoresistance in manganite thin films

    Directory of Open Access Journals (Sweden)

    Zhaoliang Liao

    2014-09-01

    Full Text Available La2/3Sr1/3MnO3 films with uniaxial magnetic anisotropy were coherently grown on NdGaO3 (110 substrates. The uniaxial anisotropy has strong effect on magnetoresistance (MR. A positive MR was observed when the current is along magnetic easy axis under the current-field perpendicular geometry. In contrast, no positive MR is observed when current is along the magnetic hard axis regardless of the field direction. Our analysis indicates that the anomalous anisotropic MR effect arises from the uniaxial magnetic anisotropy caused stripe domains which contribute to strong anisotropic domain wall resistivity.

  9. DC bias immune nanocrystalline magnetic cores made of Fe73Nb3Cu1B7Si16 ribbon with induced transverse magnetic anisotropy

    Science.gov (United States)

    Nosenko, Anton; Rudenko, Olexandr; Mika, Taras; Yevlash, Igor; Semyrga, Olexandr; Nosenko, Viktor

    2016-02-01

    The comparative analysis of magnetic properties of cut cores made of nanocrystalline Fe73Nb3Cu1B7Si16 alloy ribbon and cores made of the same ribbon with preliminary tension-induced transverse magnetic anisotropy was carried out. The possibility of improving magnetic properties of cut cores, decreasing loss, and increasing DC bias immunity of reversible magnetic permeability is presented. The influence of induced magnetic anisotropy on DC bias immunity of reversible magnetic permeability was investigated. The advantages and disadvantages of new cores (made of ribbon heated under tensile stress) over cut ones were determined.

  10. DC bias immune nanocrystalline magnetic cores made of Fe73Nb3Cu1B7Si16 ribbon with induced transverse magnetic anisotropy.

    Science.gov (United States)

    Nosenko, Anton; Rudenko, Olexandr; Mika, Taras; Yevlash, Igor; Semyrga, Olexandr; Nosenko, Viktor

    2016-12-01

    The comparative analysis of magnetic properties of cut cores made of nanocrystalline Fe73Nb3Cu1B7Si16 alloy ribbon and cores made of the same ribbon with preliminary tension-induced transverse magnetic anisotropy was carried out. The possibility of improving magnetic properties of cut cores, decreasing loss, and increasing DC bias immunity of reversible magnetic permeability is presented. The influence of induced magnetic anisotropy on DC bias immunity of reversible magnetic permeability was investigated. The advantages and disadvantages of new cores (made of ribbon heated under tensile stress) over cut ones were determined.

  11. Perpendicular magnetic anisotropy induced by tetragonal distortion of FeCo alloy films grown on Pd(001).

    Science.gov (United States)

    Winkelmann, Aimo; Przybylski, Marek; Luo, Feng; Shi, Yisheng; Barthel, Jochen

    2006-06-30

    We grew tetragonally distorted FexCo1-x alloy films on Pd(001). Theoretical first-principles calculations for such films predicted a high saturation magnetization and a high uniaxial magnetic anisotropy energy for specific values of the lattice distortion c/a and the alloy composition x. The magnetic anisotropy was investigated using the magneto-optical Kerr effect. An out-of-plane easy axis of magnetization was observed for Fe0.5Co0.5 films in the thickness range of 4 to 14 monolayers. The magnetic anisotropy energy induced by the tetragonal distortion is estimated to be almost 2 orders of magnitude larger than the value for bulk FeCo alloys. Using LEED Kikuchi patterns, a change of the easy axis of magnetization can be related to a decrease of the tetragonal distortion with thickness.

  12. Effect of induced shape anisotropy on magnetic properties of ferromagnetic cobalt nanocubes.

    Science.gov (United States)

    Srikala, D; Singh, V N; Banerjee, A; Mehta, B R

    2010-12-01

    We report on the synthesis of ferromagnetic cobalt nanocubes of various sizes using thermal pyrolysis method and the effect of shape anisotropy on the static and dynamic magnetic properties were studied. Shape anisotropy of approximately 10% was introduced in nanocubes by making nanodiscs using a linear chain amine surfactant during synthesis process. It has been observed that, ferromagnetism persisted above room temperature and a sharp drop in magnetic moment at low temperatures in zero-field cooled magnetization may be associated with the spin disorder due to the effective anisotropy present in the system. Dynamic magnetic properties were studied using RF transverse susceptibility measurements at different temperatures and the singularities due to anisotropy fields were probed at low temperatures. Symmetrically located broad peaks are observed in the frozen state at the effective anisotropy fields and the peak structure is strongly affected by shape anisotropy and temperature. Irrespective of size the shape anisotropy gave rise to higher coercive fields and larger transverse susceptibility ratio at all temperatures. The role of shape anisotropy and the size of the particles on the observed magnetic behaviour were discussed.

  13. Combined effect of demagnetizing field and induced magnetic anisotropy on the magnetic properties of manganese-zinc ferrite composites

    Energy Technology Data Exchange (ETDEWEB)

    Babayan, V. [Centre of Polymer Systems, Polymer Centre, Tomas Bata University in Zlin, nam T. G. Masaryka 5555, 760 01 Zlin (Czech Republic); Kazantseva, N.E., E-mail: nekazan@yahoo.com [Centre of Polymer Systems, Polymer Centre, Tomas Bata University in Zlin, nam T. G. Masaryka 5555, 760 01 Zlin (Czech Republic); Moucka, R. [Centre of Polymer Systems, Polymer Centre, Tomas Bata University in Zlin, nam T. G. Masaryka 5555, 760 01 Zlin (Czech Republic); Sapurina, I. [Institute of Macromolecular Compounds, Russian Academy of Sciences, 199004 St. Petersburg (Russian Federation); Spivak, Yu.M.; Moshnikov, V.A. [St. Petersburg Electrotechnical University ' LETI' , 197376 St. Petersburg (Russian Federation)

    2012-01-15

    This work is devoted to the analysis of factors responsible for the high-frequency shift of the complex permeability ({mu}*) dispersion region in polymer composites of manganese-zinc (MnZn) ferrite, as well as to the increase in their thermomagnetic stability. The magnetic spectra of the ferrite and its composites with polyurethane (MnZn-PU) and polyaniline (MnZn-PANI) are measured in the frequency range from 1 MHz to 3 GHz in a longitudinal magnetization field of up to 700 Oe and in the temperature interval from -20 {sup o}S to +150 {sup o}S. The approximation of the magnetic spectra by a model, which takes into account the role of domain wall motion and magnetization rotation, allows one to determine the specific contribution of resonance processes associated with domain wall motion and the natural ferromagnetic resonance to the {mu}*. It is established that, at high frequencies, the {mu}* of the MnZn ferrite is determined solely by magnetization rotation, which occurs in the region of natural ferromagnetic resonance when the ferrite is in the 'single domain' state. In the polymer composites of the MnZn ferrite, the high-frequency permeability is also determined mainly by the magnetization rotation; however, up to high values of magnetizing fields, there is a contribution of domain wall motion, thus the 'single domain' state in ferrite is not reached. The frequency and temperature dependence of {mu}* in polymer composites are governed by demagnetizing field and the induced magnetic anisotropy. The contribution of the induced magnetic anisotropy is crucial for MnZn-PANI. It is attributed to the elastic stresses that arise due to the domain wall pinning by a polyaniline film adsorbed on the surface of the ferrite during in-situ polymerization. - Highlights: > Polyaniline (PANI) coating significantly changes magnetic properties of MnZn ferrite. > Coated ferrite exhibits higher coercivity, thermomagnetic stability, and resonance frequency shifts

  14. Combined effect of demagnetizing field and induced magnetic anisotropy on the magnetic properties of manganese-zinc ferrite composites

    Science.gov (United States)

    Babayan, V.; Kazantseva, N. E.; Moučka, R.; Sapurina, I.; Spivak, Yu. M.; Moshnikov, V. A.

    2012-01-01

    This work is devoted to the analysis of factors responsible for the high-frequency shift of the complex permeability (μ*) dispersion region in polymer composites of manganese-zinc (MnZn) ferrite, as well as to the increase in their thermomagnetic stability. The magnetic spectra of the ferrite and its composites with polyurethane (MnZn-PU) and polyaniline (MnZn-PANI) are measured in the frequency range from 1 MHz to 3 GHz in a longitudinal magnetization field of up to 700 Ое and in the temperature interval from -20 °С to +150 °С. The approximation of the magnetic spectra by a model, which takes into account the role of domain wall motion and magnetization rotation, allows one to determine the specific contribution of resonance processes associated with domain wall motion and the natural ferromagnetic resonance to the μ*. It is established that, at high frequencies, the μ* of the MnZn ferrite is determined solely by magnetization rotation, which occurs in the region of natural ferromagnetic resonance when the ferrite is in the “single domain” state. In the polymer composites of the MnZn ferrite, the high-frequency permeability is also determined mainly by the magnetization rotation; however, up to high values of magnetizing fields, there is a contribution of domain wall motion, thus the “single domain” state in ferrite is not reached. The frequency and temperature dependence of μ* in polymer composites are governed by demagnetizing field and the induced magnetic anisotropy. The contribution of the induced magnetic anisotropy is crucial for MnZn-PANI. It is attributed to the elastic stresses that arise due to the domain wall pinning by a polyaniline film adsorbed on the surface of the ferrite during in-situ polymerization.

  15. Magnetic anisotropy in nanostructures

    CERN Document Server

    Eisenbach, M

    2001-01-01

    method for solving the LDA Kohn-Sham equation. This extended code allows us to perform fully relativistic calculations to enable us to investigate the spin orbit coupling effects leading to anisotropies and potentially non collinear ordering of magnetic moments in these systems of magnetic inclusions in copper. With this approach we find that depending on the orientation of the atoms along the 100 or 110 direction in copper the ground state orientation of the magnetic moments in the chain is either perpendicular or parallel to the chain direction, when the magnetic dipolar interaction energy is added to the final ab initio result. In this thesis we investigate the effect of magnetic anisotropies in nanostructured materials. The main emphasis in our work presented here is on systems that have an underlying one dimensional structure, like nanowires or atomic chains. In a simple classical one dimensional model we show the rich ground state structure of magnetic orientations one might expect to find in such syste...

  16. Magnetic-anisotropy-induced spin blockade in a single-molecule transistor

    Science.gov (United States)

    Luo, Guangpu; Park, Kyungwha

    2016-11-01

    We present a mechanism for a spin blockade effect associated with a change in the type of magnetic anisotropy over oxidation state in a single molecule transistor, by taking an example of an individual Eu2(C8H8)3 molecule weakly coupled to nonmagnetic electrodes without linker groups. The molecule switches its magnetization direction from in-plane to out-of-plane when it is charged. In other words, the magnetic anisotropy of the molecule changes from easy plane to easy axis when the molecule is charged. By solving the master equation based on a model Hamiltonian, we find that current through the molecule is highly suppressed at low bias independently of gate voltage due to the interplay between spin selection rules and the change in the type of magnetic anisotropy. Transitions between the lowest magnetic levels in successive charge states are forbidden because the magnetic levels differ by |Δ M |>1 /2 due to the change in the type of magnetic anisotropy, although the total spins differ by |Δ S |=1 /2 . This current suppression can be lifted by significant B field, and the threshold B field varies as a function of the field direction and the strength of magnetic anisotropy. The spin blockade effect sheds light on switching the magnetization direction by non-spin-polarized current and on exploring effects of this property coupled to other molecular degrees of freedom.

  17. Effect of induced shape anisotropy on magnetic properties of ferromagnetic cobalt nanocubes

    OpenAIRE

    Srikala, D.; Singh, V. N.; Banerjee, A.; Mehta, B. R.

    2010-01-01

    We report on the synthesis of ferromagnetic cobalt nanocubes of various sizes using thermal pyrolysis method and the effect of shape anisotropy on the static and dynamic magnetic properties were studied. Shape anisotropy of approximately 10 % was introduced in nanocubes by making nanodiscs using a linear chain amine surfactant during synthesis process. It has been observed that, ferromagnetism persisted above room temperature and a sharp drop in magnetic moment at low temperatures in zero-fie...

  18. Shape-induced ultrahigh magnetic anisotropy and ferromagnetic resonance frequency of micropatterned thin Permalloy films

    NARCIS (Netherlands)

    Zhuang, Y.; Vroubel, M.; Rejaei, B.; Burghartz, J.N.; Attenborough, K.

    2006-01-01

    Magnetic anisotropy Hk>200 Oe was observed from bar-shaped Permalloy strips. The film was deposited on sputtered Cr seed layer by electroplating under ∼ 800 Oe external magnetic field. Tiny degradation of Hk was observed after 30 min postannealing at 400 °C in the absence of external magnetic field.

  19. Inner Core Anisotropy Due to the Magnetic Field--induced Preferred Orientation of Iron.

    Science.gov (United States)

    Karato, S

    1993-12-10

    Anisotropy of the inner core of the Earth is proposed to result from the lattice preferred orientation of anisotropic iron crystals during their solidification in the presence of a magnetic field. The resultant seismic anisotropy is related to the geometry of the magnetic field in the core. This hypothesis implies that the observed anisotropy (fast velocity along the rotation axis) indicates a strong toroidal field in the core, which supports a strong field model for the geodynamo if the inner core is made of hexagonal close-packed iron.

  20. Antiferromagnet-induced perpendicular magnetic anisotropy in ferromagnetic/antiferromagnetic/ferromagnetic trilayers

    Science.gov (United States)

    Wang, Bo-Yao; Lin, Po-Han; Tsai, Ming-Shian; Shih, Chun-Wei; Lee, Meng-Ju; Huang, Chun-Wei; Jih, Nae-Yeou; Wei, Der-Hsin

    2016-08-01

    This study demonstrates the effect of antiferromagnet-induced perpendicular magnetic anisotropy (PMA) on ferromagnetic/antiferromagnetic/ferromagnetic (FM/AFM/FM) trilayers and reveals its interplay with a long-range interlayer coupling between separated FM layers. In epitaxially grown 12 monolayer (ML) Ni/Co/Mn/5 ML Co/Cu(001) films, magnetic hysteresis loops and element-resolved magnetic domain imaging showed that the magnetization direction of the top layers of 12 ML Ni/Co films could be changed from the in-plane direction to the perpendicular direction, when the thickness of the Mn films (tMn) was greater than a critical value close to the thickness threshold associated with the onset of AFM ordering (tMn=3.5 ML). The top FM layers exhibited a significantly enhanced PMA when tMn increased further, and this enhancement can be attributed to a strengthened AFM ordering of the volume moments of the Mn films, as evidenced by the presence of induced domain frustration. By contrast, the long-range interlayer coupling presented clear effects only when tMn was at a lower coverage.

  1. Gauge-Origin Independent Calculations of the Anisotropy of the Magnetically Induced Current Densities.

    Science.gov (United States)

    Fliegl, Heike; Jusélius, Jonas; Sundholm, Dage

    2016-07-21

    Gauge-origin independent current density susceptibility tensors have been computed using the gauge-including magnetically induced current (GIMIC) method. The anisotropy of the magnetically induced current density (ACID) functions constructed from the current density susceptibility tensors are therefore gauge-origin independent. The ability of the gauge-origin independent ACID function to provide quantitative information about the current flow along chemical bonds has been assessed by integrating the cross-section area of the ACID function in the middle of chemical bonds. Analogously, the current strength susceptibility passing a given plane through the molecule is obtained by numerical integration of the current flow parallel to the normal vector of the integration plane. The cross-section area of the ACID function is found to be strongly dependent on the exact location of the integration plane, which is in sheer contrast to the calculated ring-current strength susceptibilities that are practically independent of the chosen position of the integration plane. The gauge-origin independent ACID functions plotted for different isosurface values show that a visual assessment of the current flow and degree of aromaticity depends on the chosen isosurface. The present study shows that ACID functions are not an unambiguous means to estimate the degree of molecular aromaticity according to the magnetic criterion and to determine the current pathway of complex molecular rings.

  2. Dependence of Memory Effects of Induced Magnetic Anisotropy on Pressure and Possibility of Using These Effects in Industry

    Science.gov (United States)

    Vechfinskii, V. S.; Remizov, A. E.

    2016-05-01

    This paper examines the dependence of memory effects of induced magnetic anisotropy (IMA) on pressure. The authors suggest an empirical formula for this dependence and analyze the possibility of using IMA properties in aviation industry, particularly in wear control of gas turbine engines.

  3. Study of the magnetic anisotropy induced in CoFeSiB amorphous ribbons by solidification in a magnetic field using giant magnetoimpedance measurements

    Energy Technology Data Exchange (ETDEWEB)

    Garcia, J.A. [Departmento de Fisica, Universidad de Oviedo, Calvo Sotelo s/n, 33007, Oviedo (Spain); Saad, A. [Departmento de Fisica, Universidad de Oviedo, Calvo Sotelo s/n, 33007, Oviedo (Spain) and Laboratorio de Solidos Amorfos, Departmento de Fisica, Facultad de Ingenieria, Universidad de Buenos Aires, Paseo de Colon 850, C10063ACV Capital Federal (Argentina)]. E-mail: asaad@fi.uba.ar; Garcia-Arribas, A. [Departemento de Electricidad y Electronica, Universidad del Pais Vasco, Apartado 644, 48080 Bilbao (Spain); Santos, J.D. [Departmento de Fisica, Universidad de Oviedo, Calvo Sotelo s/n, 33007, Oviedo (Spain); Elbaile, L. [Departmento de Fisica, Universidad de Oviedo, Calvo Sotelo s/n, 33007, Oviedo (Spain); Tejedor, M. [Departmento de Fisica, Universidad de Oviedo, Calvo Sotelo s/n, 33007, Oviedo (Spain)

    2004-12-31

    Magnetoimpedance effect was used as a tool to investigate the effectiveness of the method to induce magnetic anisotropy by applying a DC magnetic field during the melt spinning process in amorphous magnetic ribbons. Amorphous ribbons of composition Co{sub 69}Fe{sub 4}Si{sub 15}B{sub 12} were melt spun with and without applying the DC field in order to compare the results. From the different magnetoimpedance response to the external field in both kinds of ribbons, the induced magnetic anisotropy can be studied. Magnetoimpedance demonstrates to be a fine instrument to detect small changes of magnetic anisotropy and it is a good method to be employed in very narrow ribbons where other techniques are ineffective or unfeasible.

  4. Giant magnetoimpedance effect in melt-spun Co-based amorphous ribbons and wires with induced magnetic anisotropy

    Science.gov (United States)

    Tiberto, P.; Vinai, F.; Rampado, O.; Chiriac, H.; Ovari, T. A.

    1999-05-01

    GMI in Co 68.25Fe 4.5Si 12.25B 15 melt-spun amorphous wires and ribbons has been studied. Selected samples have been submitted to DC Joule-heating to induce circular and transverse magnetic anisotropy. Hysteresis loops have been measured using a fluxmetric technique. The results were interpreted in terms of circumferential and transverse permeability correlated with the magnetic domain structure.

  5. Magnetic anisotropy induced by crystallographic orientation and morphological alignment in directionally-solidified eutectic Mn-Sb alloy

    Science.gov (United States)

    Lou, Chang-Sheng; Liu, Tie; Dong, Meng; Wu, Chun; Shao, Jian-Guo; Wang, Qiang

    2017-02-01

    The influences of the crystallographic orientation and morphological alignment upon the magnetic anisotropic behavior of polycrystalline materials were investigated. Microstructures obtained in eutectic Mn-Sb alloys via directional solidification simultaneously displayed crystallographic orientation and morphological alignment. Both the crystallographic orientation and the morphological alignment were able to induce magnetic anisotropy in the alloys, wherein the influence of the crystallographic orientation and the morphological alignment upon the magnetic anisotropic behavior of the alloys strongly depended upon their directions and exhibited either mutual promotion or competition. These findings may provide useful guidance for the fabrication design of functional magnetic materials.

  6. Large Voltage-Induced Changes in the Perpendicular Magnetic Anisotropy of an MgO-Based Tunnel Junction with an Ultrathin Fe Layer

    Science.gov (United States)

    Nozaki, Takayuki; Kozioł-Rachwał, Anna; Skowroński, Witold; Zayets, Vadym; Shiota, Yoichi; Tamaru, Shingo; Kubota, Hitoshi; Fukushima, Akio; Yuasa, Shinji; Suzuki, Yoshishige

    2016-04-01

    We study the voltage control of perpendicular magnetic anisotropy in an ultrathin Fe layer sandwiched between the Cr buffer and MgO tunneling barrier layers. A high-interface magnetic anisotropy energy of 2.1 mJ /m2 is achieved in the Cr/ultrathin Fe /MgO structure. A large voltage-induced perpendicular magnetic anisotropy change is observed under the negative-bias voltage applications for the case of the Fe layer thinner than 0.6 nm. The amplitude of the voltage-induced anisotropy energy change exhibits a strong Fe-thickness dependence and it reaches as high as 290 fJ /Vm . The observed high values of the surface anisotropy and voltage-induced anisotropy energy change demonstrate the feasibility of voltage-driven spintronic devices.

  7. Field-induced slow magnetic relaxation in a six-coordinate mononuclear cobalt(II) complex with a positive anisotropy.

    Science.gov (United States)

    Vallejo, Julia; Castro, Isabel; Ruiz-García, Rafael; Cano, Joan; Julve, Miguel; Lloret, Francesc; De Munno, Giovanni; Wernsdorfer, Wolfgang; Pardo, Emilio

    2012-09-26

    The novel mononuclear Co(II) complex cis-[Co(II)(dmphen)(2)(NCS)(2)]·0.25EtOH (1) (dmphen = 2,9-dimethyl-1,10-phenanthroline) features a highly rhombically distorted octahedral environment that is responsible for the strong positive axial and rhombic magnetic anisotropy of the high-spin Co(II) ion (D = +98 cm(-1) and E = +8.4 cm(-1)). Slow magnetic relaxation effects were observed for 1 in the presence of a dc magnetic field, constituting the first example of field-induced single-molecule magnet behavior in a mononuclear six-coordinate Co(II) complex with a transverse anisotropy energy barrier.

  8. Spin–orbit torque induced magnetization switching in Pt/Co/Ta structures with perpendicular magnetic anisotropy

    Science.gov (United States)

    Yun, Jijun; Li, Dong; Cui, Baoshan; Guo, Xiaobin; Wu, Kai; Zhang, Xu; Wang, Yupei; Zuo, Yalu; Xi, Li

    2017-10-01

    Spin–orbit torque (SOT) induced magnetization switching is investigated in Pt/Co/Ta stacks with perpendicular magnetic anisotropy with the variation of the thickness of Ta layer (t Ta). SOT is characterized by an effective spin Hall angle θ SH, which is determined by an anomalous Hall resistance measurements method based on a macrospin model. A high charge current induced magnetization switching efficiency is achieved by the enhanced injection efficiency of spin currents from bottom Pt and top Ta with opposite signs of θ SH. When t Ta  =  4 nm, the enhanced effective θ SH for Pt/Co/Ta shows a maximum value around 0.356, which is larger than the sum of |θ SH| for Pt and Ta and is ascribed to an additional interfacial SOT at Co/Ta interface. θ SH gradually decreases with increasing Ta layer thickness beyond 4 nm, which can be explained by the improved crystallinity of Ta layer. Our results confirm a way to decrease the switching current density in SOT-based spintronic devices.

  9. Determination of the electric field induced anisotropy change in sub-100 nm perpendicularly magnetized devices

    Directory of Open Access Journals (Sweden)

    Jiancheng Huang

    2016-05-01

    Full Text Available We measure the voltage or electric field (EF modulated change in anisotropy using two methods on the same nanometer sized device: 1 Directly using the area of the hard axis magnetization loop and 2 Indirectly using the switching field distribution method. Both methods yield similar values of efficiency. With the indirect method, the efficiency derived from the thermal stability was found to be more consistent than that from the anisotropy field. Our data also suggests that memory devices that rely solely on EF effects may benefit from larger device sizes.

  10. Magnetic thermal stability of permalloy microstructures with shape-induced bi-axial anisotropy

    Science.gov (United States)

    Telepinsky, Yevgeniy; Sinwani, Omer; Mor, Vladislav; Schultz, Moty; Klein, Lior

    2016-02-01

    We study the thermal stability of the magnetization states in permalloy microstructures in the form of two crossing elongated ellipses, a shape which yields effective bi-axial magnetic anisotropy in the overlap area. We prepare the structure with the magnetization along one of the easy axes of magnetization and measure the waiting time for switching when a magnetic field favoring the other easy axis is applied. The waiting time for switching is measured as a function of the applied magnetic field and temperature. We determine the energy barrier for switching and estimate the thermal stability of the structures. The experimental results are compared with numerical simulations. The results indicate exceptional stability which makes such structures appealing for a variety of applications including magnetic random access memory based on the planar Hall effect.

  11. Thermally induced perpendicular magnetic anisotropy in CoFeB/MgO/CoFeB based magnetic tunnel junction

    Science.gov (United States)

    Kulkarni, Prabhanjan D.; Khan, Jakeer; Predeep, P.; Chowdhury, P.

    2016-05-01

    Thin films of CoFeB/MgO/CoFeB based MTJ structure were deposited using UHV magnetron sputtering system and post annealing treatment in the temperature range from 100 to 400 °C has been carried out to understand their magnetic anisotropic properties. Though the as-deposited stack possesses in-plane magnetic anisotropy, the changeover to perpendicular magnetic anisotropy happens at temperature above 200 °C. The PMA is maximum (4.5 x 106 erg/cm3) when annealed at 300°C and the stack retains PMA till 350 °C, which is necessary in CMOS technology. The stack regains in-plane magnetic anisotropy at higher annealing temperatures due to intermixing at interfaces.

  12. Modification of perpendicular magnetic anisotropy and domain wall velocity in Pt/Co/Pt by voltage-induced strain.

    Science.gov (United States)

    Shepley, P M; Rushforth, A W; Wang, M; Burnell, G; Moore, T A

    2015-01-21

    The perpendicular magnetic anisotropy K(eff), magnetization reversal, and field-driven domain wall velocity in the creep regime are modified in Pt/Co(0.85-1.0 nm)/Pt thin films by strain applied via piezoelectric transducers. K(eff), measured by the extraordinary Hall effect, is reduced by 10 kJ/m(3) by tensile strain out-of-plane ε(z) = 9 × 10(-4), independently of the film thickness, indicating a dominant volume contribution to the magnetostriction. The same strain reduces the coercive field by 2-4 Oe, and increases the domain wall velocity measured by wide-field Kerr microscopy by 30-100%, with larger changes observed for thicker Co layers. We consider how strain-induced changes in the perpendicular magnetic anisotropy can modify the coercive field and domain wall velocity.

  13. Growth induced magnetic anisotropy in amorphous thin films. Annual progress report year 1, November 4, 1994--October 31, 1995

    Energy Technology Data Exchange (ETDEWEB)

    Hellman, F. [Univ. of California, San Diego, La Jolla, CA (United States). Dept. of Physics

    1995-07-01

    The work in the past year has primarily involved three areas of magnetic thin films: amorphous rare earth-transition metal alloys, epitaxial COPt3 thin films, and exchange coupled antiferromagnetic insulators. In the amorphous alloys, the authors have focused on understanding the cause and the effect of the growth-surface-induced perpendicular magnetic anisotropy. Using the results of previous work, they are able to control this anisotropy quite precisely. This anisotropy is predicted to have dramatic and as-yet unobserved effects on the underlying nature of the magnetism. The work on the epitaxial Co-Pt alloys was originally undertaken as a comparison study to the amorphous alloys. The authors have discovered that these alloys exhibit a remarkable new phenomena; a surface-induced miscibility gap in a material which is believed to be completely miscible in the bulk. This miscibility gap is 100% correlated with the perpendicular anisotropy, although the connection is not yet clear, and is presumably linked to a magnetic energy of mixing which tends to drive a material towards clustering. The problem of exchange coupling in multilayers impacts many of the current research areas in magnetism. NiO/CoO multilayers can be prepared with coherent interfaces. The specific heat shows unambiguously the ordering of the spins in the layers. The results show clearly the transition from a single transition temperature to two distinct transitions with increasing thickness of the individual layers. From this data, the authors are able to determine the interface magnetic exchange coupling constant and the effect on the transition temperature of finite layer thickness.

  14. Magnetic field-induced gluonic (inverse) catalysis and pressure (an)isotropy in QCD

    CERN Document Server

    Bali, G S; Endrodi, G; Gruber, F; Schaefer, A

    2013-01-01

    We study the influence of strong external magnetic fields on gluonic and fermionic observables in the QCD vacuum at zero and nonzero temperatures, via lattice simulations with N_f=1+1+1 staggered quarks of physical masses. The gluonic action density is found to undergo magnetic catalysis at low temperatures and inverse magnetic catalysis near and above the transition temperature, similar to the quark condensate. Moreover, the gluonic action develops an anisotropy: the chromo-magnetic field parallel to the external field is enhanced, while the chromo-electric field in this direction is suppressed. We demonstrate that the same hierarchy is obtained using the Euler-Heisenberg effective action. Conversely, the topological charge density correlator does not reveal a significant anisotropy up to magnetic fields eB~1 GeV^2. Furthermore, we show that the pressure remains isotropic even for nonzero magnetic fields, if it is defined through a compression of the system at fixed external field. In contrast, if the flux o...

  15. On the Driving Forces of Magnetically Induced Martensitic Transformation in Directionally Solidified Polycrystalline Ni-Mn-In Meta-Magnetic Shape Memory Alloy with Structural Anisotropy

    Science.gov (United States)

    Hu, Qiaodan; Zhou, Zhenni; Yang, Liang; Huang, Yujin; Li, Jun; Li, Jianguo

    2017-08-01

    The magnetic anisotropy energy (MAE) in the ferromagnetic shape memory alloys (FSMAs) provides the driving forces to obtain large magnetic field induced strain (MFIS) by rearranging the martensitic variants. However, to date, no significant MAE was observed in the new class of Ni-Mn-Z (Z = In, Sn, Sb) metamagnetic shape memory alloys (MSMAs). Here, we report a significant magnetic anisotropy in Ni48Mn35In17 Heusler alloy with a [110]A fiber texture prepared by the directional solidification. In this case, when the applied magnetic field is along the [110]A direction, a larger magnetization change is obtained compared with that of the randomly oriented samples, which increases the driving forces for the magnetically induced martensitic transformation (MIMT). In contrast, along the [110]A direction, the magnetocaloric effect (MCE) is enhanced by 60 pct, the MFIS is improved by 20 pct, and the critical field for the MFIS is reduced by 0.5 T. Such a peculiar magnetic behavior could be well explained by a proposed model on the viewpoint of the transformation of ferromagnetic austenite phase. Furthermore, considering the thermodynamics aspects, we demonstrate that two main magnetic energies of the Zeeman energy and the MAE in the MSMAs assist each other to promote the MIMT, instead of opposing each other in the FSMAs. This discovery of the strong magnetic anisotropy in highly textured polycrystals provides a feasible route to enhance the MIMT, and new insights to design and prepare the Ni-Mn-based Heusler alloys for practical applications.

  16. Induced magnetic anisotropy in Si-free nanocrystalline soft magnetic materials: A transmission x-ray diffraction study

    Energy Technology Data Exchange (ETDEWEB)

    Parsons, R., E-mail: rparsons01@gmail.com; Suzuki, K. [Department of Materials Science and Engineering, Monash University, Clayton, Victoria 3800 (Australia); Yanai, T. [Graduate School of Engineering, Nagasaki University, Nagasaki 852-8521 (Japan); Kishimoto, H.; Kato, A. [Toyota Motor Corporation, Mishuku, Susono, Shizuoka 410-1193 (Japan); Ohnuma, M. [Faculty and Graduate School of Engineering, Hokkaido University, Sapporo 060-8628 (Japan)

    2015-05-07

    In order to better understand the origin of field-induced anisotropy (K{sub u}) in Si-free nanocrystalline soft magnetic alloys, the lattice spacing of the bcc-Fe phase in nanocrystalline Fe{sub 94−x}Nb{sub 6}B{sub x} (x = 10, 12, 14) alloys annealed under an applied magnetic field has been investigated by X-ray diffraction in transmission geometry (t-XRD) with the diffraction vector parallel and perpendicular to the field direction. The saturation magnetostriction (λ{sub s}) of nanocrystalline Fe{sub 94−x}Nb{sub 6}B{sub x} was found to increase linearly with the volume fraction of the residual amorphous phase and is well described by taking into account the volume-weighted average of two local λ{sub s} values for the bcc-Fe nanocrystallites (−5 ± 2 ppm) and the residual amorphous matrix (+8 ± 2 ppm). The lattice distortion required to produce the measured K{sub u} values (∼100 J/m{sup 3}) was estimated via the inverse magnetostrictive effect using the measured λ{sub s} values and was compared to the lattice spacing estimations made by t-XRD. The lattice strain required to produce K{sub u} under the magnetoelastic model was not observed by the t-XRD experiments and so the findings of this study suggest that the origin of magnetic field induced K{sub u} cannot be explained through the magnetoelastic effect.

  17. Ga+ ion irradiation-induced changes in magnetic anisotropy of a Pt/Co/Pt thin film studied by X-ray magnetic circular dichroism

    Directory of Open Access Journals (Sweden)

    Liedke M. O.

    2013-01-01

    Full Text Available Ga+ ion irradiation-induced changes in magnetic anisotropy of a Pt/Co/Pt ultrathin film are investigated by means of the X-ray magnetic circular dichroism (XMCD technique. A large difference in the Co orbital moment is observed between out-of-plane and in-plane directions of the film at moderate Ga+ fluences of ~1-2×1014 ions/cm2, which corresponds to the perpendicular magnetic anisotropy (PMA, while further increased fluences reduce the orbital moment difference, resulting in in-plane magnetization. In contrast, at much higher Ga+ fluences of ~5×1015 ions/cm2, at which PMA is observed again, no significant difference is found in the orbital moment of Co between out-of-plane and in-plane directions. Different origins are thus suggested for the appearance of PMA induced by the irradiation between moderate and high Ga+ fluences.

  18. Electric polarization induced by transverse magnetic field in the anisotropy-controlled conical helimagnet Ba2(Mg1-xZnx)2Fe12O22

    Science.gov (United States)

    Ishiwata, S.; Taguchi, Y.; Tokunaga, Y.; Murakawa, H.; Onose, Y.; Tokura, Y.

    2009-05-01

    Microscopic origin of magnetic-field (B) induced electric polarization (P) potentially up to near room temperature has been investigated for helimagnets Ba2(Mg1-xZnx)2Fe12O22 with controlled magnetic anisotropy by revealing B - and x -dependent changes of magnetoelectric responses. As Zn concentration (x) increases, the B -induced P rapidly diminishes, accompanying the change in the magnetic-easy surface from conical to planar. Possible spin structures are proposed to explain the observed B dependence of P in terms of the spin-current model. The results indicate the important role of magnetic anisotropy in the B -induced ferroelectric state of this class of helimagnets.

  19. Interdiffusion in epitaxial ultrathin Co2FeAl/MgO heterostructures with interface-induced perpendicular magnetic anisotropy

    Science.gov (United States)

    Wen, Zhenchao; Hadorn, Jason Paul; Okabayashi, Jun; Sukegawa, Hiroaki; Ohkubo, Tadakatsu; Inomata, Koichiro; Mitani, Seiji; Hono, Kazuhiro

    2017-01-01

    The interfacial atomic structure of epitaxial ultrathin Co2FeAl/MgO(001) heterostructures, which is related to the interface-induced perpendicular magnetic anisotropy (PMA), was investigated using scanning transmission electron microscopy, energy dispersive X-ray spectroscopy, and X-ray magnetic circular dichroism. Al atoms from the Co2FeAl layer significantly interdiffused into MgO, forming an Al-deficient Co-Fe-Al/Mg-Al-O structure near the Co2FeAl/MgO interface. This atomic replacement may have enhanced the PMA, which is consistent with the observed large perpendicular orbital magnetic moments of Fe atoms at the interface. This work suggests that control of interdiffusion at ferromagnet/barrier interfaces is critical for designing an interface-induced PMA system.

  20. Pressure-Induced Enhanced Magnetic Anisotropy in Mn(N(CN)2)2

    Energy Technology Data Exchange (ETDEWEB)

    Quintero, P. A. [University of Florida, Gainesville; Rajan, D. [University of Florida, Gainesville; Peprah, M. K. [University of Florida, Gainesville; Brinzari, T. V. [University of Florida, Gainesville; Fishman, Randy Scott [ORNL; Talham, Daniel R. [University of Florida, Gainesville; Meisel, Mark W. [University of Florida, Gainesville

    2015-01-01

    Using DC and AC magnetometry, the pressure dependence of the magnetization of the threedimensional antiferromagnetic coordination polymer Mn(N(CN)2)2 was studied up to 12 kbar and down to 8 K. The magnetic transition temperature, Tc, increases dramatically with applied pressure (P), where a change from Tc(P = ambient) = 16:0 K to Tc(P = 12:1 kbar) = 23:5 K was observed. In addition, a marked difference in the magnetic behavior is observed above and below 7.1 kbar. Specifically, for P < 7:1 kbar, the differences between the field-cooled and zero-field-cooled (fc-zfc) magnetizations, the coercive field, and the remanent magnetization decrease with increasing pressure. However, for P > 7:1 kbar, the behavior is inverted. Additionally, for P > 8:6 kbar, minor hysteresis loops are observed. All of these effects are evidence of the increase of the superexchange interaction and the appearance of an enhanced exchange anisotropy with applied pressure.

  1. Current-induced spin-orbit torque magnetization switching in a MnGa/Pt film with a perpendicular magnetic anisotropy

    Science.gov (United States)

    Ranjbar, Reza; Suzuki, Kazuya Z.; Sasaki, Yuta; Bainsla, Lakhan; Mizukami, Shigemi

    2016-12-01

    Current-induced magnetization switching is demonstrated in a micron sized Hall bar consisting of Pt-capped ultrathin ferrimagnetic MnGa films. The films showed a low magnetization M s ≃ 150 kA/m and a large perpendicular magnetic anisotropy (PMA) field μ 0HK\\text{eff} ≃ 2.5 T, indicating a PMA thickness t product K\\text{u}\\text{eff}t ≃ 0.47 mJ/m2, which is relatively larger than those reported for other material films with PMA. Magnetization switching induced by an in-plane electrical current was examined with the application of an in-plane magnetic field. The phase diagram of the switching current vs the in-plane magnetic field is qualitatively consistent with that of the torque due to the spin-Hall effect in the Pt layer.

  2. Competing magnetic anisotropies in obliquely deposited thin permalloy film

    Energy Technology Data Exchange (ETDEWEB)

    Belyaev, B.A. [Siberian Federal University, 79, pr. Svobodnyi, Krasnoyarsk 660041 (Russian Federation); Kirensky Institute of Physics, Siberian Branch of the Russian Academy of Sciences, 50/38, Akademgorodok, Krasnoyarsk 660036 (Russian Federation); Reshetnev Siberian State Aerospace University, 31, pr. Imeni Gazety “Krasnoyarskii Rabochii”, Krasnoyarsk 660014 (Russian Federation); Izotov, A.V. [Siberian Federal University, 79, pr. Svobodnyi, Krasnoyarsk 660041 (Russian Federation); Kirensky Institute of Physics, Siberian Branch of the Russian Academy of Sciences, 50/38, Akademgorodok, Krasnoyarsk 660036 (Russian Federation); Solovev, P.N., E-mail: platon.solovev@gmail.com [Siberian Federal University, 79, pr. Svobodnyi, Krasnoyarsk 660041 (Russian Federation)

    2016-01-15

    Distribution of the magnetic anisotropy in thin film prepared by thermal vacuum oblique deposition of permalloy with small off-normal angle of incident in the presence of an external magnetic field has been studied by ferromagnetic resonance technique. On local area of the sample, a mutual compensation of near orthogonal in-plane uniaxial magnetic anisotropies induced by oblique deposition and by applied magnetic field has been found. Moreover, in addition to the uniaxial (twofold) magnetic anisotropy, fourfold and sixfold magnetic anisotropies have been observed in the sample. To explain the obtained high-order anisotropies, we assumed that the sample has exchange coupled adjacent regions or phases with different parameters of magnetic anisotropy. The results of the micromagnetic analysis of a two-layer model of the sample confirm the hypothesis.

  3. Growth of perpendicularly magnetized thin films on a polymer buffer and voltage-induced change of magnetic anisotropy at the MgO|CoFeB interface

    Directory of Open Access Journals (Sweden)

    D. D. Lam

    2015-06-01

    Full Text Available We show that perpendicularly magnetized thin films can be grown onto polyimide, a potentially flexible substrate. With polar Kerr magnetometry, we demonstrate that the coercive field of CoFeB thin film can be modulated by applying a back gate voltage. Our proposed multi-layered structure is suitable for surface-sensitive measurements of the voltage-induced change in anisotropy, and could be used to realize flexible spintronics devices.

  4. Magnetic anisotropy and porosity of Antarctic chondrites

    OpenAIRE

    Hamano,Yozo/Yomogida,Kiyoshi

    1982-01-01

    Magnetic susceptibility anisotropy and porosity were measured in eleven Antarctic meteorites. These meteorites are ordinary chondrites (H and L type) in various metamorphic stages. Large magnetic anisotropy has been observed in most of the chondrites. The foliation type of the anisotropy, inferred from the shape of the susceptibility ellipsoid indicates that a uniaxial compressional type deformation is responsible for the anisotropy. The degree of the anisotropy and the porosity do not correl...

  5. In-plane current induced domain wall nucleation and its stochasticity in perpendicular magnetic anisotropy Hall cross structures

    Science.gov (United States)

    Sethi, P.; Murapaka, C.; Lim, G. J.; Lew, W. S.

    2015-11-01

    Hall cross structures in magnetic nanowires are commonly used for electrical detection of magnetization reversal in which a domain wall (DW) is conventionally nucleated by a local Oersted field. In this letter, we demonstrate DW nucleation in Co/Ni perpendicular magnetic anisotropy nanowire at the magnetic Hall cross junction. The DWs are nucleated by applying an in-plane pulsed current through the nanowire without the need of a local Oersted field. The change in Hall resistance, detected using anomalous Hall effect, is governed by the magnetic volume switched at the Hall junction, which can be tuned by varying the magnitude of the applied current density and pulse width. The nucleated DWs are driven simultaneously under the spin transfer torque effect when the applied current density is above a threshold. The possibility of multiple DW generation and variation in magnetic volume switched makes nucleation process stochastic in nature. The in-plane current induced stochastic nature of DW generation may find applications in random number generation.

  6. In-plane current induced domain wall nucleation and its stochasticity in perpendicular magnetic anisotropy Hall cross structures

    Energy Technology Data Exchange (ETDEWEB)

    Sethi, P.; Murapaka, C.; Lim, G. J.; Lew, W. S., E-mail: wensiang@ntu.edu.sg [School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371 (Singapore)

    2015-11-09

    Hall cross structures in magnetic nanowires are commonly used for electrical detection of magnetization reversal in which a domain wall (DW) is conventionally nucleated by a local Oersted field. In this letter, we demonstrate DW nucleation in Co/Ni perpendicular magnetic anisotropy nanowire at the magnetic Hall cross junction. The DWs are nucleated by applying an in-plane pulsed current through the nanowire without the need of a local Oersted field. The change in Hall resistance, detected using anomalous Hall effect, is governed by the magnetic volume switched at the Hall junction, which can be tuned by varying the magnitude of the applied current density and pulse width. The nucleated DWs are driven simultaneously under the spin transfer torque effect when the applied current density is above a threshold. The possibility of multiple DW generation and variation in magnetic volume switched makes nucleation process stochastic in nature. The in-plane current induced stochastic nature of DW generation may find applications in random number generation.

  7. Tuning the Magnetic Anisotropy at a Molecule-Metal Interface

    DEFF Research Database (Denmark)

    Bairagi, K.; Bellec, A.; Repain, V.

    2015-01-01

    We demonstrate that a C60 overlayer enhances the perpendicular magnetic anisotropy of a Co thin film, inducing an inverse spin reorientation transition from in plane to out of plane. The driving force is the C60/Co interfacial magnetic anisotropy that we have measured quantitatively in situ...

  8. Magnetic and structural investigation of growth induced magnetic anisotropies in Fe50Co50 thin films

    Directory of Open Access Journals (Sweden)

    Neri I.

    2013-01-01

    Full Text Available In this paper, we investigate the magnetic properties of Fe50 Co50 polycrystalline thin films, grown by dc-magnetron sputtering, with thickness (t ranging from 2.5 nm up to 100 nm. We focused on the magnetic properties of the samples to highlight the effects of possible intrinsic stress that may develop during growth, and their dependence on film thickness. Indeed, during film deposition, due to the growth technique and growth conditions, a metallic film may display an intrinsic compressive or tensile stress. In our case, due to the Fe50Co50 magnetolastic properties, this stress may in its turn promote the development of magnetic anisotropies. Samples magnetic properties were monitored with a SQUID magnetometer and a magneto–optic Kerr effect apparatus, using both an in–plane and an out–of–plane magnetic field. Magnetoresistance measurements were collected, as well, to further investigate the magnetic behavior of the samples. Indications about the presence of intrinsic stress were obtained accessing samples curvature with an optical profilometer. For t ≤ 20 nm, the shape of the in-plane magnetization loops is squared and coercivity increases with t, possibly due to fact that, for small t values, the grain size grows with t. The magnetoresistive response is anisotropic in character. For t > 20 nm, coercivity smoothly decreases, the approach to saturation gets slower and the shape of the whole loop gets less and less squared. The magnetoresistive effect becomes almost isotropic and its intensity increases of about one order of magnitude. These results suggest that the magnetization reorientation process changes for t > 20 nm, and are in agreement with the progressive development of an out-of-plane easy axis. This hypothesis is substantiated by profilometric analysis that reveals the presence of an in-plane compressive stress.

  9. Anomalous Hall hysteresis in T m3F e5O12/Pt with strain-induced perpendicular magnetic anisotropy

    Science.gov (United States)

    Tang, Chi; Sellappan, Pathikumar; Liu, Yawen; Xu, Yadong; Garay, Javier E.; Shi, Jing

    2016-10-01

    We demonstrate robust interface strain-induced perpendicular magnetic anisotropy in atomically flat ferrimagnetic insulator T m3F e5O12 (TIG) films grown with pulsed laser deposition on a substituted G d3G a5O12 substrate which maximizes the tensile strain at the interface. In bilayers consisting of Pt and TIG, we observe large squared Hall hysteresis loops over a wide range of thicknesses of Pt at room temperature. When a thin Cu layer is inserted between Pt and TIG, the Hall hysteresis magnitude decays but stays finite as the thickness of Cu increases up to 5 nm. However, if the Cu layer is placed atop Pt instead, the Hall hysteresis magnitude is consistently larger than when the Cu layer with the same thickness is inserted in between for all Cu thicknesses. These results suggest that both the proximity-induced ferromagnetism and spin current contribute to the anomalous Hall effect.

  10. Ru Catalyst-Induced Perpendicular Magnetic Anisotropy in MgO/CoFeB/Ta/MgO Multilayered Films.

    Science.gov (United States)

    Liu, Yiwei; Zhang, Jingyan; Wang, Shouguo; Jiang, Shaolong; Liu, Qianqian; Li, Xujing; Wu, Zhenglong; Yu, Guanghua

    2015-12-09

    The high oxygen storage/release capability of the catalyst Ru is used to manipulate the interfacial electronic structure in spintronic materials to obtain perpendicular magnetic anisotropy (PMA). Insertion of an ultrathin Ru layer between the CoFeB and Ta layers in MgO/CoFeB/Ta/MgO films effectively induces PMA without annealing. Ru plays a catalytic role in Fe-O-Ta bonding and isolation at the metal-oxide interface to achieve moderate interface oxidation. In contrast, PMA cannot be obtained in the sample with a Mg insertion layer or without an insertion layer because of the lack of a catalyst. Our work would provide a new approach toward catalyst-induced PMA for future CoFeB-based spintronic device applications.

  11. Pulse-Current-Induced Switching of Ta/CoFeB/MgO with Perpendicular Magnetic Anisotropy

    Science.gov (United States)

    Hung, Yu-Ming; Rehm, Laura; Wolf, Georg; Kent, Andrew D.

    2015-03-01

    We study current-induced switching of thin magnetic layers with perpendicular magnetic anisotropy using in-plane currents and the spin-Hall effect in the quasi-static (swept current) and pulsed-current regimes. Our aim is to investigate the dynamics and efficiency of spin-transfer switching. The layer stacks consists of β-Ta(5nm)/Co40Fe40B20(0.8nm)/MgO(2nm)/Ta(2nm) layers on oxidized silicon substrates. Hall bar structures with dimensions of 15 × 180 μm2 and cross shaped devices with width of 6 μm are investigated with DC transport and pulse measurement, respectively. In DC transport experiments, we could switch the magnetization states reproducibly by varying the in-plane field and current. In pulsed experiments, we measured the dependence of the switching probability on pulse amplitude and duration in the presence of an in-plane field. A histogram analysis indicates the existence of intermediate states and suggests incoherent magnetization switching. Nearly 100% switching probability could be achieved at high enough pulse amplitude of 25.5 MA/cm2 with 10 ns pulse duration and an applied field of ~120 mT. Supported by SRC-INDEX program.

  12. Where is magnetic anisotropy field pointing to?

    CERN Document Server

    Gutowski, Marek W

    2013-01-01

    The desired result of magnetic anisotropy investigations is the determination of value(s) of various anisotropy constant(s). This is sometimes difficult, especially when the precise knowledge of saturation magnetization is required, as it happens in ferromagnetic resonance (FMR) studies. In such cases we usually resort to `trick' and fit our experimental data to the quantity called \\emph{anisotropy field}, which is strictly proportional to the ratio of the searched anisotropy constant and saturation magnetization. Yet, this quantity is scalar, simply a number, and is therefore of little value for modeling or simulations of the magnetostatic or micromagnetic structures. Here we show how to `translate' the values of magnetic anisotropy constants into the complete vector of magnetic anisotropy field. Our derivation is rigorous and covers the most often encountered cases, from uniaxial to cubic anisotropy.

  13. Diverse effects of two-dimensional and step flow growth mode induced microstructures on the magnetic anisotropies of SrRuO[subscript3] thin films

    Energy Technology Data Exchange (ETDEWEB)

    Yoo, Y.Z.; Chmaissem, O.; Kolesnik, S.; Ullah, A.; Lurio, L.B.; Brown, D.E.; Brady, J.; Dabrowski, B.; Kimball, C.W.; Haji-Sheikh, M.; Genis, A.P. (NIU)

    2010-12-03

    Geometrical anisotropy axes of diverse SrRuO{sub 3} (SRO) films grown by random and directional two-dimensional and step flow modes are determined and their characteristic angular magnetizations are understood in terms of growth mode induced structural effects. Two-dimensional SRO films possess single-crystal-like structural qualities. Angular magnetization measurements show sharp minima and indicate the films easy axis to be in the [310] direction. In contrast, examination of step flow SRO films shows the presence of degenerate multiple in-plane domains and the anisotropy axis in a direction close to [110] even though directional surface steps are clearly visible.

  14. Full-Heusler Co2FeSi alloy thin films with perpendicular magnetic anisotropy induced by MgO-interface

    OpenAIRE

    Takamura, Yota; Suzuki, Takahiro; Fujino, Yorinobu; Nakagawa, Shigeki

    2013-01-01

    The authors demonstrated that L21-ordered full-Heusler Co2FeSi (CFS) alloy film with thickness of 100 nm were formed by facing targets sputtering (FTS) method at a substrate temperature TS = 300 deg C. Degrees of L21- and B2- order for the film were 0.37, and 0.96, respectively. Furthermore, full-Heusler CFS alloy thin films with perpendicular magnetic anisotropy (PMA) induced by MgO-interface magnetic anisotropy were successfully formed by the FTS method. The CFS/MgO stacking layers showed P...

  15. Full-Heusler Co2FeSi alloy thin films with perpendicular magnetic anisotropy induced by MgO-interfaces

    Science.gov (United States)

    Takamura, Yota; Suzuki, Takahiro; Fujino, Yorinobu; Nakagawa, Shigeki

    2014-05-01

    A 100-nm-thick L21-ordered full-Heusler Co2FeSi (CFS) alloy film was fabricated using the facing targets sputtering (FTS) method at a substrate temperature TS of 300 °C. The degrees of L21- and B2-order for the film were 37% and 96%, respectively. In addition, full-Heusler CFS alloy thin films with perpendicular magnetic anisotropy (PMA) induced by the magnetic anisotropy of MgO-interfaces were also successfully fabricated using the FTS method. The CFS/MgO stacked layers exhibited PMA when the CFS layer had a thickness of 0.6 nm ≤ dCFS ≤ 1.0 nm. The PMA in these structures resulted from the CFS/MgO interfacial perpendicular magnetic anisotropy.

  16. Growth of Co Nanomagnet Arrays with Enhanced Magnetic Anisotropy

    Science.gov (United States)

    Fernández, Laura; Ilyn, Maxim; Magaña, Ana; Vitali, Lucia; Ortega, José Enrique

    2016-01-01

    A trigon structure formed by submonolayer gadolinium deposition onto Au(111) is revealed as a robust growth template for Co nanodot arrays. Scanning Tunneling Microscopy and X‐Ray Magnetic Circular Dichroism measurements evidence that the Co nanoislands behave as independent magnetic entities with an out‐of‐plane easy axis of anisotropy and enhanced magnetic anisotropy values, as compared to other self‐organized Co nanodot superlattices. The large strain induced by the lattice mismatch at the interface between Co and trigons is discussed as the main reason for the increased magnetic anisotropy of the nanoislands. PMID:27711268

  17. Magnetic Anisotropy in the Radula of Chiton

    Institute of Scientific and Technical Information of China (English)

    ZHAO Jian-Gao; QIAN Xia; LIU Wei; LIU Chuan-lin; ZHAN Wen-Shan

    2000-01-01

    Radular teeth of chitons were studied by using magnetic torque-meter and transmission electron microscopy (TEM). The magnetic torque curves give clear evidence of presence of strong uni-axial magnetic anisotropy. The easy axis is along the length direction of tongue-like radula. The TEM pattern shows that long chip-like magnetite nano-scaled particles packed in the radular teeth with both uni-axial shape anisotropy and magneto-crystalline anisotropy.

  18. Magnetic Anisotropy in the Radula of Chiton

    Science.gov (United States)

    Zhao, Jian-Gao; Qian, Xia; Liu, Wei; Liu, Chuan-Lin; Zhan, Wen-Shan

    2000-07-01

    Radular teeth of chitons were studied by using magnetic torque-meter and transmission electron microscopy (TEM). The magnetic torque curves give clear evidence of presence of strong uni-axial magnetic anisotropy. The easy axis is along the length direction of tongue-like radula. The TEM pattern shows that long chip-like magnetite nano-scaled particles packed in the radular teeth with both uni-axial shape anisotropy and magneto-crystalline anisotropy.

  19. Anisotropy induced wave birefringence in bounded supercritical plasma confined in a multicusp magnetic field

    Science.gov (United States)

    Dey, Indranuj; Bhattacharjee, Sudeep

    2011-04-01

    Laboratory observation of rotation of the polarization axis (θc˜20°-40° with respect to vacuum) of a penetrating electromagnetic wave through a bounded supercritical plasma (plasma frequency ωp>wave frequency ω), confined in a multicusp magnetic field is reported. Birefringence of the radial and polar wave electric field components (Er and Eθ) has been identified as the cause for the rotation, similar to a magneto-optic medium, however, with distinct differences owing to the presence of wave induced resonances. Numerical simulation results obtained by solving the Maxwell's equations by incorporating the plasma and magnetostatic field inhomogeneities within a conducting boundary shows a reasonable agreement with the experimental results.

  20. Frequency dispersion of the magnetic anisotropy field in metallic magnetic films with the plane anisotropy of electrical conductivity

    Energy Technology Data Exchange (ETDEWEB)

    Zimin, A.B.; Kornev, Y.V.; Sementsova, T.M.; Sidorenkov, V.V.

    1986-07-01

    Presence of the frequency dispersion of the field of induced single axis magnetic anisotropy and the angular position of the axis of easy magnetization in the film plane has been determined in metallic magnetic films with plane anisotropy of electrical conductivity. Theoretical dependences have been obtained which given satisfactory agreement with experimental data for cobalt and permalloy films prepared by sputtering on glass substrates and using the incident molecular beam under an angle with the substrate.

  1. Carrier-dependent magnetic anisotropy of Gd-adsorbed graphene

    Science.gov (United States)

    Lu, Yuan; Zhou, Tie-ge; Shao, Bin; Zuo, Xu; Feng, Min

    2016-05-01

    Using first-principles calculation based on density functional theory, we study the magnetic anisotropy of Gd-adsorbed graphene and its dependence on carrier accumulation. We show that carrier accumulation not only impacts the magnitude of magnetic anisotropy but also switches its sign. Hole accumulation enhances the perpendicular anisotropy up to ˜16 meV per Gd atom, while electron accumulation switches the anisotropy from perpendicular to in-plane direction. Moreover, we find that the first order perturbation of spin-orbit coupling interaction induces a pseudo-gap at Γ for the perpendicular magnetization, which leads to the the anomalous magnetic anisotropy for the neutral composite. Our findings pave the way for magneto-electric materials based on rare-earth-decorated graphene for voltage-controlled spintronics.

  2. Tuning the Magnetic Anisotropy at a Molecule-Metal Interface.

    Science.gov (United States)

    Bairagi, K; Bellec, A; Repain, V; Chacon, C; Girard, Y; Garreau, Y; Lagoute, J; Rousset, S; Breitwieser, R; Hu, Yu-Cheng; Chao, Yen Cheng; Pai, Woei Wu; Li, D; Smogunov, A; Barreteau, C

    2015-06-19

    We demonstrate that a C(60) overlayer enhances the perpendicular magnetic anisotropy of a Co thin film, inducing an inverse spin reorientation transition from in plane to out of plane. The driving force is the (60)/Co interfacial magnetic anisotropy that we have measured quantitatively in situ as a function of the (60) coverage. Comparison with state-of-the-art ab initio calculations show that this interfacial anisotropy mainly arises from the local hybridization between (60) p(z) and Co d(z(2)) orbitals. By generalizing these arguments, we also demonstrate that the hybridization of (60) with a Fe(110) surface decreases the perpendicular magnetic anisotropy. These results open the way to tailor the interfacial magnetic anisotropy in organic-material-ferromagnet systems.

  3. Carrier-dependent magnetic anisotropy of Gd-adsorbed graphene

    Directory of Open Access Journals (Sweden)

    Yuan Lu

    2016-05-01

    Full Text Available Using first-principles calculation based on density functional theory, we study the magnetic anisotropy of Gd-adsorbed graphene and its dependence on carrier accumulation. We show that carrier accumulation not only impacts the magnitude of magnetic anisotropy but also switches its sign. Hole accumulation enhances the perpendicular anisotropy up to ∼16 meV per Gd atom, while electron accumulation switches the anisotropy from perpendicular to in-plane direction. Moreover, we find that the first order perturbation of spin-orbit coupling interaction induces a pseudo-gap at Γ for the perpendicular magnetization, which leads to the the anomalous magnetic anisotropy for the neutral composite. Our findings pave the way for magneto-electric materials based on rare-earth-decorated graphene for voltage-controlled spintronics.

  4. Effect of a pinning field on the critical current density for current-induced domain wall motion in perpendicular magnetic anisotropy nanowires.

    Science.gov (United States)

    Ooba, Ayaka; Fujimura, Yuma; Takahashi, Kota; Komine, Takashi; Sugita, Ryuji

    2012-09-01

    In this study, the effect of a pinning field on the critical current density for current-induced domain wall motion in nanowires with perpendicular magnetic anisotropy was investigated using micromagnetic simulations. In order to estimate the pinning field in notched nanowires, we conducted wall energy calculations for nanowires with various saturation magnetizations. The pinning field increased as the notch size increased. The pinning field decreased as the saturation magnetization decreased. As a result, the decreased in the pinning field causes the reduction of the critical current density. Therefore, a significant reduction of the critical current density can be obtained by decreasing the saturation magnetization, even if wall pinning occurs.

  5. Surface magnetic anisotropy in amorphous alloys

    Energy Technology Data Exchange (ETDEWEB)

    Tejedor, M.; Rubio, H.; Elbaile, L.; Iglesias, R. (Univ. de Oviedo (Spain). Dept. de Fisica)

    1993-11-01

    The total in-plane magnetic anisotropy and the in-plane surface magnetic anisotropy constants have been measured in nearly-zero magnetostrictive amorphous ribbons in as-quenched state. The magnetostatic energy of a two-dimensional square-lattice of parallelepipeds or ellipsoids, whose dimensions are determined by the parameters characterizing the roughness, is evaluated. From the results obtained, they can conclude that the in-plane surface anisotropy can be magnetostatic in origin but it has little influence on the total in-plane magnetic anisotropy of the ribbon.

  6. Magnetoelastically induced perpendicular magnetic anisotropy and perpendicular exchange bias of CoO/CoPt multilayer films

    Science.gov (United States)

    Guo, Lei; Wang, Yue; Wang, Jian; Muraishi, Shinji; Sannomiya, Takumi; Nakamura, Yoshio; Shi, Ji

    2015-11-01

    The effects of magnetoelastically induced perpendicular magnetic anisotropy (PMA) on perpendicular exchange bias (PEB) have been studied in [CoO5nm/CoPt5nm]5 multilayer films. After deposition at room temperature, [CoO5nm/CoPt5nm]5 multilayer films were post-annealed at 100 °C, 250 °C, 300 °C and 375 °C for 3 h. In-plane tensile stress of CoPt layer was calculated by sin2 φ method, and we found it increased gradually upon annealing from 0.99 GPa (as-deposited) up to 3.02 GPa (300 °C-annealed). As to the magnetic property, significant enhancement of PMA was achieved in [CoO5nm/CoPt5nm]5 multilayer films after annealing due to the increase of CoPt layer in-plane tensile stress. With the enhancement of magnetoelastically induced PMA, great improvement of PEB was also achieved in [CoO5nm/CoPt5nm]5 multilayer films, which increased from 130 Oe (as-deposited) up to 1060 Oe (300 °C-annealed), showing the same change tendency as PMA and the strong correlation with CoPt layer in-plane tensile stress. We consider it is the increase of CoPt layer in-plane tensile stress that leads to the enhancement of CoPt layer PMA, which is favorable for the spins in CoPt layer aligning to a more perpendicular direction. And thus the enhanced PMA with more perpendicular spins alignment in CoPt layer results in the improved PEB in [CoO5nm/CoPt5nm]5 multilayer films through enhanced perpendicular spins coupling at CoO/CoPt interfaces.

  7. Nanoscale magnetic ratchets based on shape anisotropy

    Science.gov (United States)

    Cui, Jizhai; Keller, Scott M.; Liang, Cheng-Yen; Carman, Gregory P.; Lynch, Christopher S.

    2017-02-01

    Controlling magnetization using piezoelectric strain through the magnetoelectric effect offers several orders of magnitude reduction in energy consumption for spintronic applications. However strain is a uniaxial effect and, unlike directional magnetic field or spin-polarized current, cannot induce a full 180° reorientation of the magnetization vector when acting alone. We have engineered novel ‘peanut’ and ‘cat-eye’ shaped nanomagnets on piezoelectric substrates that undergo repeated deterministic 180° magnetization rotations in response to individual electric-field-induced strain pulses by breaking the uniaxial symmetry using shape anisotropy. This behavior can be likened to a magnetic ratchet, advancing magnetization clockwise with each piezostrain trigger. The results were validated using micromagnetics implemented in a multiphysics finite elements code to simulate the engineered spatial and temporal magnetic behavior. The engineering principles start from a target device function and proceed to the identification of shapes that produce the desired function. This approach opens a broad design space for next generation magnetoelectric spintronic devices.

  8. Hydrogen-plasma-induced magnetocrystalline anisotropy ordering in self-assembled magnetic nanoparticle monolayers.

    Science.gov (United States)

    Weddemann, Alexander; Meyer, Judith; Regtmeier, Anna; Janzen, Irina; Akemeier, Dieter; Hütten, Andreas

    2013-01-01

    Self-assembled two-dimensional arrays of either 14 nm hcp-Co or 6 nm ε-Co particle components were treated by hydrogen plasma for various exposure times. A change of hysteretic sample behavior depending on the treatment duration is reported, which can be divided in two time scales: oxygen reduction increases the particle magnetization during the first 20 min, which is followed by an alteration of the magnetic response shape. The latter depends on the respective particle species. Based on the Landau-Lifshitz equations for a discrete set of magnetic moments, we propose a model that relates the change of the hysteresis loops to a dipole-driven ordering of the magnetocrystalline easy axes within the particle plane due to the high spatial aspect ratio of the system.

  9. Hydrogen-plasma-induced magnetocrystalline anisotropy ordering in self-assembled magnetic nanoparticle monolayers

    Directory of Open Access Journals (Sweden)

    Alexander Weddemann

    2013-03-01

    Full Text Available Self-assembled two-dimensional arrays of either 14 nm hcp-Co or 6 nm ε-Co particle components were treated by hydrogen plasma for various exposure times. A change of hysteretic sample behavior depending on the treatment duration is reported, which can be divided in two time scales: oxygen reduction increases the particle magnetization during the first 20 min, which is followed by an alteration of the magnetic response shape. The latter depends on the respective particle species. Based on the Landau–Lifshitz equations for a discrete set of magnetic moments, we propose a model that relates the change of the hysteresis loops to a dipole-driven ordering of the magnetocrystalline easy axes within the particle plane due to the high spatial aspect ratio of the system.

  10. Temperature-induced transition of magnetic anisotropy between in-plane and out-of-plane directions in GaMnAs film

    Science.gov (United States)

    Lee, Sangyeop; Choi, Seonghoon; Bac, Seul-Ki; Lee, Hakjoon; Yoo, Taehee; Lee, Sanghoon; Liu, X.; Furdyna, J. K.

    2016-10-01

    We used the Hall effect and magnetization measurements to investigate the temperature dependence of the magnetic anisotropy of a ferromagnetic semiconductor GaMnAs film grown on a (001) GaAs substrate. The Hall effect was systematically measured by applying an external magnetic field within and normal to the film plane. The switching behavior of the magnetization during the reversal process revealed the coexistence of in-plane and out-of-plane magnetic anisotropies in the film. However, these two types of magnetic anisotropies strongly depended on the temperature. Specifically, the out-of-plane anisotropy was dominant in the low-temperature region (i.e., 3-10 K), whereas the in-plane anisotropy became dominant in the temperature region higher than 15 K. This temperature dependent change in the magnetic anisotropy was further confirmed using direct magnetization measurements.

  11. The influence of applied tensile stress on power loss in Co-rich amorphous Co-Fe-Si-B ribbons with induced magnetic anisotropy

    DEFF Research Database (Denmark)

    Nielsen, H; Nielsen, K; Nielsen, Otto V

    1982-01-01

    The influence on power loss PTof applied tensile stress σ in amorphous (Co0.89Fe0.11)72Mo3Si15B10(lambda_{s} > 0) and Co73Mo2Si15B10(lambda_{s} <0) ribbons with different induced magnetic anisotropy Kuis reported. The losses are measured under sinusoidal flux conditions atf = 50Hz,J_{max} = 0.57T...

  12. Magnetic anisotropy of lecithin membranes. A new anisotropy susceptometer.

    OpenAIRE

    Scholz, F.; Boroske, E; Helfrich, W.

    1984-01-01

    Cylindrical giant vesicles prepared from egg lecithin and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) are oriented in an external magnetic field and observed by phase contrast microscopy. The anisotropic part of the diamagnetic susceptibility of the lecithin membrane is determined from the distribution of angles between the magnetic field and the long cylinder axis due to thermal fluctuations. The anisotropy of DMPC is found to be larger by a factor of 2 than that of egg lecithin. This...

  13. Effect of anisotropy on small magnetic clusters

    CERN Document Server

    Hucht, Alfred; Sil, Shreekantha; Entel, Peter; 10.1103/PhysRevB.84.104438

    2012-01-01

    The effect of dipolar interaction and local uniaxial anisotropy on the magnetic response of small spin clusters where spins are located on the vertices of icosahedron, cuboctahedron, tetrahedron and square geometry have been investigated. We consider the ferromagnetic and antiferromagnetic spin-1/2 and spin-1 Heisenberg model with uniaxial anisotropy and dipolar interaction and apply numerical exact diagonalization technique in order to study the influence of frustration and anisotropy on the ground state properties of the spin-clusters. The ground state magnetization, spin-spin correlation and several thermodynamic quantities such as entropy and specific heat are calculated as a function of temperature and magnetic field.

  14. Magnetic behaviour of amorphous ribbons with creep-induced helical anisotropy and their fluxgate properties

    DEFF Research Database (Denmark)

    Füzer, Jan; Brauer, Peter; Nielsen, Otto V

    1998-01-01

    We have induced a helical destributionby a tortional and tensile stress annealing, in low magnetostriction amorphous ribbons. In this paper we report a theoretical studyof predicted magnetisation curvesand the comparisonwith experimental measurements.......We have induced a helical destributionby a tortional and tensile stress annealing, in low magnetostriction amorphous ribbons. In this paper we report a theoretical studyof predicted magnetisation curvesand the comparisonwith experimental measurements....

  15. Magnetic behaviour of amorphous ribbons with creep-induced helical anisotropy and their fluxgate properties

    DEFF Research Database (Denmark)

    Füzer, Jan; Brauer, Peter; Nielsen, Otto V

    1998-01-01

    We have induced a helical destributionby a tortional and tensile stress annealing, in low magnetostriction amorphous ribbons. In this paper we report a theoretical studyof predicted magnetisation curvesand the comparisonwith experimental measurements.......We have induced a helical destributionby a tortional and tensile stress annealing, in low magnetostriction amorphous ribbons. In this paper we report a theoretical studyof predicted magnetisation curvesand the comparisonwith experimental measurements....

  16. Nanopatterned CoPt alloys with perpendicular magnetic anisotropy

    Science.gov (United States)

    Makarov, D.; Bermúdez-Ureña, E.; Schmidt, O. G.; Liscio, F.; Maret, M.; Brombacher, C.; Schulze, S.; Hietschold, M.; Albrecht, M.

    2008-10-01

    CoPt alloy films with perpendicular magnetic anisotropy were grown on SiO2 nanoparticle arrays with particle sizes as small as 10 nm. In order to induce perpendicular magnetic anisotropy in the CoPt film, a MgO seed layer was sputter deposited. Despite the fact that neighboring CoPt film caps are interconnected, individual caps appear as single domain and for most of them their magnetization orientation can be reversed individually. This behavior might be caused by domain wall nucleation and pinning preferentially at the rim of each cap. Thus, arrays of magnetic caps with defined pinning sites can be considered as a percolated perpendicular medium.

  17. Atomic Pair-Correlation Anisotropy Induced by Magnetic Annealing of Ferromagnetic Fe22.5Ni77.5 Permalloy

    Science.gov (United States)

    Sparks, Cullie; Robertson, Lee; Ice, Gene; Bai, Jianming

    2002-03-01

    Diffuse x-ray scattering measurements have been made on ferromagnetic Fe22.5Ni77.5, permalloy, annealed in a 3000 G magnetic field at 450° C. These measurements reveal a long predicted anisotropic alignment of the Fe-Ni, Fe-Fe and Ni-Ni near-neighbor pairs relative to the magnetic field direction when annealed at temperatures below the Curie Temperature but high enough for diffusion to occur. Our direct measurements show that the Fe-Fe and Ni-Ni first neighbor pairs preferentially align along the annealing direction of the magnetic field for fields in the [100], [110] and [111] crystallographic directions. Fe-Ni pairs prefer to align perpendicular to the direction of the applied field. The size of the observed anisotropy in the atom pair distribution follows that observed in their magnetic properties1; the anisotropy increases from [100] to [110] to [111]. This first direct verification that magnetic annealing preferentially aligns the direction of the atomic pairs will be discussed. 1. S. Chikazumi, J. Phys. Soc. Japan 11, 551 (1956).

  18. Magnetic anisotropies of rare-earth compounds

    Science.gov (United States)

    Loewenhaupt, M.; Rotter, M.; Kramp, S.

    2000-03-01

    There are two kinds of magnetic anisotropy in rare-earth compounds: the single-ion anisotropy caused by the crystal field (CF) and the anisotropy of the two-ion interactions. Both types of anisotropy have to be considered to arrive at a consistent description of the magnetic properties of the orthorhombic intermetallic compound NdCu 2. From the analysis of NdCu 2 we can derive predictions for the type of ordering in other isostructural RCu 2 compounds, that agree well with experimental results: If the magnetic moments point into the crystallographic b-direction, an ordering wave vector of (2/3 0 0) is expected. If the moments are oriented perpendicular to b then the ordering wave vector is (2/3 1 0) .

  19. Formation of Magnetic Anisotropy by Lithography.

    Science.gov (United States)

    Kim, Si Nyeon; Nam, Yoon Jae; Kim, Yang Doo; Choi, Jun Woo; Lee, Heon; Lim, Sang Ho

    2016-05-24

    Artificial interface anisotropy is demonstrated in alternating Co/Pt and Co/Pd stripe patterns, providing a means of forming magnetic anisotropy using lithography. In-plane hysteresis loops measured along two principal directions are explained in depth by two competing shape and interface anisotropies, thus confirming the formation of interface anisotropy at the Co/Pt and Co/Pd interfaces of the stripe patterns. The measured interface anisotropy energies, which are in the range of 0.2-0.3 erg/cm(2) for both stripes, are smaller than those observed in conventional multilayers, indicating a decrease in smoothness of the interfaces when formed by lithography. The demonstration of interface anisotropy in the Co/Pt and Co/Pd stripe patterns is of significant practical importance, because this setup makes it possible to form anisotropy using lithography and to modulate its strength by controlling the pattern width. Furthermore, this makes it possible to form more complex interface anisotropy by fabricating two-dimensional patterns. These artificial anisotropies are expected to open up new device applications such as multilevel bits using in-plane magnetoresistive thin-film structures.

  20. Anisotropy of rare-earth magnets

    Institute of Scientific and Technical Information of China (English)

    R.Skomski; D.J.Sellmyer

    2009-01-01

    Rare-earth intermetallics such as Nd2FeI4B and Sm-Co are widely used as high-performance permanent magnets,because they combine high magnetocrystalline anisotropy with reasonable magnetization and Curie temperature.The anisotropy is a combined effect of spin-orbit coupling and electrostatic crystal-field interactions.The main contribution comes from the rare-earth 4f electrons,which are well-screened from the crystalline environment but exhibit a strong spin-orbit coupling.In this limit,the magnetocrystalline anisotropy has a very transparent physical interpretation,the anisotropy energy essentially being equal to the energy of Hund's-rules 4f ion in the crystal field.The corresponding expression for the lowest-order uniaxial anisotropy constant K1 is used to discuss rare-earth substitutions,which have recently attracted renewed interest due to shifts in the rare-earth production and demand.Specific phenomena reviewed in this article are the enhancement of the anisotropy of Sm2Fe17 due to interstitial nitrogen,the use of Sm-Co magnets for high-temperature applications,and the comparison of rare-earth single-ion anisotropy with other single-ion and two-ion mechanisms.

  1. Optically induced spin wave dynamics in [Co/Pd]{sub 8} antidot lattices with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Pal, S.; Das, K.; Barman, A., E-mail: abarman@ybose.res.in [Thematic Unit of Excellence on Nanodevice Technology and Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700 098 (India); Klos, J. W.; Gruszecki, P.; Krawczyk, M., E-mail: krawczyk@amu.edu.pl [Faculty of Physics, A. Mickiewicz University in Poznan, Umultowska 85, 61-614 Poznań (Poland); Hellwig, O. [San Jose Research Center, HGST, a Western Digital Company, 3403 Yerba Buena Rd., San Jose, California 95135 (United States)

    2014-10-20

    We present an all-optical time-resolved measurement of spin wave (SW) dynamics in a series of antidot lattices based on [Co(0.75 nm)/Pd(0.9 nm)]{sub 8} multilayer (ML) systems with perpendicular magnetic anisotropy. The spectra depend significantly on the areal density of the antidots. The observed SW modes are qualitatively reproduced by the plane wave method. The interesting results found in our measurements and calculations at small lattice constants can be attributed to the increase of areal density of the shells with modified magnetic properties probably due to distortion of the regular ML structure by the Ga ion bombardment and to increased coupling between localized modes. We propose and discuss the possible mechanisms for this coupling including exchange interaction, tunnelling, and dipolar interactions.

  2. FANTEN: a new web-based interface for the analysis of magnetic anisotropy-induced NMR data

    Energy Technology Data Exchange (ETDEWEB)

    Rinaldelli, Mauro; Carlon, Azzurra; Ravera, Enrico; Parigi, Giacomo, E-mail: parigi@cerm.unifi.it; Luchinat, Claudio, E-mail: luchinat@cerm.unifi.it [University of Florence, CERM and Department of Chemistry “Ugo Schiff” (Italy)

    2015-01-15

    Pseudocontact shifts (PCSs) and residual dipolar couplings (RDCs) arising from the presence of paramagnetic metal ions in proteins as well as RDCs due to partial orientation induced by external orienting media are nowadays routinely measured as a part of the NMR characterization of biologically relevant systems. PCSs and RDCs are becoming more and more popular as restraints (1) to determine and/or refine protein structures in solution, (2) to monitor the extent of conformational heterogeneity in systems composed of rigid domains which can reorient with respect to one another, and (3) to obtain structural information in protein–protein complexes. The use of both PCSs and RDCs proceeds through the determination of the anisotropy tensors which are at the origin of these NMR observables. A new user-friendly web tool, called FANTEN (Finding ANisotropy TENsors), has been developed for the determination of the anisotropy tensors related to PCSs and RDCs and has been made freely available through the WeNMR ( http://fanten-enmr.cerm.unifi.it:8080 http://fanten-enmr.cerm.unifi.it:8080 ) gateway. The program has many new features not available in other existing programs, among which the possibility of a joint analysis of several sets of PCS and RDC data and the possibility to perform rigid body minimizations.

  3. FANTEN: a new web-based interface for the analysis of magnetic anisotropy-induced NMR data.

    Science.gov (United States)

    Rinaldelli, Mauro; Carlon, Azzurra; Ravera, Enrico; Parigi, Giacomo; Luchinat, Claudio

    2015-01-01

    Pseudocontact shifts (PCSs) and residual dipolar couplings (RDCs) arising from the presence of paramagnetic metal ions in proteins as well as RDCs due to partial orientation induced by external orienting media are nowadays routinely measured as a part of the NMR characterization of biologically relevant systems. PCSs and RDCs are becoming more and more popular as restraints (1) to determine and/or refine protein structures in solution, (2) to monitor the extent of conformational heterogeneity in systems composed of rigid domains which can reorient with respect to one another, and (3) to obtain structural information in protein-protein complexes. The use of both PCSs and RDCs proceeds through the determination of the anisotropy tensors which are at the origin of these NMR observables. A new user-friendly web tool, called FANTEN (Finding ANisotropy TENsors), has been developed for the determination of the anisotropy tensors related to PCSs and RDCs and has been made freely available through the WeNMR ( http://fanten-enmr.cerm.unifi.it:8080 ) gateway. The program has many new features not available in other existing programs, among which the possibility of a joint analysis of several sets of PCS and RDC data and the possibility to perform rigid body minimizations.

  4. ANISOTROPY DETERMINATIONS IN EXCHANGE SPRING MAGNETS.

    Energy Technology Data Exchange (ETDEWEB)

    LEWIS,L.H.; HARLAND,C.L.

    2002-08-18

    Ferromagnetic nanocomposites, or ''exchange spring'' magnets, possess a nanoscaled microstructure that allows intergrain magnetic exchange forces to couple the constituent grains and alter the system's effective magnetic anisotropies. While the effects of the anisotropy alterations are clearly seen in macroscopic magnetic measurement, it is extremely difficult to determine the detailed effects of the system's exchange coupling, such as the interphase exchange length, the inherent domain wall widths or the effective anisotropies of the system. Clarification of these materials parameters may be obtained from the ''micromagnetic'' phenomenological model, where the assumption of magnetic reversal initiating in the magnetically-soft regions of the exchange-spring maqet is explicitly included. This approach differs from that typically applied by other researchers and allows a quantitative estimate of the effective anisotropies of an exchange spring system. Hysteresis loops measured on well-characterized nanocomposite alloys based on the composition Nd{sub 2}Fe{sub 14}B + {alpha}-Fe at temperatures above the spin reorientation temperature were analyzed within the framework of the micromagnetic phenomenological model. Preliminary results indicate that the effective anisotropy constant in the material is intermediate to that of bulk {alpha}-Fe and bulk Nd{sub 2}Fe{sub 14}B and increases with decreasing temperature. These results strongly support the idea that magnetic reversal in nanocomposite systems initiates in the lower-anisotropy regions of the system, and that the soft-phase regions become exchange-hardened by virtue of their proximity to the magnetically-hard regions.

  5. Magnetization of superparamagnetics in the state of mechanical anisotropy

    OpenAIRE

    Ugulava, Archil; Chkhaidze, Simon; Kekutia, Shalva; Rostomashvili, Zurab

    2015-01-01

    The internal energy of magnetic anisotropy for some nanoparticles dominates over the thermal energy even at room temperature. Strong magnetic anisotropy of nanoparticles can significantly affect the process of magnetization of the magnetic fluid. This influence is substantial if the system of nanoparticles is in a state of mechanical anisotropy in which the anisotropy axes of the particles have the same direction. In this work, it is shown that the magnetization curve of the magnetic fluid in...

  6. Strain-induced modulation of perpendicular magnetic anisotropy in Ta/CoFeB/MgO structures investigated by ferromagnetic resonance

    Science.gov (United States)

    Yu, Guoqiang; Wang, Zhenxing; Abolfath-Beygi, Maryam; He, Congli; Li, Xiang; Wong, Kin L.; Nordeen, Paul; Wu, Hao; Carman, Gregory P.; Han, Xiufeng; Alhomoudi, Ibrahim A.; Amiri, Pedram Khalili; Wang, Kang L.

    2015-02-01

    We demonstrate strain-induced modulation of perpendicular magnetic anisotropy (PMA) in (001)-oriented [Pb(Mg1/3Nb2/3)O3](1-x)-[PbTiO3]x (PMN-PT) substrate/Ta/CoFeB/MgO/Ta structures using ferromagnetic resonance (FMR). An in-plane biaxial strain is produced by applying voltage between the two surfaces of the PMN-PT substrate, and is transferred to the ferromagnetic CoFeB layer, which results in tuning of the PMA of the CoFeB layer. The strain-induced change in PMA is quantitatively extracted from the experimental FMR spectra. It is shown that both first and second-order anisotropy terms are affected by the electric field, and that they have opposite voltage dependencies. A very large value of the voltage-induced perpendicular magnetic anisotropy modulation of ˜7000 fJ/V.m is obtained through this strain-mediated coupling. Using this FMR technique, the magnetostriction coefficient λ is extracted for the ultrathin 1.1 nm Co20Fe60B20 layer, and is found to be 3.7 × 10-5, which is approximately 4 times larger than the previously reported values for CoFeB films thicker than 5 nm. In addition, the effect of strain on the effective damping constant (αeff) is also studied and no obvious modulation of the αeff is observed. The results are relevant to the development of CoFeB-MgO magnetic tunnel junctions for memory applications.

  7. Strain-induced perpendicular magnetic anisotropy in L a2CoMn O6 -ɛ thin films and its dependence on film thickness

    Science.gov (United States)

    Galceran, Regina; López-Mir, Laura; Bozzo, Bernat; Cisneros-Fernández, José; Santiso, José; Balcells, Lluís; Frontera, Carlos; Martínez, Benjamín

    2016-04-01

    Ferromagnetic insulating L a2CoMn O6 -ɛ (LCMO) epitaxial thin films grown on top of SrTi O3 (001) substrates present a strong magnetic anisotropy favoring the out-of-plane (OP) orientation of the magnetization with a large anisotropy field (˜70 kOe for film thickness of about 15 nm). Diminishing oxygen off-stoichiometry of the film enhances the anisotropy. We attribute this to the concomitant shrinkage of the OP cell parameter and to the increasing of the tensile strain of the films. Consistently, LCMO films grown on (LaAlO3)0.3(Sr2AlTaO6) 0.7 and LaAl O3 substrates (with a larger OP lattice parameter and compressive stress) display in-plane (IP) magnetic anisotropy. Thus, we link the strong magnetic anisotropy observed in LCMO to the film stress: tensile strain favors perpendicular anisotropy, and compressive stress favors IP anisotropy. We also report on the thickness dependence of the magnetic properties. Perpendicular anisotropy, saturation magnetization, and Curie temperature are maintained over a large range of film thickness.

  8. Role of stochastic anisotropy and shear on magnetic field lines diffusion

    Energy Technology Data Exchange (ETDEWEB)

    Negrea, M [Department of Physics, University of Craiova, Association Euratom-MEdC, Romania 13 A.I.Cuza Str, 200585 Craiova (Romania); Petrisor, I [Department of Physics, University of Craiova, Association Euratom-MEdC, Romania 13 A.I.Cuza Str, 200585 Craiova (Romania); Weyssow, B [Physique Statistique-Plasmas, Association Euratom-Etat Belge, Universite Libre de Bruxelles, Campus Plaine, Bd. du Triomphe, 1050 Brussels (Belgium)

    2007-11-15

    Anisotropy in the magnetic fluctuation spectrum (stochastic anisotropy) and magnetic shear induce variations of global averaged quantities such as the running and the asymptotic diffusion tensors that can be investigated using a semi-analytical method. The study considers ranges for the anisotropy parameter, magnetic Kubo number and shear parameter leading to contrasting dynamical behaviors. In particular, the trapping of the stochastic magnetic field lines is analyzed. An asymptotic 'poloidal' velocity larger for stronger anisotropy is obtained for the wandering of the magnetic field lines for different values of the paramete0008.

  9. Computing magnetic anisotropy constants of single molecule magnets

    Indian Academy of Sciences (India)

    S Ramasesha; Shaon Sahoo; Rajamani Raghunathan; Diptiman Sen

    2009-09-01

    We present here a theoretical approach to compute the molecular magnetic anisotropy parameters, and for single molecule magnets in any given spin eigenstate of exchange spin Hamiltonian. We first describe a hybrid constant -valence bond (VB) technique of solving spin Hamiltonians employing full spatial and spin symmetry adaptation and we illustrate this technique by solving the exchange Hamiltonian of the Cu6Fe8 system. Treating the anisotropy Hamiltonian as perturbation, we compute the and values for various eigenstates of the exchange Hamiltonian. Since, the dipolar contribution to the magnetic anisotropy is negligibly small, we calculate the molecular anisotropy from the single-ion anisotropies of the metal centers. We have studied the variation of and by rotating the single-ion anisotropies in the case of Mn12Ac and Fe8 SMMs in ground and few low-lying excited states of the exchange Hamiltonian. In both the systems, we find that the molecular anisotropy changes drastically when the single-ion anisotropies are rotated. While in Mn12Ac SMM values depend strongly on the spin of the eigenstate, it is almost independent of the spin of the eigenstate in Fe8 SMM. We also find that the value is almost insensitive to the orientation of the anisotropy of the core Mn(IV) ions. The dependence of on the energy gap between the ground and the excited states in both the systems has also been studied by using different sets of exchange constants.

  10. Oscillatory magnetic anisotropy and spin-reorientation induced by heavy-metal cap in Cu/FeCo/M (M =Hf or Ta): A first-principles study

    Science.gov (United States)

    Ong, P. V.; Kioussis, Nicholas; Amiri, P. Khalili; Wang, K. L.

    2016-11-01

    Using ab initio electronic structure calculations we have investigated the effect of the thickness of a heavy-metal (HM) cap on the magnetic anisotropy of the Cu /FeCo /HM (n ) thin film where HM = Hf and Ta with thicknesses of n =0 -10 monolayers (MLs). We find that the Hf cap results in a large perpendicular magnetic anisotropy (PMA), which exhibits quasiperiodic oscillation with a period of two MLs. In contrast, the Ta-capped heterostructure exhibits a spin reorientation from out-of-plane to in-plane magnetization orientation at two MLs of Ta. Moreover, the MA remains negative and depends weakly on the Ta-cap thickness beyond the critical thickness. The underlying mechanism of the PMA oscillation is the periodic change in spin-flip spin-orbit coupling between the minority-spin Fe d (x z ,y z ) and majority Fe d (z2) at Γ ¯, which is induced by the hybridization with Hf at the FeCo/Hf interface. Our results help resolve the contradictory experiments regarding the role of the FeCo/Ta interface on the PMA of the MgO/FeCo/Ta junction. The calculations reveal that the ferromagnet/Hf is promising for spintronic applications and that the capping material and thickness are additional parameters for optimizing the functional properties of spintronic devices.

  11. Magnetic anisotropy in rare-earth metals

    DEFF Research Database (Denmark)

    Nielsen, Mourits; Bjerrum Møller, Hans; Lindgård, Per-Anker;

    1970-01-01

    The magnetic field dependence of the energy of long- wavelength magnons in Tb-10%Ho has been studied by inelastic neutron scattering. The results agree with the `frozen-lattice' model, provided that the second-order magnetoelastic effect is taken into account. The planar anisotropy is almost...

  12. Scanning Kerr microscopy study of current-induced switching in Ta/CoFeB/MgO films with perpendicular magnetic anisotropy

    Science.gov (United States)

    Durrant, C. J.; Hicken, R. J.; Hao, Qiang; Xiao, Gang

    2016-01-01

    Ta/CoFeB/MgO trilayers with perpendicular magnetic anisotropy are expected to play a key role in the next generation of current and electric field switched memory and logic devices. In this study, we combine scanning Kerr microscopy with electrical transport measurements to gain insight into the underlying mechanisms of current-induced switching within such devices. We find switching to be a stochastic, domain-wall-driven process, the speed of which is strongly dependent on the switching current. Kerr imaging shows domain nucleation at one edge of the device, which modeling reveals is likely assisted by the out-of-plane component of the Oersted field. Further domain growth, leading to magnetization reversal, may still be dominated by spin torques, but the Oersted field provides an additional mechanism with which to control the switching process.

  13. Texture induced microwave background anisotropies

    Energy Technology Data Exchange (ETDEWEB)

    Borrill, Julian; Copeland, Edmund J.; Liddle, Andrew R.; Stebbins, Albert; Veeraraghavan, Shoba

    1994-03-01

    We use numerical simulations to calculate the cosmic microwave background anisotropy induced by the evolution of a global texture field, with special emphasis on individual textures. Both spherically symmetric and general configurations are analyzed, and in the latter case we consider field configurations which exhibit unwinding events and also ones which do not. We compare the results given by evolving the field numerically under both the expanded core (XCORE) and non-linear sigma model (NLSM) approximations with the analytic predictions of the NLSM exact solution for a spherically symmetric self-similar (SSSS) unwinding. We find that the random unwinding configuration spots' typical peak height is 60-75\\% and angular size typically only 10% of those of the SSSS unwinding, and that random configurations without an unwinding event nonetheless may generate indistinguishable hot and cold spots. A brief comparison is made with other work.

  14. CMB anisotropies from primordial inhomogeneous magnetic fields

    CERN Document Server

    Lewis, A

    2004-01-01

    Primordial inhomogeneous magnetic fields of the right strength can leave a signature on the CMB temperature anisotropy and polarization. Potentially observable contributions to polarization B-modes are generated by vorticity and gravitational waves sourced by the magnetic anisotropic stress. We compute the corresponding CMB transfer functions in detail including the effect of neutrinos. The shear rapidly causes the neutrino anisotropic stress to cancel the stress from the magnetic field, suppressing the production of gravitational waves and vorticity on super-horizon scales after neutrino decoupling. A significant large scale signal from tensor modes can only be produced before neutrino decoupling, and the actual amplitude is somewhat uncertain. Plausible values suggest primordial nearly scale invariant fields of ~ 10^(-10)G today may be observable from their large scale tensor anisotropy. They can be distinguished from primordial gravitational waves by their non-Gaussianity. Vector mode vorticity sources B-m...

  15. Uniaxial contribution to the magnetic anisotropy of La{sub 0.67}Sr{sub 0.33}MnO{sub 3} thin films induced by orthorhombic crystal structure

    Energy Technology Data Exchange (ETDEWEB)

    Boschker, Hans; Mathews, Mercy; Brinks, Peter [Faculty of Science and Technology and MESA, Institute for Nanotechnology, University of Twente, 7500 AE, Enschede (Netherlands); Houwman, Evert, E-mail: e.p.houwman@utwente.nl [Faculty of Science and Technology and MESA, Institute for Nanotechnology, University of Twente, 7500 AE, Enschede (Netherlands); Vailionis, Arturas [Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305 (United States); Koster, Gertjan; Blank, Dave H.A.; Rijnders, Guus [Faculty of Science and Technology and MESA, Institute for Nanotechnology, University of Twente, 7500 AE, Enschede (Netherlands)

    2011-11-15

    La{sub 0.67}Sr{sub 33}MnO{sub 3} (LSMO) thin films under compressive strain have an orthorhombic symmetry with (11-bar0){sub o} and (001){sub o} in-plane orientations. (The subscript o denotes the orthorhombic symmetry.) Here, we grew LSMO on cubic (LaAlO{sub 3}){sub 0.3}-(Sr{sub 2}AlTaO{sub 6}){sub 0.7} (LSAT) substrates and observed a uniaxial contribution to the magnetic anisotropy which is related to the orthorhombic crystal structure. Since the lattice mismatch is equal in the two directions, the general understanding of anisotropy in LSMO, which relates the uniaxial anisotropy to differences in strain, cannot explain the results. These findings suggest that the oxygen octahedra rotations associated with the orthorhombic structure result in a change in magnetic coupling between the [11-bar0]{sub o} and [0 0 1]{sub o} directions, which determines the anisotropy. We expect these findings to lead to a better understanding of the microscopic origin of the magnetocrystalline anisotropy in LSMO. - Highlights: > Orthorhombic LSMO films are grown coherently and untwinned on cubic LSAT substrates. > The films are described by both biaxial anisotropy and uniaxial anisotropy. > The uniaxial part of the anisotropy is induced by the orthorhombic symmetry of LSMO.

  16. Irreversible magnetic processes under biaxial and uniaxial magnetic anisotropies

    Directory of Open Access Journals (Sweden)

    S. Pokharel

    2016-05-01

    Full Text Available Irreversible magnetic processes have been investigated in magnetic systems with two different anisotropy symmetries (uniaxial and biaxial through angular measurement of the switching field, the irreversible susceptibility and the magnetic viscosity. These two systems consist of two-dimensional cobalt ferrite hetero-structures epitaxially grown on (100 and (110 MgO substrate. It is found that for uniaxial anisotropy the irreversible characteristics of the magnetization are large and display a strong angular dependence, which exhibits its maximum at the easy axis and drops quickly to vanish at the hard axis. However, for biaxial anisotropy the magnetization irreversible characteristics are considerably reduced and are less sensitive to the field angle.

  17. Surface contribution to the anisotropy of magnetic nanoparticles

    OpenAIRE

    Garanin, D. A.; Kachkachi, H.

    2002-01-01

    We calculate the contribution of the Neel surface anisotropy to the effective anisotropy of magnetic nanoparticles of spherical shape cut out of a simple cubic lattice. The effective anisotropy arises because deviations of atomic magnetizations from collinearity and thus the energy depends on the orientation of the global magnetization. The result is second order in the Neel surface anisotropy, scales with the particle volume and has cubic symmetry with preferred directions [+-1,+-1,+-1].

  18. Effective magnetic anisotropy manipulation by oblique deposition in magnetostatically coupled Co nanostrip arrays

    Science.gov (United States)

    Kozlov, A. G.; Stebliy, M. E.; Ognev, A. V.; Samardak, A. S.; Davydenko, A. V.; Chebotkevich, L. A.

    2017-01-01

    We report on an experimental investigation of magnetic properties and domain structure of single nanostrips and their magnetostatically coupled arrays possessing the shape anisotropy and anisotropy induced by oblique deposition, which are oriented at different angles to each other. The orientation of the effective anisotropy and the value of coercive force of nanostrip arrays depends on the angle between directions of the induced anisotropies. Micromagnetic simulations, performed to determine possible spin configurations especially within domain walls, support the experimentally observed magnetic domain structure. An influence of dipole-dipole interaction between magnetostatically coupled nanostrips on the domain structure and coercive force of arrays are discussed. We demonstrate the experimental validation of an early-proposed theoretical model for determination of the effective magnetic anisotropy through the combination of induced anisotropies.

  19. Random magnetic anisotropy: Switching and coercivity behavior

    Science.gov (United States)

    Creswell, A.; Paul, D. I.

    1990-05-01

    Starting from a Hamiltonian based on the random magnetic anisotropy model to describe the magnetic characteristics of amorphous materials such as TbFe2, we determine the low-temperature dependence of the coercivity as well as the magnetization dynamics of these materials. Our model features clusters, each characterized by its anisotropy direction. The exchange energy term entering the Hamiltonian is represented by an effective exchange interaction acting in the intercluster regions. Our Hamiltonian has a minimum in each of the two opposite hemispheres defined by the applied field. We derive the temperature-dependent coercivity by calculating the field necessary to have the one metastable minimum disappear. Our results agree well with experimental data for reasonable values of the parameters. We study the dynamics of the magnetization at 0 K by performing a numerical integration of the equations of motion derived from our Hamiltonian augmented by a Gilbert and Kelly damping term. The average magnetization of the material is reevaluated at each integration step in order for the mean-field approximation for exchange to remain physically meaningful. We obtain the time dependence of the magnetization, determine the switching fields and switching times, and study the influence of the exchange on the results.

  20. Programming magnetic anisotropy in polymeric microactuators.

    Science.gov (United States)

    Kim, Jiyun; Chung, Su Eun; Choi, Sung-Eun; Lee, Howon; Kim, Junhoi; Kwon, Sunghoon

    2011-10-01

    Polymeric microcomponents are widely used in microelectromechanical systems (MEMS) and lab-on-a-chip devices, but they suffer from the lack of complex motion, effective addressability and precise shape control. To address these needs, we fabricated polymeric nanocomposite microactuators driven by programmable heterogeneous magnetic anisotropy. Spatially modulated photopatterning was applied in a shape-independent manner to microactuator components by successive confinement of self-assembled magnetic nanoparticles in a fixed polymer matrix. By freely programming the rotational axis of each component, we demonstrate that the polymeric microactuators can undergo predesigned, complex two- and three-dimensional motion.

  1. Magnetic anisotropy of grain boundaries in nanocrystalline Ni

    Science.gov (United States)

    Bian, Q.; Niewczas, M.

    2017-01-01

    Temperature-dependent magnetic anisotropy due to grain boundaries in nanocrystalline Ni has been studied by simulating experimental magnetization data with the stochastic Landau-Lifshitz-Gilbert theory. In the model the grain boundary magnetic anisotropy energy is expressed as the sum of the uniaxial anisotropy and the cubic anisotropy, characterized by Kua and Kca anisotropy constants. By comparing the calculated magnetization with the experimental magnetization measurements at finite temperatures, the values of Kua and Kca can be determined. For nanocrystalline Ni it is found that with increasing temperature Kua decreases and Kca increases. At low temperatures Kua dominates the grain boundary anisotropy energy, whereas Kca is very small and it can be neglected. At room temperature Kua and Kca are of the same order with the corresponding ratio Kua /Kca ≈ 1.9 , both coefficients are much larger than the magnetocrystalline anisotropy constant.

  2. Magnetic properties and magnetoimpedance of FeCoNi/CuBe electroplated tubes with different features of field-annealing induced magnetic anisotropy

    Science.gov (United States)

    El Kammouni, R.; Chlenova, A. A.; Volchkov, S. O.; Kurlyandskaya, G. V.

    2017-02-01

    The effect of field annealing (in direct (DC) or alternating current (AC) field) on the structure, magnetic properties and giant magnetoimpedance (GMI) of CuBe/ Fe19Co17Ni64 electroplated tubes was studied. The field and frequency dependences of total impedance and its real part were comparatively analyzed together with magnetization processes features. The GMI sensitivity with respect to an applied field was the subject of special attention in view of possible applications of these materials in small magnetic field sensors. The maximum GMI ratio depends strongly on the heat treatments. The DC field annealing leads to the highest total impedance GMI ratio (ΔZ/Z=250%) and real part of the total impedance GMI ratio (ΔR/R=640%), compared to as-cast and AC field annealed samples. The external field response of DC annealed samples presented a single peak GMI response as a consequence of a strong contribution of the longitudinal effective anisotropy. At the same time, the maximum obtained sensitivity of 13.5%/Oe for DC case is much lower compared to the highest sensitivity values obtained for as-prepared (28.6%/Oe) and DC field annealed (22.0%/Oe) tubes for the low frequency of 2.5 MHz. The weak dependence of ΔZ/Z ratio in the case of AC field annealed samples in the high frequency range is an important advantage for particular sensor applications.

  3. Topological defects and misfit strain in magnetic stripe domains of lateral multilayers with perpendicular magnetic anisotropy.

    Science.gov (United States)

    Hierro-Rodriguez, A; Cid, R; Vélez, M; Rodriguez-Rodriguez, G; Martín, J I; Álvarez-Prado, L M; Alameda, J M

    2012-09-14

    Stripe domains are studied in perpendicular magnetic anisotropy films nanostructured with a periodic thickness modulation that induces the lateral modulation of both stripe periods and in-plane magnetization. The resulting system is the 2D equivalent of a strained superlattice with properties controlled by interfacial misfit strain within the magnetic stripe structure and shape anisotropy. This allows us to observe, experimentally for the first time, the continuous structural transformation of a grain boundary in this 2D magnetic crystal in the whole angular range. The magnetization reversal process can be tailored through the effect of misfit strain due to the coupling between disclinations in the magnetic stripe pattern and domain walls in the in-plane magnetization configuration.

  4. Microstructural, Magnetic Anisotropy, and Magnetic Domain Structure Correlations in Epitaxial FePd Thin Films with Perpendicular Magnetic Anisotropy

    Science.gov (United States)

    Skuza, J. R.; Clavero, C.; Yang, K.; Wincheski, B.; Lukaszew, R. A.

    2009-01-01

    L1(sub 0)-ordered FePd epitaxial thin films were prepared using dc magnetron sputter deposition on MgO (001) substrates. The films were grown with varying thickness and degree of chemical order to investigate the interplay between the microstructure, magnetic anisotropy, and magnetic domain structure. The experimentally measured domain size/period and magnetic anisotropy in this high perpendicular anisotropy system were found to be correlated following the analytical energy model proposed by Kooy and Enz that considers a delicate balance between the domain wall energy and the demagnetizing stray field energy.

  5. Shape-induced anisotropy in antiferromagnetic nanoparticles

    OpenAIRE

    H. Gomonay; Kondovych, S.; Loktev, V.

    2013-01-01

    High fraction of the surface atoms considerably enhances the influence of size and shape on the magnetic and electronic properties of nanoparticles. Shape effects in ferromagnetic nanoparticles are well understood and allow to set and control the parameters of a sample that affect its magnetic anisotropy during production. In the present paper we study the shape effects in the other widely used magnetic materials -- antiferromagnets, -- which possess vanishingly small or zero macroscopic magn...

  6. Domain wall motion driven by spin Hall effect—Tuning with in-plane magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Rushforth, A. W., E-mail: andrew.rushforth@nottingham.ac.uk [School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD (United Kingdom)

    2014-04-21

    This letter investigates the effects of in-plane magnetic anisotropy on the current induced motion of magnetic domain walls in systems with dominant perpendicular magnetic anisotropy, where accumulated spins from the spin Hall effect in an adjacent heavy metal layer are responsible for driving the domain wall motion. It is found that that the sign and magnitude of the domain wall velocity in the uniform flow regime can be tuned significantly by the in-plane magnetic anisotropy. These effects are sensitive to the ratio of the adiabatic and non-adiabatic spin transfer torque parameters and are robust in the presence of pinning and thermal fluctuations.

  7. Magnetic Anisotropy and Field‐induced Slow  Relaxation of Magnetization in Tetracoordinate   CoII Compound [Co(CH3‐im2Cl2

    Directory of Open Access Journals (Sweden)

    Ivan Nemec

    2017-02-01

    Full Text Available Static and dynamic magnetic properties of the tetracoordinate CoII complex [Co(CH3‐im2Cl2], (1, CH3‐im = N‐methyl‐imidazole, studied using thorough analyses of magnetometry, and High‐Frequency and ‐Field EPR (HFEPR measurements, are reported. The study was supported by ab initio complete active space self‐consistent field (CASSCF calculations. It has been revealed that 1 possesses a large magnetic anisotropy with a large rhombicity (magnetometry: D = −13.5 cm−1, E/D = 0.33; HFEPR: D = −14.5(1 cm−1, E/D = 0.16(1. These experimental results agree well with the theoretical calculations (D = −11.2 cm−1, E/D = 0.18. Furthermore, it has been revealed that 1 behaves as a field‐induced single‐ion magnet with a relatively large spin‐reversal barrier (Ueff = 33.5 K. The influence of the Cl–Co–Cl angle on magnetic anisotropy parameters was evaluated using the CASSCF calculations.

  8. Investigation of magnetic properties in thick CoFeB alloy films for controllable anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Ke; Huang, Ya; Chen, Ruofei; Xu, Zhan [Huaqiao University, College of Information Science and Engineering, Xiamen City (China)

    2016-02-15

    CoFeB alloy material has attracted interest for its wide uses in magnetic memory devices and sensors. We investigate magnetic properties of thick Co{sub 40}Fe{sub 40}B{sub 20} films in the thickness range from 10 to 100 nm sandwiched by MgO and Ta layers. Strong in-plane uniaxial magnetic anisotropy is revealed in the as-deposited amorphous films by angular dependent magnetic measurements, and the growth-induced anisotropy is found to strongly depend on the film thickness. A fourfold cubic magnetic anisotropy develops with annealing, as a result of improved crystalline structure in films confirmed by X-ray diffraction measurements. The observed magnetic properties can be explained by the superposition of the uniaxial and additional cubic magnetic anisotropy, tuned by annealing temperature. (orig.)

  9. Investigation of magnetic properties in thick CoFeB alloy films for controllable anisotropy

    Science.gov (United States)

    Wang, Ke; Huang, Ya; Chen, Ruofei; Xu, Zhan

    2016-02-01

    CoFeB alloy material has attracted interest for its wide uses in magnetic memory devices and sensors. We investigate magnetic properties of thick Co40Fe40B20 films in the thickness range from 10 to 100 nm sandwiched by MgO and Ta layers. Strong in-plane uniaxial magnetic anisotropy is revealed in the as-deposited amorphous films by angular dependent magnetic measurements, and the growth-induced anisotropy is found to strongly depend on the film thickness. A fourfold cubic magnetic anisotropy develops with annealing, as a result of improved crystalline structure in films confirmed by X-ray diffraction measurements. The observed magnetic properties can be explained by the superposition of the uniaxial and additional cubic magnetic anisotropy, tuned by annealing temperature.

  10. Perpendicular magnetic anisotropy of two-dimensional Rashba ferromagnets

    Science.gov (United States)

    Kim, Kyoung-Whan; Lee, Kyung-Jin; Lee, Hyun-Woo; Stiles, M. D.

    2016-11-01

    We compute the magnetocrystalline anisotropy energy within two-dimensional Rashba models. For a ferromagnetic free-electron Rashba model, the magnetic anisotropy is exactly zero regardless of the strength of the Rashba coupling, unless only the lowest band is occupied. For this latter case, the model predicts in-plane anisotropy. For a more realistic Rashba model with finite band width, the magnetic anisotropy evolves from in-plane to perpendicular and back to in-plane as bands are progressively filled. This evolution agrees with first-principles calculations on the interfacial anisotropy, suggesting that the Rashba model captures energetics leading to anisotropy originating from the interface provided that the model takes account of the finite Brillouin zone. The results show that the electron density modulation by doping or an external voltage is more important for voltage-controlled magnetic anisotropy than the modulation of the Rashba parameter.

  11. Modification of magnetic anisotropy in metallic glasses using high-energy ion beam irradiation

    Indian Academy of Sciences (India)

    K V Amrute; U R Mhatre; S K Sinha; D C Kothari; R Nagarajan; D Kanjilal

    2002-05-01

    Heavy ion irradiation in the electronic stopping power region induces macroscopic dimensional change in metallic glasses and introduces magnetic anisotropy in some magnetic materials. The present work is on the irradiation study of ferromagnetic metallic glasses, where both dimensional change and modification of magnetic anisotropy are expected. Magnetic anisotropy was measured using Mössbauer spectroscopy of virgin and irradiated Fe40Ni40B20 and Fe40Ni38Mo4B18 metallic glass ribbons. 90 MeV 127I beam was used for the irradiations. Irradiation doses were 5 × 1013 and 7.5 × 1013 ions/cm2. The relative intensity ratios 23 of the second and third lines of the Mössbauer spectra were measured to determine the magnetic anisotropy. The virgin samples of both the materials display in-plane magnetic anisotropy, i.e., the spins are oriented parallel to the ribbon plane. Irradiation is found to cause reduction in magnetic anisotropy. Near-complete randomization of magnetic moments is observed at high irradiation doses. Correlation is found between the residual stresses introduced by ion irradiation and the change in magnetic anisotropy.

  12. Determination of magnetic anisotropy of magnetically hard materials

    Science.gov (United States)

    Richter, H. J.

    1990-03-01

    The determination of the first-order anisotropy field strength using the torsion pendulum method is described. Since the applied field need not necessarily be in the range of the anisotropy field, this method is particularly useful for characterizing modern permanent magnet materials which have a very high uniaxial anisotropy. The method requires oriented samples. Measurements were made on polycrystalline samples of NdFeB, SmCo, and barium ferrite. The method is described and error sources are discussed. It is pointed out that the torsion pendulum method is closely related to reversible transverse susceptibility measurements. It is shown both experimentally and theoretically, that using susceptibility measurements similar results can be obtained. The susceptibility method is, however, not applicable to conducting materials at present.

  13. Strain-induced macroscopic magnetic anisotropy from smectic liquid-crystalline elastomer-maghemite nanoparticle hybrid nanocomposites.

    Science.gov (United States)

    Haberl, Johannes M; Sánchez-Ferrer, Antoni; Mihut, Adriana M; Dietsch, Hervé; Hirt, Ann M; Mezzenga, Raffaele

    2013-06-21

    We combine tensile strength analysis and X-ray scattering experiments to establish a detailed understanding of the microstructural coupling between liquid-crystalline elastomer (LCE) networks and embedded magnetic core-shell ellipsoidal nanoparticles (NPs). We study the structural and magnetic re-organization at different deformations and NP loadings, and the associated shape and magnetic memory features. In the quantitative analysis of a stretching process, the effect of the incorporated NPs on the smectic LCE is found to be prominent during the reorientation of the smectic domains and the softening of the nanocomposite. Under deformation, the soft response of the nanocomposite material allows the organization of the nanoparticles to yield a permanent macroscopically anisotropic magnetic material. Independent of the particle loading, the shape-memory properties and the smectic phase of the LCEs are preserved. Detailed studies on the magnetic properties demonstrate that the collective ensemble of individual particles is responsible for the macroscopic magnetic features of the nanocomposite.

  14. Tunnel Junction with Perpendicular Magnetic Anisotropy: Status and Challenges

    Directory of Open Access Journals (Sweden)

    Mengxing Wang

    2015-08-01

    Full Text Available Magnetic tunnel junction (MTJ, which arises from emerging spintronics, has the potential to become the basic component of novel memory, logic circuits, and other applications. Particularly since the first demonstration of current induced magnetization switching in MTJ, spin transfer torque magnetic random access memory (STT-MRAM has sparked a huge interest thanks to its non-volatility, fast access speed, and infinite endurance. However, along with the advanced nodes scaling, MTJ with in-plane magnetic anisotropy suffers from modest thermal stability, high power consumption, and manufactural challenges. To address these concerns, focus of research has converted to the preferable perpendicular magnetic anisotropy (PMA based MTJ, whereas a number of conditions still have to be met before its practical application. This paper overviews the principles of PMA and STT, where relevant issues are preliminarily discussed. Centering on the interfacial PMA in CoFeB/MgO system, we present the fundamentals and latest progress in the engineering, material, and structural points of view. The last part illustrates potential investigations and applications with regard to MTJ with interfacial PMA.

  15. Effects of Surface Anisotropy on Magnetic Vortex Core

    OpenAIRE

    Pylypovskyi, Oleksandr V.; Sheka, Denis D.; Kravchuk, Volodymyr P.; Gaididei, Yuri

    2013-01-01

    The vortex core shape in the three dimensional Heisenberg magnet is essentially influenced by a surface anisotropy. We predict that depending of the surface anisotropy type there appears barrel- or pillow-shaped deformation of the vortex core along the magnet thickness. Our theoretical study is well confirmed by spin-lattice simulations.

  16. The magnetization processes and critical transition in a nanogranular magnetic film with perpendicular anisotropy.

    Science.gov (United States)

    Kalita, V M; Lozenko, A F; Ryabchenko, S M; Los, A V; Sitnikov, A V; Stognei, O V

    2013-02-13

    The mechanisms and properties of the equilibrium magnetization process for nanogranular films with perpendicular anisotropy placed in a tilted magnetic field are considered. The contributions of the effects of canting and flipping of the granules' magnetic moments to the process of film magnetization are studied. A critical behavior of the film magnetization at the transition, induced by a tilted magnetic field, from a state with non-uniform orientation of the granules' magnetic moments to one with a similar orientation is revealed. The results obtained within the two-level model of the orientation of the particles' magnetic moments are in good agreement with the experimental data for Co-Al(2)O(3) (61 at.% Co) granular film. The perpendicular anisotropy of the granules in this film originates mainly from their elongated shape. It is shown that in the non-uniform state the magnetostatic energy of a granular film with similarly oriented elongated granules can be described by the sum of contributions of two types: quasi-single-granular and quasi-film. The effective constant of the single-particle anisotropy of the granules in this case turns out to be dependent on the factor of volume filling of the film by granules, but not on its magnetization.

  17. Perpendicular magnetic anisotropy of Co85Cr15/Pt multilayers

    Institute of Scientific and Technical Information of China (English)

    Pol Hwang; Baohe Li; Tao Yang; Zhonghai Zhai; Fengwu Zhu

    2004-01-01

    The CoCr/Pt bilayers and (CoCr/Pt)20 multilayers with Pt underlayer were prepared by DC magnetron sputtering. The effects of prepared condition on perpendicular magnetic anisotropy were investigated. The results show that the thickness of Pt underlayer has a great effect on the microstructure and perpendicular magnetic anisotropy of CoCr/Pt bilayers and (CoCr/Pt)20 multilayers.When the thickness of Pt underlayer increases, Pt(111) and CoCr(002) peaks of both CoCr/Pt bilayers and (CoCr/Pt)20 multilayers increase and the bilayer periodicity of the multilayers is improved. The effective magnetic anisotropy of (CoCr/Pt)20 multilayers with Pt underlayer was much larger than that of CoCr/Pt bilayers. The (CoCr/Pt)20 multilayers has a stronger perpendicular magnetic anisotropy than that of CoCr/Pt bilayers. This is ascribed to the interface magnetic anisotropy of the multilayers.

  18. In-plane magnetic anisotropy along the width in amorphous magnetic ribbons

    Energy Technology Data Exchange (ETDEWEB)

    Tejedor, M.; Garcia, J.A.; Carrizo, J.; Elbaile, L. E-mail: elbaile@pinon.ccu.uniovi.es; Santos, J.D.; Mira, J.; Rivas, J

    2004-05-01

    A study about the variation of the in-plane magnetic anisotropy along the width of the ribbon is carried out in Co- and Fe-based amorphous magnetic ribbons. From the measurements of the anisotropy in as-quenched, mechanical polished and annealed samples the origin of the lack of homogeneity of the in-plane magnetic anisotropy in wide amorphous ribbons is determined. In addition a shape magnetic anisotropy that we think is originated by the edge effect was found.

  19. STUDYING THE INTERSTELLAR MAGNETIC FIELD FROM ANISOTROPIES IN VELOCITY CHANNELS

    Energy Technology Data Exchange (ETDEWEB)

    Esquivel, A. [Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Apartado Postal 70-543, 04510 México D.F., México (Mexico); Lazarian, A. [Astronomy Department, University of Wisconsin–Madison, 475 N. Charter Street, Madison, WI (United States); Pogosyan, D., E-mail: esquivel@nucleares.unam.mx, E-mail: lazarian@astro.wisc.edu, E-mail: pogosyan@ualberta.ca [Physics Department, University of Alberta, Edmonton, AB (Canada)

    2015-11-20

    Turbulence in the interstellar medium is anisotropic due to the ubiquitous magnetic fields. This anisotropy depends on the strength of the magnetic field and leaves an imprint on observations of spectral line maps. We use a grid of ideal magnetohydrodynamic simulations of driven turbulence and produce synthetic position–position–velocity maps to study the turbulence anisotropy in velocity channels of various resolutions. We found that the average structure function of velocity channels is aligned with the projection of the magnetic field on the plane of the sky. We also found that the degree of such anisotropy increases with the magnitude of the magnetic field. For thick velocity channels (low velocity resolution), the anisotropy is dominated by density, and the degree of anisotropy in these maps allows one to distinguish sub-Alfvénic and super-Alfvénic turbulence regimes, but it also depends strongly on the sonic Mach number. For thin channels (high velocity resolution), we find that the anisotropy depends less on the sonic Mach number. An important limitation of this technique is that it only gives a lower limit on the magnetic field strength because the anisotropy is related only to the magnetic field component on the plane of the sky. It can, and should, be used in combination with other techniques to estimate the magnetic field, such as the Fermi-Chandrasekhar method, anisotropies in centroids, Faraday rotation measurements, or direct line-of-sight determinations of the field from Zeeman effect observations.

  20. Perpendicular magnetic anisotropy in the Heusler alloy Co2TiSi/GaAs(001 hybrid structure

    Directory of Open Access Journals (Sweden)

    M. T. Dau

    2015-05-01

    Full Text Available Investigation of the thickness dependence of the magnetic anisotropy in B2-type Co2TiSi films on GaAs(001, shows a pronounced perpendicular magnetic anisotropy at 10 K for thicknesses up to 13.5 nm. We have evidenced that the interfacial anisotropy induced by interface clusters has a strong influence on the perpendicular magnetic anisotropy of this hybrid structure, especially at temperatures lower than the blocking temperature of the clusters (28 K. However, as this influence can be ruled out at higher temperatures, the perpendicular magnetic anisotropy which is found to persist up to room-temperature can be ascribed to the magnetic properties of the Co2TiSi films. For thicknesses larger than 15.0 nm, we observe an alignment of the magnetic easy axis parallel to the sample surface, which is most likely due to the shape anisotropy and the film structure.

  1. Stress induced magnetic anisotropy of CoFe2O4 thin films using pulsed laser deposition

    NARCIS (Netherlands)

    Pham Duc Thang, P.D.T.; Rijnders, Augustinus J.H.M.; Blank, David H.A.

    2007-01-01

    Cobalt ferrite (CoFe2O4) thin films (E70 nm) were epitaxially grown on TiO2-terminated (0 0 1) SrTiO3 substrates by pulsed laser deposition (PLD). Films with very smooth surface, which follow the terrace of the substrate, were obtained at temperatures below 600 1C. The magnetic properties of CoFe2O4

  2. Random anisotropy induced by structural disorder

    Science.gov (United States)

    Martinez, B.; Labarta, A.; Badia, F.; Tejada, J.

    1992-02-01

    As a direct consequence of the structural disorder, inherent to the amorphous state, local electrostatic fields are highly irregular. Due to the interplay between those highly irregular local electrostatic fields and the aspherical 4f electron clouds of the rare earth atoms, local anisotropy axis, directed along directions that vary randomly in space, may be generated. These directions are determined by the local arrangement of atoms; therefore, some information about amorphous structure may be obtained through the study of the magnetization curve.

  3. Magnetic anisotropies in ferromagnetic and exchange-coupled systems on rippled surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Liedke, Maciej Oskar; Liedke, Bartosz; Marko, Daniel; Keller, Adrian; Muecklich, Arndt; Facsko, Stefan; Fassbender, Juergen [FZ Dresden-Rossendorf, FWI, Dresden (Germany); Cizmar, Erik; Zvyagin, Sergei; Wosnitza, Joachim [FZ Dresden-Rossendorf, HLD, Dresden (Germany)

    2008-07-01

    The influence of a surface and interface modulation on the magnetic properties of ferromagnetic materials (Py, Fe and Co) and an exchange bias system (Py/FeMn) is studied. A periodic surface modulation (the so-called ripples) is achieved by low energy ion erosion. Subsequently the magnetic stack is deposited. Due to the film morphology a strong uniaxial anisotropy is induced in the ferromagnetic layers, which is fixed in its orientation along ripples elongation. In the case of the exchange bias system the direction of the induced unidirectional anisotropy can be varied by means of different field annealing cycles. For all mutual orientations both anisotropy contributions are superimposed independently. The angular dependence of the magnetization reversal behavior can be described perfectly by a coherent rotation model. In addition, the magnitude of the uniaxial and the unidirectional anisotropy scales with the step density or wave length of the rippled substrate, which is in full agreement with theoretical predictions.

  4. Tailoring of in-plane magnetic anisotropy in polycrystalline cobalt thin films by external stress

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Dileep, E-mail: dkumar@csr.res.in [UGC-DAE Consortium for Scientic Research, Khandwa Road, Indore 452001 (India); Singh, Sadhana [UGC-DAE Consortium for Scientic Research, Khandwa Road, Indore 452001 (India); Vishawakarma, Pramod [School of Nanotechnology, RGPV, Bhopal 462036 (India); Dev, Arun Singh; Reddy, V.R. [UGC-DAE Consortium for Scientic Research, Khandwa Road, Indore 452001 (India); Gupta, Ajay [Amity Center for Spintronic Materials, Amity University, Sector 125, Noida 201303 (India)

    2016-11-15

    Polycrystalline Co films of nominal thickness ~180 Å were deposited on intentionally curved Si substrates. Tensile and compressive stresses of 100 MPa and 150 MPa were induced in the films by relieving the curvature. It has been found that, within the elastic limit, presence of stress leads to an in-plane magnetic anisotropy in the film and its strength increases with increasing stress. Easy axis of magnetization in the films is found to be parallel/ transverse to the compressive /tensile stresses respectively. The origin of magnetic anisotropy in the stressed films is understood in terms of magneto- elastic coupling, where the stress try to align the magnetic moments in order to minimize the magneto-elastic as well as anisotropy energy. Tensile stress is also found to be responsible for the surface smoothening of the films, which is attributed to the movement of the atoms associated with the applied stress. The present work provides a possible way to tailor the magnetic anisotropy and its direction in polycrystalline and amorphous films using external stress. - Highlights: • Tensile and compressive stresses were induced in Co films by removing the bending force from the substrates after film deposition. • Controlled external mechanical stress is found to be responsible for magnetic anisotropies in amorphous and polycrystalline thin films, where crystalline anisotropy is absent. • Tensile stress leads to surface smoothening of the polycrystalline Co films.

  5. Effects of surface anisotropy on magnetic vortex core

    Energy Technology Data Exchange (ETDEWEB)

    Pylypovskyi, Oleksandr V., E-mail: engraver@univ.net.ua [Taras Shevchenko National University of Kiev, 01601 Kiev (Ukraine); Sheka, Denis D. [Taras Shevchenko National University of Kiev, 01601 Kiev (Ukraine); Kravchuk, Volodymyr P.; Gaididei, Yuri [Institute for Theoretical Physics, 03143 Kiev (Ukraine)

    2014-06-01

    The vortex core shape in the three dimensional Heisenberg magnet is essentially influenced by a surface anisotropy. We predict that depending of the surface anisotropy type there appears barrel- or pillow-shaped deformation of the vortex core along the magnet thickness. Our theoretical study is well confirmed by spin–lattice simulations. - Highlights: • The shape of magnetic vortex core is essentially influenced by SA (surface anisotropy). • We predict barrel- or pillow-shaped deformation of the vortex depending on SA. • The variational approach fully describes the vortex core deformation. • We performed spin–lattice simulations to detect SA influence on the vortex core.

  6. Canonical Transform Method for Treating Strongly Anisotropy Magnets

    DEFF Research Database (Denmark)

    Cooke, J. F.; Lindgård, Per-Anker

    1977-01-01

    An infinite-order perturbation approach to the theory of magnetism in magnets with strong single-ion anisotropy is given. This approach is based on a canonical transformation of the system into one with a diagonal crystal field, an effective two-ion anisotropy, and reduced ground-state corrections....... A matrix-element matching procedure is used to obtain an explicit expression for the spin-wave energy to second order. The consequences of this theory are illustrated by an application to a simple example with planar anisotropy and an external magnetic field. A detailed comparison between the results...

  7. Nanomagnets with high shape anisotropy and strong crystalline anisotropy: perspectives on magnetic force microscopy.

    Science.gov (United States)

    Campanella, H; Jaafar, M; Llobet, J; Esteve, J; Vázquez, M; Asenjo, A; del Real, R P; Plaza, J A

    2011-12-16

    We report on a new approach for magnetic imaging, highly sensitive even in the presence of external, strong magnetic fields. Based on FIB-assisted fabricated high-aspect-ratio rare-earth nanomagnets, we produce groundbreaking magnetic force tips with hard magnetic character where we combine a high aspect ratio (shape anisotropy) together with strong crystalline anisotropy (rare-earth-based alloys). Rare-earth hard nanomagnets are then FIB-integrated to silicon microcantilevers as highly sharpened tips for high-field magnetic imaging applications. Force resolution and domain reversing and recovery capabilities are at least one order of magnitude better than for conventional magnetic tips. This work opens new, pioneering research fields on the surface magnetization process of nanostructures based either on relatively hard magnetic materials-used in magnetic storage media-or on materials like superparamagnetic particles, ferro/antiferromagnetic structures or paramagnetic materials.

  8. Reorientation of magnetic anisotropy in obliquely sputtered metallic thin films

    NARCIS (Netherlands)

    Lisfi, A.; Lodder, J.C.; Wormeester, H.; Poelsema, B.

    2002-01-01

    Reorientation in the magnetic anisotropy as a function of film thickness has been observed in Co-Ni and Co thin films, obliquely sputtered on a polyethylene terephthalate substrate at a large incidence angle (70°). This effect is a consequence of the low magnetocrystalline anisotropy of the films (f

  9. On the origin of perpendicular magnetic anisotropy in strained Fe-Co(-X) films

    Science.gov (United States)

    Reichel, L.; Edström, A.; Pohl, D.; Rusz, J.; Eriksson, O.; Schultz, L.; Fähler, S.

    2017-02-01

    Very high magnetic anisotropies have been theoretically predicted for strained Fe-Co(-X) and indeed several experiments on epitaxial thin films seemed to confirm strain induced anisotropy enhancement. This study presents a critical analysis of the different contributions to perpendicular anisotropy: volume, interface and surface anisotropies. Tracing these contributions, thickness series of single layer films as well as multilayers with Au-Cu buffers/interlayers of different lattice parameters have been prepared. The analysis of their magnetic anisotropy reveals a negligible influence of the lattice parameter of the buffer. Electronic effects, originating from both, the Au-Cu interface and the film surface, outrange the elastic effects. Surface anisotropy, however, exceeds the interface anisotropy by more than a factor of three. A comparison with results from density functional theory suggests, that the experimentally observed strong perpendicular surface anisotropy originates from a deviation from an ideal oxide-free surface. Accordingly, tailored Fe-Co-X/oxide interfaces may open a route towards high anisotropy in rare-earth free materials.

  10. Anisotropy of the magnetic susceptibility of gallium

    Science.gov (United States)

    Pankey, T.

    1960-01-01

    The bulk magnetic susceptibilities of single gallium crystals and polycrystalline gallium spheres were measured at 25??C. The following anisotropic diamagnetic susceptibilities were found: a axis (-0.119??0. 001)??10-6 emu/g, b axis (-0.416??0.002)??10 -6 emu/g, and c axis (-0.229??0.001) emu/g. The susceptibility of the polycrystalline spheres, assumed to be the average value for the bulk susceptibility of gallium, was (-0.257??0.003)??10-6 emu/g at 25??C, and (-0.299??0.003)??10-6 emu/g at -196??C. The susceptibility of liquid gallium was (0.0031??0.001) ??10-6 emu/g at 30??C and 100??C. Rotational diagrams of the susceptibilities in the three orthogonal planes of the unit cell were not sinusoidal. The anisotropy in the single crystals was presumably caused by the partial overlap of Brillouin zone boundaries by the Fermi-energy surface. The large change in susceptibility associated with the change in state was attributed to the absence of effective mass influence in the liquid state. ?? 1960 The American Institute of Physics.

  11. Magnetic Moment and Anisotropy of Individual Co Atoms on Graphene

    Science.gov (United States)

    Donati, F.; Dubout, Q.; Autès, G.; Patthey, F.; Calleja, F.; Gambardella, P.; Yazyev, O. V.; Brune, H.

    2013-12-01

    We report on the magnetic properties of single Co atoms on graphene on Pt(111). By means of scanning tunneling microscopy spin-excitation spectroscopy, we infer a magnetic anisotropy of K=-8.1meV with out-of-plane hard axis and a magnetic moment of 2.2μB. Co adsorbs on the sixfold graphene hollow site. Upon hydrogen adsorption, three differently hydrogenated species are identified. Their magnetic properties are very different from those of clean Co. Ab initio calculations support our results and reveal that the large magnetic anisotropy stems from strong ligand field effects due to the interaction between Co and graphene orbitals.

  12. Magnetic anisotropies of (Ga,Mn)As films and nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Hoffmann, Frank

    2011-02-02

    In this work the magnetic anisotropies of the diluted magnetic semiconductor (Ga,Mn)As were investigated experimentally. (Ga,Mn)As films show a superposition of various magnetic anisotropies which depend sensitively on various parameters such as temperature, carrier concentration or lattice strain. However, the anisotropies of lithographically prepared (Ga,Mn)As elements differ significantly from an unpatterned (Ga,Mn)As film. In stripe-shaped structures this behaviour is caused by anisotropic relaxation of the compressive lattice strain. In order to determine the magnetic anisotropies of individual (Ga,Mn)As nanostructures a combination of ferromagnetic resonance and time-resolved scanning Kerr microscopy was employed in this thesis. In addition, local changes of the magnetic anisotropy in circular and rectangular structures were visualized by making use of spatially resolved measurements. Finally, also the influence of the laterally inhomogeneous magnetic anisotropies on the static magnetic properties, such as coercive fields, was investigated employing spatially resolved static MOKE measurements on individual (Ga,Mn)As elements. (orig.)

  13. Colossal anisotropy of the magnetic properties of doped lithium nitrodometalates

    Energy Technology Data Exchange (ETDEWEB)

    Antropov, Vladimir P [Ames Laboratory; Antonov, Victor N [Ames Laboratory

    2014-09-01

    We present a first-principles investigation of the electronic structure and physical properties of doped lithium nitridometalates Li2(Li1-xMx)N (LiMN) with M = Cr, Mn, Fe, Co, and Ni. The diverse properties include the equilibrium magnetic moments, magneto-crystalline anisotropy, magneto-optical Kerr spectra, and x-ray magnetic circular dichroism. We explain the colossal magnetic anisotropy in LiFeN by its unique electronic structure which ultimately leads to a series of unusual physical properties. The most unique property is a complete suppression of relativistic effects and freezing of orbital moments for in-plane orientation of the magnetization. This leads to the colossal spatial anisotropy of many magnetic properties including energy, Kerr, and dichroism effects. LiFeN is identified as an ultimate single-ion anisotropy system where a nearly insulating state can be produced by a spin orbital coupling alone. A very nontrivial strongly fluctuating and sign changing character of the magnetic anisotropy with electronic 3d-atomic doping is predicted theoretically. A large and highly anisotropic Kerr effect due to the interband transitions between atomic-like Fe 3d bands is found for LiFeN. A giant anisotropy of the x-ray magnetic circular dichroism for the Fe K spectrum and a very weak one for the Fe L2,3 spectra in LiFeN are also predicted.

  14. Is the magnetic anisotropy proportional to the orbital moment?

    Energy Technology Data Exchange (ETDEWEB)

    Skomski, R; Kashyap, A; Enders, A

    2011-04-01

    The relation between orbital moment and magnetic anisotropy is investigated by model calculations, which show that only a part of the spin-orbit coupling contributes to the anisotropy. A large part of the anisotropy energy, about 50% for iron series elements and nearly 100% for rare-earths, is stored in the nonrelativistic part of the Hamiltonian. A feature important for x-ray magnetic circular dichroism is that the orbital moment of heavy atoms rotates with the spin moment, whereas in light atoms, the orbital moment is recreated in each different direction. In the discussion, we consider three examples of current interest in different areas of magnetism, namely, spin-orbit coupling in Gd3+ and Eu2+, surface anisotropy of Nd2Fe14B, and multiferroic magnetization switching using rare-earths. (C) 2011 American Institute of Physics. [doi:10.1063/1.3562445

  15. Influence of magnetic anisotropy on the superferromagnetic ordering in nanocomposites

    DEFF Research Database (Denmark)

    Mørup, Steen; Christiansen, Gunnar Dan

    1993-01-01

    Magnetic interaction between ultrafine particles may result in superferromagnetism, i.e., ordering of the magnetic moments of particles which would be superparamagnetic if they were noninteracting. In this article we discuss the influence of the magnetic anisotropy on the temperature dependence o...

  16. Competitive and cooperative anisotropy in magnetic nanocrystal chains of magnetotactic bacteria

    Science.gov (United States)

    Koulialias, D.; García-Rubio, I.; Rahn-Lee, L.; Komeili, A.; Löffler, J. F.; Gehring, A. U.; Charilaou, M.

    2016-08-01

    The formation of cellular magnetic dipoles by chain assemblies of stable single-domain magnetite nanocrystals is a characteristic feature in magnetotactic bacteria (MTB). The dipole strength depends on the competition or cooperation between the various anisotropic energy contributions, mainly between the magnetocrystalline and the interaction-induced shape anisotropy. Ferromagnetic resonance spectroscopy and numerical simulations of intracellular magnetite assemblies in the MTB Desulfovibrio magneticus strain RS-1 show that the alignment of elongated nanocrystallites leads to a predominant uniaxial anisotropy, which is enhanced when the magnetocrystalline symmetry is collinear to the chain, i.e., the anisotropies are cooperative vs. being competitive. This direct insight into the anisotropy variations in chain assemblies provides a physical framework to tailor magnetic nanocomposites, where the collective magnetic properties result from the interactions between the individual nanocrystalline constituents.

  17. Control of magnetic domains in Co/Pd multilayered nanowires with perpendicular magnetic anisotropy.

    Science.gov (United States)

    Noh, Su Jung; Miyamoto, Yasuyoshi; Okuda, Mitsunobu; Hayashi, Naoto; Kim, Young Keun

    2012-01-01

    Magnetic domain wall (DW) motion induced by spin transfer torque in magnetic nanowires is of emerging technological interest for its possible applications in spintronic memory or logic devices. Co/Pd multilayered magnetic nanowires with perpendicular magnetic anisotropy were fabricated on the surfaces of Si wafers by ion-beam sputtering. The nanowires had different sized widths and pinning sites formed by an anodic oxidation method via scanning probe microscopy (SPM) with an MFM tip. The magnetic domain structure was changed by an anodic oxidation method. To discover the current-induced DW motion in the Co/Pd nanowires, we employed micromagnetic modeling based on the Landau-Lifschitz-Gilbert (LLG) equation. The split DW motions and configurations due to the edge effects of pinning site and nanowire appeared.

  18. Cubic versus spherical magnetic nanoparticles: the role of surface anisotropy.

    Science.gov (United States)

    Salazar-Alvarez, G; Qin, J; Sepelák, V; Bergmann, I; Vasilakaki, M; Trohidou, K N; Ardisson, J D; Macedo, W A A; Mikhaylova, M; Muhammed, M; Baró, M D; Nogués, J

    2008-10-08

    The magnetic properties of maghemite (gamma-Fe2O3) cubic and spherical nanoparticles of similar sizes have been experimentally and theoretically studied. The blocking temperature, T(B), of the nanoparticles depends on their shape, with the spherical ones exhibiting larger T(B). Other low temperature properties such as saturation magnetization, coercivity, loop shift or spin canting are rather similar. The experimental effective anisotropy and the Monte Carlo simulations indicate that the different random surface anisotropy of the two morphologies combined with the low magnetocrystalline anisotropy of gamma-Fe2O3 is the origin of these effects.

  19. Magnetic ordering and anisotropy in heavy atom radicals.

    Science.gov (United States)

    Winter, Stephen M; Hill, Stephen; Oakley, Richard T

    2015-03-25

    Recent developments in stable radical chemistry have afforded "heavy atom" radicals, neutral open-shell (S = 1/2) molecular species containing heavy p-block elements (S, Se), which display solid-state magnetic properties once considered exclusive to conventional metal-based magnets. These highly spin-delocalized radicals do not associate in the solid state and yet display extensive networks of close intermolecular interactions. Spin density on the heavy atoms allows for increased isotropic and spin-orbit mediated anisotropic exchange effects. Structural variations induced by chemical modification and physical pressure, coupled with ab-initio methods to estimate exchange energies, have facilitated the development of predictive structure/property relationships. These results, coupled with detailed theoretical analyses and magnetic resonance spectroscopic measurements, have provided insight into the magnetic structure of ferromagnetic and spin-canted antiferromagnetic ordered materials as well as an understanding of the importance of spin-orbit coupling contributions to magnetic hysteresis and anisotropy. Isotropic and anisotropic ferromagnetic exchange can also be enhanced indirectly by the incorporation of heavy atoms into nonspin-bearing sites, where they can contribute to multi-orbital spin-orbit coupling.

  20. Research Update: Magnetoionic control of magnetization and anisotropy in layered oxide/metal heterostructures

    Directory of Open Access Journals (Sweden)

    K. Duschek

    2016-03-01

    Full Text Available Electric field control of magnetization and anisotropy in layered structures with perpendicular magnetic anisotropy is expected to increase the versatility of spintronic devices. As a model system for reversible voltage induced changes of magnetism by magnetoionic effects, we present several oxide/metal heterostructures polarized in an electrolyte. Room temperature magnetization of Fe-O/Fe layers can be changed by 64% when applying only a few volts in 1M KOH. In a next step, the bottom interface of the in-plane magnetized Fe layer is functionalized by an L10 FePt(001 underlayer exhibiting perpendicular magnetic anisotropy. During subsequent electrocrystallization and electrooxidation, well defined epitaxial Fe3O4/Fe/FePt heterostructures evolve. The application of different voltages leads to a thickness change of the Fe layer sandwiched between Fe-O and FePt. At the point of transition between rigid magnet and exchange spring magnet regime for the Fe/FePt bilayer, this induces a large variation of magnetic anisotropy.

  1. Low-temperature magnetic anisotropy in micas and chlorite

    DEFF Research Database (Denmark)

    Biedermann, Andrea R.; Bender Koch, Christian; Lorenz, Wolfram E A;

    2014-01-01

    of magnetic susceptibility. Because diamagnetic and paramagnetic susceptibility are both linearly dependent on field, separation of the anisotropic contributions requires understanding how the degree of anisotropy of the paramagnetic susceptibility changes as a function of temperature. Note that diamagnetic...... of approximately 6.3-8.7 for individual samples of muscovite, phlogopite and chlorite on cooling from RT to 77 K and between 11.2 and 12.4 for biotite. A decrease in temperature enhances the paramagnetic anisotropy in a mineral. Biotite exhibits a relatively stronger enhancement due to the onset of magnetic......Phyllosilicates, such as micas and chlorite, are common rock-forming minerals and often show preferred orientation in deformed rocks. In combination with single-crystal anisotropy, this leads to anisotropy of physical properties in the rock, such as magnetic susceptibility. In order to effectively...

  2. Three-dimensional mapping of single-atom magnetic anisotropy.

    Science.gov (United States)

    Yan, Shichao; Choi, Deung-Jang; Burgess, Jacob A J; Rolf-Pissarczyk, Steffen; Loth, Sebastian

    2015-03-11

    Magnetic anisotropy plays a key role in the magnetic stability and spin-related quantum phenomena of surface adatoms. It manifests as angular variations of the atom's magnetic properties. We measure the spin excitations of individual Fe atoms on a copper nitride surface with inelastic electron tunneling spectroscopy. Using a three-axis vector magnet we rotate the magnetic field and map out the resulting variations of the spin excitations. We quantitatively determine the three-dimensional distribution of the magnetic anisotropy of single Fe atoms by fitting the spin excitation spectra with a spin Hamiltonian. This experiment demonstrates the feasibility of fully mapping the vector magnetic properties of individual spins and characterizing complex three-dimensional magnetic systems.

  3. Fourfold magnetic anisotropy, coercivity and magnetization reversal of Co/V bilayers grown on MgO(0 0 1)

    Energy Technology Data Exchange (ETDEWEB)

    Calleja, J F [Departamento de Fisica, Facultad de Ciencias, Universidad de Oviedo, Calvo Sotelo s/n, 33007 Oviedo (Spain); Muro, M GarcIa del [Departament de Fisica Fonamental and Institut de Nanociencia i Nanotecnologia IN2UB de la Universitat de Barcelona, MartIi Franques, 1, E-08028 Barcelona (Spain); Presa, B [Departamento de Fisica, Facultad de Ciencias, Universidad de Oviedo, Calvo Sotelo s/n, 33007 Oviedo (Spain); Matarranz, R [Departamento de Fisica, Facultad de Ciencias, Universidad de Oviedo, Calvo Sotelo s/n, 33007 Oviedo (Spain); Corrales, J A [Departmento de Informatica, Universidad de Oviedo, Edificio Departamental 1, Campus de Viesques s/n, 33204 Gijon (Spain); Labarta, A [Departament de Fisica Fonamental and Institut de Nanociencia i Nanotecnologia IN2UB de la Universitat de Barcelona, MartIi Franques, 1, E-08028 Barcelona (Spain); Contreras, M C [Departamento de Fisica, Facultad de Ciencias, Universidad de Oviedo, Calvo Sotelo s/n, 33007 Oviedo (Spain)

    2007-11-21

    Magnetic anisotropy and magnetization reversal of Al/Co/V/MgO(0 0 1) thin films have been investigated. The films were fabricated by magnetron sputtering. The roles of both Co and V layers thicknesses have been studied. Magnetic characterization has been carried out by transverse susceptibility (TS) measurements and hysteresis loops. Cobalt is grown in the hcp structure on V with the c axis parallel to the film plane. Two types of hcp Co crystal are grown with the c axes perpendicular to each other. This structure gives rise to a fourfold magnetic anisotropy. When the V layer thickness is below 40 A a superimposed uniaxial anisotropy develops, the effect of which is a depression in the TS, in agreement with theoretical calculations. This uniaxial anisotropy is induced by the substrate and due to a discontinuous growth of the V layer. For hcp Co grown on V, the magnetic anisotropy rapidly increases with Co layer thickness. In this case, unexpected shifted hysteresis loops along the hard axes were observed when the films were not saturated. This has been explained by taking into account the magnetization reversal along the hard axis: it proceeds via magnetization rotation of some portions of the film at high fields, and by domain wall motion of the rest of the film at lower field values.

  4. Perpendicular magnetic anisotropy and the magnetization process in CoFeB/Pd multilayer films

    DEFF Research Database (Denmark)

    Ngo, Duc-The; Quach, Duy-Truong; Hung, Tran Quang

    2014-01-01

    with an effective uniaxial anisotropy up to 7.7 × 106 Jm−3 and a saturation magnetization as low as 200 emu cm−3 are achieved. The surface/interfacial anisotropy of the CoFeB/Pd interfaces—the main contribution to the PMA—is separated from the effective uniaxial anisotropy of the films and appears to increase...

  5. Cosmic Ray Small Scale Anisotropies and Local Turbulent Magnetic Fields

    CERN Document Server

    López-Barquero, Vanessa; Xu, S; Desiati, P; Lazarian, A

    2015-01-01

    Cosmic ray anisotropy is observed in a wide energy range and at different angular scales by a variety of experiments. However, a comprehensive and satisfactory explanation has been elusive for over a decade now. The arrival distribution of cosmic rays on Earth is the convolution of the distribution of their sources and of the effects of geometry and properties of the magnetic field through which particles propagate. It is generally believed that the anisotropy topology at the largest angular scale is adiabatically shaped by diffusion in the structured interstellar magnetic field. On the contrary, the medium and small angular scale structure could be an effect of non diffusive propagation of cosmic rays in perturbed magnetic fields. In particular, a possible explanation of the observed small scale anisotropy observed at TeV energy scale, may come from the effect of particle scattering in turbulent magnetized plasmas. We perform numerical integration of test particle trajectories in low-$\\beta$ compressible mag...

  6. Chiral asymmetry driven by unidirectional magnetic anisotropy in Spin-Orbitronic systems

    Science.gov (United States)

    Perna, Paolo; Ajejas, Fernando; Maccariello, Davide; Guerrero, Ruben; Camarero, Julio; Miranda, Rodolfo

    2016-10-01

    Spin-Orbit (SO) effects of a ferromagnetic (FM) layer can be artificially modified by interfacial exchange coupling with an anti-ferro magnet (AFM). Non-symmetric magnetization reversals as well as asymmetric transport behaviors are distinctive signatures of the symmetry-breaking induced by such interfacial coupling. We present a complete picture of the symmetry of the SO effects by studying the magneto-transport properties of single FM film and FM/AFM systems (exchanged-biased bilayer and spin-valve structures) with specific in-plane magnetic anisotropy. Single FM films with a well-defined (two-fold) uniaxial magnetic anisotropy display symmetric magnetization reversals and magneto-resistance responses for any value and direction of the applied magnetic field. On the contrary, in the exchange-biased structures, the exchange interaction at the interface between the FM and AFM layers is responsible of chiral asymmetries in magnetization reversal pathways as well as in the magneto-resistance behaviors. Such asymmetries are directly related to the additional unidirectional (one-fold) magnetic anisotropy imposed by the AFM. In particular, chiral reversals and MR responses are found around the magnetization hard-axis direction. This has been shown in FM/AFM bilayer and spin-valve (where the MR outputs are related to different transport phenomena, i.e. anisotropic magneto-resistance and giant magneto-resistance respectively), hence indicating that the chiral asymmetries are intrinsic of systems with unidirectional anisotropy.

  7. CoTaZr/Pd multilayer with perpendicular magnetic anisotropy

    Directory of Open Access Journals (Sweden)

    Yong Chang Lau

    2013-08-01

    Full Text Available We report a novel perpendicularly magnetized thin film [Co91.5Ta4.5Zr4/Pd]5 multilayer, which exhibits strong perpendicular magnetic anisotropy when grown on 5 nm of Pd and Ru seed layers. The Pd-seeded multilayer annealed at 300 °C shows an effective uniaxial anisotropy constant, Keff = 1.1 MJ m−3, with an anisotropy field as high as 1.6 T. The perpendicular anisotropy is sustained on annealing at 400 °C for 1 h. X-ray diffraction on multilayers with 30 repeats suggests that the use of amorphous CoTaZr reduces the stress of the stack, compared to [Co/Pd] multilayer.

  8. A Dzyaloshinskii-Moriya Anisotropy in nanomagnets with in-plane magnetization

    Science.gov (United States)

    Cubukcu, M.; Sampaio, J.; Khvalkovskiy, A. V.; Apalkov, D.; Cros, V.; Reyren, N.

    The Dzyaloshinskii-Moriya interaction (DMI) is known to be a direct manifestation of spin-orbit coupling in systems with broken inversion symmetry. We present a new anisotropy for in-plane-magnetized nanomagnets which is due to the interfacial DMI. This new anisotropy depends on the shape of the magnet, and is perpendicular to the demagnetization shape anisotropy. The DMI anisotropy term that we introduce here results from the DMI energy reduction due to an out-of-plane tilt of the spins at the edges that are oriented perpendicular to the magnetization. For large enough DMI, the reduction of the DMI and anisotropy energies takes over the demagnetization energy cost when magnetization lies along the minor axis of a structure. Our experimental, numerical and analytical results demonstrate this prediction in magnets of elongated shape for small enough volume (and thus quasi-uniform magnetization). Our results also provide the first experimental evidence of the interfacial DMI-induced tilt of the spins at the borders. This work was supported by the Samsung Global MRAM Innovation Program.

  9. Magnetic anisotropy and mechanism of magnetic relaxation in Er(III) single-ion magnets.

    Science.gov (United States)

    Singh, Saurabh Kumar; Gupta, Tulika; Rajaraman, Gopalan

    2014-10-20

    Magnetic anisotropy is a key component in the design of single-molecule magnets (SMMs) possessing a large barrier height for magnetization reversal. Lanthanide-based SMMs are the most promising candidates in this arena as they offer a large magnetic anisotropy due to the presence of strong spin-orbit coupling. Among lanthanides, Er(III) complexes are gaining attention in the area of SMMs, because of their intriguing magnetic properties and attractive blocking temperatures. Here, we have undertaken detailed ab initio calculations on four structurally diverse Er(III) SMMs to shed light on how the magnetic anisotropy is influenced by the role of symmetry and structural distortions. The employed CASSCF+RASSI calculations have offered rationale for the observed differences in the estimated Ueff values for the studied complexes and also offered hints to the mechanism of magnetic relaxation. The differences in the mechanism of magnetic relaxations are further analyzed based on the Er-ligand interactions, which is obtained by analyzing the charges, densities, luminescent behavior and the frontier molecular orbitals. Our calculations, for the first time, have highlighted the importance of high symmetry environment and ligand donor strength in obtaining large Ueff values for the Er(III) complexes. We have examined these possibilities by modeling several structures with variable coordination numbers and point group symmetry. These results signify the need of a detailed understanding on the shape of the anisotropy and the point group symmetry in order to achieve large Ueff values in Er(III) single-ion magnets.

  10. Pembuatan Bonded Anisotropi Magnet NdFeB dan Karakterisasinya

    OpenAIRE

    Nuraini, Siti

    2015-01-01

    Research on fabrications of bonded magnets NdFeB type MQA-37-16 with polivynil chloride binder has been done. The purpose of this study the effect of field strength and orientation on the physical and magnetic properties in the manufacture of bonded magnets NdFeB. Preparation process by dry mixing powder magnets NdFeB and polivynil chloride binder bi using Shaker Mill. For each sample takes 4 grams total mass of bonded magnet NdFeB. Printing is done isotropic and anisotropy using a magnetic f...

  11. Variable variance Preisach model for multilayers with perpendicular magnetic anisotropy

    Science.gov (United States)

    Franco, A. F.; Gonzalez-Fuentes, C.; Morales, R.; Ross, C. A.; Dumas, R.; Åkerman, J.; Garcia, C.

    2016-08-01

    We present a variable variance Preisach model that fully accounts for the different magnetization processes of a multilayer structure with perpendicular magnetic anisotropy by adjusting the evolution of the interaction variance as the magnetization changes. We successfully compare in a quantitative manner the results obtained with this model to experimental hysteresis loops of several [CoFeB/Pd ] n multilayers. The effect of the number of repetitions and the thicknesses of the CoFeB and Pd layers on the magnetization reversal of the multilayer structure is studied, and it is found that many of the observed phenomena can be attributed to an increase of the magnetostatic interactions and subsequent decrease of the size of the magnetic domains. Increasing the CoFeB thickness leads to the disappearance of the perpendicular anisotropy, and such a minimum thickness of the Pd layer is necessary to achieve an out-of-plane magnetization.

  12. Magnetic anisotropy in GaMnAs; Magnetische Anisotropie in GaMnAs

    Energy Technology Data Exchange (ETDEWEB)

    Daeubler, Joachim

    2009-07-02

    The goal of the present work was the detailed investigation of the impact of parameters like vertical strain, hole concentration, substrate orientation and patterning on the MA in GaMnAs. At first a method is introduced enabling us to determine the MA from angle-dependent magnetotransport measurements. This method was used to analyze the impact of vertical strain {epsilon}{sub zz} on the MA in a series of GaMnAs layers with a Mn content of 5% grown on relaxed InGaAs-templates. While hole concentration and Curie temperature were found to be unaffected by vertical strain, a significant dependence of the MA on {epsilon}{sub zz} was found. The most pronounced dependence was observed for the anisotropy parameter B{sub 2} {sub perpendicular} {sub to}, representing the intrinsic contribution to the MA perpendicular to the layer plane. For this parameter a linear dependence on {epsilon}{sub zz} was found, resulting in a strain-induced transition of the magnetic easy axis with increasing strain from in-plane to out-of-plane at {epsilon}{sub zz} {approx} -0.13%. Post-growth annealing of the samples leads to an outdiffusion and/or regrouping of the highly mobile Mn interstitial donor defects, resulting in an increase in both p and T{sub C}. For the annealed samples, the transition from in-plane to out-of-plane easy axis takes place at {epsilon}{sub zz} {approx} -0.07%. From a comparison of as-grown and annealed samples, B{sub 2} {sub perpendicular} {sub to} was found to be proportional to both p and {epsilon}{sub zz}, B{sub 2} {sub perpendicular} {sub to} {proportional_to} p .{epsilon}{sub zz}. To study the influence of substrate orientation on the magnetic properties of GaMnAs, a series of GaMnAs layers with Mn contents up to 5% was grown on (001)- and (113)A-oriented GaAs substrates. The hole densities and Curie temperatures, determined from magnetotransport measurements, are drastically reduced in the (113)A layers. The differences in the magnetic properties of (113)A- and

  13. Magnetic anisotropy of ultrafine 316L stainless steel fibers

    Science.gov (United States)

    Shyr, Tien-Wei; Huang, Shih-Ju; Wur, Ching-Shuei

    2016-12-01

    An as-received 316L stainless steel fiber with a diameter of 20 μm was drawn using a bundle drawing process at room temperature to form ultrafine stainless steel fibers with diameters of 12, 8, and 6 μm. The crystalline phases of the fibers were analyzed using the X-ray diffraction (XRD) profile fitting technique. The grain sizes of γ-austenite and α‧-martensite were reduced to nanoscale sizes after the drawing process. XRD analysis and focused ion beam-scanning electron microscope observations showed that the newly formed α‧-martensitic grains were closely arrayed in the drawing direction. The magnetic property was measured using a superconducting quantum interference device vibrating sample magnetometer. The magnetic anisotropy of the fibers was observed by applying a magnetic field parallel and perpendicular to the fiber axis. The results showed that the microstructure anisotropy including the shape anisotropy, magnetocrystalline anisotropy, and the orientation of the crystalline phases strongly contributed to the magnetic anisotropy.

  14. On the origin of magnetic anisotropy in two dimensional CrI3

    Science.gov (United States)

    Lado, J. L.; Fernández-Rossier, J.

    2017-09-01

    The observation of ferromagnetic order in a monolayer of CrI3 has been recently reported, with a Curie temperature of 45 K and off-plane easy axis. Here we study the origin of magnetic anisotropy, a necessary ingredient to have magnetic order in two dimensions, combining two levels of modeling, density functional calculations and spin model Hamiltonians. We find two different contributions to the magnetic anisotropy of the material, favoring off-plane magnetization and opening a gap in the spin wave spectrum. First, ferromagnetic super-exchange across the ≃90 degree Cr-I-Cr bonds, are anisotropic, due to the spin-orbit interaction of the ligand I atoms. Second, a much smaller contribution that comes from the single ion anisotropy of the S  =  3/2 Cr atom. Our results permit to establish the XXZ Hamiltonian, with a very small single ion anisotropy, as the adequate spin model for this system. Using spin wave theory we estimate the Curie temperature and we highlight the essential role played by the gap that magnetic anisotropy induces on the magnon spectrum.

  15. Approach to fabricating Co nanowire arrays with perpendicular anisotropy: Application of a magnetic field during deposition

    Energy Technology Data Exchange (ETDEWEB)

    Ge, Shihui; Li, Chao; Ma, Xiao; Li, Wei; Xi, Li; Li, C. X.

    2001-07-01

    Cobalt (Co) nanowire arrays were electrodeposited into the pores of polycarbonate membranes. A magnetic field parallel or perpendicular to the membrane plane was applied during deposition to control the wire growth. X-ray diffraction, transmission electron microscopy, and vibrating sample magnetometer were employed to investigate the structure as well as the magnetic properties of the nanowire arrays. The results show that the magnetic field applied during deposition strongly influences the growth of Co nanowires, inducing variations in their crystalline structure and magnetic properties. The sample deposited with the field perpendicular to the membrane plane exhibits a perpendicular magnetic anisotropy with greatly enhanced coercivity and squareness as a result of the preferred growth of Co grains with the c axis perpendicular to the film plane. In contrast, the deposition in a parallel magnetic field forces Co grains to grow with the c axis parallel to the film plane, resulting in in-plane anisotropy. {copyright} 2001 American Institute of Physics.

  16. Perpendicular magnetic anisotropy in Co$_2$Fe$_{0.4}$Mn$_{0.6}$Si

    OpenAIRE

    Ludbrook, Bartholomew M.; Ruck, Ben J.; Granville, Simon

    2016-01-01

    We report perpendicular magnetic anisotropy (PMA) in the half-metallic ferromagnetic Heusler alloy Co$_2$Fe$_{0.4}$Mn$_{0.6}$Si (CFMS) in a MgO/CFMS/Pd trilayer stack. PMA is found for CFMS thicknesses between 1 and 2 nm, with a magnetic anisotropy energy density of $K_U = 1.5\\times 10^6$ erg/cm$^3$ for t$_{\\tiny \\textrm{CFMS}} = 1.5$ nm. Both the MgO and Pd layer are necessary to induce the PMA. We measure a tunable anomalous Hall effect, where its sign and magnitude vary with both the CFMS ...

  17. Perpendicular magnetic anisotropy in Co2Fe0.4Mn0.6Si

    Science.gov (United States)

    Ludbrook, B. M.; Ruck, B. J.; Granville, S.

    2016-07-01

    We report perpendicular magnetic anisotropy (PMA) in the half-metallic ferromagnetic Heusler alloy Co2Fe0.4Mn0.6Si (CFMS) in a MgO/CFMS/Pd trilayer stack. PMA is found for CFMS thicknesses between 1 and 2 nm, with a magnetic anisotropy energy density of KU=1.5 ×106 erg/cm3 for tCFMS=1.5 nm. Both the MgO and Pd layer are necessary to induce the PMA. We measure a tunable anomalous Hall effect, where its sign and magnitude vary with both the CFMS and Pd thickness.

  18. Effect of defects, magnetocrystalline anisotropy, and shape anisotropy on magnetic structure of iron thin films by magnetic force microscopy

    Directory of Open Access Journals (Sweden)

    Ke Xu

    2017-05-01

    Full Text Available Microstructures of magnetic materials, including defects and crystallographic orientations, are known to strongly influence magnetic domain structures. Measurement techniques such as magnetic force microscopy (MFM thus allow study of correlations between microstructural and magnetic properties. The present work probes effects of anisotropy and artificial defects on the evolution of domain structure with applied field. Single crystal iron thin films on MgO substrates were milled by Focused Ion Beam (FIB to create different magnetically isolated squares and rectangles in [110] crystallographic orientations, having their easy axis 45° from the sample edge. To investigate domain wall response on encountering non-magnetic defects, a 150 nm diameter hole was created in the center of some samples. By simultaneously varying crystal orientation and shape, both magnetocrystalline anisotropy and shape anisotropy, as well as their interaction, could be studied. Shape anisotropy was found to be important primarily for the longer edge of rectangular samples, which exaggerated the FIB edge effects and provided nucleation sites for spike domains in non-easy axis oriented samples. Center holes acted as pinning sites for domain walls until large applied magnetic fields. The present studies are aimed at deepening the understanding of the propagation of different types of domain walls in the presence of defects and different crystal orientations.

  19. Perpendicular magnetic anisotropy and magnetization dynamics in oxidized CoFeAl films.

    Science.gov (United States)

    Wu, Di; Zhang, Zhe; Li, Le; Zhang, Zongzhi; Zhao, H B; Wang, J; Ma, B; Jin, Q Y

    2015-07-20

    Half-metallic Co-based full-Heusler alloys with perpendicular magnetic anisotropy (PMA), such as Co2FeAl in contact with MgO, are receiving increased attention recently due to its full spin polarization for high density memory applications. However, the PMA induced by MgO interface can only be realized for very thin magnetic layers (usually below 1.3 nm), which would have strong adverse effects on the material properties of spin polarization, Gilbert damping parameter, and magnetic stability. In order to solve this issue, we fabricated oxidized Co50Fe25Al25 (CFAO) films with proper thicknesses without employing the MgO layer. The samples show controllable PMA by tuning the oxygen pressure (PO2) and CFAO thickness (tCFAO), large perpendicular anisotropy field of ~8.0 kOe can be achieved at PO2 = 12% for the sample of tCFAO = 2.1 nm or at PO2 = 7% for tCFAO = 2.8 nm. The loss of PMA at thick tCFAO or high PO2 results mainly from the formation of large amount of CoFe oxides, which are superparamagnetic at room temperature but become hard magnetic at low temperatures. The magnetic CFAO films, with strong PMA in a relatively wide thickness range and small intrinsic damping parameter below 0.028, would find great applications in developing advanced spintronic devices.

  20. Ab initio studies of magnetic anisotropy energy in highly Co-doped ZnO

    Science.gov (United States)

    Łusakowski, A.; Szuszkiewicz, W.

    2017-03-01

    Density functional theory (DFT) calculations of the energy of magnetic anisotropy for diluted magnetic semiconductor (Zn,Co)O were performed using OpenMX package with fully relativistic pseudopotentials. The analysis of the band spin-orbit interaction and the magnetic ion's surrounding on magnetic anisotropy have been provided. As a result, the calculations show that the magnetic anisotropy in (Zn,Co)O solid solution, mainly of the single ion anisotropy type has been caused by Co ions.

  1. LDA+DMFT Approach to Magnetocrystalline Anisotropy of Strong Magnets

    Directory of Open Access Journals (Sweden)

    Jian-Xin Zhu

    2014-05-01

    Full Text Available The new challenges posed by the need of finding strong rare-earth-free magnets demand methods that can predict magnetization and magnetocrystalline anisotropy energy (MAE. We argue that correlated electron effects, which are normally underestimated in band-structure calculations, play a crucial role in the development of the orbital component of the magnetic moments. Because magnetic anisotropy arises from this orbital component, the ability to include correlation effects has profound consequences on our predictive power of the MAE of strong magnets. Here, we show that incorporating the local effects of electronic correlations with dynamical mean-field theory provides reliable estimates of the orbital moment, the mass enhancement, and the MAE of YCo_{5}.

  2. Magnetization switching behavior with competing anisotropies in epitaxial Co3FeN /MnN exchange-coupled bilayers

    Science.gov (United States)

    Hajiri, T.; Yoshida, T.; Jaiswal, S.; Filianina, M.; Borie, B.; Ando, H.; Asano, H.; Zabel, H.; Kläui, M.

    2016-11-01

    We report unusual magnetization switching processes and angular-dependent exchange bias effects in fully epitaxial Co3FeN /MnN bilayers, where magnetocrystalline anisotropy and exchange coupling compete, probed by longitudinal and transverse magneto-optic Kerr effect (MOKE) magnetometry. The MOKE loops show multistep jumps corresponding to the nucleation and propagation of 90∘ domain walls in as-grown bilayers. By inducing exchange coupling, we confirm changes of the magnetization switching process due to the unidirectional anisotropy field of the exchange coupling. Taking into account the experimentally obtained values of the fourfold magnetocrystalline anisotropy, the unidirectional anisotropy field, the exchange-coupling constant, and the uniaxial anisotropy including its direction, the calculated angular-dependent exchange bias reproduces the experimental results. These results demonstrate the essential role of the competition between magnetocrystalline anisotropy and exchange coupling for understanding and tailoring exchange-coupling phenomena usable for engineering switching in fully epitaxial bilayers made of tailored materials.

  3. Exotic skyrmion crystals in chiral magnets with compass anisotropy

    Science.gov (United States)

    Chen, J. P.; Zhang, Dan-Wei; Liu, J.-M.

    2016-07-01

    The compass-type anisotropy appears naturally in diverse physical contexts with strong spin-orbit coupling (SOC) such as transition metal oxides and cold atomic gases etc, and it has been receiving substantial attention. Motivated by recent studies and particularly recent experimental observations on helimagnet MnGe, we investigate the critical roles of this compass-type anisotropy in modulating various spin textures of chiral magnets with strong SOC, by Monte Carlo simulations based on a classical Heisenberg spin model with Dzyaloshinsky-Moriya interaction and compass anisotropy. A phase diagram with emergent spin orders in the space of compass anisotropy and out-of-plane magnetic field is presented. In this phase diagram, we propose that a hybrid super-crystal structure consisting of alternating half-skyrmion and half-anti-skyrmion is the possible zero-field ground state of MnGe. The simulated evolution of the spin structure driven by magnetic field is in good accordance with experimental observations on MnGe. Therefore, this Heisenberg spin model successfully captures the main physics responsible for the magnetic structures in MnGe, and the present work may also be instructive to research on the magnetic states in other systems with strong SOC.

  4. Resolving the controversy of a possible relationship between perpendicular magnetic anisotropy and the magnetic damping parameter

    Energy Technology Data Exchange (ETDEWEB)

    Shaw, Justin M.; Nembach, Hans T.; Silva, T. J. [National Institute of Standards and Technology, Electromagnetics Division, Boulder, Colorado 80305 (United States)

    2014-08-11

    We use broadband ferromagnetic resonance spectroscopy to systematically measure the Landau-Lifshitz damping parameter, perpendicular anisotropy, and the orbital moment asymmetry in Co{sub 90}Fe{sub 10}/Ni multilayers. No relationship is found between perpendicular magnetic anisotropy and the damping parameter in this material. However, inadequate accounting for inhomogeneous linewidth broadening, spin-pumping, and two-magnon scattering could give rise to an apparent relationship between anisotropy and damping. In contrast, the orbital-moment asymmetry and the perpendicular anisotropy are linearly proportional to each other. These results demonstrate a fundamental mechanism by which perpendicular anisotropy can be varied independently of the damping parameter.

  5. Perpendicular Magnetic Anisotropy in Fe-N Thin Films: Threshold Field for Irreversible Magnetic Stripe Domain Rotation

    Science.gov (United States)

    Garnier, L.-C.; Eddrief, M.; Fin, S.; Bisero, D.; Fortuna, F.; Etgens, V. H.; Marangolo, M.

    The magnetic properties of an iron nitride thin film obtained by ion implantation have been investigated. N2+ ions were implanted in a pristine iron layer epitaxially grown on ZnSe/GaAs(001). X-ray diffraction measurements revealed the formation of body-centered tetragonal N-martensite whose c-axis is perpendicular to the thin film plane and c-parameter is close to that of α‧-Fe8N. Magnetic measurements disclosed a weak perpendicular magnetic anisotropy (PMA) whose energy density KPMA was assessed to about 105J/m3. A sharp decline of the in-plane magnetocrystalline anisotropy (MCA) was also observed, in comparison with the body-centered cubic iron. The origin of the PMA is attributed to the MCA of N-martensite and/or stress-induced anisotropy. As a result of the PMA, weak magnetic stripe domains with a period of about 130nm aligned along the last saturating magnetic field direction were observed at remanence by magnetic force microscopy. The application of an increasing in-plane magnetic field transverse to the stripes Htrans highlighted a threshold value (μ0Htrans≈0.1T) above which these magnetic domains irreversibly rotated. Interestingly, below this threshold, the stripes do not rotate, leading to a zero remanent magnetization along the direction of the applied field. The interest of this system for magnetization dynamics is discussed.

  6. Texture-induced microwave background anisotropies

    Energy Technology Data Exchange (ETDEWEB)

    Borrill, J.; Copeland, E.J.; Liddle, A.R.; Stebbins, A.; Veeraraghavan, S. (School of Mathematical and Physical Sciences, University of Sussex, Falmer, Brighton BN1 9QH (United Kingdom) Blackett Laboratory, Imperial College of Science and Technology, Prince Consort Road, London SW7 2BZ (United Kingdom) NASA/Fermilab Astrophysics Center, Fermi National Accelerator Laoratory, Batavia, Illinois 60510 (United States) NASA Goddard Space Flight Center, Code 685, Greenbelt, Maryland 20771 (United States) Steward Observatory, University of Arizona, Tucson, Arizona 85721 (United States))

    1994-08-15

    We use numerical simulations to calculate the cosmic microwave background anisotropy induced by the evolution of a global texture field, with special emphasis on individual textures. Both spherically symmetric and general configurations are analyzed, and in the latter case we consider field configurations which exhibit unwinding events and also ones which do not. We compare the results given by evolving the field numerically under both the expanded core (XCORE) and nonlinear [sigma] model (NLSM) approximations with the analytic predictions of the NLSM exact solution for a spherically symmetric self-similar (SSSS) unwinding. We find that the random unwinding configuration spots' typical peak height is 60--75 % and angular size typically only 10% of those of the SSSS unwinding, and that random configurations without an unwinding event nonetheless may generate indistinguishable hot and cold spots. A brief comparison is made with other work.

  7. Nanomechanical measurement of magnetostriction and magnetic anisotropy in (Ga,Mn)As.

    Science.gov (United States)

    Masmanidis, S C; Tang, H X; Myers, E B; Li, Mo; De Greve, K; Vermeulen, G; Van Roy, W; Roukes, M L

    2005-10-28

    A GaMnAs nanoelectromechanical resonator is used to obtain the first measurement of magnetostriction in a dilute magnetic semiconductor. Resonance frequency shifts induced by field-dependent magnetoelastic stress are used to simultaneously map the magnetostriction and magnetic anisotropy constants over a wide range of temperatures. Owing to the central role of carriers in controlling ferromagnetic interactions in this material, the results appear to provide insight into a unique form of magnetoelastic behavior mediated by holes.

  8. Magnetization Switching in a Small Disk with Shape Anisotropy

    Institute of Scientific and Technical Information of China (English)

    LU Dong-Li; XU Chen

    2010-01-01

    @@ We study the precessional switching of a single domain,uniaxial magnetic disk with shape anisotropy by the micromagnetic simulation.The results show that magnetic switching can be driven by a smaller magnetic field pulse in an elliptic disk with its long semiaxis perpendicular to the easy axis than in a circular disk.The shape anisotropy can change the height of the energy barrier,thus we may obtain an optimal fast magnetization switching by tuning the aspect ratio of the disk under the thermal stability condition.The switching behavior of the elliptic and circular disks is studied in detail.It is found that only properly choosing the pulse amplitude and duration can realize the fast precessional switching.

  9. Magnetic anisotropy of polycrystalline magnetoferritin investigated by SQUID and electron magnetic resonance

    Science.gov (United States)

    Moro, F.; de Miguel, R.; Jenkins, M.; Gómez-Moreno, C.; Sells, D.; Tuna, F.; McInnes, E. J. L.; Lostao, A.; Luis, F.; van Slageren, J.

    2014-06-01

    Magnetoferritin molecules with an average inorganic core diameter of 5.7±1.6 nm and polycrystalline internal structure were investigated by a combination of transmission electron microscopy, magnetic susceptibility, magnetization, and electron magnetic resonance (EMR) experiments. The temperature and frequency dependence of the magnetic susceptibility allowed for the determination of the magnetic anisotropy on an experimental time scale which spans from seconds to nanoseconds. In addition, angle-dependent EMR experiments were carried out for the determination of the nanoparticle symmetry and internal magnetic field. Due to the large surface to volume ratio, the nanoparticles show larger and uniaxial rather than cubic magnetic anisotropies compared to bulk maghemite and magnetite.

  10. Microwave magnetic properties of the oriented CoIr soft magnetic film with negative magnetocrystalline anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Tao, E-mail: wtao@lzu.edu.cn [Institute of Applied Magnetics, Key Laboratory of Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou 730000 (China); Wang, Ying; Tan, Guoguo; Li, Fashen [Institute of Applied Magnetics, Key Laboratory of Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou 730000 (China); Ishio, Shunji [VBL of Akita University, Gakuen Machi 1-1, Tegata, Akita 010-8502 (Japan)

    2013-05-15

    The natural resonance frequency of the oriented soft magnetic thin film with in-plane uniaxial anisotropy and negative magnetocrystalline anisotropy (K{sub u}{sup grain}) was investigated in hcp structure of Co{sub 80}Ir{sub 20} film with the c-axis perpendicular to the film plane. As the out-of-plane anisotropy field contained the field produced by negative K{sub u}{sup grain} besides the demagnetization field, the natural resonance frequency was enhanced dramatically compared with the conventional soft magnetic film without magnetocrystalline anisotropy. Through solving the equation of magnetization precession, the initial permeability of this kind of film was shown to be unrelated to the negative K{sub u}{sup grain} and yet determined by the in-plane uniaxial anisotropy field and the saturation magnetization of the film.

  11. Artificially engineered Heusler ferrimagnetic superlattice exhibiting perpendicular magnetic anisotropy

    OpenAIRE

    Ma, Q.L.; X. M. Zhang; Miyazaki, T.; Mizukami, S.

    2015-01-01

    To extend density limits in magnetic recording industry, two separate strategies were developed to build the storage bit in last decade, introduction of perpendicular magnetic anisotropy (PMA) and adoption of ferrimagnetism/antiferromagnetism. Meanwhile, these properties significantly improve device performance, such as reducing spin-transfer torque energy consumption and decreasing signal-amplitude-loss. However, materials combining PMA and antiferromagnetism rather than transition-metal/rar...

  12. Nonmonotonic effects of perpendicular magnetic anisotropy on current-driven vortex wall motions in magnetic nanostripes

    Science.gov (United States)

    Su, Yuan-Chang; Lei, Hai-Yang; Hu, Jing-Guo

    2015-09-01

    In a magnetic nanostripe, the effects of perpendicular magnetic anisotropy (PMA) on the current-driven horizontal motion of vortex wall along the stripe and the vertical motion of the vortex core are studied by micromagnetic simulations. The results show that the horizontal and vertical motion can generally be monotonously enhanced by PMA. However, when the current is small, a nonmonotonic phenomenon for the horizontal motion is found. Namely, the velocity of the horizontal motion firstly decreases and then increases with the increase of the PMA. We find that the reason for this is that the PMA can firstly increase and then decrease the confining force induced by the confining potential energy. In addition, the PMA always enhances the driving force induced by the current. Project supported by the National Natural Science Foundation of China (Grant Nos. 11247026 and 11374253).

  13. Reversible strain control of magnetic anisotropy in magnetoelectric heterostructures at room temperature

    Science.gov (United States)

    Staruch, Margo; Gopman, Daniel B.; Iunin, Yury L.; Shull, Robert D.; Cheng, Shu Fan; Bussmann, Konrad; Finkel, Peter

    2016-11-01

    The ability to tune both magnetic and electric properties in magnetoelectric (ME) composite heterostructures is crucial for multiple transduction applications including energy harvesting or magnetic field sensing, or other transduction devices. While large ME coupling achieved through interfacial strain-induced rotation of magnetic anisotropy in magnetostrictive/piezoelectric multiferroic heterostructures has been demonstrated, there are presently certain restrictions for achieving a full control of magnetism in an extensive operational dynamic range, limiting practical realization of this effect. Here, we demonstrate the possibility of generating substantial reversible anisotropy changes through induced interfacial strains driven by applied electric fields in magnetostrictive thin films deposited on (0 1 1)-oriented domain-engineered ternary relaxor ferroelectric single crystals with extended temperature and voltage ranges as compared to binary relaxors. We show, through a combination of angular magnetization and magneto-optical domain imaging measurements, that a 90° in-plane rotation of the magnetic anisotropy and propagation of magnetic domains with low applied electric fields under zero electric field bias are realized. To our knowledge, the present value attained for converse magnetoelectric coupling coefficient is the highest achieved in the linear piezoelectric regime and expected to be stable for a wide temperature range, thus representing a step towards practical ME transduction devices.

  14. Spin kinetic Monte Carlo method for nanoferromagnetism and magnetization dynamics of nanomagnets with large magnetic anisotropy

    Institute of Scientific and Technical Information of China (English)

    LIU Bang-gui; ZHANG Kai-cheng; LI Ying

    2007-01-01

    The Kinetic Monte Carlo (KMC) method based on the transition-state theory, powerful and famous for sim-ulating atomic epitaxial growth of thin films and nanostruc-tures, was used recently to simulate the nanoferromagnetism and magnetization dynamics of nanomagnets with giant mag-netic anisotropy. We present a brief introduction to the KMC method and show how to reformulate it for nanoscale spin systems. Large enough magnetic anisotropy, observed exper-imentally and shown theoretically in terms of first-principle calculation, is not only essential to stabilize spin orientation but also necessary in making the transition-state barriers dur-ing spin reversals for spin KMC simulation. We show two applications of the spin KMC method to monatomic spin chains and spin-polarized-current controlled composite nano-magnets with giant magnetic anisotropy. This spin KMC method can be applied to other anisotropic nanomagnets and composite nanomagnets as long as their magnetic anisotropy energies are large enough.

  15. Magnetic anisotropies in ultrathin bismuth iron garnet films

    Energy Technology Data Exchange (ETDEWEB)

    Popova, Elena, E-mail: popova@physique.uvsq.fr [Groupe d' Etude de la Matière Condensée (GEMaC), CNRS/Université de Versailles-Saint-Quentin, 45 Avenue des Etats-Unis, 78035 Versailles (France); Franco Galeano, Andres Felipe [Laboratoire PROcédés, Matériaux et Energie Solaire (PROMES), CNRS/Université de Perpignan Via Domitia, 52 Avenue Paul Alduy, 66860 Perpignan (France); Deb, Marwan [Groupe d' Etude de la Matière Condensée (GEMaC), CNRS/Université de Versailles-Saint-Quentin, 45 Avenue des Etats-Unis, 78035 Versailles (France); Warot-Fonrose, Bénédicte [Centre d' Elaboration de Matériaux et d' Etudes Structurales (CEMES), CNRS, 29 rue Jeanne Marvig, 31055 Toulouse (France); Transpyrenean Associated Laboratory for Electron Microscopy (TALEM), CEMES-INA, CNRS–Universidad de Zaragoza (Spain); Kachkachi, Hamid [Laboratoire PROcédés, Matériaux et Energie Solaire (PROMES), CNRS/Université de Perpignan Via Domitia, 52 Avenue Paul Alduy, 66860 Perpignan (France); Gendron, François [Institut des NanoSciences de Paris (INSP), CNRS/Université Pierre et Marie Curie-Paris 6, 4 place Jussieu, Boîte courrier 840, 75252 Paris Cedex 05 (France); Ott, Frédéric [Laboratoire Léon Brillouin (LLB), CNRS/CEA, Bâtiment 563, CEA Saclay, 91191 Gif sur Yvette Cedex (France); and others

    2013-06-15

    Ultrathin bismuth iron garnet Bi{sub 3}Fe{sub 5}O{sub 12} films were grown epitaxially on (001)-oriented gadolinium gallium garnet substrates. Film thickness varied from two to three dozens of unit cells. Bi{sub 3}Fe{sub 5}O{sub 12} films grow pseudomorphically on substrates up to a thickness of 20 nm, and then a lattice relaxation occurs. Magnetic properties of the films were studied as a function of bismuth iron garnet thickness. The magnetization and cubic anisotropy decrease with decreasing film thickness. The uniaxial magnetocrystalline anisotropy is constant for all film thicknesses. For two unit cell thick films, the easy magnetization axis changes from in-plane to perpendicular to the plane direction. Such a reorientation takes place as a result of the competition of constant uniaxial perpendicular anisotropy with weakening film magnetization. - Highlights: ► Ultrathin Bi{sub 3}Fe{sub 5}O{sub 12} films were grown epitaxially on structure-matching substrates. ► Magnetic properties of Bi{sub 3}Fe{sub 5}O{sub 12} were studied down to the thickness of 2.5 nm. ► Reorientation of easy magnetization axis as a function of film thickness was observed.

  16. Magnetized initial conditions for CMB anisotropies

    Science.gov (United States)

    Giovannini, Massimo

    2004-12-01

    This paper introduces a systematic treatment of the linear theory of scalar gravitational perturbations in the presence of a fully inhomogeneous magnetic field. The analysis is conducted both in the synchronous and in the conformally Newtonian gauges. The cosmological plasma is assumed to be composed of cold dark matter, baryons, photons, neutrinos. The problem of superhorizon initial conditions for the fluid variables of the various species and for the coupled system of Boltzmann-Einstein equations is discussed in the presence of an inhomogeneous magnetic field. The tight-coupling approximation for the Boltzmann hierarchy is extended to the case where gravitating magnetic fields are included.

  17. The magnetic properties of the spin-1 Heisenberg antiferromagnetic chain with single-ion anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Gangsan; Zhu, Rengui, E-mail: rgzhu@mail.ahnu.edu.cn

    2015-02-15

    The magnetic properties of the spin-1 Heisenberg antiferromagnetic chain with exchange anisotropy and single-ion anisotropy are studied by the double-time Green's function method. The determinative equations for the critical temperature, the magnetization, and the zero-field susceptibility are derived analytically. The effects of the anisotropies on the magnetic properties are presented.

  18. Magnetic tunnel junctions with non-collinear anisotropy axes for sensor applications

    CERN Document Server

    Grigorenko, A N

    2003-01-01

    Magnetic tunnel junctions (MTJ) with non-collinear anisotropy axes of magnetic layers have been fabricated for reading head and sensor applications. It is shown that crossed anisotropies of magnetic layers improve sensor sensitivity and time-response compared to the conventional case of aligned anisotropies. The developed micromagnetic model is in good agreement with magnetoresistive properties of fabricated junctions.

  19. Switching current density reduction in perpendicular magnetic anisotropy spin transfer torque magnetic tunneling junctions

    Energy Technology Data Exchange (ETDEWEB)

    You, Chun-Yeol [Department of Physics, Inha University, Incheon 402-751 (Korea, Republic of)

    2014-01-28

    We investigate the switching current density reduction of perpendicular magnetic anisotropy spin transfer torque magnetic tunneling junctions using micromagnetic simulations. We find that the switching current density can be reduced with elongated lateral shapes of the magnetic tunnel junctions, and additional reduction can be achieved by using a noncollinear polarizer layer. The reduction is closely related to the details of spin configurations during switching processes with the additional in-plane anisotropy.

  20. Application of the anisotropy field distribution method to arrays of magnetic nanowires

    OpenAIRE

    De La Torre Medina, Joaquin; Darques, Michaël; Piraux, Luc; Encinas, Armando

    2009-01-01

    The applicability of the anisotropy field distribution method and the conditions required for an accurate determination of the effective anisotropy field in arrays of magnetic nanowires have been evaluated. In arrays of magnetic nanowires that behave as ideal uniaxial systems having only magnetostatic contributions to the effective anisotropy field, i.e., shape anisotropy and magnetostatic coupling, the method yields accurate values of the average anisotropy field at low-moderate dipolar coup...

  1. Secondary CMB anisotropies from bulk motions in the presence of stochastic magnetic fields

    CERN Document Server

    Kunze, Kerstin E

    2013-01-01

    Bulk motions of electrons along the line of sight induce secondary temperature fluctuations in the post-decoupling, reionized universe. In the presence of a magnetic field not only the scalar mode but also the vector mode act as a source for the bulk motion. The resulting angular power spectrum of temperature anisotropies of the cosmic microwave background is calculated assuming a simple model of reionization.Contributions from the standard adiabatic, curvature mode and a non helical magnetic field are included. The contribution due to magnetic fields with field strengths of order nG and negative magnetic spectral indices dominates for multipoles larger than $\\ell \\sim 10^4$.

  2. Anisotropy-Tuned Magnetic Order in Pyrochlore Iridates

    Science.gov (United States)

    Lefrançois, E.; Simonet, V.; Ballou, R.; Lhotel, E.; Hadj-Azzem, A.; Kodjikian, S.; Lejay, P.; Manuel, P.; Khalyavin, D.; Chapon, L. C.

    2015-06-01

    The magnetic behavior of polycrystalline samples of Er2Ir2O7 and Tb2Ir2O7 pyrochlores is studied by magnetization measurements and neutron diffraction. Both compounds undergo a magnetic transition at 140 and 130 K, respectively, associated with an ordering of the Ir sublattice, signaled by thermomagnetic hysteresis. In Tb2Ir2O7 , we show that the Ir molecular field leads the Tb magnetic moments to order below 40 K in the all-in-all-out magnetic arrangement. No sign of magnetic long-range order on the Er sublattice is evidenced in Er2Ir2O7 down to 0.6 K where a spin freezing is detected. These contrasting behaviors result from the competition between the Ir molecular field and the different single-ion anisotropy of the rare-earth elements on which it is acting. Additionally, this strongly supports the all-in-all-out iridium magnetic order.

  3. Magnetic anisotropy and quantized spin waves in hematite nanoparticles

    DEFF Research Database (Denmark)

    Klausen, Stine Nyborg; Lefmann, Kim; Lindgård, Per-Anker

    2004-01-01

    We report on the observation of high-frequency collective magnetic excitations, (h) over bar omegaapproximate to1.1 meV, in hematite (alpha-Fe2O3) nanoparticles. The neutron scattering experiments include measurements at temperatures in the range 6-300 K and applied fields up to 7.5 T as well...... the temperature dependence of the magnetic anisotropy, which is strongly related to the suppression of the Morin transition in nanoparticles of hematite. Further, the localization of the signal in both energy and momentum transfer brings evidence for finite-size quantization of spin waves in the system....... as polarization analysis. We give an explanation for the field- and temperature dependence of the excitations, which are found to have strongly elliptical out-of-plane precession. The frequency of the excitations gives information on the magnetic anisotropy constants in the system. We have in this way determined...

  4. Large magnetic anisotropy in ferrihydrite nanoparticles synthesized from reverse micelles

    Energy Technology Data Exchange (ETDEWEB)

    Duarte, E L [Instituto de Fisica, Universidade de Sao Paulo, CP 66318, Sao Paulo, 05315-970 (Brazil); Itri, R [Instituto de Fisica, Universidade de Sao Paulo, CP 66318, Sao Paulo, 05315-970 (Brazil); Jr, E Lima [Instituto de Fisica, Universidade de Sao Paulo, CP 66318, Sao Paulo, 05315-970 (Brazil); Baptista, M S [Instituto de Quimica, Universidade de Sao Paulo, Avenida Professor Lineu Prestes 748, Sao Paulo (Brazil); Berquo, T S [Institute for Rock Magnetism, University of Minnesota, 100 Union Street SE, Minneapolis, MN 55455-0128 (United States); Goya, G F [Instituto de Nanociencias de Aragon (INA), Universidad de Zaragoza, Pedro Cerbuna 12 (50009), Zaragoza (Spain)

    2006-11-28

    Six-line ferrihydrite (FH) nanoparticles have been synthesized in the core of reverse micelles, used as nanoreactors to obtain average particle sizes {approx} 2-4 nm. The blocking temperatures T{sub B}{sup m} extracted from magnetization data increased from {approx}10 to 20 K for increasing particle size. Low-temperature Moessbauer measurements allowed us to observe the onset of differentiated contributions from the particle core and surface as the particle size increases. The magnetic properties measured in the liquid state of the original emulsion showed that the ferrihydrite phase is not present in the liquid precursor, but precipitates in the micelle cores after the free water is freeze-dried. Systematic susceptibility {chi}{sub ac}(f,T) measurements showed the dependence of the effective magnetic anisotropy energies E{sub a} with particle volume, and yielded an effective anisotropy value of K{sub eff} = 312 {+-} 10 kJ m{sup -3}.

  5. Manifold domain structure of double films with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Coffey, D; Diez-Ferrer, J L; Corredor, E C; Arnaudas, J I [Instituto de Nanociencia de Aragon, Universidad de Zaragoza, Zaragoza (Spain); Ciria, M, E-mail: ciria@unizar.es [Departamento de Fisica de la Materia Condensada, Universidad de Zaragoza, Zaragoza (Spain)

    2011-03-23

    We present epitaxial structures made of twin nickel blocks with perpendicular magnetic anisotropy separated by a copper layer which, for some values of this interleaving layer, show domain structures with four levels of contrast in magnetic force microscopy images. This manifold domain structure implies that the magnetization in the Ni blocks, in addition to the parallel orientation, undergoes a non-collinear configuration with respect to each other. To explain this result we consider a magnetoelastic domain structure with M in the plane that can elude the clamping done by the substrate with an average strain of -42 x 10{sup -6} ({approx}70% of the bulk value). Thus, the out-of-plane anisotropy is balanced and a biquadratic exchange coupling can stabilize the non-collinear domain configurations between the Ni blocks.

  6. Interfacial oxygen migration and its effect on the magnetic anisotropy in Pt/Co/MgO/Pt films

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Xi; Feng, Chun, E-mail: fengchun@ustb.edu.cn, E-mail: ghyu@mater.ustb.edu.cn; Liu, Yang; Jiang, Shaolong; Hua Li, Ming; Hua Yu, Guang, E-mail: fengchun@ustb.edu.cn, E-mail: ghyu@mater.ustb.edu.cn [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Long Wu, Zheng [Analytical and Testing Center, Beijing Normal University, Beijing 100875 (China); Yang, Feng [State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249 (China)

    2014-02-03

    This paper reports the interfacial oxygen migration effect and its induced magnetic anisotropy evolution in Pt/Co/MgO/Pt films. During depositing the MgO layer, oxygen atoms from the MgO combine with the neighboring Co atoms, leading to the formation of CoO at the Co/MgO interface. Meanwhile, the films show in-plane magnetic anisotropy (IMA). After annealing, most of the oxygen atoms in CoO migrate back to the MgO layer, resulting in obvious improvement of Co/MgO interface and the enhancement of effective Co-O orbital hybridization. These favor the evolution of magnetic anisotropy from IMA to perpendicular magnetic anisotropy (PMA). The oxygen migration effect is achieved by the redox reaction at the Co/MgO interface. On the contrary, the transfer from IMA to PMA cannot be observed in Pt/Co/Pt films due to the lack of interfacial oxygen migration.

  7. NANO-MULTILAYERS WITH HIGH PERPENDICULAR ANISOTROPY FOR MAGNETIC RECORDING

    Institute of Scientific and Technical Information of China (English)

    T. Yang; B.H. Li; K. Kang; T. Suzuki

    2003-01-01

    (FePt/Ag)n nano-multilayers were deposited on MgO (100) single crystal with laser ablation and then subjected to annealing. FePt L1o grains with (001) texture and thus a large perpendicular magnetic anisotropy constant Ku of the order of 106J/m3 were formed. A thick Ag layer is found to be favorable for decreasing the dispersion of the easy axis for magnetization. The measurement of time decay of magnetization gave rise to a small activation volume of the order of 10-25 m3, showing the promising of being the recording medium for future high density perpendicular recording.

  8. Two-dimensional chiral asymmetry in unidirectional magnetic anisotropy structures

    Directory of Open Access Journals (Sweden)

    P. Perna

    2016-05-01

    Full Text Available We investigate the symmetry-breaking effects of magnetic nanostructures that present unidirectional (one-fold magnetic anisotropy. Angular and field dependent transport and magnetic properties have been studied in two different exchange-biased systems, i.e. ferromagnetic (FM/ antiferromagnetic (AFM bilayer and spin-valve structures. We experimentally show the direct relationships between the magnetoresistance (MR response and the magnetization reversal pathways for any field value and direction. We demonstrate that even though the MR signals are related to different transport phenomena, namely anisotropic magnetoresistance (AMR and giant magnetoresistance (GMR, chiral asymmetries are found around the magnetization hard-axis direction, in both cases originated from the one-fold symmetry of the interfacial exchange coupling. Our results indicate that the chiral asymmetry of transport and magnetic behaviors are intrinsic of systems with an unidirectional contribution.

  9. Perpendicular magnetic anisotropy of CoSiB/Pt multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Park, J. S.; Yim, H. I. [Sookmyung Women' s University, Seoul (Korea, Republic of); Hwang, J. Y.; Lee, S. B. [Hanyang University, Seoul (Korea, Republic of); Kim, T. W. [Sejong University, Seoul (Korea, Republic of)

    2010-12-15

    We have investigated the perpendicular magnetic anisotropy of [CoSiB t{sub CoSiB}/Pt t{sub Pt}]{sub n} multilayers as a function of the CoSiB and the Pt thicknesses and the number of repetition of the CoSiB/Pt bilayers. The coercivity (H{sub c}) and the saturation magnetization (M{sub s}) of the amorphous ferromagnetic material Co{sub 75}Si{sub 15}B{sub 10} were taken to be 1.6 Oe and 407 emu/cm{sup 3}, respectively. The H{sub c} in [CoSiB t{sub CoSiB}/Pt 14 A]{sub 5} multilayers increases with increasing t{sub CoSiB} to reach a maximum at t{sub CoSiB} = 3 A and then decreases for t{sub CoSiB} > 3 A. The highest H{sub c} of 224 Oe and the highest perpendicular magnetic anisotropy K{sub u} of 2 x 10{sup 6} erg/cm{sup 3} were obtained in the [CoSiB 3 A/Pt 14 A]{sub 5} multilayer. Additional Pt layers do not contribute to the perpendicular magnetic anisotropy. The single-domain structure evolves into a striped multidomain structure as the bilayer repetition number n increases above 6.

  10. Orbital magnetism in axially deformed sodium clusters From scissors mode to dia-para magnetic anisotropy

    CERN Document Server

    Nesterenko, V O; Reinhard, P G; Iudice, N L; De Souza-Cruz, F F; Marinelli, J R

    2002-01-01

    Low-energy orbital magnetic dipole excitations, known as scissors mode (SM), are studied in alkali metal clusters. Subsequent dynamic and static effects are explored. The treatment is based on a self-consistent microscopic approach using the jellium approximation for the ionic background and the Kohn-Sham mean field for the electrons. The microscopic origin of SM and its main features (structure of the mode in light and medium clusters, separation into low- and high-energy plasmons, coupling high-energy M1 scissors and E2 quadrupole plasmons, contributions of shape isomers, etc) are discussed. The scissors M1 strength acquires large values with increasing cluster size. The mode is responsible for the van Vleck paramagnetism of spin-saturated clusters. Quantum shell effects induce a fragile interplay between Langevin diamagnetism and van Vleck paramagnetism and lead to a remarkable dia-para anisotropy in magnetic susceptibility of particular light clusters. Finally, several routes for observing the SM experime...

  11. Write operation in MRAM with voltage controlled magnetic anisotropy

    Science.gov (United States)

    Munira, Kamaram; Pandey, Sumeet; Sandhu, Gurtej

    In non-volatile Magnetic RAM, information is saved in the bistable configuration of the free layer in a magnetic tunnel junction (MTJ). New information can be written to the free layer through magnetic induction (Toggle MRAM) or manipulation of magnetization using electric currents (Spin Transfer Torque MRAM or STT-MRAM). Both of the writing methods suffer from a shortcoming in terms of energy efficiency. This limitation on energy performance is brought about by the need for driving relatively large electrical charge currents through the devices for switching. In STT-MRAM, the nonzero voltage drop across the resistive MTJ leads to significant power dissipation. An energy efficient way to write may be with the assistance of voltage controlled magnetic anisotropy (VCMA), where voltage applied across the MTJ creates an electric field that modulates the interfacial anisotropy between the insulator and free layer. However, VCMA cannot switch the free layer completely by 180 degree rotation of magnetization. It can lower the barrier between the two stable configurations or at best, cancel the barrier, allowing 90 degree rotation. A second mechanism, spin torque or magnetic field, is needed to direct the final switching destination.

  12. Spin-orbit torque-assisted switching in magnetic insulator thin films with perpendicular magnetic anisotropy

    Science.gov (United States)

    Li, Peng; Liu, Tao; Chang, Houchen; Kalitsov, Alan; Zhang, Wei; Csaba, Gyorgy; Li, Wei; Richardson, Daniel; Demann, August; Rimal, Gaurab; Dey, Himadri; Jiang, J. S.; Porod, Wolfgang; Field, Stuart B.; Tang, Jinke; Marconi, Mario C.; Hoffmann, Axel; Mryasov, Oleg; Wu, Mingzhong

    2016-09-01

    As an in-plane charge current flows in a heavy metal film with spin-orbit coupling, it produces a torque on and thereby switches the magnetization in a neighbouring ferromagnetic metal film. Such spin-orbit torque (SOT)-induced switching has been studied extensively in recent years and has shown higher efficiency than switching using conventional spin-transfer torque. Here we report the SOT-assisted switching in heavy metal/magnetic insulator systems. The experiments used a Pt/BaFe12O19 bilayer where the BaFe12O19 layer exhibits perpendicular magnetic anisotropy. As a charge current is passed through the Pt film, it produces a SOT that can control the up and down states of the remnant magnetization in the BaFe12O19 film when the film is magnetized by an in-plane magnetic field. It can reduce or increase the switching field of the BaFe12O19 film by as much as about 500 Oe when the film is switched with an out-of-plane field.

  13. Spin–orbit torque-assisted switching in magnetic insulator thin films with perpendicular magnetic anisotropy

    Science.gov (United States)

    Li, Peng; Liu, Tao; Chang, Houchen; Kalitsov, Alan; Zhang, Wei; Csaba, Gyorgy; Li, Wei; Richardson, Daniel; DeMann, August; Rimal, Gaurab; Dey, Himadri; Jiang, J. S.; Porod, Wolfgang; Field, Stuart B.; Tang, Jinke; Marconi, Mario C.; Hoffmann, Axel; Mryasov, Oleg; Wu, Mingzhong

    2016-01-01

    As an in-plane charge current flows in a heavy metal film with spin–orbit coupling, it produces a torque on and thereby switches the magnetization in a neighbouring ferromagnetic metal film. Such spin–orbit torque (SOT)-induced switching has been studied extensively in recent years and has shown higher efficiency than switching using conventional spin-transfer torque. Here we report the SOT-assisted switching in heavy metal/magnetic insulator systems. The experiments used a Pt/BaFe12O19 bilayer where the BaFe12O19 layer exhibits perpendicular magnetic anisotropy. As a charge current is passed through the Pt film, it produces a SOT that can control the up and down states of the remnant magnetization in the BaFe12O19 film when the film is magnetized by an in-plane magnetic field. It can reduce or increase the switching field of the BaFe12O19 film by as much as about 500 Oe when the film is switched with an out-of-plane field. PMID:27581060

  14. Spin splitting anisotropy in single diluted magnetic nanowire heterostructures.

    Science.gov (United States)

    Szymura, Małgorzata; Wojnar, Piotr; Kłopotowski, Łukasz; Suffczyński, Jan; Goryca, Mateusz; Smoleński, Tomasz; Kossacki, Piotr; Zaleszczyk, Wojciech; Wojciechowski, Tomasz; Karczewski, Grzegorz; Wojtowicz, Tomasz; Kossut, Jacek

    2015-03-11

    We study the impact of the nanowire shape anisotropy on the spin splitting of excitonic photoluminescence. The experiments are performed on individual ZnMnTe/ZnMgTe core/shell nanowires as well as on ZnTe/ZnMgTe core/shell nanowires containing optically active magnetic CdMnTe insertions. When the magnetic field is oriented parallel to the nanowire axis, the spin splitting is several times larger than for the perpendicular field. We interpret this pronounced anisotropy as an effect of mixing of valence band states arising from the strain present in the core/shell geometry. This interpretation is further supported by theoretical calculations which allow to reproduce experimental results.

  15. Temperature dependence of magnetic anisotropies in ultra-thin films

    CERN Document Server

    Hucht, A

    1999-01-01

    shown that in contrast to other works the temperature driven spin reorientation transition in the monolayer is discontinuous also in the simulations, whereas in general it is continuous for the bilayer. Consequently the molecular field theory and the Monte Carlo simulations agree qualitatively. Exemplary for thicker films the influence of an external magnetic field is investigated in the bilayer, furthermore the effective anisotropies K sub n (T) of the phenomenological Landau theory are calculated numerically for the microscopic model. Analytic expressions for the dependence of the anisotropies K sub n (T) on the parameters of the model are obtained by the means of perturbation theory, which lead to a deeper understanding of the spin reorientation transition. Accordingly to this the origin for the spin reorientation transition lies in the differing temperature dependence of the dipolar and spin-orbit parts of the K sub n (T). Additionally the magnetization in the surface of the film decreases more rapidly wi...

  16. Perpendicular magnetic anisotropy and magnetization dynamics in oxidized CoFeAl films

    Science.gov (United States)

    Wu, Di; Zhang, Zhe; Li, Le; Zhang, Zongzhi; Zhao, H. B.; Wang, J.; Ma, B.; Jin, Q. Y.

    2015-07-01

    Half-metallic Co-based full-Heusler alloys with perpendicular magnetic anisotropy (PMA), such as Co2FeAl in contact with MgO, are receiving increased attention recently due to its full spin polarization for high density memory applications. However, the PMA induced by MgO interface can only be realized for very thin magnetic layers (usually below 1.3 nm), which would have strong adverse effects on the material properties of spin polarization, Gilbert damping parameter, and magnetic stability. In order to solve this issue, we fabricated oxidized Co50Fe25Al25 (CFAO) films with proper thicknesses without employing the MgO layer. The samples show controllable PMA by tuning the oxygen pressure (PO2) and CFAO thickness (tCFAO), large perpendicular anisotropy field of ~8.0 kOe can be achieved at PO2 = 12% for the sample of tCFAO = 2.1 nm or at PO2 = 7% for tCFAO = 2.8 nm. The loss of PMA at thick tCFAO or high PO2 results mainly from the formation of large amount of CoFe oxides, which are superparamagnetic at room temperature but become hard magnetic at low temperatures. The magnetic CFAO films, with strong PMA in a relatively wide thickness range and small intrinsic damping parameter below 0.028, would find great applications in developing advanced spintronic devices.

  17. Magnetic anisotropy investigations of (Ga,Mn)As with a large epitaxial strain

    Energy Technology Data Exchange (ETDEWEB)

    Juszyński, P.; Gryglas-Borysiewicz, M.; Szczytko, J.; Tokarczyk, M.; Kowalski, G. [Faculty of Physics, University of Warsaw, Hoża 69, 00-681 Warsaw (Poland); Sadowski, J. [Max-IV Laboratory, Lund University, Lund SE-221 00 (Sweden); Institute of Physics, PAS, Al. Lotników 32/46, 02-668 Warsaw (Poland); Wasik, D. [Faculty of Physics, University of Warsaw, Hoża 69, 00-681 Warsaw (Poland)

    2015-12-15

    Magnetic properties of 20 nm thick (Ga,Mn)As layer deposited on (Ga,In)As buffer with very large epitaxial tensile strain are investigated. Ga{sub 1−x}In{sub x}As buffer with x=30% provides a 2% lattice mismatch, which is an important extension of the mismatch range studied so far (up to 0.5%). Evolution of magnetic anisotropy as a function of temperature is determined by magnetotransport measurements. Additionally, results of direct measurements of magnetization are shown. - Highlights: • Magnetic anisotropy parameter in (Ga,Mn)As with a large epitaxial strain is determined. • Extension of a linear magnetic anisotropy dependence on lattice mismatch up to 2% is presented. • A linear dependence of magnetic anisotropy on magnetization is established. • Magnetic anisotropy dependence on temperature is shown. • Electrical transport measurements are successfully applied to study magnetic anisotropy.

  18. Direct Observation of Magnetic Anisotropy in an Individual Fe4 Single-Molecule Magnet

    NARCIS (Netherlands)

    Burzuri, E.; Zyazin, A.S.; Cornia, A.; Van der Zant, H.S.J.

    2012-01-01

    We study three-terminal charge transport through individual Fe4 single-molecule magnets. Magnetic anisotropy of the single molecule is directly observed by introducing a spectroscopic technique based on measuring the position of the degeneracy point as a function of gate voltage and applied magnetic

  19. Direct Observation of Magnetic Anisotropy in an Individual Fe4 Single-Molecule Magnet

    NARCIS (Netherlands)

    Burzuri, E.; Zyazin, A.S.; Cornia, A.; Van der Zant, H.S.J.

    2012-01-01

    We study three-terminal charge transport through individual Fe4 single-molecule magnets. Magnetic anisotropy of the single molecule is directly observed by introducing a spectroscopic technique based on measuring the position of the degeneracy point as a function of gate voltage and applied magnetic

  20. Artificially engineered Heusler ferrimagnetic superlattice exhibiting perpendicular magnetic anisotropy

    Science.gov (United States)

    Ma, Q. L.; Zhang, X. M.; Miyazaki, T.; Mizukami, S.

    2015-01-01

    To extend density limits in magnetic recording industry, two separate strategies were developed to build the storage bit in last decade, introduction of perpendicular magnetic anisotropy (PMA) and adoption of ferrimagnetism/antiferromagnetism. Meanwhile, these properties significantly improve device performance, such as reducing spin-transfer torque energy consumption and decreasing signal-amplitude-loss. However, materials combining PMA and antiferromagnetism rather than transition-metal/rare-earth system were rarely developed. Here, we develop a new type of ferrimagnetic superlattice exhibiting PMA based on abundant Heusler alloy families. The superlattice is formed by [MnGa/Co2FeAl] unit with their magnetizations antiparallel aligned. The effective anisotropy (Kueff) over 6 Merg/cm3 is obtained, and the SL can be easily built on various substrates with flexible lattice constants. The coercive force, saturation magnetization and Kueff of SLs are highly controllable by varying the thickness of MnGa and Co2FeAl layers. The SLs will supply a new choice for magnetic recording and spintronics memory application such as magnetic random access memory.

  1. Artificially engineered Heusler ferrimagnetic superlattice exhibiting perpendicular magnetic anisotropy.

    Science.gov (United States)

    Ma, Q L; Zhang, X M; Miyazaki, T; Mizukami, S

    2015-01-19

    To extend density limits in magnetic recording industry, two separate strategies were developed to build the storage bit in last decade, introduction of perpendicular magnetic anisotropy (PMA) and adoption of ferrimagnetism/antiferromagnetism. Meanwhile, these properties significantly improve device performance, such as reducing spin-transfer torque energy consumption and decreasing signal-amplitude-loss. However, materials combining PMA and antiferromagnetism rather than transition-metal/rare-earth system were rarely developed. Here, we develop a new type of ferrimagnetic superlattice exhibiting PMA based on abundant Heusler alloy families. The superlattice is formed by [MnGa/Co2FeAl] unit with their magnetizations antiparallel aligned. The effective anisotropy (K(u)(eff)) over 6 Merg/cm(3) is obtained, and the SL can be easily built on various substrates with flexible lattice constants. The coercive force, saturation magnetization and K(u)(eff) of SLs are highly controllable by varying the thickness of MnGa and Co2FeAl layers. The SLs will supply a new choice for magnetic recording and spintronics memory application such as magnetic random access memory.

  2. Anisotropy of magnetic susceptibility used to detect coring-induced sediment disturbance and filter palaeomagnetic secular variation data: IODP sites M0061 and M0062 (Baltic Sea)

    Science.gov (United States)

    Snowball, Ian; Almqvist, Bjarne; Lougheed, Bryan; Svensson, Anna; Wiers, Steffen; Herrero-Bervera, Emilio

    2017-04-01

    Inspired by palaeomagnetic data obtained from two sites (M0061 and M0062) cored during IODP Expedition 347 - Baltic Sea Paleoenvironment we studied the Hemsön Alloformation, which is a series of brackish water muds consisting of horizontal planar and parallel laminated (varved) silty clays free from bioturbation. We determined the anisotropy of magnetic susceptibility (AMS) and characteristic remanence (ChRM) directions of a total of 1,102 discrete samples cut from (i) IODP cores recovered by an Advanced Piston corer and (ii) a series of six sediment cores recovered from the same sites by a Kullenberg piston corer. Systematic core splitting, sub-sampling methods and measurements were applied to all sub-samples. We experimentally tested for field-impressed AMS of these muds, in which titanomagnetite carries magnetic remanence and this test was negative. The AMS is likely determined by paramagnetic minerals. As expected for horizontally bedded sediments, the vast majority of the K1 (maximum) and K2 (intermediate) axes had inclinations close to 0 degrees and the AMS shape parameter (T) indicates an oblate fabric. The declinations of the K1 and K2 directions of the sub-samples taken from Kullenberg cores showed a wide distribution around the bedding plane, with no preferred alignment along any specimen axis. Exceptions are samples from the upper 1.5 m of some of these cores, in which the K1 and K2 directions were vertical, the K3 (minimum) axis shallow and T became prolate. We conclude that the Kullenberg corer, which penetrated the top sediments with a pressure of approximately 15 bar, occasionally under-sampled during penetration and vertically stretched the top sediments. Sub-samples from the upper sections of Kullenberg cores had relatively steep ChRM inclinations and we rejected samples that had a prolate, vertically oriented AMS ellipsoid. Surprisingly, the declinations of the K1 axis of all sub-samples taken from IODP APC core sections, which were not oriented

  3. Strain-assisted magnetization reversal in Co/Ni multilayers with perpendicular magnetic anisotropy.

    Science.gov (United States)

    Gopman, D B; Dennis, C L; Chen, P J; Iunin, Y L; Finkel, P; Staruch, M; Shull, R D

    2016-06-14

    Multifunctional materials composed of ultrathin magnetic films with perpendicular magnetic anisotropy combined with ferroelectric substrates represent a new approach toward low power, fast, high density spintronics. Here we demonstrate Co/Ni multilayered films with tunable saturation magnetization and perpendicular anisotropy grown directly on ferroelectric PZT [Pb(Zr0.52Ti0.48)O3] substrate plates. Electric fields up to ±2 MV/m expand the PZT by 0.1% and generate at least 0.02% in-plane compression in the Co/Ni multilayered film. Modifying the strain with a voltage can reduce the coercive field by over 30%. We also demonstrate that alternating in-plane tensile and compressive strains (less than 0.01%) can be used to propagate magnetic domain walls. This ability to manipulate high anisotropy magnetic thin films could prove useful for lowering the switching energy for magnetic elements in future voltage-controlled spintronic devices.

  4. Strain-assisted magnetization reversal in Co/Ni multilayers with perpendicular magnetic anisotropy

    Science.gov (United States)

    Gopman, D. B.; Dennis, C. L.; Chen, P. J.; Iunin, Y. L.; Finkel, P.; Staruch, M.; Shull, R. D.

    2016-06-01

    Multifunctional materials composed of ultrathin magnetic films with perpendicular magnetic anisotropy combined with ferroelectric substrates represent a new approach toward low power, fast, high density spintronics. Here we demonstrate Co/Ni multilayered films with tunable saturation magnetization and perpendicular anisotropy grown directly on ferroelectric PZT [Pb(Zr0.52Ti0.48)O3] substrate plates. Electric fields up to ±2 MV/m expand the PZT by 0.1% and generate at least 0.02% in-plane compression in the Co/Ni multilayered film. Modifying the strain with a voltage can reduce the coercive field by over 30%. We also demonstrate that alternating in-plane tensile and compressive strains (less than 0.01%) can be used to propagate magnetic domain walls. This ability to manipulate high anisotropy magnetic thin films could prove useful for lowering the switching energy for magnetic elements in future voltage-controlled spintronic devices.

  5. Engineering perpendicular magnetic anisotropy in Fe via interstitial nitrogenation: N choose K

    Directory of Open Access Journals (Sweden)

    Hongbin Zhang

    2016-11-01

    Full Text Available In this work, combining experimental results and first principles calculations, we show that interstitial nitrogen not only serves for inducing tetragonality in α′-Fe8Nx but is also essential for achieving a high degree of perpendicular magneto-crystalline anisotropy, K. Our results demonstrate that the orbital magnetic moments of the iron atoms above and below N in the direction of magnetization are much more susceptible to the applied magnetic field than their in-plane counterparts, leading to a giant value of K as compared to a hypothetical distorted material without N.

  6. Engineering perpendicular magnetic anisotropy in Fe via interstitial nitrogenation: N choose K

    Science.gov (United States)

    Zhang, Hongbin; Dirba, Imants; Helbig, Tim; Alff, Lambert; Gutfleisch, Oliver

    2016-11-01

    In this work, combining experimental results and first principles calculations, we show that interstitial nitrogen not only serves for inducing tetragonality in α'-Fe8Nx but is also essential for achieving a high degree of perpendicular magneto-crystalline anisotropy, K. Our results demonstrate that the orbital magnetic moments of the iron atoms above and below N in the direction of magnetization are much more susceptible to the applied magnetic field than their in-plane counterparts, leading to a giant value of K as compared to a hypothetical distorted material without N.

  7. Engineering Curvature-Induced Anisotropy in Thin Ferromagnetic Films

    Science.gov (United States)

    Tretiakov, Oleg A.; Morini, Massimiliano; Vasylkevych, Sergiy; Slastikov, Valeriy

    2017-08-01

    We investigate the effect of large curvature and dipolar energy in thin ferromagnetic films with periodically modulated top and bottom surfaces on magnetization behavior. We predict that the dipolar interaction and surface curvature can produce perpendicular anisotropy which can be controlled by engineering special types of periodic surface structures. Similar effects can be achieved by a significant surface roughness in the film. We demonstrate that, in general, the anisotropy can point in an arbitrary direction depending on the surface curvature. Furthermore, we provide simple examples of these periodic surface structures to show how to engineer particular anisotropies in thin films.

  8. Structural and Magnetic Anisotropy in Amorphous Terbium-Iron Thin Films

    Science.gov (United States)

    Hufnagel, Todd Clayton

    1995-01-01

    High density, removable media magnetooptic disk drives have recently begun to make significant gains in the information mass storage market. The media in these disks are amorphous rare-earth/transition-metal (RE-TM) alloys. One vital property of these materials is a large perpendicular magnetic anisotropy; that is, an easy axis of magnetization which is perpendicular to the plane of the film. A variety of theories, sometimes contradictory, have been proposed to account for this surprising presence of an anisotropic property in an amorphous material. Recent research indicates that there is an underlying atomic-scale structural anisotropy which is responsible for the observed magnetic anisotropy. Several different types of structural anisotropy have been proposed to account for the observed magnetic anisotropy, including pair-ordering anisotropy (anisotropic chemical short-range order) and bond orientation anisotropy (an anisotropy in coordination number or distances independent of chemical ordering). We have studied the structural origins of perpendicular magnetic anisotropy in amorphous Tb-Fe thin films by employing high-energy and anomalous dispersion x-ray scattering. The as-deposited films show a clear structural anisotropy, with a preference for Tb-Fe near neighbors to align in the out-of-plane direction. These films also have a large perpendicular magnetic anisotropy. Upon annealing, the magnetic anisotropy energy drops significantly, and we see a corresponding reduction in the structural anisotropy. The radial distribution functions indicate that the number of Tb-Fe near-neighbors increases in the in-plane direction, but does not change in the out-of-plane direction. Therefore, the distribution of Tb-Fe near-neighbors becomes more uniform upon annealing. We propose that the observed reduction in perpendicular magnetic anisotropy energy is a result of this change in structure. Our results support the pair -ordering anisotropy model of the structural anisotropy

  9. Field orientation dependence of magnetization reversal in thin films with perpendicular magnetic anisotropy

    Science.gov (United States)

    Fallarino, Lorenzo; Hovorka, Ondrej; Berger, Andreas

    2016-08-01

    The magnetization reversal process of hexagonal-close-packed (hcp) (0001) oriented Co and C o90R u10 thin films with perpendicular magnetic anisotropy (PMA) has been studied as a function of temperature and applied magnetic field angle. Room temperature pure cobalt exhibits two characteristic reversal mechanisms. For angles near in-plane field orientation, the magnetization reversal proceeds via instability of the uniform magnetic state, whereas in the vicinity of the out-of-plane (OP) orientation, magnetization inversion takes place by means of domain nucleation. Temperature dependent measurements enable the modification of the magnetocrystalline anisotropy and reveal a gradual disappearance of the domain nucleation process during magnetization reversal for elevated temperatures. Ultimately, this suppression of the domain nucleation process leads to the exclusive occurrence of uniform state instability reversal for all field orientations at sufficiently high temperature. Comparative magnetic measurements of C o90R u10 alloy samples allow the identification and confirmation of the high temperature remanent magnetization state of cobalt as an OP stripe domain state despite the reduction of magnetocrystalline anisotropy. Detailed micromagnetic simulations supplement the experimental results and corroborate the physical understanding of the temperature dependent behavior. Moreover, they enable a comprehensive identification of the complex energy balance in magnetic films with PMA, for which three different magnetic phases occur for sufficiently high anisotropy values, whose coexistence point is tricritical in nature.

  10. Sputtering of cobalt film with perpendicular magnetic anisotropy on disorder-free graphene

    Directory of Open Access Journals (Sweden)

    Mahdi Jamali

    2014-10-01

    Full Text Available Growth of thin cobalt film with perpendicular magnetic anisotropy has been investigated on pristine graphene for spin logic and memory applications. By reduction of the kinetic energy of the sputtered atoms using indirect sputtered deposition, deposition induced defects in the graphene layer have been controlled. Cobalt film on graphene with perpendicular magnetic anisotropy has been developed. Raman spectroscopy of the graphene surface shows very little disorder induced in the graphene by the sputtering process. In addition, upon increasing the cobalt film thickness, the disorder density increases on the graphene and saturates for thicknesses of Co layers above 1 nm. The AFM image indicates a surface roughness of about 0.86 nm. In addition, the deposited film forms a granular structure with a grain size of about 40 nm.

  11. Sputtering of cobalt film with perpendicular magnetic anisotropy on disorder-free graphene

    Energy Technology Data Exchange (ETDEWEB)

    Jamali, Mahdi; Lv, Yang; Zhao, Zhengyang; Wang, Jian-Ping, E-mail: jpwang@umn.edu [Department of Electrical and Computer Engineering, University of Minnesota, 4-174 200 Union Street SE, Minneapolis, MN 55455 (United States)

    2014-10-15

    Growth of thin cobalt film with perpendicular magnetic anisotropy has been investigated on pristine graphene for spin logic and memory applications. By reduction of the kinetic energy of the sputtered atoms using indirect sputtered deposition, deposition induced defects in the graphene layer have been controlled. Cobalt film on graphene with perpendicular magnetic anisotropy has been developed. Raman spectroscopy of the graphene surface shows very little disorder induced in the graphene by the sputtering process. In addition, upon increasing the cobalt film thickness, the disorder density increases on the graphene and saturates for thicknesses of Co layers above 1 nm. The AFM image indicates a surface roughness of about 0.86 nm. In addition, the deposited film forms a granular structure with a grain size of about 40 nm.

  12. Modified magnetic anisotropy at LaCoO3/La0.7Sr0.3MnO3 interfaces

    Science.gov (United States)

    Cabero, M.; Nagy, K.; Gallego, F.; Sander, A.; Rio, M.; Cuellar, F. A.; Tornos, J.; Hernandez-Martin, D.; Nemes, N. M.; Mompean, F.; Garcia-Hernandez, M.; Rivera-Calzada, A.; Sefrioui, Z.; Reyren, N.; Feher, T.; Varela, M.; Leon, C.; Santamaria, J.

    2017-09-01

    Controlling magnetic anisotropy is an important objective towards engineering novel magnetic device concepts in oxide electronics. In thin film manganites, magnetic anisotropy is weak and it is primarily determined by the substrate, through induced structural distortions resulting from epitaxial mismatch strain. On the other hand, in cobaltites, with a stronger spin orbit interaction, magnetic anisotropy is typically much stronger. In this paper, we show that interfacing La0.7Sr0.3MnO3 (LSMO) with an ultrathin LaCoO3 (LCO) layer drastically modifies the magnetic anisotropy of the manganite, making it independent of the substrate and closer to the magnetic isotropy characterizing its rhombohedral structure. Ferromagnetic resonance measurements evidence a tendency of manganite magnetic moments to point out-of-plane suggesting non collinear magnetic interactions at the interface. These results may be of interest for the design of oxide interfaces with tailored magnetic structures for new oxide devices.

  13. Modified magnetic anisotropy at LaCoO3/La0.7Sr0.3MnO3 interfaces

    Directory of Open Access Journals (Sweden)

    M. Cabero

    2017-09-01

    Full Text Available Controlling magnetic anisotropy is an important objective towards engineering novel magnetic device concepts in oxide electronics. In thin film manganites, magnetic anisotropy is weak and it is primarily determined by the substrate, through induced structural distortions resulting from epitaxial mismatch strain. On the other hand, in cobaltites, with a stronger spin orbit interaction, magnetic anisotropy is typically much stronger. In this paper, we show that interfacing La0.7Sr0.3MnO3 (LSMO with an ultrathin LaCoO3 (LCO layer drastically modifies the magnetic anisotropy of the manganite, making it independent of the substrate and closer to the magnetic isotropy characterizing its rhombohedral structure. Ferromagnetic resonance measurements evidence a tendency of manganite magnetic moments to point out-of-plane suggesting non collinear magnetic interactions at the interface. These results may be of interest for the design of oxide interfaces with tailored magnetic structures for new oxide devices.

  14. Probing the Intergalactic Magnetic Field with the Anisotropy of the Extragalactic Gamma-ray Background

    Science.gov (United States)

    Venters, T. M.; Pavlidou, V.

    2013-01-01

    The intergalactic magnetic field (IGMF) may leave an imprint on the angular anisotropy of the extragalactic gamma-ray background through its effect on electromagnetic cascades triggered by interactions between very high energy photons and the extragalactic background light. A strong IGMF will deflect secondary particles produced in these cascades and will thus tend to isotropize lower energy cascade photons, thereby inducing a modulation in the anisotropy energy spectrum of the gamma-ray background. Here we present a simple, proof-of-concept calculation of the magnitude of this effect and demonstrate that current Fermi data already seem to prefer nonnegligible IGMF values. The anisotropy energy spectrum of the Fermi gamma-ray background could thus be used as a probe of the IGMF strength.

  15. Validation of the Anhysteretic Magnetization Model for Soft Magnetic Materials with Perpendicular Anisotropy

    Directory of Open Access Journals (Sweden)

    Roman Szewczyk

    2014-07-01

    Full Text Available The paper presents results of validation of the anhysteretic magnetization model for a soft amorphous alloy with significant perpendicular anisotropy. The validation was carried out for the Jiles-Atherton model with Ramesh extension considering anisotropy. Due to the fact that it is difficult to measure anhysteretic magnetization directly, the soft magnetic core with negligible hysteresis was used. The results of validation indicate that the Jiles-Atherton model with Ramesh extension should be corrected to allow accurate modeling of the anhysteretic magnetization. The corrected model may be applied for modeling the cores of current transformers operating in a wide range of measured currents.

  16. Second order anisotropy contribution in perpendicular magnetic tunnel junctions.

    Science.gov (United States)

    Timopheev, A A; Sousa, R; Chshiev, M; Nguyen, H T; Dieny, B

    2016-06-01

    Hard-axis magnetoresistance loops were measured on perpendicular magnetic tunnel junction pillars of diameter ranging from 50 to 150 nm. By fitting these loops to an analytical model, the effective anisotropy fields in both free and reference layers were derived and their variations in temperature range between 340 K and 5 K were determined. It is found that a second-order anisotropy term of the form -K2cos(4)θ must be added to the conventional uniaxial -K1cos(2)θ term to explain the experimental data. This higher order contribution exists both in the free and reference layers. At T = 300 K, the estimated -K2/K1 ratios are 0.1 and 0.24 for the free and reference layers, respectively. The ratio is more than doubled at low temperatures changing the ground state of the reference layer from "easy-axis" to "easy-cone" regime. The easy-cone regime has clear signatures in the shape of the hard-axis magnetoresistance loops. The existence of this higher order anisotropy was also confirmed by ferromagnetic resonance experiments on FeCoB/MgO sheet films. It is of interfacial nature and is believed to be due to spatial fluctuations at the nanoscale of the first order anisotropy parameter at the FeCoB/MgO interface.

  17. Velocity Anisotropy as a Diagnostic of the Magnetization of the Interstellar Medium and Molecular clouds

    CERN Document Server

    Esquivel, Alejandro

    2011-01-01

    We use a set of magnetohydrodynamics (MHD) simulations of fully-developed (driven) turbulence to study the anisotropy in the velocity field that is induced by the presence of the magnetic field. In our models we study turbulence characterized by sonic Mach numbers M_s from 0.7 to 7.5, and Alfven Mach numbers M_A from 0.4 to 7.7. These are used to produce synthetic observations (centroid maps) that are analyzed. To study the effect of large scale density fluctuations and of white noise we have modified the density fields and obtained new centroid maps, which are analyzed. We show that restricting the range of scales at which the anisotropy is measured makes the method robust against such fluctuations. We show that the anisotropy in the structure function of the maps reveals the direction of the magnetic field for M_A \\lesssim 1.5, regardless of the sonic Mach number. We found that the degree of anisotropy can be used to determine the degree of magnetization (i.e. M_A) for M_A \\lesssim 1.5. To do this, one need...

  18. Perpendicular magnetic anisotropy influence on voltage-driven spin-diode effect in magnetic tunnel junctions: A micromagnetic study

    Science.gov (United States)

    Frankowski, Marek; Chȩciński, Jakub; Skowroński, Witold; Stobiecki, Tomasz

    2017-05-01

    We study the influence of the perpendicular magnetic anisotropy on the voltage-induced ferromagnetic resonance in magnetic tunnel junctions (MTJs). An MTJ response to the applied radio-frequency voltage excitation is investigated using micromagnetic calculations with the free layer oriented both in-plane and out-of-plane. Our model allows for a quantitative description of the magnetic system parameters such as resonance frequency, sensitivity or quality factor and for a distinction between material-dependent internal damping and disorder-dependent effective damping. We find that the sensitivity abruptly increases up to three orders of magnitude near the anisotropy transition regime, while the quality factor declines due to effective damping increase. We attribute the origin of this behaviour to the changes of the exchange energy in the system, which is calculated using micromagnetic approach.

  19. Interfacial tuning of perpendicular magnetic anisotropy and spin magnetic moment in CoFe/Pd multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Ngo, D.-T., E-mail: ndthe82@gmail.com [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Meng, Z.L. [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Tahmasebi, T. [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Data Storage Institute, A-STAR (Agency for Science Technology and Research), 5 Engineering Drive 1, Singapore 117608 (Singapore); Yu, X. [Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603 (Singapore); Thoeng, E. [Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603 (Singapore); Department of Physics, National University of Singapore, Singapore 117542 (Singapore); Yeo, L.H. [Department of Physics, National University of Singapore, Singapore 117542 (Singapore); Rusydi, A., E-mail: phyandri@nus.edu.sg [Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603 (Singapore); Department of Physics, National University of Singapore, Singapore 117542 (Singapore); Han, G.C [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Teo, K.-L., E-mail: eleteokl@nus.edu.sg [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore)

    2014-01-15

    We report on a strong perpendicular magnetic anisotropy in [CoFe 0.4 nm/Pd t]{sub 6} (t=1.0–2.0 nm) multilayers fabricated by DC sputtering in an ultrahigh vacuum chamber. Saturation magnetization, M{sub s}, and uniaxial anisotropy, K{sub u}, of the multilayers decrease with increasing the spacing thickness; with a M{sub s} of 155 emu/cc and a K{sub u} of 1.14×10{sup 5} J/m{sup 3} at a spacing thickness of t=2 nm. X-ray absorption spectroscopy and X-ray magnetic circular dichroism measurements reveal that spin and orbital magnetic moments of Co and Fe in CoFe film decrease as a function of Pd thickness, indicating the major contribution of surface/interfacial magnetism to the magnetic properties of the film. - Highlights: • Strong perpendicular magnetic anisotropy essentially contributed by interfacial anisotropy. • Controllably magnetic properties with low M{sub s}, high K{sub u}, high P. • Interfacial magnetic moments modified by CoFe/Pd interfaces with strong spin–orbit coupling. • Narrow Bloch walls with Néel caps. • Superior magnetic characteristics for spin-torque applications.

  20. Magnetic field-dependent shape anisotropy in small patterned films studied using rotating magnetoresistance

    OpenAIRE

    Xiaolong Fan; Hengan Zhou; Jinwei Rao; Xiaobing Zhao; Jing Zhao; Fengzhen Zhang; Desheng Xue

    2015-01-01

    Based on the electric rotating magnetoresistance method, the shape anisotropy of a Co microstrip has been systematically investigated. We find that the shape anisotropy is dependent not only on the shape itself, but also on the magnetization distribution controlled by an applied magnetic field. Together with micro-magnetic simulations, we present a visualized picture of how non-uniform magnetization affects the values and polarities of the anisotropy constants and . From the perspective of po...

  1. Magnetism of One-Dimensional Dipolar-Interaction Spin Chains with Perpendicular Anisotropy*

    Institute of Scientific and Technical Information of China (English)

    ZHANG Kai-Cheng; ZHU Yan

    2011-01-01

    We have investigated the magnetism of one-dimensional dipolar-interaction spin chains with perpendicular anisotropy by simulation.The behaviors of the magnetizations and the orientation correlations change dramatically as the anisotropy increases to the critical value.The domain length can be controlled by adjusting the temperature and the external field as well as the anisotropy.These properties are interesting and arise from the competition between the anisotropy and the interaction along the chain.

  2. Manipulating magnetic anisotropies of Co/MgO(001) ultrathin films via oblique deposition

    Science.gov (United States)

    Sheraz Ahmad, Syed; He, Wei; Tang, Jin; Zhang, Yong Sheng; Hu, Bo; Ye, Jun; Gul, Qeemat; Zhang, Xiang-Qun; Cheng, Zhao-Hua

    2016-09-01

    We present a systematic investigation of magnetic anisotropy induced by oblique deposition of Co thin films on MgO (001) substrates by molecular beam epitaxy at different deposition angles, i.e., 0°, 30°, 45°, 60°, and 75° with respect to the surface normal. Low energy electron diffraction (LEED), surface magneto-optical Kerr effect (SMOKE), and anisotropic magnetoresistance (AMR) setups were employed to investigate the magnetic properties of cobalt films. The values of in-plane uniaxial magnetic anisotropy (UMA) constant Ku and four-fold magnetocrystalline anisotropy constant K1 were derived from magnetic torque curves on the base of AMR results. It was found that the value of Ku increases with increasing deposition angle with respect to the surface normal, while the value of K1 remains almost constant for all the samples. Furthermore, by using MOKE results, the Ku values of the films deposited obliquely were also derived from the magnetization curves along hard axis. The results of AMR method were then compared with that of hard axis fitting method (coherent rotation) and found that both methods have almost identical values of UMA constant for each sample. Project supported by the Chinese Academy of Sciences-The World Academy of Sciences (CAS-TWAS) Fellowship Program, the National Basic Research Program of China (Grant Nos. 2015CB921403 and 2012CB933102), and the National Natural Science Foundation of China (Grant Nos. 51427801, 11374350, and 11274361).

  3. Stress-anneal-induced magnetic anisotropy in highly textured Fe-Ga and Fe-Al magnetostrictive strips for bending-mode vibrational energy harvesters

    Directory of Open Access Journals (Sweden)

    Jung Jin Park

    2016-05-01

    Full Text Available Magnetostrictive Fe-Ga and Fe-Al alloys are promising materials for use in bending-mode vibrational energy harvesters. For this study, 50.8 mm × 5.0 mm × 0.5 mm strips of Fe-Ga and Fe-Al were cut from 0.50-mm thick rolled sheet. An atmospheric anneal was used to develop a Goss texture through an abnormal grain growth process. The anneal lead to large (011 grains that covered over 90% of sample surface area. The resulting highly-textured Fe-Ga and Fe-Al strips exhibited saturation magnetostriction values (λsat =  λ∥ − λ⊥ of ∼280 ppm and ∼130 ppm, respectively. To maximize 90° rotation of magnetic moments during bending of the strips, we employed compressive stress annealing (SA. Samples were heated to 500°C, and a 100-150 MPa compressive stress was applied while at 500°C for 30 minutes and while being cooled. The effectiveness of the SA on magnetic moment rotation was inferred by comparing post-SA magnetostriction with the maximum possible yield of rotated magnetic moments, which is achieved when λ∥ = λsat and λ⊥ = 0. The uniformity of the SA along the sample length and the impact of the SA on sensing/energy harvesting performance were then assessed by comparing pre- and post-SA bending-stress-induced changes in magnetization at five different locations along the samples. The SA process with a 150 MPa compressive load improved Fe-Ga actuation along the sample length from 170 to 225 ppm (from ∼60% to within ∼80% of λsat. The corresponding sensing/energy harvesting performance improved by as much as a factor of eight in the best sample, however the improvement was not at all uniform along the sample length. The SA process with a 100 MPa compressive load improved Fe-Al actuation along the sample length from 60 to 73 ppm (from ∼46% to ∼56% of λsat, indicating only a marginally effective SA and suggesting the need for modification of the SA protocol. In spite of this, the SA was effective at improving the sensing

  4. Stress-anneal-induced magnetic anisotropy in highly textured Fe-Ga and Fe-Al magnetostrictive strips for bending-mode vibrational energy harvesters

    Science.gov (United States)

    Park, Jung Jin; Na, Suok-Min; Raghunath, Ganesh; Flatau, Alison B.

    2016-05-01

    Magnetostrictive Fe-Ga and Fe-Al alloys are promising materials for use in bending-mode vibrational energy harvesters. For this study, 50.8 mm × 5.0 mm × 0.5 mm strips of Fe-Ga and Fe-Al were cut from 0.50-mm thick rolled sheet. An atmospheric anneal was used to develop a Goss texture through an abnormal grain growth process. The anneal lead to large (011) grains that covered over 90% of sample surface area. The resulting highly-textured Fe-Ga and Fe-Al strips exhibited saturation magnetostriction values (λsat = λ∥ - λ⊥) of ˜280 ppm and ˜130 ppm, respectively. To maximize 90° rotation of magnetic moments during bending of the strips, we employed compressive stress annealing (SA). Samples were heated to 500°C, and a 100-150 MPa compressive stress was applied while at 500°C for 30 minutes and while being cooled. The effectiveness of the SA on magnetic moment rotation was inferred by comparing post-SA magnetostriction with the maximum possible yield of rotated magnetic moments, which is achieved when λ∥ = λsat and λ⊥ = 0. The uniformity of the SA along the sample length and the impact of the SA on sensing/energy harvesting performance were then assessed by comparing pre- and post-SA bending-stress-induced changes in magnetization at five different locations along the samples. The SA process with a 150 MPa compressive load improved Fe-Ga actuation along the sample length from 170 to 225 ppm (from ˜60% to within ˜80% of λsat). The corresponding sensing/energy harvesting performance improved by as much as a factor of eight in the best sample, however the improvement was not at all uniform along the sample length. The SA process with a 100 MPa compressive load improved Fe-Al actuation along the sample length from 60 to 73 ppm (from ˜46% to ˜56% of λsat, indicating only a marginally effective SA and suggesting the need for modification of the SA protocol. In spite of this, the SA was effective at improving the sensing/energy harvesting

  5. DFT calculations of magnetic anisotropy energy of Ge(1-x)Mn(x)Te ferromagnetic semiconductor.

    Science.gov (United States)

    Łusakowski, A; Bogusławski, P; Story, T

    2015-06-10

    Density functional theory (DFT) calculations of the energy of magnetic anisotropy for diluted ferromagnetic semiconductor Ge(1-x)Mn(x)Te were performed using OpenMX package with fully relativistic pseudopotentials. The influence of hole concentration and magnetic ion neighbourhood on magnetic anisotropy energy is presented. Analysis of microscopic mechanism of magnetic anisotropy is provided, in particular the role of spin-orbit coupling, spin polarization and spatial changes of electron density are discussed. The calculations are in accordance with the experimental observation of perpendicular magnetic anisotropy in rhombohedral Ge(1-x)Mn(x)Te (1 1 1) thin layers.

  6. DFT calculations of magnetic anisotropy energy of Ge1-xMnxTe ferromagnetic semiconductor

    Science.gov (United States)

    Łusakowski, A.; Bogusławski, P.; Story, T.

    2015-06-01

    Density functional theory (DFT) calculations of the energy of magnetic anisotropy for diluted ferromagnetic semiconductor Ge1-xMnxTe were performed using OpenMX package with fully relativistic pseudopotentials. The influence of hole concentration and magnetic ion neighbourhood on magnetic anisotropy energy is presented. Analysis of microscopic mechanism of magnetic anisotropy is provided, in particular the role of spin-orbit coupling, spin polarization and spatial changes of electron density are discussed. The calculations are in accordance with the experimental observation of perpendicular magnetic anisotropy in rhombohedral Ge1-xMnxTe (1 1 1) thin layers.

  7. Influence of boron diffusion on the perpendicular magnetic anisotropy in Ta|CoFeB|MgO ultrathin films

    Energy Technology Data Exchange (ETDEWEB)

    Sinha, Jaivardhan; Gruber, Maria; Kodzuka, Masaya; Ohkubo, Tadakatsu; Mitani, Seiji; Hono, Kazuhiro; Hayashi, Masamitsu, E-mail: hayashi.masamitsu@nims.go.jp [National Institute for Materials Science, Tsukuba 305-0047 (Japan)

    2015-01-28

    We have studied structural and magnetic properties of Ta|CoFeB|MgO heterostructures using cross-section transmission electron microscopy (TEM), electron energy loss spectrum (EELS) imaging, and vibrating sample magnetometry. From the TEM studies, the CoFeB layer is found to be predominantly amorphous for as deposited films, whereas small crystallites, diameter of ∼5 nm, are observed in films annealed at 300 °C. We find that the presence of such nanocrystallites is not sufficient for the occurrence of perpendicular magnetic anisotropy. Using EELS, we find that boron diffuses into the Ta underlayer upon annealing. The Ta underlayer thickness dependence of the magnetic anisotropy indicates that ∼0.2 nm of Ta underlayer is enough to absorb the boron from the CoFeB layer and induce perpendicular magnetic anisotropy. Boron diffusion upon annealing becomes limited when the CoFeB layer thickness is larger than ∼2 nm, which coincides with the thickness at which the saturation magnetization M{sub S} and the interface magnetic anisotropy K{sub I} drop by ∼20%. These results show the direct role which boron plays in determining the perpendicular magnetic anisotropy in CoFeB|MgO heterostructures.

  8. Low coercivity giant magnetoresistance with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Jeong-Seop; Yoon, Jungbum; Kang, Mool-Bit; You, Chun-Yeol, E-mail: cyyou@inha.ac.kr

    2014-05-01

    We find the perpendicular magnetic anisotropy giant magnetoresistance structure, whose coercivity is less than 10 Oe. We reveal that the coercivity of free layer can be smaller than 5 Oe in Co/Pd/Cu/[Co/Pd]{sub 4} multilayer structure with a TiO{sub 2} seed layer. The TiO{sub 2} seed layer plays a critical role in the small coercivity of free layer. The GMR ratio is around 1–1.8% for the out-of-plane magnetic fields, and the maximum MR sensitivity of 0.12%/Oe is achieved. - Highlights: • We find an extremely small coercivity giant magnetoresistance (GMR) structure for the out-of-plane magnetic field. • The key ingredient of small coercivity is a TiO{sub 2} seed layer. • Such a small coercivity GMR structure will be useful for automotive applications such as wheel speed, rotation, and position sensors.

  9. Highly Efficient Domain Walls Injection in Perpendicular Magnetic Anisotropy Nanowire.

    Science.gov (United States)

    Zhang, S F; Gan, W L; Kwon, J; Luo, F L; Lim, G J; Wang, J B; Lew, W S

    2016-04-21

    Electrical injection of magnetic domain walls in perpendicular magnetic anisotropy nanowire is crucial for data bit writing in domain wall-based magnetic memory and logic devices. Conventionally, the current pulse required to nucleate a domain wall is approximately ~10(12) A/m(2). Here, we demonstrate an energy efficient structure to inject domain walls. Under an applied electric potential, our proposed Π-shaped stripline generates a highly concentrated current distribution. This creates a highly localized magnetic field that quickly initiates the nucleation of a magnetic domain. The formation and motion of the resulting domain walls can then be electrically detected by means of Ta Hall bars across the nanowire. Our measurements show that the Π-shaped stripline can deterministically write a magnetic data bit in 15 ns even with a relatively low current density of 5.34 × 10(11) A/m(2). Micromagnetic simulations reveal the evolution of the domain nucleation - first, by the formation of a pair of magnetic bubbles, then followed by their rapid expansion into a single domain. Finally, we also demonstrate experimentally that our injection geometry can perform bit writing using only about 30% of the electrical energy as compared to a conventional injection line.

  10. Highly Efficient Domain Walls Injection in Perpendicular Magnetic Anisotropy Nanowire

    Science.gov (United States)

    Zhang, S. F.; Gan, W. L.; Kwon, J.; Luo, F. L.; Lim, G. J.; Wang, J. B.; Lew, W. S.

    2016-04-01

    Electrical injection of magnetic domain walls in perpendicular magnetic anisotropy nanowire is crucial for data bit writing in domain wall-based magnetic memory and logic devices. Conventionally, the current pulse required to nucleate a domain wall is approximately ~1012 A/m2. Here, we demonstrate an energy efficient structure to inject domain walls. Under an applied electric potential, our proposed Π-shaped stripline generates a highly concentrated current distribution. This creates a highly localized magnetic field that quickly initiates the nucleation of a magnetic domain. The formation and motion of the resulting domain walls can then be electrically detected by means of Ta Hall bars across the nanowire. Our measurements show that the Π-shaped stripline can deterministically write a magnetic data bit in 15 ns even with a relatively low current density of 5.34 × 1011 A/m2. Micromagnetic simulations reveal the evolution of the domain nucleation – first, by the formation of a pair of magnetic bubbles, then followed by their rapid expansion into a single domain. Finally, we also demonstrate experimentally that our injection geometry can perform bit writing using only about 30% of the electrical energy as compared to a conventional injection line.

  11. Effects of the galactic magnetic field upon large scale anisotropies of extragalactic cosmic rays

    Energy Technology Data Exchange (ETDEWEB)

    Harari, D.; Mollerach, S.; Roulet, E., E-mail: harari@cab.cnea.gov.ar, E-mail: mollerach@cab.cnea.gov.ar, E-mail: roulet@cab.cnea.gov.ar [CONICET, Centro Atómico Bariloche, Bustillo 9500, 8400 Bariloche (Argentina)

    2010-11-01

    The large scale pattern in the arrival directions of extragalactic cosmic rays that reach the Earth is different from that of the flux arriving to the halo of the Galaxy as a result of the propagation through the galactic magnetic field. Two different effects are relevant in this process: deflections of trajectories and (de)acceleration by the electric field component due to the galactic rotation. The deflection of the cosmic ray trajectories makes the flux intensity arriving to the halo from some direction to appear reaching the Earth from another direction. This applies to any intrinsic anisotropy in the extragalactic distribution or, even in the absence of intrinsic anisotropies, to the dipolar Compton-Getting anisotropy induced when the observer is moving with respect to the cosmic rays rest frame. For an observer moving with the solar system, cosmic rays traveling through far away regions of the Galaxy also experience an electric force coming from the relative motion (due to the rotation of the Galaxy) of the local system in which the field can be considered as being purely magnetic. This produces small changes in the particles momentum that can originate large scale anisotropies even for an isotropic extragalactic flux.

  12. Perpendicular magnetic anisotropy in Mn2CoAl thin film

    Science.gov (United States)

    Sun, N. Y.; Zhang, Y. Q.; Fu, H. R.; Che, W. R.; You, C. Y.; Shan, R.

    2016-01-01

    Heusler compound Mn2CoAl (MCA) is attracting more attentions due to many novel properties, such as high resistance, semiconducting behavior and suggestion as a spin-gapless material with a low magnetic moment. In this work, Mn2CoAl epitaxial thin film was prepared on MgO(100) substrate by magnetron sputtering. The transport property of the film exhibits a semiconducting-like behavior. Moreover, our research reveals that perpendicular magnetic anisotropy (PMA) can be induced in very thin Mn2CoAl films resulting from Mn-O and Co-O bonding at Mn2CoAl/MgO interface, which coincides with a recent theoretical prediction. PMA and low saturation magnetic moment could lead to large spin-transfer torque with low current density in principle, and thus our work may bring some unanticipated Heusler compounds into spintronics topics such as the domain wall motion and the current-induced magnetization reversal.

  13. Determination of spin torque efficiencies in heterostructures with perpendicular magnetic anisotropy

    Science.gov (United States)

    Pai, Chi-Feng; Mann, Maxwell; Tan, Aik Jun; Beach, Geoffrey S. D.

    2016-04-01

    We report that by measuring a current-induced hysteresis loop shift versus in-plane bias magnetic field, the spin-Hall effect (SHE) contribution of the current-induced effective field per current density χSHE can be estimated for Pt- and Ta-based magnetic heterostructures with perpendicular magnetic anisotropy. We apply this technique to a Pt-based sample with its ferromagnetic (FM) layer being wedged deposited and discover an extra effective field contribution χWedged due to the asymmetric nature of the deposited FM layer. We confirm the correlation between χWedged and the asymmetric depinning process in FM layer during magnetization switching by magneto-optical Kerr microscopy. These results indicate the possibility of engineering deterministic spin-orbit torque switching by controlling the symmetry of domain expansion through the materials growth process.

  14. Finite electric field effects in the large perpendicular magnetic anisotropy surface Pt/Fe/Pt(001): a first-principles study.

    Science.gov (United States)

    Tsujikawa, Masahito; Oda, Tatsuki

    2009-06-19

    We investigate crystalline magnetic anisotropy in the electric field (EF) for the FePt surface which has a large perpendicular anisotropy, by means of the first-principles approach. Anisotropy is reduced linearly with respect to the inward EF, associated with the induced spin density around the Fe layer. Although the magnetic anisotropy energy (MAE) density reveals large variation around the atoms, the intrinsic contribution to the MAE is found to mainly come from the Fe layer. The surface without the capping Pt layer also shows similar linear dependence.

  15. Nonlinear evolution of cosmic magnetic fields and cosmic microwave background anisotropies

    Science.gov (United States)

    Tashiro, Hiroyuki; Sugiyama, Naoshi; Banerjee, Robi

    2006-01-01

    In this work we investigate the effects of primordial magnetic fields on cosmic microwave background anisotropies (CMB). Based on cosmological magneto-hydro dynamic (MHD) simulations [R. Banerjee and K. Jedamzik, Phys. Rev. DPRVDAQ0556-2821 70, 123003 (2004).10.1103/PhysRevD.70.123003] we calculate the CMB anisotropy spectra and polarization induced by fluid fluctuations (Alfvén modes) generated by primordial magnetic fields. The strongest effect on the CMB spectra comes from the transition epoch from a turbulent regime to a viscous regime. The balance between magnetic and kinetic energy until the onset of the viscous regime provides a one to one relation between the comoving coherence length L and the comoving magnetic field strength B, such as L˜30(B/10-9Gauss)3pc. The resulting CMB temperature and polarization anisotropies for the initial power law index of the magnetic fields n>3/2 are somewhat different from the ones previously obtained by using linear perturbation theory. In particular, differences can appear on intermediate scales l20000. On scales l0.7Mpc for the most extreme case, or B0.8Mpc for the most conservative case. We may also expect higher signals on large scales of the polarization spectra compared to linear calculations. The signal may even exceed the B-mode polarization from gravitational lensing depending on the strength of the primordial magnetic fields. On very small scales, the diffusion damping scale of nonlinear calculations turns out to be much smaller than the one of linear calculations if the comoving magnetic field strength B>16nGauss. If the magnetic field strength is smaller, the diffusion scales become smaller too. Therefore we expect to have both, temperature and polarization anisotropies, even beyond l>10000 regardless of the strength of the magnetic fields. The peak values of the temperature anisotropy and the B-mode polarization spectra are approximately 40μK and a few μK, respectively.

  16. Direct observation of massless domain wall dynamics in nanostripes with perpendicular magnetic anisotropy.

    Science.gov (United States)

    Vogel, J; Bonfim, M; Rougemaille, N; Boulle, O; Miron, I M; Auffret, S; Rodmacq, B; Gaudin, G; Cezar, J C; Sirotti, F; Pizzini, S

    2012-06-15

    Domain wall motion induced by nanosecond current pulses in nanostripes with perpendicular magnetic anisotropy (Pt/Co/AlO(x)) is shown to exhibit negligible inertia. Time-resolved magnetic microscopy during current pulses reveals that the domain walls start moving, with a constant speed, as soon as the current reaches a constant amplitude, and no or little motion takes place after the end of the pulse. The very low "mass" of these domain walls is attributed to the combination of their narrow width and high damping parameter α. Such a small inertia should allow accurate control of domain wall motion by tuning the duration and amplitude of the current pulses.

  17. Perpendicular Magnetic Anisotropy in Co-Based Full Heusler Alloy Thin Films

    Science.gov (United States)

    Wu, Y.; Xu, X. G.; Miao, J.; Jiang, Y.

    2015-12-01

    Half-metallic Co-based full Heusler alloys have been qualified as promising functional materials in spintronic devices due to their high spin polarization. The lack of perpendicular magnetic anisotropy (PMA) is one of the biggest obstacles restricting their application in next generation ultrahigh density storage such as magnetic random access memory (MARM). How to induce the PMA in Co-based full Heusler alloy thin films has attracted much research interest of scientists. This paper presents an overview of recent progress in this research area. We hope that this paper would provide some guidance and ideas to develop highly spin-polarized Co-based Heusler alloy thin films with PMA.

  18. Experimental investigation of magnetic anisotropy in spin vortex discs

    Energy Technology Data Exchange (ETDEWEB)

    Garraud, N., E-mail: ngarraud@ufl.edu; Arnold, D. P. [Department of Electrical and Computer Engineering, University of Florida, Gainesville, Florida 32611 (United States)

    2014-05-07

    We present experimental 2D vector vibrating sample magnetometer measurements to demonstrate the shape anisotropy effects occurring in micrometer-diameter supermalloy spin vortex discs. Measurements made for different disc sizes and orientations confirm the out-of-plane susceptibility is several orders of magnitude smaller than the in-plane susceptibility. These results validate with a high certitude that spin vortices with high diameter to thickness ratio retain in-plane-only magnetization, even when subjected to fields in the out-of-plane direction. These results contribute to further computational simulations of the dynamics of spin vortex structures in colloidal suspensions where external fields may be applied in any arbitrary direction.

  19. Anomalous enhancement in interfacial perpendicular magnetic anisotropy through uphill diffusion.

    Science.gov (United States)

    Das, Tanmay; Kulkarni, Prabhanjan D; Purandare, S C; Barshilia, Harish C; Bhattacharyya, Somnath; Chowdhury, Prasanta

    2014-06-17

    We observed interfacial chemical sharpening due to uphill diffusion in post annealed ultrathin multilayer stack of Co and Pt, which leads to enhanced interfacial perpendicular magnetic anisotropy (PMA). This is surprising as these elements are considered as perfectly miscible. This chemical sharpening was confirmed through quantitative energy dispersive x-ray (EDX) spectroscopy and intensity distribution of images taken on high angle annular dark field (HAADF) detector in Scanning Transmission Electron Microscopic (STEM) mode. This observation demonstrates an evidence of miscibility gap in ultrathin coherent Co/Pt multilayer stacks.

  20. Two Polymorphic Forms of a Six-Coordinate Mononuclear Cobalt(II) Complex with Easy-Plane Anisotropy: Structural Features, Theoretical Calculations, and Field-Induced Slow Relaxation of the Magnetization.

    Science.gov (United States)

    Roy, Subhadip; Oyarzabal, Itziar; Vallejo, Julia; Cano, Joan; Colacio, Enrique; Bauza, Antonio; Frontera, Antonio; Kirillov, Alexander M; Drew, Michael G B; Das, Subrata

    2016-09-06

    A mononuclear cobalt(II) complex [Co(3,5-dnb)2(py)2(H2O)2] {3,5-Hdnb = 3,5-dinitrobenzoic acid; py = pyridine} was isolated in two polymorphs, in space groups C2/c (1) and P21/c (2). Single-crystal X-ray diffraction analyses reveal that 1 and 2 are not isostructural in spite of having equal formulas and ligand connectivity. In both structures, the Co(II) centers adopt octahedral {CoN2O4} geometries filled by pairs of mutually trans terminal 3,5-dnb, py, and water ligands. However, the structures of 1 and 2 disclose distinct packing patterns driven by strong intermolecular O-H···O hydrogen bonds, leading to their 0D→2D (1) or 0D→1D (2) extension. The resulting two-dimensional layers and one-dimensional chains were topologically classified as the sql and 2C1 underlying nets, respectively. By means of DFT theoretical calculations, the energy variations between the polymorphs were estimated, and the binding energies associated with the noncovalent interactions observed in the crystal structures were also evaluated. The study of the direct-current magnetic properties, as well as ab initio calculations, reveal that both 1 and 2 present a strong easy-plane magnetic anisotropy (D > 0), which is larger for the latter polymorph (D is found to exhibit values between +58 and 117 cm(-1) depending on the method). Alternating current dynamic susceptibility measurements show that these polymorphs exhibit field-induced slow relaxation of the magnetization with Ueff values of 19.5 and 21.1 cm(-1) for 1 and 2, respectively. The analysis of the whole magnetic data allows the conclusion that the magnetization relaxation in these polymorphs mainly takes place through a virtual excited state (Raman process). It is worth noting that despite the notable difference between the supramolecular networks of 1 and 2, they exhibit almost identical magnetization dynamics. This fact suggests that the relaxation process is intramolecular in nature and that the virtual state involved in the

  1. Dynamical skyrmion state in a spin current nano-oscillator with perpendicular magnetic anisotropy.

    Science.gov (United States)

    Liu, R H; Lim, W L; Urazhdin, S

    2015-04-03

    We study the spectral characteristics of spin current nano-oscillators based on the Pt/[Co/Ni] magnetic multilayer with perpendicular magnetic anisotropy. By varying the applied magnetic field and current, both localized and propagating spin wave modes of the oscillation are achieved. At small fields, we observe an abrupt onset of the modulation sidebands. We use micromagnetic simulations to identify this state as a dynamical magnetic skyrmion stabilized in the active device region by spin current injection, whose current-induced dynamics is accompanied by the gyrotropic motion of the core due to the skew deflection. Our results demonstrate a practical route for controllable skyrmion manipulation by spin current in magnetic thin films.

  2. Enhanced orbital magnetic moments in magnetic heterostructures with interface perpendicular magnetic anisotropy.

    Science.gov (United States)

    Ueno, Tetsuro; Sinha, Jaivardhan; Inami, Nobuhito; Takeichi, Yasuo; Mitani, Seiji; Ono, Kanta; Hayashi, Masamitsu

    2015-10-12

    We have studied the magnetic layer thickness dependence of the orbital magnetic moment in magnetic heterostructures to identify contributions from interfaces. Three different heterostructures, Ta/CoFeB/MgO, Pt/Co/AlOx and Pt/Co/Pt, which possess significant interface contribution to the perpendicular magnetic anisotropy, are studied as model systems. X-ray magnetic circular dichroism spectroscopy is used to evaluate the relative orbital moment, i.e. the ratio of the orbital to spin moments, of the magnetic elements constituting the heterostructures. We find that the relative orbital moment of Co in Pt/Co/Pt remains constant against its thickness whereas the moment increases with decreasing Co layer thickness for Pt/Co/AlOx, suggesting that a non-zero interface orbital moment exists for the latter system. For Ta/CoFeB/MgO, a non-zero interface orbital moment is found only for Fe. X-ray absorption spectra shows that a particular oxidized Co state in Pt/Co/AlOx, absent in other heterosturctures, may give rise to the interface orbital moment in this system. These results show element specific contributions to the interface orbital magnetic moments in ultrathin magnetic heterostructures.

  3. Ab initio modelling of magnetic anisotropy in Sr3NiPtO6

    NARCIS (Netherlands)

    Pradipto, A. -M.; Broer, R.; Picozzi, S.

    2016-01-01

    First principles calculations in the framework of Density Functional Theory (DFT) and wavefunction-based correlated methods have been performed to investigate in detail the magnetic anisotropy in Sr3NiPtO6. This material is known for the easy-plane anisotropy with a large anisotropy constant of abou

  4. Magnetic Anisotropy and Magnetization Switching in Ferromagnetic GaMnAs

    Science.gov (United States)

    Limmer, W.; Daeubler, J.; Glunk, M.; Hummel, T.; Schoch, W.; Schwaiger, S.; Tabor, M.; Sauer, R.

    Characteristic features of diluted ferromagnetic semiconductors such as the anisotropic magnetoresistance or the spin polarization of charge carriers are intimately connected with a macroscopic magnetization. Since the orientation of the magnetization is controlled by magnetic anisotropy (MA), a detailed knowledge of this anisotropy is indispensable for the design of novel spintronic devices. In this article, angle-dependent magnetotransport is demonstrated to be an excellent tool for probing MA as an alternative to the standard ferromagnetic-resonance method. Moreover, its ability to trace the motion of the magnetization vector in a variable external magnetic field makes it ideally suitable for studying magnetization switching, a potential basic effect in future logical devices. The MA of a series of differently strained GaMnAs samples is analyzed by means of model calculations in a single-domain picture based on a series expansion of the resistivity tensor and a numerical minimization of the free enthalpy.

  5. Magnetic anisotropy in rapidly quenched amorphous glass-coated nanowires

    Science.gov (United States)

    Óvári, T.-A.; Rotărescu, C.; Atițoaie, A.; Corodeanu, S.; Lupu, N.; Chiriac, H.

    2016-07-01

    Results on the roles played by the magnetoelastic and magnetostatic anisotropy terms in the magnetic behavior of glass-coated magnetostrictive amorphous nanowires prepared by means of rapid solidification are reported. Their contributions have been analyzed both experimentally, through hysteresis loop measurements, and theoretically, using micromagnetic simulations. All the investigated samples exhibit a magnetically bistable behavior, characterized by a single-step magnetization reversal when the applied field reaches a critical threshold value, called switching field. The combined interpretation of the experimental and theoretical data allows one to understand the effect of the magnetoelastic term on the value of the switching field, on one hand, and the effect of the magnetostatic term on the nucleation mechanism on the other, both with an essential impact on the characteristics of the nanowires' magnetic bistability. The results are crucial for understanding the basic magnetic properties of these novel rapidly solidified ultrathin magnetic wires, as well as for tailoring their properties according to the specific requirements of various sensing applications.

  6. Effect of soft underlayer magnetic anisotropy on perpendicular recording process

    Science.gov (United States)

    Lim, C. K.; Kim, E. S.; Yoon, S. Y.; Kong, S. H.; Lee, H. S.; Oh, H. S.; Kim, Y. S.

    2007-03-01

    The presence of the soft magnetic underlayer (SUL) in perpendicular magnetic recording (PMR) media is essential for the application. It is commonly understood that the SUL provides the return flux path and enhances the writing field by enhancing the recording field from the write pole. However, SUL increases the magnetic noise during the read back process due to magnetic domain walls in the SUL. Hence, it is common to grow SUL with large uniaxial or unidirectional magnetic anisotropy field ( H k) to reduce domain wall noise. In this paper, we explore the effect of increasing SUL H k on the recording process. We studied this effect by using the finite element micromagnetic simulation. Our simulation results show that the contribution of SUL to the writing field amplitude is reduced with increasing H k. This reduction in magnetic field from high H k SUL actually improves the recording performance due to the better field gradient at SUL. The simulation results are qualitatively consistent with the actual experimental data obtained from the Guzik measurement.

  7. How to probe transverse magnetic anisotropy of a single-molecule magnet by electronic transport?

    Science.gov (United States)

    Misiorny, M.; Burzuri, E.; Gaudenzi, R.; Park, K.; Leijnse, M.; Wegewijs, M.; Paaske, J.; Cornia, A.; van der Zant, H.

    We propose an approach for in-situ determination of the transverse magnetic anisotropy (TMA) of an individual molecule by electronic transport measurements, see Phys. Rev. B 91, 035442 (2015). We study a Fe4 single-molecule magnet (SMM) captured in a gateable junction, a unique tool for addressing the spin in different redox states of a molecule. We show that, due to mixing of the spin eigenstates of the SMM, the TMA significantly manifests itself in transport. We predict and experimentally observe the pronounced intensity modulation of the Coulomb peak amplitude with the magnetic field in the linear-response transport regime, from which the TMA parameter E can be estimated. Importantly, the method proposed here does not rely on the small induced tunnelling effects and, hence, works well at temperatures and electron tunnel broadenings by far exceeding the tunnel splittings and even E itself. We deduce that the TMA for a single Fe4 molecule captured in a junction is substantially larger than the bulk value. Work supported by the Polish Ministry of Science and Education as `Iuventus Plus' project (IP2014 030973) in years 2015-2016.

  8. Physical properties of elongated magnetic particles: magnetization and friction coefficient anisotropies.

    Science.gov (United States)

    Vereda, Fernando; de Vicente, Juan; Hidalgo-Alvarez, Roque

    2009-06-02

    Anisotropy counts: A brief review of the main physical properties of elongated magnetic particles (EMPs) is presented. The most important characteristic of an EMP is the additional contribution of shape anisotropy to the total anisotropy energy of the particle, when compared to spherical magnetic particles. The electron micrograph shows Ni-ferrite microrods fabricated by the authors.We present an overview of the main physical properties of elongated magnetic particles (EMPs), including some of their more relevant properties in suspension. When compared to a spherical magnetic particle, the most important characteristic of an EMP is an additional contribution of shape anisotropy to the total anisotropy energy of the particle. Increasing aspect ratios also lead to an increase in both the critical single-domain size of a magnetic particle and its resistance to thermally activated spontaneous reversal of the magnetization. For single-domain EMPs, magnetization reversal occurs primarily by one of two modes, coherent rotation or curling, the latter being facilitated by larger aspect ratios. When EMPs are used to prepare colloidal suspensions, other physical properties come into play, such as their anisotropic friction coefficient and the consequent enhanced torque they experience in a shear flow, their tendency to align in the direction of an external field, to form less dense sediments and to entangle into more intricate aggregates. From a more practical point of view, EMPs are discussed in connection with two interesting types of magnetic colloids: magnetorheological fluids and suspensions for magnetic hyperthermia. Advances reported in the literature regarding the use of EMPs in these two systems are included. In the final section, we present a summary of the most relevant methods documented in the literature for the fabrication of EMPs, together with a list of the most common ferromagnetic materials that have been synthesized in the form of EMPs.

  9. Magnetic anisotropy of polycrystalline magnetoferritin investigated by SQUID and electron magnetic resonance

    Energy Technology Data Exchange (ETDEWEB)

    Moro, F., E-mail: fabrizio.moro@nottingham.ac.uk [School of Physics, University of Nottingham, NG7 2RD Nottingham (United Kingdom); Miguel, R. de [Laboratorio de Microscopías Avanzadas (LMA), Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza, 50018 Zaragoza (Spain); Jenkins, M. [Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-CSIC, 50009 Zaragoza (Spain); Gómez-Moreno, C. [Laboratorio de Microscopías Avanzadas (LMA), Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza, 50018 Zaragoza (Spain); Sells, D.; Tuna, F. [EPSRC National UK EPR Facility, Photon Science Institute, University of Manchester, Manchester, M13 9PL (United Kingdom); McInnes, E.J.L. [EPSRC National UK EPR Facility, Photon Science Institute, University of Manchester, Manchester, M13 9PL (United Kingdom); School of Chemistry, University of Manchester, Manchester M13 9PL (United Kingdom); Lostao, A. [Laboratorio de Microscopías Avanzadas (LMA), Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza, 50018 Zaragoza (Spain); Fundación ARAID (Spain); Luis, F. [Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-CSIC, 50009 Zaragoza (Spain); Slageren, J. van [Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart (Germany)

    2014-06-01

    Magnetoferritin molecules with an average inorganic core diameter of 5.7±1.6 nm and polycrystalline internal structure were investigated by a combination of transmission electron microscopy, magnetic susceptibility, magnetization, and electron magnetic resonance (EMR) experiments. The temperature and frequency dependence of the magnetic susceptibility allowed for the determination of the magnetic anisotropy on an experimental time scale which spans from seconds to nanoseconds. In addition, angle-dependent EMR experiments were carried out for the determination of the nanoparticle symmetry and internal magnetic field. Due to the large surface to volume ratio, the nanoparticles show larger and uniaxial rather than cubic magnetic anisotropies compared to bulk maghemite and magnetite. - Highlights: • Synthesis of polycristalline magnetoferritin with average particle size of 5.7 nm. • Observation of surface effects and estimation of the anisotropy constant and energy barrier by a combined SQUID and EMR study. • Deviation of Gilbert relaxation of the magnetization in magnetoferritin. • Determination of particle symmetry and internal magnetic field by angle-dependent EMR studies.

  10. In-plane magnetic anisotropies in Ni/FeMn and Ni90Fe10/FeMn exchange biased bilayers

    Science.gov (United States)

    Pires, M. J. M.; de Oliveira, R. B.; Martins, M. D.; Ardisson, J. D.; Macedo, W. A. A.

    2007-12-01

    The in-plane magnetic anisotropy in Ni/FeMn and Ni90Fe10/FeMn exchange-biased bilayers prepared by co-evaporation under molecular beam epitaxy conditions is investigated employing longitudinal magneto-optical Kerr effect (MOKE) and ferromagnetic resonance (FMR). The exchange anisotropy was induced by a magnetic field cooling immediately after the deposition of the bilayers. Besides the induced term, the presence of an additional uniaxial anisotropy in the FM layers was detected both by MOKE and FMR, and the characteristic directions of these two anisotropy terms are not coincident. The interplay between the anisotropy contributions is discussed considering micromagnetic simulations and the in-plane resonance condition for different magnetic field orientation. X-ray diffraction, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy were used to complement the characterization of the samples.

  11. Detecting compaction disequilibrium with anisotropy of magnetic susceptibility

    Science.gov (United States)

    Schwehr, Kurt; Tauxe, Lisa; Driscoll, Neal; Lee, Homa

    2006-11-01

    In clay-rich sediment, microstructures and macrostructures influence how sediments deform when under stress. When lithology is fairly constant, anisotropy of magnetic susceptibility (AMS) can be a simple technique for measuring the relative consolidation state of sediment, which reflects the sediment burial history. AMS can reveal areas of high water content and apparent overconsolidation associated with unconformities where sediment overburden has been removed. Many other methods for testing consolidation and water content are destructive and invasive, whereas AMS provides a nondestructive means to focus on areas for additional geotechnical study. In zones where the magnetic minerals are undergoing diagenesis, AMS should not be used for detecting compaction state. By utilizing AMS in the Santa Barbara Basin, we were able to identify one clear unconformity and eight zones of high water content in three cores. With the addition of susceptibility, anhysteretic remanent magnetization, and isothermal remanent magnetization rock magnetic techniques, we excluded 3 out of 11 zones from being compaction disequilibria. The AMS signals for these three zones are the result of diagenesis, coring deformation, and burrows. In addition, using AMS eigenvectors, we are able to accurately show the direction of maximum compression for the accumulation zone of the Gaviota Slide.

  12. Seed layer impact on structural and magnetic properties of [Co/Ni] multilayers with perpendicular magnetic anisotropy

    Science.gov (United States)

    Liu, Enlong; Swerts, J.; Devolder, T.; Couet, S.; Mertens, S.; Lin, T.; Spampinato, V.; Franquet, A.; Conard, T.; Van Elshocht, S.; Furnemont, A.; De Boeck, J.; Kar, G.

    2017-01-01

    [Co/Ni] multilayers with perpendicular magnetic anisotropy (PMA) have been researched and applied in various spintronic applications. Typically, the seed layer material is studied to provide the desired face-centered cubic (fcc) texture to the [Co/Ni] to obtain PMA. The integration of [Co/Ni] in back-end-of-line processes also requires the PMA to survive post-annealing. In this paper, the impact of NiCr, Pt, Ru, and Ta seed layers on the structural and magnetic properties of [Co(0.3 nm)/Ni(0.6 nm)] multilayers is investigated before and after annealing. The multilayers were deposited in-situ on different seeds via physical vapor deposition at room temperature. The as-deposited [Co/Ni] films show the required fcc(111) texture on all seeds, but PMA is only observed on Pt and Ru. In-plane magnetic anisotropy is obtained on NiCr and Ta seeds, which is attributed to strain-induced PMA loss. PMA is maintained on all seeds after post-annealing up to 400 °C. The largest effective perpendicular anisotropy energy ( KUeff≈2 ×105 J/m3) after annealing is achieved on the NiCr seed. The evolution of PMA upon annealing cannot be explained by further crystallization during annealing or strain-induced PMA, nor can the observed magnetization loss and the increased damping after annealing. Here, we identify the diffusion of the non-magnetic materials from the seed into [Co/Ni] as the major driver of the changes in the magnetic properties. By selecting the seed and post-annealing temperature, the [Co/Ni] can be tuned in a broad range for both PMA and damping.

  13. Spin Orbit Torque in TbCo Films with Bulk Perpendicular Magnetic Anisotropy

    Science.gov (United States)

    Ueda, Kohei; Mann, Maxwell; Tan, Aik-Jun; Beach, Geoffrey. S. D.

    Spin-orbit torque (SOT) has generated considerable interest for manipulating magnetization in spintronic devices with ultra-low dissipation. Recent research has demonstrated that highly efficient magnetization control can be driven by current-induced SOT in ferromagnet/heavy metals bilayers with strong spin orbit coupling. However, most work on SOT has focused on ultra-thin magnetic films with interfacial perpendicular magnetic anisotropy (PMA), whereas future devices will require bulk PMA for sufficient thermal stability. Recently, Zhao et al reported SOT induced magnetization switching in a bulk PMA material; however, the films examined were still rather thin. Here we examine spin orbit torques in TbCo alloy films with bulk PMA, sandwiched between top and bottom Ta layers. By performing conventional harmonic and current-induced switching measurements, we quantified the current-induced effective fields generated by damping-like (DL) and field-like (FL) torques. The DL torque is much larger than FL torque, and corresponds to an effective spin Hall angle consistent with that of Ta. Owing to the relatively small saturation magnetized of these ferrimagnetic materials, the current-induced effective field is comparable to that observed in nm-thick Co films, despite the much larger film thicknesses used here. These results demonstrate ferromagnetic alloys with bulk PMA can be engineered to simultaneously provide thermal stability and efficient SOT switching.

  14. Full-Heusler Co2FeSi alloy thin films with perpendicular magnetic anisotropy inducedby MgO-interfaces

    OpenAIRE

    高村, 陽太; Takamura, Yota; 鈴木, 隆寛; Suzuki, Takahiro; 藤野, 頼信; Fujino, Yorinobu; 中川, 茂樹; Nakagawa, Shigeki

    2014-01-01

    A 100-nm-thick L21-ordered full-Heusler Co2FeSi (CFS) alloy film was fabricated using the facing targets sputtering (FTS) method at a substrate temperature TS of 300 ºC. The degrees of L21- and B2-order for the film were 37% and 96%, respectively. In addition, full-Heusler CFS alloy thin films with perpendicular magnetic anisotropy (PMA) induced by the magnetic anisotropy of MgO-interfaces were also successfully fabricated using the FTS method. The CFS/MgO stacked layers exhibited PMA when th...

  15. Magnetic anisotropy considerations in magnetic force microscopy studies of single superparamagnetic nanoparticles.

    Science.gov (United States)

    Nocera, Tanya M; Chen, Jun; Murray, Christopher B; Agarwal, Gunjan

    2012-12-14

    In recent years, superparamagnetic nanoparticles (SPNs) have become increasingly important in applications ranging from solid state memory devices to biomedical diagnostic and therapeutic tools. However, detection and characterization of the small and unstable magnetic moment of an SPN at the single particle level remains a challenge. Further, depending on their physical shape, crystalline structure or orientation, SPNs may also possess magnetic anisotropy, which can govern the extent to which their magnetic moments can align with an externally applied magnetic field. Here, we demonstrate how we can exploit the magnetic anisotropy of SPNs to enable uniform, highly-sensitive detection of single SPNs using magnetic force microscopy (MFM) in ambient air. Superconducting quantum interference device magnetometry and analytical transmission electron microscopy techniques are utilized to characterize the collective magnetic behavior, morphology and composition of the SPNs. Our results show how the consideration of magnetic anisotropy can enhance the ability of MFM to detect single SPNs at ambient room temperature with high force sensitivity and spatial resolution.

  16. Strong out-of-plane magnetic anisotropy in ion irradiated anatase TiO2 thin films

    Directory of Open Access Journals (Sweden)

    M. Stiller

    2016-12-01

    Full Text Available The temperature and field dependence of the magnetization of epitaxial, undoped anatase TiO2 thin films on SrTiO3 substrates was investigated. Low-energy ion irradiation was used to modify the surface of the films within a few nanometers, yet with high enough energy to produce oxygen and titanium vacancies. The as-prepared thin film shows ferromagnetism which increases after irradiation with low-energy ions. An optimal and clear magnetic anisotropy was observed after the first irradiation, opposite to the expected form anisotropy. Taking into account the experimental parameters, titanium vacancies as di-Frenkel pairs appear to be responsible for the enhanced ferromagnetism and the strong anisotropy observed in our films. The magnetic impurities concentrations was measured by particle-induced X-ray emission with ppm resolution. They are ruled out as a source of the observed ferromagnetism before and after irradiation.

  17. Thermal stability of the in-plane magnetic anisotropy and the coercivity of nanocrystalline CoFeNi films

    NARCIS (Netherlands)

    van Voorthuysen, EHD; ten Broek, FT; Chechenin, NG; Boerma, DO

    2003-01-01

    By choosing the right production parameters, in-plane, uniaxial anisotropy up to about 15 Oe (1250 J/m(3)) could be induced in electrodeposited layers of Co59Fe26Ni15. This compound consists of a mixture of FCC and BCC phases. The layers were magnetically soft and nanocrystalline with grain sizes of

  18. Micromagnetic study of magnetic domain structure and magnetization reversal in amorphous wires with circular anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Betancourt, I., E-mail: israelb@correo.unam.m [Departamento de Materiales Metalicos y Ceramicos, Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, Mexico D.F. 04510 (Mexico); Hrkac, G. [Department of Engineering Materials, University of Sheffield, Mappin St., Sheffield S1 3JD (United Kingdom); Schrefl, T. [Department of Engineering Materials, University of Sheffield, Mappin St., Sheffield S1 3JD (United Kingdom); St. Poelten University of Applied Sciences (Austria)

    2011-05-15

    In this work we present a detailed numerical investigation on the magnetic domain formation and magnetization reversal mechanism in sub-millimeter amorphous wires with negative magnetostriction by means of micromagnetic calculations. The formation of circular magnetic domains surrounding a multidomain axially oriented central nucleus was observed for the micromagnetic model representing the amorphous wire. The magnetization reversal explained by micromagnetic computations for the M-H curve is described in terms of a combined nucleation-propagation-rotational mechanism after the saturated state. Results are interpreted in terms of the effective magnetic anisotropy. - Research highlights: > Magnetic domain formation in small amorphous wires is studied by micromagnetic calculations. > Magnetization reversal in small amorphous wires is studied by micromagnetic calculations. > Formation of circular domains around an axially oriented central core was observed. > Magnetization reversal is described in terms of nucleation-propagation-rotational mechanisms. > Magnetic domains and reversal mechanism are consistent with experimental reports.

  19. Dysprosium doping induced shape and magnetic anisotropy of Fe3-xDyxO4 (x=0.01-0.1) nanoparticles

    Science.gov (United States)

    Jain, Richa; Luthra, Vandna; Gokhale, Shubha

    2016-09-01

    The effect of dysprosium doping on evolution of structural and magnetic properties of magnetite (Fe3O4) nanoparticles is reported. A standard route of co-precipitation was used for the synthesis of undoped and doped magnetite nanoparticles Fe3-xDyxO4 (x=0.0-0.1). Transmission electron microscopy (TEM) shows formation of round shaped particles with diameter in the range of 8-14 nm for undoped sample. On doping beyond x=0.01, the formation of rod like structures is initiated along with the round shaped particles. The number of rods is found to increase with increasing doping concentration. Magnetic characterization using Vibrating Sample Magnetometer (VSM) revealed doping dependent magnetic properties which can be correlated with the crystallite size as determined from X-ray diffraction (XRD). Enhancement in the saturation magnetization in the initial stages of doping can be explained on the basis of incorporation of Dy3+ ions in the inverse spinel structure at the octahedral site in place of Fe3+ ions. Subsequent decrease in saturation magnetization observed beyond x=0.03 could be attributed to precipitation of excess Dy in form of dysprosium ferrite phase.

  20. Anisotropy dependent magnetization relaxation in (Cd,Mn)Te quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Goryca, M.; Nawrocki, M. [Institute of Experimental Physics, Warsaw University, Hoza 69, 00-681 Warsaw (Poland); Kossacki, P.; Pacuski, W.; Maslana, W. [Institute of Experimental Physics, Warsaw University, Hoza 69, 00-681 Warsaw (Poland); Joined Group Nanophysique et Semiconducteurs, CNRS/CEA/ Universite Joseph Fourier Grenoble, BP 87, 38402 Saint Martin d' Heres cedex (France); Ferrand, D.; Tatarenko, S. [Joined Group Nanophysique et Semiconducteurs, CNRS/CEA/ Universite Joseph Fourier Grenoble, BP 87, 38402 Saint Martin d' Heres cedex (France); Cibert, J. [Laboratoire Louis Neel, CNRS, BP166, 38042 Grenoble cedex 9 (France)

    2006-07-01

    An optical study of magnetization relaxation is presented for p-doped quantum wells with magnetic ions. The magnetic anisotropy of the system is controlled by the heavy-light hole splitting, tuned by uniaxial strain. We show that a suppression of the magnetic anisotropy results in an enhancement of the observed relaxation rate by a factor of at least 20. This is explained by the fact that the decrease of the anisotropy results in the lowering of the energy barrier for the domain magnetization flip process. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  1. Size effects in the magnetic anisotropy of embedded cobalt nanoparticles: from shape to surface.

    Science.gov (United States)

    Oyarzún, Simón; Tamion, Alexandre; Tournus, Florent; Dupuis, Véronique; Hillenkamp, Matthias

    2015-10-06

    Strong size-dependent variations of the magnetic anisotropy of embedded cobalt clusters are evidenced quantitatively by combining magnetic experiments and advanced data treatment. The obtained values are discussed in the frame of two theoretical models that demonstrate the decisive role of the shape in larger nanoparticles and the predominant role of the surface anisotropy in clusters below 3 nm diameter.

  2. Size effects in the magnetic anisotropy of embedded cobalt nanoparticles: from shape to surface

    OpenAIRE

    Simón Oyarzún; Alexandre Tamion; Florent Tournus; Véronique Dupuis; Matthias Hillenkamp

    2015-01-01

    Strong size-dependent variations of the magnetic anisotropy of embedded cobalt clusters are evidenced quantitatively by combining magnetic experiments and advanced data treatment. The obtained values are discussed in the frame of two theoretical models that demonstrate the decisive role of the shape in larger nanoparticles and the predominant role of the surface anisotropy in clusters below 3 nm diameter.

  3. Uniaxial magnetic anisotropy of cobalt thin films on different substrates using CW-MOKE technique

    Energy Technology Data Exchange (ETDEWEB)

    Shukla, Vijay, E-mail: shuklavs@rrcat.gov.in [Laser Physics Applications Section, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India); Mukherjee, C. [Mechanical and Optical Support Section, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India); Chari, R. [Laser Physics Applications Section, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India); Rai, S. [Indus Synchrotron Utilization Division, Raja Ramnna Centre for Advanced Technology, Indore 452013 (India); Bindra, K.S. [Solid State Laser Division, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India); Banerjee, A. [BARC training school at RRCAT and Homi Bhabha National Institute, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India)

    2014-12-15

    Cobalt thin films were deposited on GaAs, Si and Glass substrates by RF-magnetron sputtering. The structure was studied using atomic force microscopy, X-ray reflectivity and grazing incidence X-ray diffraction. Magnetic properties were determined with the magneto-optic Kerr effect. The deposited films have in-plane uniaxial anisotropy and after annealing the anisotropy reduces. The reduction in anisotropy may be due to release of stress and the remaining anisotropy after annealing may be due to shape anisotropy of the particulates. - Highlights: • Deposited cobalt thin films on different substrates and annealed at 300 °C. • Characterized as-grown and annealed films by GIXRD, AFM and MOKE. • Uniaxial magnetic anisotropy observed for all the samples. • Decrease in anisotropy on annealing may be due to release of stress during deposition.

  4. Voltage-controlled magnetic anisotropy in Fe|MgO tunnel junctions studied by x-ray absorption spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Miwa, Shinji, E-mail: miwa@mp.es.osaka-u.ac.jp; Matsuda, Kensho; Tanaka, Kazuhito; Goto, Minori; Suzuki, Yoshishige [Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531 (Japan); Kotani, Yoshinori; Nakamura, Tetsuya [Japan Synchrotron Radiation Research Institute/SPring-8, Sayo, Hyogo 679-5198 (Japan)

    2015-10-19

    In this study, voltage-controlled magnetic anisotropy (VCMA) in Fe|MgO tunnel junctions was investigated via the magneto-optical Kerr effect, soft x-ray absorption spectroscopy, and magnetic circular dichroism spectroscopy. The Fe|MgO tunnel junctions showed enhanced perpendicular magnetic anisotropy under external negative voltage, which induced charge depletion at the Fe|MgO interface. Despite the application of voltages of opposite polarity, no trace of chemical reaction such as a redox reaction attributed to O{sup 2−} migration was detected in the x-ray absorption spectra of the Fe. The VCMA reported in the Fe|MgO-based magnetic tunnel junctions must therefore originate from phenomena associated with the purely electric effect, that is, surface electron doping and/or redistribution induced by an external electric field.

  5. Annealing effect on magnetic anisotropy in ultrathin (Ga,Mn)As

    Institute of Scientific and Technical Information of China (English)

    Li Yan-Yong; Wang Hua-Feng; Cao Yu-Fei; Wang Kai-You

    2013-01-01

    We investigated the effect of low temperature annealing on magnetic anisotropy in 7-nm ultrathin Ga0.94Mn0.06As devices by measuring the angle-dependent planar Hall resistance (PHR).Obvious hysteresis loops were observed during the magnetization reversal through the clockwise and counterclockwise rotations under low magnetic fields (below 1000 Gs,1 Gs =10-4 T),which can be explained by competition between Zeeman energy and magnetic anisotropic energy.It is found that the uniaxial anisotropy is dominant in the whole measured ferromagnetic range for both the as-grown ultrathin Ga0.94Mn0.06As and the annealed one.The cubic anisotropy changes more than the uniaxial anisotropy in the measured temperature ranges after annealing.This gives a useful way to tune the magnetic anisotropy of ultrathin (Ga,Mn)As devices.

  6. Influence of radial and tangential anisotropy components in single wall magnetic nanotubes. A Monte Carlo approach

    Science.gov (United States)

    Agudelo-Giraldo, J. D.; Morales-Rojas, S.; Hurtado-Marín, V. A.; Restrepo-Parra, E.

    2017-01-01

    Magnetic behaviour of nanotubes with square cell has been studied by the Monte Carlo Method, under the Metropolis algorithm and Heisenberg model. The Hamiltonian used includes nearest neighbour exchange interaction and radial and tangential direction for uniaxial anisotropy. Periodic boundary conditions were implemented at the sample's edges. Simulations were carried out varying the nanotube's diameter by changing the number of magnetic moments per ring and anisotropy values. Two transition temperatures were identified corresponding to states where moments were aligned as either ferromagnetic type or anisotropy direction. At low temperatures and low anisotropy values, the system exhibited a ferromagnetic alignment; as the anisotropy was increased, and continued in the low temperature range, spins were aligned in the anisotropy (radial or tangential) direction. As the temperature was increased, spins were reoriented in the ferromagnetic direction, generating a radial (tangential) anisotropy to ferromagnetic transition temperature. When the temperature continued increasing, the system transited toward the paramagnetic phase, appearing a ferromagnetic to paramagnetic transition phase temperature. In several cases studied here, between these two transition temperatures (anisotropy to ferromagnetic and ferromagnetic to paramagnetic transition phases), the magnetization of the system exhibited instabilities. These instabilities are caused because of the influence of the anisotropy values and the diameter of the nanotubes on the magnetic domains formation. As a consequence, there exist anisotropy values and diameters where metastable states were formed.

  7. Effect of annealing on exchange stiffness of ultrathin CoFeB film with perpendicular magnetic anisotropy

    Science.gov (United States)

    Sato, Noriyuki; White, Robert M.; Wang, Shan X.

    2016-04-01

    The effect of annealing on the exchange stiffness of ultrathin CoFeB films with perpendicular magnetic anisotropy was investigated through the observation of magnetic domain structures by magneto-optic Kerr-effect microscopy. A significant reduction of the exchange stiffness after an annealing process was observed, which is in striking contrast to a previous report that studied thick CoFeB films with in-plane magnetic anisotropy. Our results suggest that interdiffusion of non-magnetic atoms from the adjacent layer into CoFeB layer reduces the exchange stiffness, which explains the difference between the annealing effect on ultrathin and the thick CoFeB films. Thus, it is critical to prevent annealing-induced interdiffusion in order to suppress undesired sub-volume switching that degrades thermal stability of a free-layer in spin-transfer torque magnetic random access memory.

  8. INTERPRETING MAGNETIC VARIANCE ANISOTROPY MEASUREMENTS IN THE SOLAR WIND

    Energy Technology Data Exchange (ETDEWEB)

    TenBarge, J. M.; Klein, K. G.; Howes, G. G. [Department of Physics and Astronomy, University of Iowa, Iowa City, IA (United States); Podesta, J. J., E-mail: jason-tenbarge@uiowa.edu [Space Science Institute, Boulder, CO (United States)

    2012-07-10

    The magnetic variance anisotropy (A{sub m}) of the solar wind has been used widely as a method to identify the nature of solar wind turbulent fluctuations; however, a thorough discussion of the meaning and interpretation of the A{sub m} has not appeared in the literature. This paper explores the implications and limitations of using the A{sub m} as a method for constraining the solar wind fluctuation mode composition and presents a more informative method for interpreting spacecraft data. The paper also compares predictions of the A{sub m} from linear theory to nonlinear turbulence simulations and solar wind measurements. In both cases, linear theory compares well and suggests that the solar wind for the interval studied is dominantly Alfvenic in the inertial and dissipation ranges to scales of k{rho}{sub i} {approx_equal} 5.

  9. Strong enhancement of magnetic anisotropy energy in alloyed nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Negulyaev, Nikolay; Niebergall, Larissa; Stepanyuk, Valeri [Max-Planck-Institut fuer Mikrostrukturphysik, D-06120 Halle (Germany); Juarez Reyes, Lucila; Pastor, Gustavo [Institut fuer Theoretische Physik, Universitaet Kassel, D-34132 Kassel (Germany); Dorantes-Davila, Jesus [Instituto de Fisica, Universidad Autonoma de San Luis Potosi, 78000 San Luis Potosi (Mexico)

    2011-07-01

    One-dimensional atomic structures (monatomic wires and chains) are believed to be likely candidates for creation of nanostructures with large atomic orbital moments and hence with giant magnetic anisotropy energy (MAE) per atom. We investigate the possibility of tuning the MAE of 3d transition metal monowires alloyed with 5d elements (Ir, Pt). Our ab initio studies give clear evidence that in mixed 3d-5d atomic wires MAE is one and even two orders of magnitude more than in pure wires constructed of the corresponding 5d and 3d elements, respectively. Mechanisms responsible for the formation of such a strong MAE are revealed. The interplay between the structure of a monowire and its MAE is demonstrated. The contribution of both types of species (3d and 5d) into the MAE is discussed.

  10. Mononuclear single-molecule magnets: tailoring the magnetic anisotropy of first-row transition-metal complexes.

    Science.gov (United States)

    Gomez-Coca, Silvia; Cremades, Eduard; Aliaga-Alcalde, Núria; Ruiz, Eliseo

    2013-05-08

    Magnetic anisotropy is the property that confers to the spin a preferred direction that could be not aligned with an external magnetic field. Molecules that exhibit a high degree of magnetic anisotropy can behave as individual nanomagnets in the absence of a magnetic field, due to their predisposition to maintain their inherent spin direction. Until now, it has proved very hard to predict magnetic anisotropy, and as a consequence, most synthetic work has been based on serendipitous processes in the search for large magnetic anisotropy systems. The present work shows how the property can be predicted based on the coordination numbers and electronic structures of paramagnetic centers. Using these indicators, two Co(II) complexes known from literature have been magnetically characterized and confirm the predicted single-molecule magnet behavior.

  11. Magnetic anisotropy and magnetization reversal of ultrathin iron films with in-plane magnetization on Si(111) substrates

    Institute of Scientific and Technical Information of China (English)

    Liu Hao-Liang; He Wei; Du Hai-Feng; Fang Ya-Peng; Wu Qiong; Zhang Xiang-Qun; Yang Hai-Tao; Cheng Zhao-Hua

    2012-01-01

    The magnetic anisotropy and magnetization reversal of single crystal Fe films with thickness of 45 monolayer (ML) grown on Si(111) have been investigated by ferromagnetic resonance (FMR) and vibrating sample magnetometer (VSM).Owing to the significant modification of the energy surface in remanent state by slight misorientation from (111) plane and a uniaxial magnetic anisotropy,the azimuthal angular dependence of in-plane resonance field shows a six-fold symmetry with a weak uniaxial contribution,while the remanence of hysteresis loops displays a two-fold one.The competition between the first and second magnctocrystalline anisotropies may result in the switching of in-plane easy axis of the system.Combining the FMR and VSM measurements,the magnetization reversal mechanism has also been determined.

  12. Large perpendicular magnetic anisotropy of ultrathin Ru and Rh films on a NiAl(001) surface

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Dongyoo; Yang, JeongHwa; Hong, Jisang [Department of Physics, Pukyong National University, Busan 608-737 (Korea, Republic of)

    2010-10-27

    Using the full potential linearized augmented plane wave (FLAPW) method, the magnetic properties of two-dimensional Ru and Rh monolayers (MLs) on a NiAl(001) surface have been investigated. It has been found that free standing one monolayer Ru and Rh films have ferromagnetic ground state with magnetic moments of 2.21 and 1.48 {mu}{sub B}, respectively. The ferromagnetism is still observed even on a Ni terminated NiAl(001) surface, while no magnetic state is found on an Al terminated surface. The calculated magnetic moments of Ru and Rh atoms are 1.56 and 0.88 {mu}{sub B}, respectively. In addition, an induced magnetic moment in surface Ni is observed. It has been found that the free standing Ru film has perpendicular magnetization to the film surface with a magnetocrystalline anisotropy (MCA) energy of 0.66 meV/atom, while an in-plane MCA energy of 0.37 meV/atom is achieved in Rh film. Very interestingly, we find that both Ru/NiAl(001) and Rh/NiAl(001) films have perpendicular magnetic anisotropy and the calculated MCA energies are 0.66 and 1.11 meV in Ru/NiAl(001) and Rh/NiAl(001), respectively. Along with the magnetic anisotropy, we have presented theoretically calculated x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) results.

  13. Large perpendicular magnetic anisotropy of ultrathin Ru and Rh films on a NiAl(001) surface.

    Science.gov (United States)

    Kim, DongYoo; Yang, JeongHwa; Hong, Jisang

    2010-10-27

    Using the full potential linearized augmented plane wave (FLAPW) method, the magnetic properties of two-dimensional Ru and Rh monolayers (MLs) on a NiAl(001) surface have been investigated. It has been found that free standing one monolayer Ru and Rh films have ferromagnetic ground state with magnetic moments of 2.21 and 1.48 μ(B), respectively. The ferromagnetism is still observed even on a Ni terminated NiAl(001) surface, while no magnetic state is found on an Al terminated surface. The calculated magnetic moments of Ru and Rh atoms are 1.56 and 0.88 μ(B), respectively. In addition, an induced magnetic moment in surface Ni is observed. It has been found that the free standing Ru film has perpendicular magnetization to the film surface with a magnetocrystalline anisotropy (MCA) energy of 0.66 meV/atom, while an in-plane MCA energy of 0.37 meV/atom is achieved in Rh film. Very interestingly, we find that both Ru/NiAl(001) and Rh/NiAl(001) films have perpendicular magnetic anisotropy and the calculated MCA energies are 0.66 and 1.11 meV in Ru/NiAl(001) and Rh/NiAl(001), respectively. Along with the magnetic anisotropy, we have presented theoretically calculated x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) results.

  14. On the limits of uniaxial magnetic anisotropy tuning by a ripple surface pattern

    Energy Technology Data Exchange (ETDEWEB)

    Arranz, Miguel A. [Facultad de Ciencias Químicas, Universidad de Castilla-La Mancha, Avda. Camilo J. Cela 10, 13071 Ciudad Real (Spain); Colino, Jose M., E-mail: josemiguel.colino@uclm.es [Instituto de Nanociencia, Nanotecnología y Materiales Moleculares, Universidad de Castilla-La Mancha, Campus de la Fábrica de Armas, 45071 Toledo (Spain); Palomares, Francisco J. [Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas, c/ Sor Juana Inés de la Cruz 3, 28049 Madrid (Spain)

    2014-05-14

    Ion beam patterning of a nanoscale ripple surface has emerged as a versatile method of imprinting uniaxial magnetic anisotropy (UMA) on a desired in-plane direction in magnetic films. In the case of ripple patterned thick films, dipolar interactions around the top and/or bottom interfaces are generally assumed to drive this effect following Schlömann's calculations for demagnetizing fields of an ideally sinusoidal surface [E. Schlömann, J. Appl. Phys. 41, 1617 (1970)]. We have explored the validity of his predictions and the limits of ion beam sputtering to induce UMA in a ferromagnetic system where other relevant sources of magnetic anisotropy are neglected: ripple films not displaying any evidence of volume uniaxial anisotropy and where magnetocrystalline contributions average out in a fine grain polycrystal structure. To this purpose, the surface of 100 nm cobalt films grown on flat substrates has been irradiated at fixed ion energy, fixed ion fluency but different ion densities to make the ripple pattern at the top surface with wavelength Λ and selected, large amplitudes (ω) up to 20 nm so that stray dipolar fields are enhanced, while the residual film thickness t = 35–50 nm is sufficiently large to preserve the continuous morphology in most cases. The film-substrate interface has been studied with X-ray photoemission spectroscopy depth profiles and is found that there is a graded silicon-rich cobalt silicide, presumably formed during the film growth. This graded interface is of uncertain small thickness but the range of compositions clearly makes it a magnetically dead layer. On the other hand, the ripple surface rules both the magnetic coercivity and the uniaxial anisotropy as these are found to correlate with the pattern dimensions. Remarkably, the saturation fields in the hard axis of uniaxial continuous films are measured up to values as high as 0.80 kG and obey a linear dependence on the parameter ω{sup 2}/Λ/t in quantitative

  15. The variation in the magnetic fluctuation anisotropy across the front boundaries of magnetic clouds and its geomagnetic response

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    A statistical study of magnetic fluctuations near the front boundaries of magnetic clouds is approached with the method of Minimum Variance Analysis, based on the data of Imp8 and Wind spacecraft. New discoveries are that (1) fluctuation anisotropy tends to increase across the front boundaries of magnetic clouds; (2) there is a good correlation between the fluctuation anisotropy and the geomagnetic activity indices; and (3) in some cases, although there is southward field component immediately after the front boundary, Kp index descends (or Dst index ascends) with a corresponding decrease of the fluctuation anisotropy; in other cases with no distinct southward field component, Kp index ascends (or Dst index descends) with a corresponding increase of the fluctuation anisotropy. Thus we suggest that the fluctuation anisotropy might be a useful indicator in diagnosing the magnetic activities of magnetic clouds.

  16. Magnetic field-dependent shape anisotropy in small patterned films studied using rotating magnetoresistance.

    Science.gov (United States)

    Fan, Xiaolong; Zhou, Hengan; Rao, Jinwei; Zhao, Xiaobing; Zhao, Jing; Zhang, Fengzhen; Xue, Desheng

    2015-11-13

    Based on the electric rotating magnetoresistance method, the shape anisotropy of a Co microstrip has been systematically investigated. We find that the shape anisotropy is dependent not only on the shape itself, but also on the magnetization distribution controlled by an applied magnetic field. Together with micro-magnetic simulations, we present a visualized picture of how non-uniform magnetization affects the values and polarities of the anisotropy constants K1 and K2. From the perspective of potential appliantions, our results are useful in designing and understanding the performance of micro- and nano-scale patterned ferromagnetic units and the related device properties.

  17. Electron theory of perpendicular magnetic anisotropy of Co-ferrite thin films

    Directory of Open Access Journals (Sweden)

    Jun-ichiro Inoue

    2014-02-01

    Full Text Available We develop an electron theory for the t2g electrons of Co2+ ions to clarify the perpendicular magnetic anisotropy (PMA mechanism of Co-ferrite thin films by considering the spin-orbit interaction (SOI and crystal-field (CF potentials induced by the local symmetry around the Co ions and the global tetragonal symmetry of the film. Uniaxial and in-plane MA constants Ku and K1 at 0 K, respectively, are calculated for various values of SOI and CF. We show that reasonable parameter values explain the observed PMA and that the orbital moment for the in-plane magnetization reduces to nearly half of that of the out-of-plane magnetization.

  18. Electron theory of perpendicular magnetic anisotropy of Co-ferrite thin films

    Energy Technology Data Exchange (ETDEWEB)

    Inoue, Jun-ichiro; Yanagihara, Hideto; Kita, Eiji [Institute of Applied Physics, University of Tsukuba, Tsukuba 305-8573 (Japan); Niizeki, Tomohiko [Institute of Applied Physics, University of Tsukuba, Tsukuba 305-8573 (Japan); AIMR, Tohoku University, Sendai 980-8577 (Japan); Itoh, Hiroyoshi [Department of Pure and Applied Physics, Kansai University, Suita 564-8680 (Japan)

    2014-02-15

    We develop an electron theory for the t{sub 2g} electrons of Co{sup 2+} ions to clarify the perpendicular magnetic anisotropy (PMA) mechanism of Co-ferrite thin films by considering the spin-orbit interaction (SOI) and crystal-field (CF) potentials induced by the local symmetry around the Co ions and the global tetragonal symmetry of the film. Uniaxial and in-plane MA constants K{sub u} and K{sub 1} at 0 K, respectively, are calculated for various values of SOI and CF. We show that reasonable parameter values explain the observed PMA and that the orbital moment for the in-plane magnetization reduces to nearly half of that of the out-of-plane magnetization.

  19. Inter-grain interaction in random magnetic anisotropy simulation in magnetic nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Lee, S.-J.; Yanagihara, Hideto; Kita, Eiji, E-mail: kita@bk.tsukuba.ac.jp [Institute of Applied Physics, University of Tsukuba, Ibaraki 305-8573 (Japan); Inami, Nobuhito; Ono, Kanta [High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801 (Japan); Mitsumata, Chiharu [National Institute for Materials Science, Tsukuba, Ibaraki 305-0047 (Japan)

    2015-05-07

    Effect of inter-grain exchange interaction on the coercive forces was analyzed with a numerical simulation in magnetic materials with random magnetic anisotropy. The magnetization of an assembly of magnetically interacting grains with randomly oriented uniaxial anisotropy was calculated using the Landau-Lifshitz-Gilbert equation. We supposed a single spin model where the magnetizations in a grain were aligned in the same direction, for simplicity. Calculations were carried out for an N×N×N system, where the number of grains on a side, N ranged from 16 to 128. The relation between the coercive forces H{sub C} and the grain size D is represented by H{sub C}∝D{sup k}. With the increase of N, k decreased gradually and tended to reach a saturated value around k = 4.5–5, which dose not correspond to the primitive theory of the random anisotropy model where k = 6. The deviation was discussed in terms of the inter-grain interaction, essentially proportional to the inverse of D.

  20. Field-cooling induced unidirectional anisotropy in the two-dimensional Ising antiferromagnet Rb sub 2 Cu sub 1 sub - sub x Co sub x F sub 4

    CERN Document Server

    Kawecka-Magiera, B; Maksymowicz, A Z

    2000-01-01

    Small cluster approximation and Monte Carlo Metropolis algorithm are applied to demonstrate that field cooling induces a unidirectional magnetic anisotropy of small clusters of Cu in Rb sub 2 Cu sub 1 sub - sub x Co sub x F sub 4. Within the Ising model, this anisotropy appears as a net magnetization at zero magnetic field. The effect is due to a coupling between the orbital ordering within clusters of Cu impurities and the antiferromagnetic ordering of Co matrix.

  1. Out-of-Plane Magnetic Anisotropy and Microwave Permeability of Magnetoelastic FeCoSiB Amorphous Thin Films

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The amorphous magnetoelastic Fe66Co17Si1B6 thin films have been deposited by dc magnetron sputtering. A lot of "nano-trenches" have been observed on the film surfaces by AFM. The permeability of amorphous Fe66Co17Si1B6 thin films was measured within the frequency range of 0.6GHz-10.2 GHz. The ferromagnetic resonance frequency was found to be 1.2 GHz. MFM shows that the domain of thin film is a maze-type pattern, which indicates that an out-of-plane magnetic anisotropy exists. The out-of-plane anisotropy is believed due to the stress-induced magnetic anisotropy. It can be inferred that the internal stress is tensile stress and normal to the film plane.

  2. Effect of the shape anisotropy on the magnetic configuration of (Ga,Mn)As and its evolution with temperature

    OpenAIRE

    Hamaya, K.; Taniyama, T.; Koike, T.; Yamazaki, Y.

    2006-01-01

    We study the effect of the shape anisotropy on the magnetic domain configurations of a ferromagnetic semiconductor (Ga,Mn)As/GaAs(001) epitaxial wire as a function of temperature. Using magnetoresistance measurements, we deduce the magnetic configurations and estimate the relative strength of the shape anisotropy compared with the intrinsic anisotropies. Since the intrinsic anisotropy is found to show a stronger temperature dependence than the shape anisotropy, the effect of the shape anisotr...

  3. Evidence for nanoscale two-dimensional Co clusters in CoPt3 films with perpendicular magnetic anisotropy.

    Science.gov (United States)

    Cross, J O; Newville, M; Maranville, B B; Bordel, C; Hellman, F; Harris, V G

    2010-04-14

    The length scale of the local chemical anisotropy responsible for the growth-temperature-induced perpendicular magnetic anisotropy of face-centered cubic CoPt(3) alloy films was investigated using polarized extended x-ray absorption fine structure (EXAFS). These x-ray measurements were performed on a series of four (111) CoPt(3) films epitaxially grown on (0001) sapphire substrates. The EXAFS data show a preference for Co-Co pairs parallel to the film plane when the film exhibits magnetic anisotropy, and random chemical order otherwise. Furthermore, atomic pair correlation anisotropy was evidenced only in the EXAFS signal from the next neighbors to the absorbing Co atoms and from multiple scattering paths focused through the next neighbors. This suggests that the Co clusters are no more than a few atoms in extent in the plane and one monolayer in extent out of the plane. Our EXAFS results confirm the correlation between perpendicular magnetic anisotropy and two-dimensional Co segregation in CoPt(3) alloy films, and establish a length scale on the order of 10 Å for the Co clusters.

  4. Evidence for nanoscale two-dimensional Co clusters in CoPt{sub 3} films with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Cross, J O [Department of Physics, University of Washington, Seattle, WA 98195 (United States); Newville, M [Consortium for Advanced Radiation Sources, University of Chicago, Chicago, IL 60637 (United States); Maranville, B B; Hellman, F [Department of Physics, University of California at San Diego, La Jolla, CA 92093 (United States); Bordel, C [Department of Physics, University of California at Berkeley, CA 94720 (United States); Harris, V G, E-mail: cbordel@berkeley.ed [Department of Electrical and Computer Engineering, Northeastern University, Boston, MA 02115 (United States)

    2010-04-14

    The length scale of the local chemical anisotropy responsible for the growth-temperature-induced perpendicular magnetic anisotropy of face-centered cubic CoPt{sub 3} alloy films was investigated using polarized extended x-ray absorption fine structure (EXAFS). These x-ray measurements were performed on a series of four (111) CoPt{sub 3} films epitaxially grown on (0001) sapphire substrates. The EXAFS data show a preference for Co-Co pairs parallel to the film plane when the film exhibits magnetic anisotropy, and random chemical order otherwise. Furthermore, atomic pair correlation anisotropy was evidenced only in the EXAFS signal from the next neighbors to the absorbing Co atoms and from multiple scattering paths focused through the next neighbors. This suggests that the Co clusters are no more than a few atoms in extent in the plane and one monolayer in extent out of the plane. Our EXAFS results confirm the correlation between perpendicular magnetic anisotropy and two-dimensional Co segregation in CoPt{sub 3} alloy films, and establish a length scale on the order of 10 A for the Co clusters.

  5. Magnetic anisotropy and magnetostriction in nanocrystalline Fe–Al alloys obtained by melt spinning technique

    Energy Technology Data Exchange (ETDEWEB)

    García, J.A.; Carrizo, J. [Depto. de Física de la Universidad de Oviedo, c/Calvo Sotelo s/n, 33007 Oviedo (Spain); Elbaile, L., E-mail: elbaile@uniovi.es [Depto. de Física de la Universidad de Oviedo, c/Calvo Sotelo s/n, 33007 Oviedo (Spain); Lago-Cachón, D.; Rivas, M. [Depto. de Física de la Universidad de Oviedo, c/Calvo Sotelo s/n, 33007 Oviedo (Spain); Castrillo, D. [Depto. de Ciencias de los Materiales de la Universidad de Oviedo, c/Independencia, 33004 Oviedo (Spain); Pierna, A.R. [Depto. de Ingeniería Química y Medio Ambiente, EUPSS, UPV/EHU, San Sebastián (Spain)

    2014-12-15

    A study about the magnetic anisotropy and magnetostriction in ribbons of composition Fe{sub 81}Al{sub 19} and Fe{sub 70}Al{sub 30} obtained by the melt spinning technique is presented. The hysteresis loops indicate that the easy magnetization direction lies in both cases on the plane of the ribbon. Torque magnetometry measurements show that the in-plane magnetic anisotropy constant results 10100 J m{sup −3} and 490 J m{sup −3} for the Fe{sub 81}Al{sub 19} and Fe{sub 70}Al{sub 30} respectively. After a thermal treatment of 2 h at 473 K to remove the residual stresses, the in-plane magnetic anisotropy constants falls down to 2500 J m{sup −3} in the first composition and remains the same in the second one, while the easy direction remains the same. Measurements of the magnetostriction and the residual stresses of both ribbons allow us to explain the above mentioned results about the magnetic anisotropy and to conclude that the residual stresses via magnetostriction are the main source of magnetic anisotropy in the case of Fe{sub 81}Al{sub 19} ribbon but they do not influence this property in the ribbon of composition Fe{sub 70}Al{sub 30}. - Highlights: • The origin of magnetic anisotropy of Fe{sub 81}Al{sub 19} and Fe{sub 70}Al{sub 30} ribbons has been studied. • The magnetic anisotropy lies in the plane of the ribbons. • A huge difference in magnetic anisotropy between two ribbons has been observed. • Magnetostriction and residual stresses explain the magnetic anisotropy in Fe{sub 81}Al{sub 19} ribbon.

  6. Analytic theory of wall configuration and depinning mechanism in magnetic nanostructure with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Kab-Jin [School of Physics, Seoul National University, Seoul 151-742 (Korea, Republic of); Choe, Sug-Bong [School of Physics, Seoul National University, Seoul 151-742 (Korea, Republic of)], E-mail: sugbong@snu.ac.kr

    2009-07-15

    We present an analytic theory of the domain wall depinning in magnetic nanostructure with perpendicular magnetic anisotropy. The variational principle reveals that the wall is bent in the form of a circular arc which intersects the structure boundaries perpendicularly. The radius is inversely proportional to the magnetic field. With increasing the field the radius shrinks, followed by depinning from the constriction when the arc is not geometrically allowed. The depinning field is proportional to the sine of the constriction angle and the inverse of the constriction width. The validity of the theory is confirmed by comparison with the micromagnetic simulation.

  7. Engineered Heusler Ferrimagnets with a Large Perpendicular Magnetic Anisotropy

    Directory of Open Access Journals (Sweden)

    Reza Ranjbar

    2015-09-01

    Full Text Available Synthetic perpendicular magnetic anisotropy (PMA ferrimagnets consisting of 30-nm-thick D022-MnGa and Co2MnSi (CMS cubic Heusler alloys with different thicknesses of 1, 3, 5, 10 and 20 nm, buffered and capped with a Cr film, are successfully grown epitaxially on MgO substrate. Two series samples with and without post annealing at 400 °C are fabricated. The (002 peak of the cubic L21 structure of CMS films on the MnGa layer is observed, even for the 3-nm-thick CMS film for both un-annealed and annealed samples. The smaller remnant magnetization and larger switching field values of CMS (1–20 nm/MnGa (30 nm bilayers compared with 30-nm-thick MnGa indicates antiferromagnetic (AFM interfacial exchange coupling (Jex between MnGa and CMS films for both un-annealed and annealed samples. The critical thickness of the CMS film for observing PMA with AFM coupling in the CMS/MnGa bilayer is less than 10 nm, which is relatively large compared to previous studies.

  8. Ab-initio description of the magnetic shape anisotropy due to the Breit interaction

    OpenAIRE

    Bornemann, S.; Minar, J.; Braun, J.; Koedderitzsch, D.; Ebert, H.

    2010-01-01

    A quantum-mechanical description of the magnetic shape anisotropy, that is usually ascribed to the classical magnetic dipole-dipole interaction, has been developed. This is achieved by including the Breit-interaction, that can be seen as an electronic current-current interaction in addition to the conventional Coulomb interaction, within fully relativistic band structure calculations. The major sources of the magnetic anisotropy, spin-orbit coupling and the Breit-interaction, are treated cohe...

  9. M(o)ssbauer study of the field induced uniaxial anisotropy in electro-deposited FeCo alloy films

    Institute of Scientific and Technical Information of China (English)

    Li Zhi-Wei; Yang Xu; Wang Hai-Bo; Liu Xin; Li Fa-Shen

    2009-01-01

    Thin ferromagnetic films with in-plane magnetic anisotropy are promising materials for obtaining high microwave permeability. The paper reports a M(o)ssbauer study of the field induced in-plane uniaxial anisotropy in electro-deposited FeCo alloy films. The FeCo alloy films were prepared by the electro-deposition method with and without an external magnetic field applied parallel to the film plane during deposition, Vibrating sample magnetometry and M(o)ssbauer spectroscopy measurements at room temperature indicate that the film deposited in external field shows an in-plane uniaxial anisotropy with an easy direction coinciding with the external field direction and a hard direction perpendicular to the field direction, whereas the film deposited without external field does not show any in-plane anisotropy. M(o)ssbauer spectra taken in three geometric arrangements show that the magnetic moments are almost constrained in the film plane for the film deposited with applied magnetic field. Also, the magnetic moments tend to align in the direction of the applied external magnetic field during deposition, indicating that the observed anisotropy should be attributed to directional ordering of atomic pairs.

  10. Magnetic domains in epitaxial BaFe12O19 thin films with perpendicular anisotropy

    NARCIS (Netherlands)

    Lisfi, A.; Lodder, J.C.

    2002-01-01

    Magnetic domains, microstructure and magnetic properties of highly oriented barium ferrite thin films with perpendicular anisotropy have been investigated with magnetic force microscopy (MFM), VSM, SEM and TEM. Two kinds of magnetic domain are energetically favourable: (a) cluster-like structure in

  11. Electric polarization in bi-layered ferromagnetic film with combined magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Gareeva, Z.V., E-mail: gzv@anrb.ru [Institute of Molecule and Crystal Physics, Academy of Sciences, 151, prospect Octobrya, Ufa 450075 (Russian Federation); Doroshenko, R.A. [Institute of Molecule and Crystal Physics, Academy of Sciences, 151, prospect Octobrya, Ufa 450075 (Russian Federation); Mazhitova, F.A. [Bashkir State University, 32 Z. Validi str., Ufa 450076 (Russian Federation); Shulga, N.V. [Institute of Molecule and Crystal Physics, Academy of Sciences, 151, prospect Octobrya, Ufa 450075 (Russian Federation)

    2015-07-01

    Magnetoelectric phenomena become one of the most attractive fields of magnetism. One of discussable items is inhomogeneous magnetoelectricity leading to appearance of electric polarization of magnetic domain walls, improper polarization of multiferroics etc. In our article we attract attention to the modulation of electric polarization by magnetic inhomogeneity in exchange coupled ferromagnetic film whose layers differ by magnetic anisotropy. Our goal is to explore the influence of combined magnetic anisotropy (especially its cubic component) on the behavior of electric polarization of bi-layered film placed in magnetic field. We perform theoretical analysis in a frame of phenomenological modeling of spins structures considering two geometries of magnetic field (magnetic field oriented perpendicular to a film plane and magnetic field oriented in a film plane along “hard magnetization” axis). Our results show that the presence of cubic magnetic anisotropy (K{sub c}<0) in the layers allocates the planes of magnetic inhomogeneities and correspondingly the directions of electric polarization. We demonstrate that magnetic field applied along the “hard magnetization” axis leads to the rotation of electric polarization in the 45° range and magnetic field applied along normal to a film influences the magnitude of electric polarization leading to the lowering of polarization after attaining the maximum value. - Highlights: • Magnetic inhomogeneity in bi-layered ferromagnetic film generates electric polarization. • Cubic magnetic anisotropy allocates the direction of electric polarization. • Magnetic field applied along “hard magnetization” axis rotates electric polarization.

  12. Thermal Stability of Magnetic States in Circular Thin-Film Nanomagnets with Large Perpendicular Magnetic Anisotropy

    Science.gov (United States)

    Chaves-O'Flynn, Gabriel

    The scaling of the energy barrier to magnetization reversal in thin-film nanomagnets with perpendicular magnetization as a function of their lateral size is of great interest and importance for high-density magnetic random access memory devices. Experimental studies of such elements show either a quadratic or linear dependence of the energy barrier on element diameter. I will discuss a theoretical model we developed to determine the micromagnetic configurations that set the energy barrier for thermally activated reversal of a thin disk with perpendicular magnetic anisotropy as a function of disk diameter. We find a critical length in the problem that is set by the exchange and effective perpendicular magnetic anisotropy energies, with the latter including the size dependence of the demagnetization energy. For diameters smaller than this critical length, the reversal occurs by nearly coherent magnetization rotation and the energy barrier scales with the square of the diameter normalized to the critical length (for fixed film thickness), while for larger diameters, the transition state has a domain wall, and the energy barrier depends linearly on the normalized diameter. Simple analytic expressions are derived for these two limiting cases and verified using full micromagnetic simulations with the string method. Further, the effect of an applied field is considered and shown to lead to a plateau in the energy barrier versus diameter dependence at large diameters. Based on these finding I discuss the prospects and material challenges in the scaling of magnetic memory devices based on thin films with strong perpendicular magnetic anisotropy. In collaboration with G. Wolf, J. Z. Sun and A. D. Kent. Supported by NSF-DMR-1309202 and in part by Spin Transfer Technologies Inc. and the Nanoelectronics Research Initiative through the Institute for Nanoelectronics Discovery and Exploration.

  13. Review- Magnetic orientation and magnetic anisotropy in paramagnetic layered oxides containing rare-earth ions

    Directory of Open Access Journals (Sweden)

    Shigeru Horii, Atsushi Ishihara, Takayuki Fukushima, Tetsuo Uchikoshi, Hiraku Ogino, Tohru S Suzuki, Yoshio Sakka, Jun-ichi Shimoyama and Kohji Kishio

    2009-01-01

    Full Text Available The magnetic anisotropies and easy axes of magnetization at room temperature were determined, and the effects of rare-earth (RE ions were clarified for RE-based cuprates, RE-doped bismuth-based cuprates and RE-doped Bi-based cobaltite regarding the grain orientation by magnetic field. The easy axis, determined from the powder orientation in a static field of 10 T, depended qualitatively on the type of RE ion for all three systems. On the other hand, the magnetization measurement of the c-axis oriented powders, aligned in static or rotating fields, revealed that the type of RE ion strongly affected not only the directions of the easy axis but also the absolute value of magnetic anisotropy, and an appropriate choice of RE ion is required to minimize the magnetic field used for grain orientation. We also studied the possibility of triaxial grain orientation in high-critical-temperature superconductors by a modulated oval magnetic field. In particular, triaxial orientation was attempted in a high-oxygen-pressure phase of orthorhombic RE-based cuprates Y2Ba4Cu7Oy. Although the experiment was performed in epoxy resin, which is not practical, in-plane alignment within 3° was achieved.

  14. Magnetic anisotropy and anisotropic magnetoresistance in strongly phase separated manganite thin films

    Science.gov (United States)

    Kandpal, Lalit M.; Singh, Sandeep; Kumar, Pawan; Siwach, P. K.; Gupta, Anurag; Awana, V. P. S.; Singh, H. K.

    2016-06-01

    The present study reports the impact of magnetic anisotropy (MA) on magnetotransport properties such as the magnetic transitions, magnetic liquid behavior, glass transition and anisotropic magnetoresistance (AMR) in epitaxial film (thickness 42 nm) of strongly phase separated manganite La5/8-yPryCa3/8MnO3 (y≈0.4). Angle dependent magnetization measurement confirms the out-of-plane magnetic anisotropy with the magnetic easy axes aligned in the plane of the film and the magnetic hard axis along the normal to the film plane. The more prominent divergence between the zero filed cooled (ZFC) and field cooled warming (FCW) and the stronger hysteresis between the field cooled cooling (FCC) and FCW magnetization for H ∥ shows the weakening of the magnetic liquid along the magnetic hard axis. The peak at Tp≈42 K in FCW magnetization, which characterizes the onset of spin freezing shifts down to Tp≈18 K as the field direction is switched from the easy axes (H ∥) to the hard axis (H ⊥). The glass transition, which appears at Tg≈28 K for H ∥ disappears for H ⊥. The easy axis magnetization (M∣∣) appears to saturate around H~20 kOe, but the hard axis counterpart (M⊥) does not show such tendency even up to H=50 kOe. MA appears well above the ferromagnetic (FM) transition at T≈170 K, which is nearly the same as the Neel temperature (TN) of M⊥ - T . The temperature dependent resistivity measured at H=10 kOe applied along the easy axis (ρ|| - T) and the hard axis (ρ⊥ - T) shows insulator metal transition (IMT) at ≈106 K and ≈99 K in the cooling cycle, respectively. The large difference between ρ⊥ - T and ρ|| - T during the cooling cycle and in the vicinity of IMT results in huge AMR of ≈-142% and -115%. The observed properties have been explained in terms of the MA induced variation in the relative fraction of the coexisting magnetic phases.

  15. Crystallographic origin of perpendicular magnetic anisotropy in CoPt film: polarized x-ray absorption study

    Energy Technology Data Exchange (ETDEWEB)

    Pandey, K [National University of Singapore; Chen, J [National University of Singapore; Liu, T [Oak Ridge National Laboratory (ORNL); Sun, C [Singapore Synchrotron Light Source; Chow, G [National University of Singapore

    2009-01-01

    Crystallographic structure, growth induced miscibility gap and strain in Ta/Co100 xPtx (0 x 43 at%)/Ru/Ta/glass films deposited at ambient temperature were investigated using polarized x-ray absorption spectroscopy to clarify the origin of observed perpendicular magnetic anisotropy (PMA) in Co72Pt28 film. Extended x-ray absorption fine structure spectroscopy data at Co K-edge showed that Co has a similar local atomic environment and averaged interatomic distance in the in-plane and out-of-plane polarization geometries for Co72Pt28, ruling out the contribution of magneto-elastic anisotropy and growth induced structural anisotropy as the origin of PMA. A large PMA in Co72Pt28 film was attributed to the preferred hexagonal close-packed stacking as observed using the x-ray absorption near-edge structure spectroscopy.

  16. Perpendicular Magnetic Anisotropy in Amorphous Ferromagnetic CoSiB/Pd Thin-Film Layered Structures.

    Science.gov (United States)

    Jung, Sol; Yim, Haein

    2015-10-01

    Spin transfer torque (STT) induced switching of magnetization has led to intriguing and practical possibilities for magnetic random access memory (MRAM). This form of memory, called STT-MRAM, is a strong candidate for future memory applications. This application usually requires a large perpendicular magnetic anisotropy (PMA), large coercivity, and low saturation magnetization. Therefore, we propose an amorphous ferromagnetic CoSiB alloy and investigate CoSiB/Pd multilayer thin films, which have a large PMA, large coercivity, and low saturation magnetization. In this research, we propose a remarkable layered structure that could be a candidate for future applications and try to address a few factors that might affect the variation of PMA, coercivity, and saturation magnetization in the CoSiB/Pd multilayers. We investigate the magnetic properties of the CoSiB/Pd multilayers with various thicknesses of the CoSiB layer. The coercivity was obtained with a maximum of 228 Oe and a minimum value of 91 Oe in the [CoSiB 7 Å/Pd 14 Å], and [CoSiB 9 Å/Pd 14 Å], multilayers, respectively. The PMA arises from tCoSiB = 3 Å to tCoSiB = 9 Å and disappears after tCoSiB = 9 Å.

  17. Galactic magnetic fields and the large-scale anisotropy at MILAGRO

    CERN Document Server

    Battaner, E; Masip, M

    2009-01-01

    The air-shower observatory Milagro has detected a large-scale anisotropy of unknown origin in the flux of TeV cosmic rays. We propose that this anisotropy is caused by galactic magnetic fields, in particular, that it results from the combined effects of the regular and the turbulent (fluctuating) magnetic fields in our vicinity. Instead of a diffusion equation, we integrate Boltzmann's equation to show that the turbulence may define a preferred direction in the cosmic-ray propagation that is orthogonal to the local regular magnetic field. The approximate dipole anisotropy that we obtain explains well Milagro's data.

  18. Tuneable perpendicular magnetic anisotropy in single crystal [Co/Ni](111) superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Gottwald, M; Girod, S; Andrieu, S; Mangin, S, E-mail: gottwald@lpm.u-nancy.fr [Institut Jean Lamour, CNRS - Nancy Universite, BP 239, F-54506 Vandoeuvre (France)

    2010-06-15

    This paper is dedicated to the preparation of thin film with a strong perpendicular to the film plane magnetic anisotropy, behaviour of great interest for spintronics. Single-crystalline [Co/Ni] (111) superlattices have been grown by molecular beam epitaxy. The epitaxial growth of Co and Ni was controlled by using reflection high energy diffraction (RHEED), allowing us to get an accurate control of the thicknesses. The superlattices magnetic properties were studied using magnetometry. All of them exhibit strong perpendicular to the plane magnetic anisotropy. The maximum of magneto-crystalline anisotropy is obtained for one cobalt mo nolayer. A simple model which takes into account surface and volume anisotropy explains the evolution of perpendicular anisotropy in these layers.

  19. Field dependent magnetic anisotropy of Ga0.2Fe0.8 thin films

    Science.gov (United States)

    Resnick, Damon A.; McClure, A.; Kuster, C. M.; Rugheimer, P.; Idzerda, Y. U.

    2011-04-01

    Using longitudinal MOKE in combination with a variable strength rotating magnetic field, called the rotational MOKE (ROTMOKE) method, we show that the magnetic anisotropy for a Ga0.2Fe0.8 single crystal film with a thickness of 17 nm, grown on GaAs (001) with a thick ZnSe buffer layer, depends linearly on the strength of the applied magnetic field. The torque moment curves generated using ROTMOKE are well fit with a model that accounts for the uniaxial, cubic, or fourfold anisotropy, as well as additional terms with a linear dependence on the applied magnetic field. The uniaxial and cubic anisotropy fields, taken from both the hard and the easy axis scans, are seen to remain field independent. The field dependent terms are evidence of a large affect of the magnetostriction and its contribution to the effective magnetic anisotropy in GaxFe1-x thin films.

  20. Field dependent magnetic anisotropy of Fe1-xZnx thin films

    Science.gov (United States)

    Resnick, Damon A.; McClure, A.; Kuster, C. M.; Rugheimer, P.; Idzerda, Y. U.

    2013-05-01

    Using longitudinal magneto-optical Kerr effect in combination with a variable strength rotating magnetic field, called the Rotational Magneto-Optic Kerr Effect (ROTMOKE) method, we show that the magnetic anisotropy for thin Fe82Zn18 single crystal films, grown on MgO(001) substrates, depends linearly on the strength of the applied magnetic field at low fields but is constant (saturates) at fields greater than 350 Oe. The torque moment curves generated using ROTMOKE are well fit with a model that accounts for the uniaxial and cubic anisotropy with the addition of a cubic anisotropy that depends linearly on the applied magnetic field. The field dependent term is evidence of a large effect on the effective magnetic anisotropy in Fe1-xZnx thin films by the magnetostriction.

  1. Roles of the magnetic field and electric current in thermally activated domain wall motion in a submicrometer magnetic strip with perpendicular magnetic anisotropy.

    Science.gov (United States)

    Emori, Satoru; Beach, Geoffrey S D

    2012-01-18

    We have experimentally studied micrometer-scale domain wall (DW) motion driven by a magnetic field and an electric current in a Co/Pt multilayer strip with perpendicular magnetic anisotropy. The thermal activation energy for DW motion, along with its scaling with the driving field and current, has been extracted directly from the temperature dependence of the DW velocity. The injection of DC current resulted in an enhancement of the DW velocity independent of the current polarity, but produced no measurable change in the activation energy barrier. Through this analysis, the observed current-induced DW velocity enhancement can be entirely and unambiguously attributed to Joule heating.

  2. Spin structure factors of Heisenberg spin chain in the presence of anisotropy and magnetic field

    Science.gov (United States)

    Rezania, H.

    2017-02-01

    We have theoretically studied the spin structure factors of spin chain in the presence of longitudinal field and transverse anisotropy. The possible effects of easy axis magnetization are investigated in terms of anisotropy in the Heisenberg interactions. This anisotropy is considered for exchange coupling constants perpendicular to magnetic field direction. The original spin model hamiltonian is mapped to a bosonic model via a hard core bosonic transformation where an infinite hard core repulsion is imposed to constrain one boson occupation per site. Using Green's function approach, the energy spectrum of quasiparticle excitation has been obtained. The spectrum of the bosonic gas has been implemented in order to obtain two particle propagator which corresponds to spin structure factor of original Heisenberg chain model Hamiltonian. The results show the position of peak in the longitudinal structure factor at fixed value for anisotropy moves to higher frequency with magnetic field. Also the intensity of dynamical structure factor decreases with magnetic field. A small dependence of longitudinal dynamical spin structure factor on the anisotropy is observed for fixed value of magnetic field. Our results show longitudinal static structure factor is found to be monotonically increasing with magnetic field due to increase of spins aligning along magnetic field. Furthermore the dispersion behaviors of static longitudinal and transverse structure factors for different magnetic fields and anisotropy parameters are addressed.

  3. Recognizing the threshold magnetic anisotropy for inclination shallowing: Implications for correcting inclination errors of sedimentary rocks

    Directory of Open Access Journals (Sweden)

    Yongxiang eLi

    2014-05-01

    Full Text Available Post-depositional compaction is an integral part of sedimentary rock formation and thus has been reasonably deemed as a major culprit for the long-recognized inclination-shallowing problem in sedimentary rocks. Although theoretical treatment elegantly envisions magnetic anisotropy (or oblate fabrics to correspond to the degree of compaction and the magnitude of inclination flattening, such correspondence has rarely been seen in nature quantitavely, which leaves the possibility of misidentification and/or over-correction for inclination shallowing using magnetic anisotropy. This is because the extent to which oblate magnetic fabrics are developed strongly enough for inclination to start becoming shallow is not yet known. Here, we present sedimentary paleomagnetic data from two ~6 m long gravity cores GHE24L and GHE27L from the northern slope of the South China Sea to examine the down-core changes in magnetic anisotropy and inclinations, and to explore the possible connection between the two parameters. The results show that oblate fabrics are dominantly developed at depths >~2m and the degree of anisotropy displays an overall gradual increase with depth. Inclination shallowing occurs in the > 5m segment of the relatively distal core GHE27L and the amount of shallowing largely correlates with the degree of anisotropy, suggesting a causal relation between the development of magnetic anisotropy and the degree of inclination shallowing. Examination of down-core changes in inclination and magnetic anisotropy suggests that a threshold anisotropy of PAMS~1.04 and PAAR~1.10 exists for inclination shallowing in the cores. For PAAR10° if particle anisotropy is <1.4. This study provides strong field evidence that complements and substantiates the theoretical model and suggests that the threshold anisotropy can be used as a first-order criterion to identify inclination errors of some sedimentary rocks.

  4. On the Origin of the Large Magnetic Anisotropy of Rare Earth-Cobalt Compounds

    DEFF Research Database (Denmark)

    Szpunar, B.; Lindgård, Per-Anker

    1979-01-01

    Experimental data on the magnetocrystalline anisotropy in Co, YCo5, GdCo5, SmCo5 and Y2Co17 is analysed using a single-ion crystal field and isotropic exchange interaction. The large magnetic anisotropy at high temperatures in the alloys is due to significant deviations in the alloy lattices...

  5. Magnetic domain structure in thin CoPt perpendicular magnetic anisotropy films

    Directory of Open Access Journals (Sweden)

    Komine T.

    2013-01-01

    Full Text Available The relation between thickness and domain structure of Co80Pt20 perpendicular magnetic anisotropy films was investigated through experiments and micromagnetic simulation. The films with thickness over 10 nm exhibited clear maze domain structure, while for the films thinner than 10 nm the domain structure abruptly changed from maze domain to irregular and large domain as the thickness became thinner. The irregular domain had narrower domain wall width than maze domain.

  6. Structure organization and magnetic properties of microscale ferrogels: The effect of particle magnetic anisotropy

    Science.gov (United States)

    Ryzhkov, Aleksandr V.; Melenev, Petr V.; Balasoiu, Maria; Raikher, Yuriy L.

    2016-08-01

    The equilibrium structure and magnetic properties of a ferrogel object of small size (microferrogel(MFG)) are investigated by coarse-grained molecular dynamics. As a generic model of a microferrogel (MFG), a sample with a lattice-like mesh is taken. The solid phase of the MFG consists of magnetic (e.g., ferrite) nanoparticles which are mechanically linked to the mesh making some part of its nodes. Unlike previous models, the finite uniaxial magnetic anisotropy of the particles, as it is the case for real ferrogels, is taken into account. For comparison, two types of MFGs are considered: MFG-1, which dwells in virtually non-aggregated state independently of the presence of an external magnetic field, and MFG-2, which displays aggregation yet under zero field. The structure states of the samples are analyzed with the aid of angle-resolved radial distribution functions and cluster counts. The results reveal the crucial role of the matrix elasticity on the structure organization as well as on magnetization of both MFGs. The particle anisotropy, which plays insignificant role in MFG-1 (moderate interparticle magnetodipole interaction), becomes an important factor in MFG-2 (strong interaction). There, the restrictions imposed on the particle angular freedom by the elastic matrix result in notable diminution of the particle chain lengths as well as the magnetization of the sample. The approach proposed enables one to investigate a large variety of MFGs, including those of capsule type and to purposefully choose the combination of their magnetoelastic parameters.

  7. A general perspective on the magnetization reversal in cylindrical soft magnetic nanowires with dominant shape anisotropy

    Science.gov (United States)

    Kuncser, A.; Antohe, S.; Kuncser, V.

    2017-02-01

    Peculiarities of the magnetization reversal process in cylindrical Ni-Cu soft magnetic nanowires with dominant shape anisotropy are analyzed via both static and time dependent micromagnetic simulations. A reversible process involving a coherent-like spin rotation is always observed for magnetic fields applied perpendicularly to the easy axis whereas nucleation of domain walls is introduced for fields applied along the easy axis. Simple criteria for making distinction between a Stoner-Wohlfarth type rotation and a nucleation mechanism in systems with uniaxial magnetic anisotropy are discussed. Superposed reversal mechanisms can be in action for magnetic fields applied at arbitrary angles with respect to the easy axis within the condition of an enough strong axial component required by the nucleation. The dynamics of the domain wall, involving two different stages (nucleation and propagation), is discussed with respect to initial computing conditions and orientations of the magnetic field. A nucleation time of about 3 ns and corkscrew domain walls propagating with a constant velocity of about 150 m/s are obtained in case of Ni-Cu alloy (Ni rich side) NWs with diameters of 40 nm and high aspect ratio.

  8. Fabrication of isolated CoGdTb magnetic nanodots with perpendicular magnetic anisotropy.

    Science.gov (United States)

    Nam, Chunghee

    2013-03-01

    The authors report that a closely-packed hybrid nanostructure can be fabricated by using simple sputtering deposition and anodized aluminum oxide (AAO) templates. In order to isolate CoGdTb magnetic materials with the AAO template, carbon nanotubes (CNTs) were incorporated into the AAO template. Scanning electron microscopy reveals that the nanodots are formed exactly on the top of CNTs, which are placed in a regular arrangement over a wide range area. This indicates that magnetic nanodots, well-arranged over a large area, can be formed using simple sputtering deposition. Isothermal magnetization shows that the CoGdTb nanodots have perpendicular magnetic anisotropy and the strength of the dipolar interaction between the magnetic nanodots can be also controlled by adjusting the spacing between the dots.

  9. Formation of Co nanodisc with enhanced perpendicular magnetic anisotropy driven by Ga+ ion irradiation on Pt/Co/Pt films

    Science.gov (United States)

    Sakamaki, M.; Amemiya, K.; Sveklo, I.; Mazalski, P.; Liedke, M. O.; Fassbender, J.; Kurant, Z.; Wawro, A.; Maziewski, A.

    2016-11-01

    The origin of magnetic phase transition from in-plane to perpendicular magnetic anisotropy (PMA) of Pt/Co/Pt thin film by Ga+ ion irradiation at fluences of 1 -5 ×1015 ions /cm2 is investigated by means of x-ray magnetic circular dichroism (XMCD) and extended x-ray absorption fine structure (EXAFS) analyses. We find that Pt and Co atoms are mixed with each other and that Co is oxidized near the surface due to removal of the Pt overlayer. Furthermore, polarization-dependent EXAFS analysis shows that Co is firstly dispersed as separated single-atom-thick sheets in a Pt matrix at 1 ×1015 ions /cm2, then the Co sheets are divided into a few Å clusters at 5 ×1015 ions /cm2, which are regarded as nanodiscs parallel to the film plane. This process is accompanied by the appearance of an out-of-plane magnetization component and a remanence peak is observed. Because we do not observe an enhancement in anisotropy of Co orbital moment which leads to change in magnetic anisotropy through the transition at about 5 ×1015 ions /cm2, it might be possible that such nanodisc formation induces increase of magnetic anisotropy via a shape effect. By comparing with the phase transition observed at lower fluence [Phys. Rev. B 86, 024418 (2012), 10.1103/PhysRevB.86.024418], we find that the mechanism of two transitions is different, i.e., the transition at lower fluence is caused by anisotropy of orbital moment due to structural strain, while the present transition is possibly by shape effect due to nanodisc formation.

  10. The inhomogeneous ion temperature anisotropy instabilities of magnetic-field-aligned plasma sheared flow

    Science.gov (United States)

    Mikhailenko, V. V.; Mikhailenko, V. S.; Lee, Hae June

    2016-11-01

    The stability of the magnetic field aligned sheared flow with anisotropic ion temperatures, which have the anisotropic spatial inhomogeneities across the magnetic field and are comparable with or are above the electron temperature, is investigated numerically and analytically. The ion temperatures gradients across the magnetic field affect the instability development only when the inhomogeneous is the ion temperature along the magnetic field irrespective the inhomogeneity of the ion temperature across the magnetic field. In this case, the instability is developed due to the combined effect of the ion Landau damping, velocity shear, ion temperature anisotropy, and anisotropy of the ion temperature gradients. In the case when the ion temperature along the magnetic field is homogeneous, but the ion temperature across the magnetic field is inhomogeneous, the short wavelength instability develops with the wave length less than the thermal ion Larmor radius. This instability excites due to the coupled effect of the ion Landau damping, velocity shear and ion temperature anisotropy.

  11. Perpendicular magnetic anisotropy of amorphous [CoSiB/Pt]N thin films

    Science.gov (United States)

    Kim, T. W.; Choi, Y. H.; Lee, K. J.; Yoon, J. B.; Cho, J. H.; You, C.-Y.; Jung, M. H.

    2015-05-01

    Materials with perpendicular magnetic anisotropy (PMA) have been intensively studied for high-density nonvolatile memory such as spin-transfer-torque magnetic random access memory with low switching current density and high thermal stability. Compared with crystalline PMA multilayers, considerable works have been done on amorphous PMA multilayers because the amorphous materials are expected to have lower pinning site density as well as smaller domain wall width. This study is an overview of the PMA properties of amorphous [CoSiB/Pt]N multilayers with varying N, where the energy contribution is changed from domain wall energy to magnetostatic energy around N = 6. By measuring the field-induced domain wall motion, we obtain the creep exponent of μ = 1/4. These results in the amorphous PMA multilayers of [CoSiB/Pt]N demonstrate possible potential as a free layer for PMA-based memory devices.

  12. Perpendicular magnetic anisotropy of amorphous [CoSiB/Pt]{sub N} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Kim, T. W. [Department of Advanced Materials Engineering, Sejong University, Seoul 143-747 (Korea, Republic of); Choi, Y. H.; Lee, K. J.; Jung, M. H., E-mail: mhjung@sogang.ac.kr [Department of Physics, Sogang University, Seoul 121-742 (Korea, Republic of); Yoon, J. B.; Cho, J. H.; You, C.-Y. [Department of Physics, Inha University, Incheon 402-751 (Korea, Republic of)

    2015-05-07

    Materials with perpendicular magnetic anisotropy (PMA) have been intensively studied for high-density nonvolatile memory such as spin-transfer-torque magnetic random access memory with low switching current density and high thermal stability. Compared with crystalline PMA multilayers, considerable works have been done on amorphous PMA multilayers because the amorphous materials are expected to have lower pinning site density as well as smaller domain wall width. This study is an overview of the PMA properties of amorphous [CoSiB/Pt]{sub N} multilayers with varying N, where the energy contribution is changed from domain wall energy to magnetostatic energy around N = 6. By measuring the field-induced domain wall motion, we obtain the creep exponent of μ = 1/4. These results in the amorphous PMA multilayers of [CoSiB/Pt]{sub N} demonstrate possible potential as a free layer for PMA-based memory devices.

  13. Contribution of individual interfaces in the MgO/Co/Pd trilayer to perpendicular magnetic anisotropy upon annealing

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Minseok; Kim, Sanghoon; Ko, Jungho; Hong, Jongill, E-mail: hong.jongill@yonsei.ac.kr [Materials Science and Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of)

    2015-03-09

    The contribution of each interface of the MgO/Co/Pd trilayer to the perpendicular magnetic anisotropy (PMA) was studied by changing chemical and crystalline structures through annealing. We found that volumetric anisotropy in the MgO/Co/Pd trilayer was significantly increased due to enhanced magnetoelastic anisotropy caused by stress built up most likely at the MgO/Co interface during annealing. When the trilayer was annealed at 400 °C, the alloy formation at the Co/Pd interface additionally increased the volumetric anisotropy. Our x-ray magnetic circular dichroism study supported that those structural modifications led to an increase in the orbital moment through spin-orbit coupling (SOC) along the film normal two times larger than that of the as-deposited trilayer, thereby enhancing PMA greatly. Our experimental results prove that the Co/Pd interface, rather than the MgO/Co interface, plays an essential role in inducing strong PMA in the trilayer. The precise investigation of annealing effect on both volumetric and interfacial anisotropies can provide a methodological solution to improve the SOC of the trilayer that can serve as the core unit of spintronic devices.

  14. Giant perpendicular magnetic anisotropy of an Ir monolayer on a NiAl(001) surface

    Science.gov (United States)

    Kim, Dongyoo; Yang, Jeonghwa; Hong, Jisang

    2009-08-01

    Using the state-of-the-art full potential linearized augmented plane-wave method, we have investigated the magnetic properties of Os and Ir monolayer (ML) film on NiAl(001) surface. It has been found that the one ML of Os and Ir film can have ferromagnetic ground state with magnetic moment of 0.35 and 0.64μB on Ni terminated surface, whereas both films display no sign of magnetic state on Al terminated surface. In addition, the surface Ni atom has an induced magnetic moment of 0.26μB in Ir/NiAl(001), while only 0.09μB is observed in Os/NiAl(001). We attribute the existence of magnetism to the interaction between 5d of adlayer and 3d of surface Ni. Moreover, we have obtained that the Os/NiAl(001) and Ir/NiAl(001) films show a perpendicular magnetic anisotropy (PMA). Surprisingly, it appears that the Ir/NiAl(001) has a giant PMA energy of 7.18 meV.

  15. Magnetic oxide nanowires with strain-controlled uniaxial magnetic anisotropy direction

    NARCIS (Netherlands)

    Mathews, M.; Jansen, R.; Rijnders, G.; Lodder, J.C.; Blank, D.H.A.

    2009-01-01

    While magnetic nanowires generally have a preferential magnetization direction along the wire axis to minimize magnetostatic energy, it is shown here for epitaxial magnetic oxide nanowires that substrate-induced strain can be used to tailor the magnetic easy axis in any direction. La0.67Sr0.33MnO3 (

  16. Pressure anisotropy and small spatial scales induced by velocity shear

    Science.gov (United States)

    Del Sarto, D.; Pegoraro, F.; Califano, F.

    2016-05-01

    By including the full pressure tensor dynamics in a fluid plasma model, we show that a sheared velocity field can provide an effective mechanism that makes the initial isotropic pressure nongyrotropic. This is distinct from the usual gyrotropic anisotropy related to the fluid compressibility and usually accounted for in double-adiabatic models. We determine the time evolution of the pressure agyrotropy and discuss how the propagation of "magnetoelastic perturbations" can affect the pressure tensor anisotropization and its spatial filamentation, which are due to the action of both the magnetic field and the flow strain tensor. We support this analysis with a numerical integration of the nonlinear equations describing the pressure tensor evolution.

  17. Enhancement of perpendicular magnetic anisotropy and transmission of spin-Hall-effect-induced spin currents by a Hf spacer layer in W/Hf/CoFeB/MgO layer structures

    Energy Technology Data Exchange (ETDEWEB)

    Pai, Chi-Feng; Nguyen, Minh-Hai; Vilela-Leão, Luis Henrique; Buhrman, R. A., E-mail: rab8@cornell.edu [Cornell University, Ithaca, New York 14853 (United States); Belvin, Carina [Department of Physics, Wellesley College, Massachusetts 02481 (United States); Ralph, D. C. [Cornell University, Ithaca, New York 14853 (United States); Kavli Institute at Cornell, Ithaca, New York 14853 (United States)

    2014-02-24

    We report that strong perpendicular magnetic anisotropy of the ferromagnetic layer in a W/CoFeB/MgO multilayer structure can be established by inserting a Hf layer as thin as 0.25 nm between the W and CoFeB layers. The Hf spacer also allows transmission of spin currents generated by an in-plane charge current in the W layer to apply strong spin torque on the CoFeB, thereby enabling current-driven magnetic switching. The antidamping-like and field-like components of the spin torque exerted on a 1 nm CoFeB layer are of comparable magnitudes in this geometry. Both components originate from the spin Hall effect in the underlying W layer.

  18. Metastable cobalt nitride structures with high magnetic anisotropy for rare-earth free magnets.

    Science.gov (United States)

    Zhao, Xin; Ke, Liqin; Wang, Cai-Zhuang; Ho, Kai-Ming

    2016-11-23

    Metastable structures of cobalt nitrides and Fe-substituted cobalt nitrides are explored as possible candidates for rare-earth free permanent magnets. Through crystal structure searches using an adaptive genetic algorithm, new structures of ConN (n = 3…8) are found to have lower energies than those previously discovered by experiments. Some structures exhibit large magnetic anisotropy energy, reaching as high as 200 μeV per Co atom (or 2.45 MJ m(-3)) based on first-principles density functional calculation. Substituting a fraction of Co with Fe helps in stabilizing new structures and at the same time further improves the magnetic properties. Our theoretical predictions provide useful insights into a promising system for the discovery of new rare-earth free magnets by experiment.

  19. Depositional chronology and fabric of Siwalik group sediments in Central Nepal from magnetostratigraphy and magnetic anisotropy

    Science.gov (United States)

    Gautam, Pitambar; Rösler, Wolfgang

    1999-12-01

    Magnetostratigraphic research, undertaken within the past 15 years in the Siwaliks distributed along 400 km of the Sub-Himalaya in central Nepal, has proved that the sediments possess highly reliable hematite-based primary detrital remanent magnetization suitable to determine depositional chronology. In order to bring out the polarity sequences in a common chronological frame, all available data are newly correlated to the latest global magnetic polarity time scale of Cande and Kent (S.C. Cande, D.V. Kent (1995) Revised calibration of the geomagnetic polarity timescale for the Late Cretaceous and Cenozoic. Journal of Geophysical Research 100, 6093-6095). Chronological data presented are referred, in relation to the diverse lithological nomenclature, to the formations whose ages are not constrained by isotopic or paleontologic ages. The age of the sections dated by magnetostratigraphy ranges between 14 and <2 Ma. Sediment accumulation rates average to 32-50 cm kyr -1. Rock-magnetic parameters, e.g. initial susceptibility and isothermal remanent magnetization ratios, allow correlation with an accuracy of up to a few hundred meters among several kilometers thick adjacent sections. Anisotropy of magnetic susceptibility (AMS) data reveal a well-defined fabric contributed to by paramagnetic ( k=10 -5 to 3×10 -4 SI) as well as ferromagnetic minerals ( k=3×10 -4 to 10 -2 SI). AMS ellipsoids are mainly oblate along with some prolate ones and the degree of anisotropy is mostly low ( P'<1.2). The magnetic fabric is of pre-folding origin with tilt-corrected sub-vertical magnetic foliation poles. The magnetic lineations do not show parallelism to the expected paleocurrent directions. Rather, sub-parallelism between the clusters of magnetic lineation and the fold axes/bedding strikes/thrust fronts is observed. A superimposed fabric consisting of a sedimentary-compactional and an overprint induced by a mild deformation process is suggested. The latter process was active during

  20. Experimental investigation of ultrasonic velocity anisotropy in magnetic fluids: Influence of grain–grain interaction

    Indian Academy of Sciences (India)

    Kruti Shah; R V Upadhyay

    2011-08-01

    Magnetic field-induced dispersion of ultrasonic velocity in a Mn0.7Zn0.3Fe2O4 fluid (applied magnetic field is perpendicular to the ultrasonic propagation vector) is determined by employing continuous wave method. The magnitude of dispersion initially decreases with increasing field, then increases and reaches a plateau at higher fields. Results indicate that the velocity anisotropy is dominated by grain–grain interactions rather than grain–field interaction. At the critical temperature, the grain–grain interaction becomes weak as the transverse component of the particle/cluster moment is larger than the longitudinal one and the system reaches saturation even at low field. These observed variations in the field-induced anisotropy are analysed by incorporating the moment distribution of particles in Tarapov’s theory (J. Magn. Magn. Mater. 39, 51 (1983)).

  1. Giant perpendicular magnetic anisotropy of an individual atom on two-dimensional transition metal dichalcogenides

    Science.gov (United States)

    Odkhuu, Dorj

    2016-08-01

    Exploring magnetism and magnetic anisotropy in otherwise nonmagnetic two-dimensional materials, such as graphene and transition metal dichalcogenides, is at the heart of spintronics research. Herein, using first-principles calculations we explore the possibility of reaching an atomic-scale perpendicular magnetic anisotropy by carefully exploring the large spin-orbit coupling, orbital magnetism, and ligand field in a suitable choice of a two-dimensional structure with transition metal adatoms. More specifically, we demonstrate perpendicular magnetic anisotropy energies up to an order of 100 meV per atom in individual ruthenium and osmium adatoms at a monosulfur vacancy in molybdenum disulfide. We further propose a phenomenological model where a spin state transition that involves hybridization between molybdenum a1 and adatomic e' orbitals is a possible mechanism for magnetization reversal from an in-plane to perpendicular orientation.

  2. Synergy and destructive interferences between local magnetic anisotropies in binuclear complexes

    Energy Technology Data Exchange (ETDEWEB)

    Guihéry, Nathalie; Ruamps, Renaud [Laboratoire de Chimie et Physique Quantiques, UMR5625, University of Toulouse 3, Paul Sabatier, 118 route de Narbonne, 31062 Toulouse (France); Maurice, Rémi [SUBATECH, IN2P3/EMN Nantes/University of Nantes, 4 rue Alfred Kastler, BP 20722 44307, Nantes, Cedex 3 (France); Graaf, Coen de [University Rovira i Virgili, Marcelli Domingo s/n, 43007 Tarragona (Spain)

    2015-12-31

    Magnetic anisotropy is responsible for the single molecule magnet behavior of transition metal complexes. This behavior is characterized by a slow relaxation of the magnetization for low enough temperatures, and thus for a possible blocking of the magnetization. This bistable behavior can lead to possible technological applications in the domain of data storage or quantum computing. Therefore, the understanding of the microscopic origin of magnetic anisotropy has received a considerable interest during the last two decades. The presentation focuses on the determination of the anisotropy parameters of both mono-nuclear and bi-nuclear types of complexes and on the control and optimization of the anisotropic properties. The validity of the model Hamiltonians commonly used to characterize such complexes has been questioned and it is shown that neither the standard multispin Hamiltonian nor the giant spin Hamiltonian are appropriate for weakly coupled ions. Alternative models have been proposed and used to properly extract the relevant parameters. Rationalizations of the magnitude and nature of both local anisotropies of single ions and the molecular anisotropy of polynuclear complexes are provided. The synergy and interference effects between local magnetic anisotropies are studied in a series of binuclear complexes.

  3. Layering and temperature-dependent magnetization and anisotropy of naturally produced Ni/NiO multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Pappas, S. D.; Trachylis, D.; Velgakis, M. J. [Laboratory of High-Tech Materials, School of Engineering, University of Patras, 26504 Patras (Greece); Kapaklis, V.; Joensson, P. E.; Papaioannou, E. Th. [Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala (Sweden); Delimitis, A. [Chemical Process Engineering Research Institute (CPERI), Centre for Research and Technology Hellas (CERTH), 57001 Thermi, Thessaloniki (Greece); Poulopoulos, P. [Laboratory of High-Tech Materials, School of Engineering, University of Patras, 26504 Patras (Greece); Institut fuer Experimentalphysik, Freie Universitaet Berlin, Arnimallee 14, D-14195 Berlin-Dahlem (Germany); Materials Science Department, University of Patras, 26504 Patras (Greece); Fumagalli, P. [Institut fuer Experimentalphysik, Freie Universitaet Berlin, Arnimallee 14, D-14195 Berlin-Dahlem (Germany); Politis, C. [Laboratory of High-Tech Materials, School of Engineering, University of Patras, 26504 Patras (Greece); Department of Materials Science and Engineering, University of Texas at Arlington, Arlington, Texas 76019 (United States)

    2012-09-01

    Ni/NiO multilayers were grown by magnetron sputtering at room temperature, with the aid of the natural oxidation procedure. That is, at the end of the deposition of each single Ni layer, air is let to flow into the vacuum chamber through a leak valve. Then, a very thin NiO layer ({approx}1.2 nm) is formed. Simulated x-ray reflectivity patterns reveal that layering is excellent for individual Ni-layer thickness larger than 2.5 nm, which is attributed to the intercalation of amorphous NiO between the polycrystalline Ni layers. The magnetization of the films, measured at temperatures 5-300 K, has almost bulk-like value, whereas the films exhibit a trend to perpendicular magnetic anisotropy (PMA) with an unusual significant positive interface anisotropy contribution, which presents a weak temperature dependence. The power-law behavior of the multilayers indicates a non-negligible contribution of higher order anisotropies in the uniaxial anisotropy. Bloch-law fittings for the temperature dependence of the magnetization in the spin-wave regime show that the magnetization in the multilayers decreases faster as a function of temperature than the one of bulk Ni. Finally, when the individual Ni-layer thickness decreases below 2 nm, the multilayer stacking vanishes, resulting in a dramatic decrease of the interface magnetic anisotropy and consequently in a decrease of the perpendicular magnetic anisotropy.

  4. High-purity cobalt thin films with perpendicular magnetic anisotropy prepared by chemical vapor deposition

    Science.gov (United States)

    Ootera, Yasuaki; Shimada, Takuya; Kado, Masaki; Quinsat, Michael; Morise, Hirofumi; Nakamura, Shiho; Kondo, Tsuyoshi

    2015-11-01

    A study of the chemical vapor deposition (CVD) of high-purity cobalt thin films is described. The Co layer prepared by a thermal CVD technique with a Pt/Ta underlayer and a Pt cap layer shows a saturation magnetization (Ms) of ∼1.8 T and perpendicular magnetic anisotropy (PMA) with an anisotropy energy (Ku) of ∼105 J/m3. The cobalt thickness dependence of Ku reveals that the interfacial anisotropy at the Pt/Co interface is most likely the origin of the obtained PMA.

  5. Enhanced perpendicular magnetic anisotropy in Co/Ni multilayers with a thin seed layer

    Science.gov (United States)

    Kurt, H.; Venkatesan, M.; Coey, J. M. D.

    2010-10-01

    Perpendicular magnetic anisotropy (PMA) is induced in Co/Ni multilayers when they are grown on a (111) textured Au seed layer, provided it is at least 2 nm thick. The anisotropy increases with increasing Au thickness due to improved crystallinity. Postannealing treatments of as-grown [Co(0.3)/Ni(0.6)]5 (thicknesses in nanometer) multilayers enhance the coercivity and PMA up to an annealing temperature of 250 °C, but higher temperatures lead to intermixing of Co and Ni which diminishes PMA. The easy axis becomes in-plane for samples annealed at 400 °C. The improvement in PMA in Co/Ni layers due to annealing is limited by the Au seed layer thickness. Annealing also reduces the saturation magnetization by ˜15% due to the formation of superparamagnetic islands. Our results show that the PMA in Co/Ni multilayers can be improved by annealing up to 350 °C, which is required for the thermal stability of spin transfer torque memories.

  6. Perpendicular magnetic anisotropy in Fe2Cr1 - xCoxSi Heusler alloy

    Science.gov (United States)

    Wang, Yu-Pu; Qiu, Jin-Jun; Lu, Hui; Ji, Rong; Han, Gu-Chang; Teo, Kie-Leong

    2014-12-01

    Perpendicular magnetic anisotropy (PMA) was achieved in annealed Fe2Cr1 - xCoxSi (FCCS) Heusler alloys with different Co compositions x. The Co composition is varied to tune the Fermi level in order to achieve both higher spin polarization and better thermal stability. The PMA is thermally stable up to 400 oC for FCCS with x = 0, 0.3, 0.5 and 350 oC for FCCS with x = 0.7, 0.9, 1. The thickness of FCCS films with PMA ranges from 0.6 to 1.2 nm. The annealing temperature and FCCS thickness are found to greatly affect the PMA. The magnetic anisotropy energy density KU is 2.8  ×  106 erg cm-3 for 0.8 nm Fe2CrSi, and decreases as the Co composition x increases, suggesting that the PMA induced at the FCCS/MgO interface is dominated by the contribution of Fe atoms. There is a trade-off between high spin polarization and strong PMA by adjusting the Co composition.

  7. Perpendicular magnetic anisotropy in Mn{sub 2}CoAl thin film

    Energy Technology Data Exchange (ETDEWEB)

    Sun, N. Y.; Zhang, Y. Q.; Che, W. R.; Shan, R. [Shanghai Key Laboratory of Special Artificial Microstructure and Pohl Institute of Solid State Physics and School of Physics Science and Engineering, Tongji University, Shanghai 200092 (China); Fu, H. R.; You, C. Y., E-mail: caiyinyou@xaut.edu.cn [School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048 (China)

    2016-01-15

    Heusler compound Mn{sub 2}CoAl (MCA) is attracting more attentions due to many novel properties, such as high resistance, semiconducting behavior and suggestion as a spin-gapless material with a low magnetic moment. In this work, Mn{sub 2}CoAl epitaxial thin film was prepared on MgO(100) substrate by magnetron sputtering. The transport property of the film exhibits a semiconducting-like behavior. Moreover, our research reveals that perpendicular magnetic anisotropy (PMA) can be induced in very thin Mn{sub 2}CoAl films resulting from Mn-O and Co-O bonding at Mn{sub 2}CoAl/MgO interface, which coincides with a recent theoretical prediction. PMA and low saturation magnetic moment could lead to large spin-transfer torque with low current density in principle, and thus our work may bring some unanticipated Heusler compounds into spintronics topics such as the domain wall motion and the current-induced magnetization reversal.

  8. Perpendicular magnetic anisotropy in Mn2CoAl thin film

    Directory of Open Access Journals (Sweden)

    N. Y. Sun

    2016-01-01

    Full Text Available Heusler compound Mn2CoAl (MCA is attracting more attentions due to many novel properties, such as high resistance, semiconducting behavior and suggestion as a spin-gapless material with a low magnetic moment. In this work, Mn2CoAl epitaxial thin film was prepared on MgO(100 substrate by magnetron sputtering. The transport property of the film exhibits a semiconducting-like behavior. Moreover, our research reveals that perpendicular magnetic anisotropy (PMA can be induced in very thin Mn2CoAl films resulting from Mn-O and Co-O bonding at Mn2CoAl/MgO interface, which coincides with a recent theoretical prediction. PMA and low saturation magnetic moment could lead to large spin-transfer torque with low current density in principle, and thus our work may bring some unanticipated Heusler compounds into spintronics topics such as the domain wall motion and the current-induced magnetization reversal.

  9. Enhancement of perpendicular magnetic anisotropy by compressive strain in alternately layered FeNi thin films.

    Science.gov (United States)

    Sakamaki, M; Amemiya, K

    2014-04-23

    The effect of the lattice strain on magnetic anisotropy of alternately layered FeNi ultrathin films grown on a substrate, Cu(tCu = 0-70 ML)/Ni(48)Cu(52)(124 ML)/Cu(0 0 1) single crystal, is systematically studied by means of in situ x-ray magnetic circular dichroism (XMCD) and reflection high-energy electron diffraction (RHEED) analyses. To investigate the magnetic anisotropy of the FeNi layer itself, a non-magnetic substrate is adopted. From the RHEED analysis, the in-plane lattice constant, ain, of the substrate is found to shrink by 0.8% and 0.5% at tCu = 0 and 10 ML as compared to that of bulk Cu, respectively. Fe L-edge XMCD analysis is performed for n ML FeNi films grown on various ain, and perpendicular magnetic anisotropy (PMA) is observed at n = 3 and 5, whereas the film with n = 7 shows in-plane magnetic anisotropy. Moreover, it is found that PMA is enhanced with decreasing ain, in the case where a Cu spacer layer is inserted. We suppose that magnetic anisotropy in the FeNi films is mainly carried by Fe, and the delocalization of the in-plane orbitals near the Fermi level increases the perpendicular orbital magnetic moment, which leads to the enhancement of PMA.

  10. Magnetization reversal of giant perpendicular magnetic anisotropy at the magnetic-phase transition in FeRh films on MgO

    Science.gov (United States)

    Odkhuu, Dorj

    2016-02-01

    Based on first-principles calculations, we demonstrate that substitutions of transition metals Ru and Ir, neighboring and same group elements in the periodic table, for the Rh site in the vicinity of surface can induce a substantially large perpendicular magnetic anisotropy (PMA), up to an order of magnitude of 20 erg /cm2 , in FeRh films on MgO. The main driving mechanism for this huge PMA is the interplay between the dx y and dx2-y2 orbital states of the substitutional 4 d and 5 d transition metal atoms with large spin-orbit coupling. Further investigations demonstrate that magnetization direction of PMA undergoes a transition into an in-plane magnetization at the antiferromagnet → ferromagnet phase transition, which provides a viable route for achieving large and switchable PMA associated with the magnetic-phase transition in antiferromagnet spintronics.

  11. Enhancement of perpendicular magnetic anisotropy and coercivity in ultrathin Ru/Co/Ru films through the buffer layer engineering

    Science.gov (United States)

    Kolesnikov, Alexander G.; Stebliy, Maxim E.; Ognev, Alexey V.; Samardak, Alexander S.; Fedorets, Aleksandr N.; Plotnikov, Vladimir S.; Han, Xiufeng; Chebotkevich, Ludmila A.

    2016-10-01

    We present results on a study of the interplay between microstructure and the magnetic properties of ultrathin Ru/Co/Ru films with perpendicular magnetic anisotropy (PMA). To induce PMA in the Co layer, we experimentally determined thicknesses of the buffer and capping layers of Ru. The maximum value of PMA was observed for the Co thickness of 0.9 nm with the 3 nm thick capping layer. The effective anisotropy field (H eff) and coercive force (H c) of the Co layer are very sensitive to the Ru buffer layer thickness (t b). The values of H eff and H c increase approximately by two and ten times, correspondingly, when t b changes from 6 to 20 nm, owing to an increase in volume fraction of the crystalline phase as a result of the grains’ growth. PMA is found to be mainly enhanced by elastic strains induced by the lattice mismatch on the Ru/Co and Co/Ru interfaces, leading to the deformation of the Co lattice. The surface impact is determined to be less than 10% of the magneto-elastic contribution to the effective anisotropy. Observation of the magnetic domain structure by means of polar Kerr microscopy reveals that out-of-plane magnetization reversal occurs through the nucleation, growth, and annihilation of domains, where the average size drastically rises with the increasing t b.

  12. How strongly are the magnetic anisotropy and coordination numbers correlated in lanthanide based molecular magnets?

    Indian Academy of Sciences (India)

    Tulika Gupta; Gopalan Rajaraman

    2014-09-01

    Ab initio CASSCF+RASSI-SO investigations on a series of lanthanide complexes [LnIII = Dy(1), Tb(2), Ce(3), Nd(4), Pr(5) and Sm(6)] have been undertaken and in selected cases (for 1, 2, 3 and 4) coordination number (C.N.) around the LnIII ion has been gradually varied to ascertain the effect of C.N. on the magnetic anisotropy. Our calculations reveal that complex 3 possesses the highest barrier height for reorientation of magnetisation (Ueff) and predict that 3 is likely to exhibit Single Molecule Magnet (SMM) behaviour. Complex 5 on the other hand is predicted to preclude any SMM behaviour as there is no intrinsic barrier for reorientation of magnetization. Ground state anisotropy of all the complexes show mixed behaviour ranging from pure Ising type to fully rhombic behaviour. Coordination number around the lanthanide ion is found to alter the magnetic behaviour of all the lanthanide complexes studied and this is contrary to the general belief that the lanthanide ions are inert and exert small ligand field interaction.High symmetric low-coordinate LnIII complexes are found to yield large Ueff values and thus should be the natural targets for achieving very large blocking temperatures.

  13. Structure and magnetic properties of nanocrystalline ferromagnets (Ⅰ)--Effective anisotropy

    Institute of Scientific and Technical Information of China (English)

    刘涛; 徐祖雄; 赵钟涛; 马如璋; 胡天斗; 谢亚宁; 郭应焕

    1997-01-01

    The role of effective anisotropy in nanocrystalline ferromagnets is investigated. These alloys are prepared by annealing amorphous ribbons and have excellent soft magnetic properties. A two-phase model is established considering the role of the mtergranular amorphous phase. The results indicate a strong dependence of effective anisotropy on the structure and magnetic parameters of the amorphous phase as well as on the size of a grains. In view of the new model, the magnetic hardening beyond the optimally annealing temperature seems to be ascribed to the de-terioration in magnetic properties of interfacial amorphous phase.

  14. Single-ion anisotropy and transverse magnetization in the frustrated gadolinium pyrochlores

    Science.gov (United States)

    Glazkov, V. N.; Zhitomirsky, M.; Smirnov, A. I.; Marin, C.; Sanchez, J.-P.; Forget, A.; Colson, D.; Bonville, P.

    2007-04-01

    A single-ion anisotropy of the planar type is found in the pyrochlore antiferromagnet oxides Gd2M2O7 (M = Ti,Sn); its strength is comparable with the strength of the exchange coupling. Models considering the effects of the planar anisotropy predict the appearance of a transverse magnetization in an applied magnetic field. A detailed experimental study of Gd2Ti2O7 single crystals reveals that a transverse magnetization is really present at low temperatures. The magnetic phase diagram of Gd2Ti2O7 is refined.

  15. Growth and magnetic anisotropy of thin W(110)/Co films on Al2O3(112¯0)

    Science.gov (United States)

    Sellmann, R.; Fritzsche, H.; Maletta, H.; Leiner, V.; Siebrecht, R.

    2001-06-01

    The growth and magnetism of thin W(110)/Co films deposited by molecular beam epitaxy on single-crystal sapphire Al2O3(112¯0) substrates is investigated. Low-energy electron diffraction analysis shows that the Co films grow on the epitaxial W(110) substrate layer with a constant lattice strain up to a Co thickness dCo=20 Å. Pseudomorphic growth is found for the W[11¯0] direction. The thickness-dependent magnetic anisotropy is studied in situ at T=300 K by means of magneto-optical Kerr-effect measurements on a Co wedge-shaped sample prior and after coverage with a Au overlayer. After the coverage the Co wedge reveals a perpendicular magnetic anisotropy for small Co film thickness followed by a spin-reorientation transition from out-of-plane to in-plane alignment of the magnetization vector in the thickness regime 7 Å<=dCo<=9 Å. Spin-dependent neutron reflectivity data provide evidence for a pronounced magnetic anisotropy within the film plane even for relatively thick Co films. The observed decrease of the splitting between spin-up and spin-down reflectivities for decreasing temperature indicates that the spin-reorientation transition of the system W(110)/Co/Au can also be induced thermally.

  16. Magnetization reversal in magnetic dot arrays: Nearest-neighbor interactions and global configurational anisotropy

    Science.gov (United States)

    Van de Wiele, Ben; Fin, Samuele; Pancaldi, Matteo; Vavassori, Paolo; Sarella, Anandakumar; Bisero, Diego

    2016-05-01

    Various proposals for future magnetic memories, data processing devices, and sensors rely on a precise control of the magnetization ground state and magnetization reversal process in periodically patterned media. In finite dot arrays, such control is hampered by the magnetostatic interactions between the nanomagnets, leading to the non-uniform magnetization state distributions throughout the sample while reversing. In this paper, we evidence how during reversal typical geometric arrangements of dots in an identical magnetization state appear that originate in the dominance of either Global Configurational Anisotropy or Nearest-Neighbor Magnetostatic interactions, which depends on the fields at which the magnetization reversal sets in. Based on our findings, we propose design rules to obtain the uniform magnetization state distributions throughout the array, and also suggest future research directions to achieve non-uniform state distributions of interest, e.g., when aiming at guiding spin wave edge-modes through dot arrays. Our insights are based on the Magneto-Optical Kerr Effect and Magnetic Force Microscopy measurements as well as the extensive micromagnetic simulations.

  17. The manipulation of magnetic coercive field and orientation of magnetic anisotropy via electric fields

    Science.gov (United States)

    Xiang, Jun-Sen; Ye, Jun; Yang, Yun-Long; Xie, Yong; Li, Wei; Chen, Zi-Yu

    2016-08-01

    We report the effects of the electric field on the magnetic coercive field (H c) and uniaxial magnetic anisotropy (UMA) orientation of polycrystalline Ni film grown on an unpoled (0 1 1) [Pb(Mg1/3Nb2/3)O3](1-x)-[PbTiO3] x (PMN-PT) single crystal substrate. Under various electric fields, normalized magnetic hysteresis loops of Ni films change in width; this represents the change of coercive field (ΔH c). Loop shapes are found to depend on the angle between the magnetic field and the sample, where changes in the shape reveal a small rotation of UMA. All these changes show that the magnetic properties vary periodically with a periodic electric field, by strain-mediated magnetoelectric coupling in the Ni/Ag/PMN-PT/Ag heterostructure. The poled PMN-PT produces strains under electric fields in the range of  -4.2 kV cm-1  ⩽  E  ⩽  4.2 kV cm-1, then transfers it to Ni films resulting in changes to its H c and UMA. The curves of the in-plane H c and strain, at two mutually orthogonal directions, represent butterfly patterns versus the applied electric field. In addition, the changes observed in both the H c and strain show asymmetric features in two orthogonal directions, which results in a small rotation angle of the UMA of Ni as the electric field decreases. The effective manipulation of magnitude and orientation of magnetic anisotropy via electric fields in ferromagnetic/ferroelectric (FM/FE) heterostructures is an important step towards controlling the magnetic tunnel junctions.

  18. Ultra Low Energy Switching of Ferromagnet with Perpendicular Anisotropy on Topological Insulator by Voltage Controlled Magnetic Anisotropy

    Science.gov (United States)

    Ghosh, Bahniman; Pramanik, Tanmoy; Dey, Rik; Roy, Urmimala; Register, Leonard; Banerjee, Sanjay

    2015-03-01

    We propose and demonstrate, through simulation, an ultra low energy memory device on a topological insulator thin film. The device consists of a thin layer of Fe deposited on the surface of a topological insulator, Bi2Se3. The top surface of Fe is covered with MgO so that the ferromagnetic layer has perpendicular anisotropy. Current is passed on the surface of the topological insulator which switches the magnetization of the Fe ferromagnet through strong exchange interaction, between electrons contributing to the surface current on the Bi2Se3 and the d electrons in the ferromagnet, and spin transfer torque due to shunting of current through the ferromagnet. Voltage controlled magnetic anisotropy enables ultra low energy switching. Our micromagnetic simulations, predict switching time of the order of 2.4 ns and switching energy of the order of 0.16 fJ for a ferromagnetic bit with thermal stability of 90 kBT. The proposed structure combines the advantages of both large spin torque from topological insulators and those of perpendicular anisotropy materials. This work is supported by NRI SWAN and NSF NASCENT Center.

  19. Magnetic anisotropy and the phase diagram of chiral MnSb2O6

    Science.gov (United States)

    Werner, J.; Koo, C.; Klingeler, R.; Vasiliev, A. N.; Ovchenkov, Y. A.; Polovkova, A. S.; Raganyan, G. V.; Zvereva, E. A.

    2016-09-01

    The magnetic phase diagram and low-energy magnon excitations of structurally and magnetically chiral MnSb2O6 are reported. The specific heat and the static magnetization are investigated in magnetic fields up to 9 and 30 T, respectively, while the dynamic magnetic properties are probed by X-band as well as tunable high-frequency electron spin-resonance spectroscopy. Below TN=11.5 K, we observe antiferromagnetic resonance modes which imply small but finite planar anisotropy showing up in a zero-field splitting of 20 GHz. The data are well described by means of an easy-plane two-sublattice model with the anisotropy field BA=0.02 T. The exchange field BE=13 T is obtained from the saturation field derived from the pulsed-field magnetization. A crucial role of the small anisotropy for the spin structure is reflected by competing antiferromagnetic phases appearing, at T =2 K, in small magnetic fields at BC 1 ≈0.5 T and BC 2=0.9 T. We discuss the results in terms of spin reorientation and of small magnetic fields favoring helical spin structure over the cycloidal ground state which, at B =0 , is stabilized by the planar anisotropy. Above TN, short-range magnetic correlations up to ≳60 K and magnetic entropy changes well above TN reflect the frustrated triangular arrangement of Mn2 + ions in MnSb2O6 .

  20. Orbital magnetic moments in SrRu O3 epitaxial thin films with interfacially controlled magnetic anisotropy

    Science.gov (United States)

    Kan, Daisuke; Mizumaki, Masaichiro; Nishimura, Tomoe; Shimakawa, Yuichi

    2016-12-01

    Using x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) spectroscopy, we evaluated the orbital magnetic moments of itinerant ferromagnet SrRu O3 (SRO) epitaxial thin films with interfacially controlled magnetic anisotropy. We found that the orbital moment is closely correlated with the SRO's magnetic anisotropy, which can be controlled by interfacially engineering the Ru O6 octahedral rotations. For the monoclinic film with magnetization along the direction 45° from the out-of-plane direction, the orbital moment is ≈-0.1 μB/Ru along the magnetic easy axis direction and is aligned antiparallel to the direction of the spin magnetic moments. For the tetragonal film with in-plane magnetization, on the other hand, the out-of-plane component of the orbital moment is as small as ≈-0.04 μB/Ru , accounting for the film's in-plane magnetic anisotropy. Our results highlight that the magnetic anisotropy of SRO can be controlled by engineering the orbital magnetic moment through the octahedral distortions.

  1. Enhanced voltage-controlled magnetic anisotropy in magnetic tunnel junctions with an MgO/PZT/MgO tunnel barrier

    Science.gov (United States)

    Chien, Diana; Li, Xiang; Wong, Kin; Zurbuchen, Mark A.; Robbennolt, Shauna; Yu, Guoqiang; Tolbert, Sarah; Kioussis, Nicholas; Khalili Amiri, Pedram; Wang, Kang L.; Chang, Jane P.

    2016-03-01

    Compared with current-controlled magnetization switching in a perpendicular magnetic tunnel junction (MTJ), electric field- or voltage-induced magnetization switching reduces the writing energy of the memory cell, which also results in increased memory density. In this work, an ultra-thin PZT film with high dielectric constant was integrated into the tunneling oxide layer to enhance the voltage-controlled magnetic anisotropy (VCMA) effect. The growth of MTJ stacks with an MgO/PZT/MgO tunnel barrier was performed using a combination of sputtering and atomic layer deposition techniques. The fabricated MTJs with the MgO/PZT/MgO barrier demonstrate a VCMA coefficient, which is ˜40% higher (19.8 ± 1.3 fJ/V m) than the control sample MTJs with an MgO barrier (14.3 ± 2.7 fJ/V m). The MTJs with the MgO/PZT/MgO barrier also possess a sizeable tunneling magnetoresistance (TMR) of more than 50% at room temperature, comparable to the control MTJs with an MgO barrier. The TMR and enhanced VCMA effect demonstrated simultaneously in this work make the MgO/PZT/MgO barrier-based MTJs potential candidates for future voltage-controlled, ultralow-power, and high-density magnetic random access memory devices.

  2. Perpendicular magnetic anisotropy and magnetic domain structure of unpatterned and patterned Co/Pt multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Huang, J.C.A. E-mail: jcahuang@mail.ncku.edu.tw; Wu, L.C.; Chen, M.M.; Wu, T.H.; Wu, J.C.; Huang, Y.W.; Lee, C.H.; Fu, C.M

    2000-02-01

    Perpendicular magnetic anisotropy and magnetic domain structure were studied in epitaxial [Co(t{sub Co})/Pt(10 A)]{sub 30} (t{sub Co}=2, 2.5, 3, 4, 5 and 10 A) multilayers prepared on Al{sub 2}O{sub 3}(1 1 -2 0) substrate via Mo or Pt seed layer. The best perpendicular magnetic effect occurred for t{sub Co}{approx}3 A. At remnant state the domain size tends to increase as t{sub Co} decreases, and the domain structure depends strongly on the seed layer. For [Co(3 A)/Pt(10 A)]{sub 30} multilayers grown on gold grid made hole arrays, the polar coercivity inside the holes is different from those on the gold land and unpatterned area.

  3. Failure Analysis in Magnetic Tunnel Junction Nanopillar with Interfacial Perpendicular Magnetic Anisotropy.

    Science.gov (United States)

    Zhao, Weisheng; Zhao, Xiaoxuan; Zhang, Boyu; Cao, Kaihua; Wang, Lezhi; Kang, Wang; Shi, Qian; Wang, Mengxing; Zhang, Yu; Wang, You; Peng, Shouzhong; Klein, Jacques-Olivier; de Barros Naviner, Lirida Alves; Ravelosona, Dafine

    2016-01-12

    Magnetic tunnel junction nanopillar with interfacial perpendicular magnetic anisotropy (PMA-MTJ) becomes a promising candidate to build up spin transfer torque magnetic random access memory (STT-MRAM) for the next generation of non-volatile memory as it features low spin transfer switching current, fast speed, high scalability, and easy integration into conventional complementary metal oxide semiconductor (CMOS) circuits. However, this device suffers from a number of failure issues, such as large process variation and tunneling barrier breakdown. The large process variation is an intrinsic issue for PMA-MTJ as it is based on the interfacial effects between ultra-thin films with few layers of atoms; the tunneling barrier breakdown is due to the requirement of an ultra-thin tunneling barrier (e.g., MTJ and present some eventual solutions from device fabrication to system level integration to optimize the failure issues.

  4. Correlated oscillations of the magnetic anisotropy energy and orbital moment anisotropy in thin films: The role of quantum well states

    Science.gov (United States)

    Sandratskii, L. M.

    2015-10-01

    We report the first-principles study of the correlated behavior of the magnetic anisotropy energy (MAE) and orbital moment anisotropy (OMA) as the functions of the thickness N of the Fe film. The work is motivated by recent experimental studies combining photoemission, x-ray magnetic circular dichroism, and magnetic anisotropy measurements. In agreement with experiment, the correlated oscillations of MAE (N ) and OMA (N ) are obtained that have their origin in the formation of the 3d quantum well states (QWS) confined in the films. The main contribution to the oscillation amplitude comes from the surface layer. This is an interesting feature of the phenomenon consisting in the peculiar dependence of the physical quantities on the thickness of the film. We demonstrate that the band structure of the bulk Fe does not reflect adequately the properties of the 3d QWS in thin films and, therefore, does not provide the basis for understanding the oscillations of MAE (N ) and OMA (N ) . A detailed point-by-point analysis in the two-dimensional (2D) Brillouin zone (BZ) of the film shows that the contribution of the Γ point, contrary to a rather common expectation, does not play an important role in the formation of the oscillations. Instead, the most important contributions come from a broad region of the 2D BZ distant from the center of the BZ. Combining symmetry arguments and direct calculations we show that orbital moments of the electronic states possess nonzero transverse components orthogonal to the direction of the spin magnetization. The account for this feature is crucial in the point-by-point analysis of the OMA. On the basis of the calculations for noncollinear spin configurations we suggest interpretations of two interesting experimental findings: fast temperature decay of the oscillation amplitude in MAE (N ) and unexpectedly strong spin mixing of the initial states of the photoemission process.

  5. Systematic control of stress-induced anisotropy in pseudomorphic iron garnet thin films

    Energy Technology Data Exchange (ETDEWEB)

    Kubota, M., E-mail: Masashi.Kubota@dsn.rohm.co.jp [Correlated Electron Research Group (CERG) and Cross-Correlated Materials Research Group (CMRG), RIKEN Advanced Science Institute, Wako, Saitama 351-0198 (Japan); Power Electronics R and D Unit, ROHM Co., Ltd., Kyoto 615-8585 (Japan); Shibuya, K.; Tokunaga, Y. [Correlated Electron Research Group (CERG) and Cross-Correlated Materials Research Group (CMRG), RIKEN Advanced Science Institute, Wako, Saitama 351-0198 (Japan); Kagawa, F. [Department of Applied Physics and Quantum Phase Electronics Center (QPEC), University of Tokyo, Bunkyo, Tokyo 113-8656 (Japan); CREST, Japan Science and Technology Agency, Bunkyo, Tokyo 113-8656 (Japan); Tsukazaki, A. [Department of Applied Physics and Quantum Phase Electronics Center (QPEC), University of Tokyo, Bunkyo, Tokyo 113-8656 (Japan); PRESTO, Japan Science and Technology Agency, Bunkyo, Tokyo 113-8656 (Japan); Tokura, Y.; Kawasaki, M. [Correlated Electron Research Group (CERG) and Cross-Correlated Materials Research Group (CMRG), RIKEN Advanced Science Institute, Wako, Saitama 351-0198 (Japan); Department of Applied Physics and Quantum Phase Electronics Center (QPEC), University of Tokyo, Bunkyo, Tokyo 113-8656 (Japan)

    2013-08-15

    Iron garnets are one of the most well-studied magnetic materials that enabled magnetic bubble memories and magneto-optical devices employing films with a perpendicular easy axis. However, most studies have been conducted on rather thick films (>1 μm), and it has not been elucidated whether it is possible to align the magnetic easy axis perpendicular to the film plane for much thinner (<100 nm) films by overcoming shape anisotropy. We studied the effects of epitaxial strain and film composition on the magnetic properties of 50-nm-thick garnet thin films grown by pulsed-laser deposition. Y{sub 3}Fe{sub 5}O{sub 12} was selected as the most prototypical garnet and Sm{sub 3−x}Tm{sub x}Fe{sub 5}O{sub 12} (x=1, 2, 3) was selected in view of its negatively large magnetostriction constants. We employed (111) planes of single crystalline Gd{sub 3}Ga{sub 5}O{sub 12} and (CaGd){sub 3}(MgGaZr){sub 5}O{sub 12} substrates to tune the epitaxial strain. Thin films with a pseudomorphic structure were fabricated with the in-plane strain (ε{sub //}) ranging from −1.5% to +0.5%, corresponding to the stress-induced anisotropy field (H{sub A}) ranging from −40 kOe to +25 kOe, respectively. The magnetization ratio of the out-of-plane to in-plane component (M{sub ⊥}/M{sub //}) systematically varied in accord with H{sub A}, yielding M{sub ⊥}/M{sub //} >1 for thin films with H{sub A} values larger than 20 kOe. Among the films grown, Tm{sub 3}Fe{sub 5}O{sub 12} on Gd{sub 3}Ga{sub 5}O{sub 12} showed the largest ε{sub //} and H{sub A} values of +0.5% and +25 kOe, respectively, to realize an apparently perpendicular easy axis, confirmed by a large M{sub ⊥}/M{sub //} value of 7.8. Further, magnetic force microscope images showed a maze pattern typical of a perpendicularly magnetized film. These results reveal a method for tailoring the magnetic anisotropy of garnet ultrathin films by utilizing epitaxial strain. These thin films may be utilized to obtain nanoscale magnetic bubbles

  6. Magnetic anisotropy of Co thin films: Playing with the shadowing effect, magnetic field and substrate spinning

    Science.gov (United States)

    Bertelli, T. P.; Bueno, T. E. P.; Krohling, A. C.; Silva, B. C.; Rodríguez-Suárez, R. L.; Nascimento, V. P.; Paniago, R.; Krambrock, K.; Larica, C.; Passamani, E. C.

    2017-03-01

    The shape and magneto-crystalline anisotropies of 10 nm thick Co sputtered films have shown to be dependent on the oblique deposition angle (αi), the angular velocity of the substrate-holder (ωS) and the applied magnetic field (H0) during the deposition. Oblique deposition geometry is natural in our sputtering setup, being α equal to 22° at the edge of 4 in. sample-holder and 32° at its central part. X-ray diffraction analysis has evidenced a (111) texturized fcc structure for all films. Ferromagnetic resonance has shown that samples prepared under H0 of 250 Oe present dominantly the uniaxial HU field contribution independent of the ωS-value, however its magnitude depends on αi. For a non-magnetic holder, Co films show a mixture of twofold (uniaxial) with fourfold (cubic) in-plane magnetic anisotropies. The fourfold contribution is small and it is not influenced by αi or ωS within the experimental error, while the dominant twofold contribution, which is governed by the shadowing effect, is reduced for higher ωS and for samples positioned at the center of the sample-holder. In addition, the intrinsic isotropic Gilbert damping dominates the relaxation process, which is followed by anisotropic twofold scattering mechanism due to stripes and defects, interestingly not influenced by the substrate rotation during depositions.

  7. Enhanced annealing stability and perpendicular magnetic anisotropy in perpendicular magnetic tunnel junctions using W layer

    Science.gov (United States)

    Chatterjee, Jyotirmoy; Sousa, Ricardo C.; Perrissin, Nicolas; Auffret, Stéphane; Ducruet, Clarisse; Dieny, Bernard

    2017-05-01

    The magnetic properties of the perpendicular storage electrode (buffer/MgO/FeCoB/Cap) were studied as a function of annealing temperature by replacing Ta with W and W/Ta cap layers with variable thicknesses. W in the cap boosts up the annealing stability and increases the effective perpendicular anisotropy by 30% compared to the Ta cap. Correspondingly, an increase in the FeCoB critical thickness characterizing the transition from perpendicular to in-plane anisotropy was observed. Thicker W layer in the W(t)/Ta 1 nm cap layer makes the storage electrode highly robust against annealing up to 570 °C. The stiffening of the overall stack resulting from the W insertion due to its very high melting temperature seems to be the key mechanism behind the extremely high thermal robustness. The Gilbert damping constant of FeCoB with the W/Ta cap was found to be lower when compared with the Ta cap and stable with annealing. The evolution of the magnetic properties of bottom pinned perpendicular magnetic tunnel junctions (p-MTJ) stack with the W2/Ta1 nm cap layer shows back-end-of-line compatibility with increasing tunnel magnetoresistance up to the annealing temperature of 425 °C. The pMTJ thermal budget is limited by the synthetic antiferromagnetic hard layer which is stable up to 425 °C annealing temperature while the storage layer is stable up to 455 °C.

  8. Electric-Field Modulation of Interface Magnetic Anisotropy and Spin Reorientation Transition in (Co/Pt)3/PMN-PT Heterostructure.

    Science.gov (United States)

    Sun, Ying; Ba, You; Chen, Aitian; He, Wei; Wang, Wenbo; Zheng, Xiaoli; Zou, Lvkuan; Zhang, Yijun; Yang, Qu; Yan, Lingjia; Feng, Ce; Zhang, Qinghua; Cai, Jianwang; Wu, Weida; Liu, Ming; Gu, Lin; Cheng, Zhaohua; Nan, Ce-Wen; Qiu, Ziqiang; Wu, Yizheng; Li, Jia; Zhao, Yonggang

    2017-03-16

    We report electric-field control of magnetism of (Co/Pt)3 multilayers involving perpendicular magnetic anisotropy with different Co-layer thicknesses grown on Pb(Mg,Nb)O3-PbTiO3 (PMN-PT) FE substrates. For the first time, electric-field control of the interface magnetic anisotropy, which results in the spin reorientation transition, was demonstrated. The electric-field-induced changes of the bulk and interface magnetic anisotropies can be understood by considering the strain-induced change of magnetoelastic energy and weakening of Pt 5d-Co 3d hybridization, respectively. We also demonstrate the role of competition between the applied magnetic field and the electric field in determining the magnetization of the sample with the coexistence phase. Our results demonstrate electric-field control of magnetism by harnessing the strain-mediated coupling in multiferroic heterostructures with perpendicular magnetic anisotropy and are helpful for electric-field modulations of Dzyaloshinskii-Moriya interaction and Rashba effect at interfaces to engineer new functionalities.

  9. Cosmic-Ray Small-scale Anisotropies and Local Turbulent Magnetic Fields

    Science.gov (United States)

    López-Barquero, V.; Farber, R.; Xu, S.; Desiati, P.; Lazarian, A.

    2016-10-01

    Cosmic-ray anisotropy has been observed in a wide energy range and at different angular scales by a variety of experiments over the past decade. However, no comprehensive or satisfactory explanation has been put forth to date. The arrival distribution of cosmic rays at Earth is the convolution of the distribution of their sources and of the effects of geometry and properties of the magnetic field through which particles propagate. It is generally believed that the anisotropy topology at the largest angular scale is adiabatically shaped by diffusion in the structured interstellar magnetic field. On the contrary, the medium- and small-scale angular structure could be an effect of nondiffusive propagation of cosmic rays in perturbed magnetic fields. In particular, a possible explanation for the observed small-scale anisotropy observed at the TeV energy scale may be the effect of particle propagation in turbulent magnetized plasmas. We perform numerical integration of test particle trajectories in low-β compressible magnetohydrodynamic turbulence to study how the cosmic rays’ arrival direction distribution is perturbed when they stream along the local turbulent magnetic field. We utilize Liouville’s theorem for obtaining the anisotropy at Earth and provide the theoretical framework for the application of the theorem in the specific case of cosmic-ray arrival distribution. In this work, we discuss the effects on the anisotropy arising from propagation in this inhomogeneous and turbulent interstellar magnetic field.

  10. Tunable perpendicular magnetic anisotropy in GdFeCo amorphous films

    Energy Technology Data Exchange (ETDEWEB)

    Ding, Manli, E-mail: md3jx@virginia.edu [Department of Physics, University of Virginia, Charlottesville, VA 22904 (United States); Poon, S. Joseph, E-mail: sjp9x@virginia.edu [Department of Physics, University of Virginia, Charlottesville, VA 22904 (United States)

    2013-08-15

    We report the compositional and temperature dependence of magnetic compensation in amorphous ferrimagnetic Gd{sub x}Fe{sub 93−x}Co{sub 7} alloy films. Magnetic compensation is attributed to the competition between antiferromagnetic coupling of rare-earth (RE) with transition-metal (TM) ions and ferromagnetic interaction between the TM ions. The low-Gd region of x between 20 and 34 was found to exhibit compensation phenomena characterized by a low saturation magnetization and perpendicular magnetic anisotropy (PMA) near the compensation temperature. Compensation temperature was not observed in previously unreported high-Gd region of x=52–59, in qualitative agreement with results from recent model calculations. However, low magnetization was achieved at room temperature, accompanied by a large PMA with coercivity reaching ∼6.6 kOe. The observed perpendicular magnetic anisotropy of amorphous GdFeCo films probably has a structural origin consistent with certain aspects of the atomic-scale anisotropy. Our findings have broadened the composition range of transition metal-rare earth alloys for designing PMA films, making it attractive for tunable magnetic anisotropy in nanoscale devices. - Highlights: ► We measure the magnetic anisotropy of amorphous Gd{sub x}Fe{sub 93−x}Co{sub 7} films. ► The magnetization was controlled by varying the composition and temperature. ► At room temperature a large PMA with coercivity of 6.6 kOe was achieved. ► The PMA has a structural origin consistent with the atomic-scale anisotropy.

  11. Thickness dependence of magnetic anisotropy and domains in amorphous Co40Fe40B20 thin films grown on PET flexible substrates

    Science.gov (United States)

    Tang, Zhenhua; Ni, Hao; Lu, Biao; Zheng, Ming; Huang, Yong-An; Lu, Sheng-Guo; Tang, Minghua; Gao, Ju

    2017-03-01

    The amorphous Co40Fe40B20 (CoFeB) films (5-200 nm in thickness) were grown on flexible polyethylene terephthalate (PET) substrates using the DC magnetron-sputtering method. The thickness dependence of structural and magnetic properties of flexible CoFeB thin films was investigated in detail. The in-plane uniaxial magnetic anisotropy induced by strain as a function of thickness was obtained in flexible CoFeB thin films, and a critical thickness of 150 nm for in-plane magnetic anisotropy was observed. Moreover, the domains and the uniaxial anisotropy as a function of angular direction of applied magnetic field were characterized. The results show potential for designing CoFeB-based flexible spintronic devices in which the physical parameters could be tailored by controlling the thickness of the thin film.

  12. Enhancement of perpendicular magnetic anisotropy and anomalous hall effect in Co/Ni multilayers

    Science.gov (United States)

    Liu, Yiwei; Zhang, Jingyan; Jiang, Shaolong; Liu, Qianqian; Li, Xujing; Yu, Guanghua

    2016-12-01

    The perpendicular magnetic anisotropy (PMA) and the anomalous Hall effect (AHE) in Co/Ni multilayer were optimized by manipulating its interface structure (inducing HfO2 capping layer and Pt insertion) and post-annealing treatment. A strong PMA can be obtained in Co/Ni multilayers with HfO2 capping layer even after annealing at 400 °C. The heavy metal Hf may improve the interfacial spin-orbit coupling, which responsible for the enhanced PMA and high annealing stability. Moreover, the multilayer containing HfO2 capping layer also exhibited high saturation anomalous Hall resistivity through post-annealing, which is 0.85 μΩ cm after annealing at 375 °C, 211% larger than in the sample at deposited state which is only 0.27 μΩ cm. The enhancement of AHE is mainly attributed to the interface scattering through post-annealing treatment.

  13. Anatomy of electric field control of perpendicular magnetic anisotropy at Fe/MgO interfaces

    Science.gov (United States)

    Ibrahim, F.; Yang, H. X.; Hallal, A.; Dieny, B.; Chshiev, M.

    2016-01-01

    The charge-mediated effect of electric field on the perpendicular magnetic anisotropy (PMA) of Fe/MgO interfaces is investigated using first-principles calculations. We present an approach by discussing this effect in relation to the intrinsic dipole field existing at the Fe/MgO interface. A firm correlation between the PMA and the interfacial dipole is established and further verified in the absence of an applied electric field. The on-site projected PMA analysis not only elucidates that the effect of electric field on the PMA extends beyond the interfacial Fe layer, but also shows that the second Fe layer carries the largest contribution to the effect. This observation is interpreted in relation to the orbital hybridization changes induced by applying an electric field.

  14. Determination of perpendicular magnetic anisotropy in ultrathin ferromagnetic films by extraordinary Hall voltage measurement.

    Science.gov (United States)

    Moon, Kyoung-Woong; Lee, Jae-Chul; Choe, Sug-Bong; Shin, Kyung-Ho

    2009-11-01

    A magnetometric technique for detecting the magnetic anisotropy field of ferromagnetic films is described. The technique is based on the extraordinary Hall voltage measurement with rotating the film under an external magnetic field. By analyzing the angle-dependent Hall voltage based on the Stoner-Wohlfarth theory, the magnetic anisotropy field is uniquely determined. The present technique is pertinent especially for ultrathin films with strong intrinsic signal, in contrast to the conventional magnetometric techniques of which the signal is in proportion to the sample volume and geometry.

  15. Geometric control of the magnetization reversal in antidot lattices with perpendicular magnetic anisotropy

    Science.gov (United States)

    Gräfe, Joachim; Weigand, Markus; Träger, Nick; Schütz, Gisela; Goering, Eberhard J.; Skripnik, Maxim; Nowak, Ulrich; Haering, Felix; Ziemann, Paul; Wiedwald, Ulf

    2016-03-01

    While the magnetic properties of nanoscaled antidot lattices in in-plane magnetized materials have widely been investigated, much less is known about the microscopic effect of hexagonal antidot lattice patterning on materials with perpendicular magnetic anisotropy. By using a combination of first-order reversal curve measurements, magnetic x-ray microscopy, and micromagnetic simulations we elucidate the microscopic origins of the switching field distributions that arise from the introduction of antidot lattices into out-of-plane magnetized GdFe thin films. Depending on the geometric parameters of the antidot lattice we find two regimes with different magnetization reversal processes. For small antidots, the reversal process is dominated by the exchange interaction and domain wall pinning at the antidots drives up the coercivity of the system. On the other hand, for large antidots the dipolar interaction is dominating which leads to fragmentation of the system into very small domains that can be envisaged as a basis for a bit patterned media.

  16. Interfacial magnetic anisotropy of Co90Zr10 on Pt layer.

    Science.gov (United States)

    Kil, Joon Pyo; Bae, Gi Yeol; Suh, Dong Ik; Choi, Won Joon; Noh, Jae Sung; Park, Wanjun

    2014-11-01

    Spin Transfer Torque (STT) is of great interest in data writing scheme for the Magneto-resistive Random Access Memory (MRAM) using Magnetic Tunnel Junction (MTJ). Scalability for high density memory requires ferromagnetic electrodes having the perpendicular magnetic easy axis. We investigated CoZr as the ferromagnetic electrode. It is observed that interfacial magnetic anisotropy is preferred perpendicular to the plane with thickness dependence on the interfaces with Pt layer. The anisotropy energy (K(u)) with thickness dependence shows a change of magnetic-easy-axis direction from perpendicular to in-plane around 1.2 nm of CoZr. The interfacial anisotropy (K(i)) as the directly related parameters to switching and thermal stability, are estimated as 1.64 erg/cm2 from CoZr/Pt multilayered system.

  17. Exchange coupling in hybrid anisotropy magnetic multilayers quantified by vector magnetometry

    Energy Technology Data Exchange (ETDEWEB)

    Morrison, C., E-mail: C.Morrison.2@warwick.ac.uk; Miles, J. J.; Thomson, T. [School of Computer Science, University of Manchester, Manchester M13 9PL (United Kingdom); Anh Nguyen, T. N. [Materials Physics, School of ICT, KTH Royal Institute of Technology, Electrum 229, 164 40 Kista (Sweden); Spintronics Research Group, Laboratory for Nanotechnology (LNT), VNU-HCM, Ho Chi Minh City (Viet Nam); Fang, Y.; Dumas, R. K. [Department of Physics, University of Gothenburg, 412 96 Gothenburg (Sweden); Åkerman, J. [Materials Physics, School of ICT, KTH Royal Institute of Technology, Electrum 229, 164 40 Kista (Sweden); Department of Physics, University of Gothenburg, 412 96 Gothenburg (Sweden)

    2015-05-07

    Hybrid anisotropy thin film heterostructures, where layers with perpendicular and in-plane anisotropy are separated by a thin spacer, are novel materials for zero/low field spin torque oscillators and bit patterned media. Here, we report on magnetization reversal and exchange coupling in a archetypal Co/Pd (perpendicular)-NiFe (in-plane) hybrid anisotropy system studied using vector vibrating sample magnetometry. This technique allows us to quantify the magnetization reversal in each individual magnetic layer, and measure of the interlayer exchange as a function of non-magnetic spacer thickness. At large (>1 nm) spacer thicknesses Ruderman-Kittel-Kasuya-Yosida-like exchange dominates, with orange-peel coupling providing a significant contribution only for sub-nm spacer thickness.

  18. Ferromagnetic resonance measurements of (Co/Ni/Co/Pt) multilayers with perpendicular magnetic anisotropy

    Science.gov (United States)

    Sbiaa, R.; Shaw, J. M.; Nembach, H. T.; Bahri, M. Al; Ranjbar, M.; Åkerman, J.; Piramanayagam, S. N.

    2016-10-01

    Multilayers of [Co/Ni(t)/Co/Pt]×8 with varying Ni thickness were investigated for possible use as a free layer in magnetic tunnel junctions and spintronics devices. The thickness t of the Ni sub-layer was varied from 0.3 nm to 0.9 nm and the resulting magnetic properties were compared with (Co/Ni) and (Co/Pt) multilayers. As determined from magnetic force microscopy, magnetometry and ferromagnetic resonance measurements, all multilayers exhibited perpendicular magnetic anisotropy. Compared with (Co/Pt) multilayers, the sample with t of 0.9 nm showed almost the same anisotropy field of μ 0 H k   =  1.15 T but the damping constant was 40% lower. These characteristics make these multilayers attractive for spin torque based magnetoresistive devices with perpendicular anisotropy.

  19. Effective anisotropy and coercivity in nanocrystalline single-phase NdFeB permanent magnetic material

    Institute of Scientific and Technical Information of China (English)

    韩广兵; 高汝伟; 冯维存; 刘汉强; 王标; 张鹏; 陈伟; 李卫; 郭永权

    2003-01-01

    The effect of exchange-coupling interaction on the effective anisotropy and its varying tendency in nanocrystalline single-phase NdFeB permanent magnetic material have been investigated. The results show that the exchange-coupling interaction between grains makes the effective anisotropy of material, Keff, decrease with the reduction of grain size. The variation of Keff is basically the same as that of coercivity. The decrease in effective anisotropy is the main reason of the reduction of coercivity for nanocrystalline single-phase NdFeB permanent magnetic material. In order to get high anisotropy and coercivity in nanocrystalline single-phase NdFeB permanent material, the grain size should be larger than 35 nm.

  20. Determination of anisotropy constants of protein encapsulated iron oxide nanoparticles by electron magnetic resonance

    Energy Technology Data Exchange (ETDEWEB)

    Li Hongyan [Department of Physics, Montana State University, Bozeman, MT 59717 (United States); Center for Bio-Inspired Nanomaterials, Montana State University, Bozeman, MT 59717 (United States); Klem, Michael T.; Sebby, Karl B.; Singel, David J. [Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717 (United States); Center for Bio-Inspired Nanomaterials, Montana State University, Bozeman, MT 59717 (United States); Young, Mark [Department of Plant Sciences and Plant Pathology, Montana State University, Bozeman, MT 59717 (United States); Center for Bio-Inspired Nanomaterials, Montana State University, Bozeman, MT 59717 (United States); Douglas, Trevor [Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717 (United States); Center for Bio-Inspired Nanomaterials, Montana State University, Bozeman, MT 59717 (United States); Idzerda, Yves U. [Department of Physics, Montana State University, Bozeman, MT 59717 (United States); Center for Bio-Inspired Nanomaterials, Montana State University, Bozeman, MT 59717 (United States)], E-mail: Idzerda@montana.edu

    2009-02-15

    Angle-dependent electron magnetic resonance was performed on 4.9, 8.0, and 19 nm iron oxide nanoparticles encapsulated within protein capsids and suspended in water. Measurements were taken at liquid nitrogen temperature after cooling in a 1 T field to partially align the particles. The angle dependence of the shifts in the resonance field for the iron oxide nanoparticles (synthesized within Listeria-Dps, horse spleen ferritin, and cowpea chlorotic mottle virus) all show evidence of a uniaxial anisotropy. Using a Boltzmann distribution for the particles' easy-axis direction, we are able to use the resonance field shifts to extract a value for the anisotropy energy, showing that the anisotropy energy density increases with decreasing particle size. This suggests that surface anisotropy plays a significant role in magnetic nanoparticles of this size.

  1. Field-dependent perpendicular magnetic anisotropy in CoFeB thin films

    Energy Technology Data Exchange (ETDEWEB)

    Barsukov, I., E-mail: ibarsuko@uci.edu; Krivorotov, I. N. [Physics and Astronomy, University of California, Irvine, California 92697 (United States); Fu, Yu [INAC/CEA, Grenoble, 17 avenue des Martyrs, Grenoble 38054 (France); Fakultät für Physik and Center for Nanointegration (CeNIDE), Universität Duisburg-Essen, Duisburg 47048 (Germany); Gonçalves, A. M.; Sampaio, L. C. [Physics and Astronomy, University of California, Irvine, California 92697 (United States); Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud, 150, Rio de Janeiro 22.290-180, RJ (Brazil); Spasova, M.; Farle, M. [Fakultät für Physik and Center for Nanointegration (CeNIDE), Universität Duisburg-Essen, Duisburg 47048 (Germany); Arias, R. E. [Departamento de Física, FCFM, Universidad de Chile, Casilla 487-3, Santiago (Chile)

    2014-10-13

    We report ferromagnetic resonance measurements of perpendicular magnetic anisotropy in thin films of Ta/Co{sub 20}Fe{sub 60}B{sub 20}/MgO as a function of the Co{sub 20}Fe{sub 60}B{sub 20} layer thickness. The first and second order anisotropy terms show unexpectedly strong dependence on the external magnetic field applied to the system during the measurements. We propose strong interfacial spin pinning as a possible origin of the field-dependent anisotropy. Our results imply that high-field anisotropy measurements cannot be directly used for quantitative evaluation of zero-field performance parameters of CoFeB-based devices such as spin torque memory.

  2. Tunnel magnetoresistance in thermally robust Mo/CoFeB/MgO tunnel junction with perpendicular magnetic anisotropy

    Directory of Open Access Journals (Sweden)

    B. Fang

    2015-06-01

    Full Text Available We report on tunnel magnetoresistance and electric-field effect in the Mo buffered and capped CoFeB/MgO magnetic tunnel junctions (MTJs with perpendicular magnetic anisotropy. A large tunnel magnetoresistance of 120% is achieved. Furthermore, this structure shows greatly improved thermal stability and stronger electric-field-induced modulation effect in comparison with the Ta/CoFeB/MgO-based MTJs. These results suggest that the Mo-based MTJs are more desirable for next generation spintronic devices.

  3. Sequential assembly of phototunable ferromagnetic ultrathin films with perpendicular magnetic anisotropy.

    Science.gov (United States)

    Suda, Masayuki; Einaga, Yasuaki

    2009-01-01

    Getting organized: Assemblies of ferromagnetic FePt nanoparticles were generated with large perpendicular magnetic anisotropy by a magnetic-field-assisted layer-by-layer method, and subsequently layer-by-layer films consisting of L1(0)-FePt nanoparticles and organic polymers were prepared. These films are phototunable when photochromic molecules are used as polymer layers.

  4. A new approach for calculation of relaxation time and magnetic anisotropy of ferrofluids containing superparmagnetic nanoparticles

    Directory of Open Access Journals (Sweden)

    Ahmadi R.

    2012-01-01

    Full Text Available In this work, a new approach is described for the calculation of the relaxation time and magnetic anisotropy energy of magnetic nanoparticles. Ferrofluids containing monodispersed magnetite nanoparticles were synthesized via hydrothermal method and then heated using the 10 kA/m external AC magnetic fields in three different frequencies: 10, 50 and 100 kHz. By measuring the temperature variations during the application of the magnetic field, the total magnetic time constant including both Brownian and Neel relaxation times can be calculated. By measuring the magnetic core size and hydrodynamic size of particles, the magnetic anisotropy can be calculated too. Synthesized ferrofluids were characterized via TEM, XRD, VSM and PCS techniques and the results were used for the mentioned calculations.

  5. Anisotropy and magnetic property of M-type SrAl4Fe8O19 powders prepared via co-precipitation method.

    Science.gov (United States)

    He, Haiyan

    2010-01-01

    Al-substituted M-type hexaferrite is a high anisotropy material. In this paper, we report the coprecipitation synthesis of SrAl4Fe8O19 powder and the effects of preheating temperature and calcining time on the anisotropy and magnetic property of the powders. The XRD analysis indicated that the SrAl4Fe8O19 powder requests a calcining time of 3 h for formation of pure hexagonal platelike particle, and preheat treatment at 300 degrees C was favorable for the formation of single phase SrAl4Fe8O19. Calculation of c/a value with XRD data indicated that the Al-substitution and preheat treatment induced notable increase of the atomic lattice anisotropy. SEM analysis revealed that shape anisotropy of the samples decreases with the preheating. Magnetic measurement indicates that coercivity decrease and magnetization increase as decrease in shape anisotropy, but have no concern with the atomic lattice anisotropy. The no-preheated sample has a maximum coercivity up to 3.9947 kG and the sample preheated at 400 degrees C has a maximum magnetization up to 32.266 A.m2.kg(-1). The present article discusses some important patents related to catalysis of Mg-containing spinel compounds.

  6. Effect of exchange-coupling interaction on anisotropy of grain in nanoscaled magnets

    Science.gov (United States)

    Sun, Yan; Gao, Ru-wei; Han, Guang-bing; Liu, Min; Han, Bai-ping

    2007-01-01

    The effect of inter-grain exchange-coupling interaction on the anisotropy of grain in nanoscaled magnets has been investigated by putting forward an expression of anisotropy at grain boundary, K1ij(r), which is suitable for different coupling conditions, and expresses well the coherency between soft and hard grains. The average anisotropy of grain has been calculated based on K1ij(r) and the theory of partial exchange-coupling interaction. It has been found that the average anisotropy of hard or soft grain, or , increases with increasing grain size D monotonously when hard-hard or soft-soft grains couple. When soft-hard grains touch each other, with increasing D, the variation of average anisotropy of soft-hard grain depends on the anisotropy at grain interface K1sh(0), which denotes the affection degree of hard grain on the anisotropy of soft grain. Compared with other results, it is more reasonable that K1sh(0) ranges from 0.5K1h to 0.7K1h. The variations of anisotropy with D we calculated are consistent with those of coercivities given by other authors when K1ij(0) is fixed in a certain range.

  7. X-ray magnetic circular dichroism and reflection anisotropy spectroscopy Kerr effect studies of capped magnetic nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Cunniffe, J. P.; McNally, D.E.; Liberati, M.; Arenholz, E.; McGuinness, C.; McGilp, J. F.

    2010-03-02

    Aligned Co wires grown on Pt(997) under ultra-high vacuum conditions have been capped successfully by the epitaxial growth of Au monolayers (ML) at room temperature. The samples were kept under vacuum except when transferring between apparatus or when making some of the measurements. No degradation of the Co wires was detected during the measurements. The magneto-optic response of the system was measured using X-ray magnetic circular dichroism (XMCD) at the Co L{sub 2,3} edge and reflection anisotropy spectroscopy (RAS) at near normal incidence, which is sensitive to the normal component of the out-of-plane magnetization via the Kerr effect (MOKE). Capping the wires significantly impacts their magnetic properties. Comparison of the magneto-optic response of the system at X-ray and optical energies reveals small differences that are attributed to the induced moment in the Pt substrate and Au capping layer not picked up by the element specific XMCD measurements. The sensitivity of RAS-MOKE is sufficient to allow the determination of the easy axis direction of the capped wires to within a few degrees. The results for a 6-atom-wide Co wire sample, capped with 6 ML of Au, are consistent with the capped wires possessing perpendicular magnetization.

  8. Perpendicular magnetic anisotropy in CoXPd100-X alloys for magnetic tunnel junctions

    Science.gov (United States)

    Clark, B. D.; Natarajarathinam, A.; Tadisina, Z. R.; Chen, P. J.; Shull, R. D.; Gupta, S.

    2017-08-01

    CoFeB/MgO-based perpendicular magnetic tunnel junctions (p-MTJ's) with high anisotropy and low damping are critical for spin-torque transfer random access memory (STT-RAM). Most schemes of making the pinned CoFeB fully perpendicular require ferrimagnets with high damping constants, a high temperature-grown L10 alloy, or an overly complex multilayered synthetic antiferromagnet (SyAF). We report a compositional study of perpendicular CoxPd alloy-pinned Co20Fe60B20/MgO based MTJ stacks, grown at moderate temperatures in a planetary deposition system. The perpendicular anisotropy of the CoxPd alloy films can be tuned based on the layer thickness and composition. The films were characterized by alternating gradient magnetometry (AGM), energy-dispersive X-rays (EDX), and X-ray diffraction (XRD). Current-in-plane tunneling (CIPT) measurements have also been performed on the compositionally varied CoxPd MTJ stacks. The CoxPd alloy becomes fully perpendicular at approximately x = 30% (atomic fraction) Co. Full-film MTJ stacks of Si/SiO2/MgO (13)/CoXPd100-x (50)/Ta (0.3)/CoFeB (1)/MgO (1.6)/CoFeB (1)/Ta (5)/Ru (10), with the numbers enclosed in parentheses being the layer thicknesses in nm, were sputtered onto thermally oxidized silicon substrates and in-situ lamp annealed at 400 °C for 5 min. CIPT measurements indicate that the highest TMR is observed for the CoPd composition with the highest perpendicular magnetic anisotropy.

  9. Perpendicular magnetic anisotropy of CoPt-AlN composite film with nano-fiber structure

    Energy Technology Data Exchange (ETDEWEB)

    Chen, C.C.; Toyoshima, H.; Hashimoto, M. [University of Electro-Communications, Department of Applied Physics and Chemistry, Tokyo (Japan); Shi, J.; Nakamura, Y. [Tokyo Institute of Technology, Department of Metallurgy and Ceramics Science, Tokyo (Japan)

    2005-06-01

    Co-Pt-AlN films were prepared by sputtering a Co-Pt-Al composite target in Ar+N{sub 2} atmosphere. Upon thermal annealing at elevated temperatures, fcc CoPt and a-AlN are formed in the films as phases separated from one other. Both phases develop as fiber-like columnar grains vertical to the substrate and with their lateral size less than 10 nm. Because of the shape anisotropy of the magnetic fiber grains the CoPt-AlN film shows a perpendicular magnetic anisotropy at a thickness equal to or larger than about 25 nm while the Co-TiN and CoPt-TiO{sub 2} films do not unless their thicknesses reach 50 and 100 nm, respectively. This suggests that both the shape anisotropy of the CoPt magnetic fiber grains and their mutual separation in an a-AlN medium work more effectively in the formation with the perpendicular magnetic anisotropy. Such a perpendicular magnetic anisotropy of the CoPt-AlN film associated with the nano-scale feature makes it a very promising candidate for future recording media with ultra-high area density. (orig.)

  10. Excitation of magnetic inhomogeneities in three-layer ferromagnetic structure with different parameters of the magnetic anisotropy and exchange

    Energy Technology Data Exchange (ETDEWEB)

    Ekomasov, E.G., E-mail: EkomasovEG@gmail.com [Bashkir State University, 32, Validy Str., Ufa, 450076 (Russian Federation); Murtazin, R.R. [Bashkir State University, 32, Validy Str., Ufa, 450076 (Russian Federation); Nazarov, V.N. [Institute of Molecule and Crystal Physics Ufa Research Centre of Russian Academy of Sciences, Prospekt Oktyabrya 151, Ufa, 450075 (Russian Federation)

    2015-07-01

    The generation and evolution of magnetic inhomogeneities, emerging in a thin flat layer with the parameters of the magnetic anisotropy and exchange interaction, with the parameters different from other two thick layers of the three-layer ferromagnetic structure, were investigated. The parameters ranges that determine the possibility of their existence were found. The possibility of the external magnetic field influence on the structure and dynamic properties of localized magnetic inhomogeneities was shown. - Highlights: • The generation of magnetic inhomogeneities in the three-layer ferromagnetic. • The influence of an external field on the parameters of magnetic inhomogeneities. • Numerical study of the structure and dynamics of magnetic inhomogeneities.

  11. Magnetic anisotropy of thin sputtered MgB2 films on MgO substrates in high magnetic fields

    Directory of Open Access Journals (Sweden)

    Savio Fabretti

    2014-03-01

    Full Text Available We investigated the magnetic anisotropy ratio of thin sputtered polycrystalline MgB2 films on MgO substrates. Using high magnetic field measurements, we estimated an anisotropy ratio of 1.35 for T = 0 K with an upper critical field of 31.74 T in the parallel case and 23.5 T in the perpendicular case. Direct measurements of a magnetic-field sweep at 4.2 K show a linear behavior, confirmed by a linear fit for magnetic fields perpendicular to the film plane. Furthermore, we observed a change of up to 12% of the anisotropy ratio in dependence of the film thickness.

  12. Copper dusting effects on perpendicular magnetic anisotropy in Pt/Co/Pt tri-layers

    Directory of Open Access Journals (Sweden)

    Vineeth Mohanan Parakkat

    2016-05-01

    Full Text Available The effect of Cu dusting on perpendicular magnetic anisotropy of sputter grown Pt/Co/Pt stack in which the Cu layer is in proximity with that of Co is investigated in this work. We used magneto optic Kerr effect microscopy measurements to study the variation in the reversal mechanisms in films with Co thicknesses below 0.8nm by systematically varying their perpendicular magnetic anisotropy using controlled Cu dusting. Cu dusting was done separately above and below the cobalt layer in order to understand the role of bottom and top Pt layers in magnetization reversal mechanisms of sputtered Pt/Co/Pt stack. The introduction of even 0.3nm thick Cu layer below the cobalt layer drastically affected the perpendicular magnetic anisotropy as evident from the nucleation behavior. On the contrary, even a 4nm thick top Cu layer had little effect on the reversal mechanism. These observations along with magnetization data was used to estimate the role of top and bottom Pt in the origin of perpendicular magnetic anisotropy as well as magnetization switching mechanism in Pt/Co/Pt thin films. Also, with an increase in the bottom Cu dusting from 0.2 to 0.4nm there was an increase in the number of nucleation sites resulting in the transformation of domain wall patterns from a smooth interface type to a finger like one and finally to maze type.

  13. Copper dusting effects on perpendicular magnetic anisotropy in Pt/Co/Pt tri-layers

    Science.gov (United States)

    Parakkat, Vineeth Mohanan; Ganesh, K. R.; Anil Kumar, P. S.

    2016-05-01

    The effect of Cu dusting on perpendicular magnetic anisotropy of sputter grown Pt/Co/Pt stack in which the Cu layer is in proximity with that of Co is investigated in this work. We used magneto optic Kerr effect microscopy measurements to study the variation in the reversal mechanisms in films with Co thicknesses below 0.8nm by systematically varying their perpendicular magnetic anisotropy using controlled Cu dusting. Cu dusting was done separately above and below the cobalt layer in order to understand the role of bottom and top Pt layers in magnetization reversal mechanisms of sputtered Pt/Co/Pt stack. The introduction of even 0.3nm thick Cu layer below the cobalt layer drastically affected the perpendicular magnetic anisotropy as evident from the nucleation behavior. On the contrary, even a 4nm thick top Cu layer had little effect on the reversal mechanism. These observations along with magnetization data was used to estimate the role of top and bottom Pt in the origin of perpendicular magnetic anisotropy as well as magnetization switching mechanism in Pt/Co/Pt thin films. Also, with an increase in the bottom Cu dusting from 0.2 to 0.4nm there was an increase in the number of nucleation sites resulting in the transformation of domain wall patterns from a smooth interface type to a finger like one and finally to maze type.

  14. Experimental evidence of skyrmion-like configurations in bilayer nanodisks with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Stebliy, Maxim E., E-mail: stebliyme@gmail.com; Kolesnikov, Alexander G.; Davydenko, Alexander V.; Ognev, Alexey V.; Samardak, Alexander S.; Chebotkevich, Ludmila A. [Laboratory of Thin Film Technologies, School of Natural Sciences, Far Eastern Federal University, Vladivostok 690950 (Russian Federation)

    2015-05-07

    Formation and existence of magnetic skyrmion-like configurations in bilayer nanodisks (Ta(3 nm)/[Co(0.37 nm)/Ni(0.58 nm)]{sub 10}){sub 2} with perpendicular magnetic anisotropy are shown experimentally at room temperature. Magnetization reversal through the skyrmion state is studied using magnetic hysteresis measurements. An evolution of skyrmion configurations in the nanodisk structure is analyzed. Experimental methods and micromagnetic simulations help to understand the magnetization reversal processes occurring through the stable skyrmion-like configurations. Formation of the intermediate C-states during magnetization reversal is demonstrated. The skyrmion number for all possible spin configurations is calculated.

  15. Preparation of Mn{sub 3-x}Ga Heusler thin films with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Glas, Manuel; Ebke, Daniel; Thomas, Patrick; Reiss, Guenter [Thin Films and Physics of Nanostructures, Physics Department, Bielefeld University (Germany)

    2011-07-01

    Recently, the integration of materials with perpendicular magnetic anisotropy into magnetic tunnel junctions (MTJs) has found a lot of attraction due to the predicted lowered current densities for spin transfer switching and a higher thermal stability. Because of the predicted high spin polarization and the low magnetic moment Mn{sub 3}Ga is a promising material for future spin torque transfer (STT) magnetic switching devices. For this work, we have fabricated Mn{sub 3-x}Ga Heusler thin films with varying stoichiometries into half magnetic tunnel junctions. The effect of Heusler film composition will be discussed with respect to the magnetic and crystal properties.

  16. High perpendicular magnetic anisotropy in D022-Mn3+xGe tetragonal Heusler alloy films

    Science.gov (United States)

    Sugihara, A.; Mizukami, S.; Yamada, Y.; Koike, K.; Miyazaki, T.

    2014-03-01

    We prepared D022-Mn3+xGe (-0.67 ≤ x ≤ 0.35) epitaxial thin films on MgO(001) substrates with Cr(001) buffer layers and systematically investigated the dependence of their perpendicular magnetic anisotropy constant, saturation magnetization, coercivity, and tetragonal axial ratio (c/a) on their composition and substrate temperature. Single-phase D022 crystal structures were formed in films with compositions of 0 ≤ x ≤ 0.35, prepared at 400 °C. The D022-Mn3Ge films exhibited perpendicular magnetization with a magnetic squareness close to unity. Performing magnetic torque measurements at an applied field of 140 kOe, we estimated a perpendicular magnetic anisotropy constant of 11.8 ± 0.5 Merg/cm3, the highest and the most reliable value yet reported.

  17. Determination of the in-plane anisotropy field in hexagonal systems via rotational magnetization: Theoretical model and Monte Carlo simulations

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The magnetic anisotropy field in thin films with in-plane uniaxial anisotropy can be deduced from the VSM magnetization curves measured in magnetic fields of constant magnitudes. This offers a new possibility of applying rotational magnetization curves to determine the firstand second-order anisotropy constant in these films. In this paper we report a theoretical derivation of rotational magnetization curve in hexagonal crystal system with easy-plane anisotropy based on the principle of the minimum total energy. This model is applied to calculate and analyze the rotational magnetization process for magnetic spherical particles with hexagonal easy-plane anisotropy when rotating the external magnetic field in the basal plane. The theoretical calculations are consistent with Monte Carlo simulation results. It is found that to well reproduce experimental curves, the effect of coercive force on the magnetization reversal process should be fully considered when the intensity of the external field is much weaker than that of the anisotropy field. Our research proves that the rotational magnetization curve from VSM measurement provides an effective access to analyze the in-plane anisotropy constant K3 in hexagonal compounds, and the suitable experimental condition to measure K3 is met when the ratio of the magnitude of the external field to that of the anisotropy field is around 0.2.

  18. Spin waves in terbium. III. Magnetic anisotropy at zero wave vector

    DEFF Research Database (Denmark)

    Houmann, Jens Christian Gylden; Jensen, J.; Touborg, P.

    1975-01-01

    The energy gap at zero wave vector in the spin-wave dispersion relation of ferromagnetic. Tb has been studied by inelastic neutron scattering. The energy was measured as a function of temperature and applied magnetic field, and the dynamic anisotropy parameters were deduced from the results...... the effects of zero-point deviations from the fully aligned ground state, and we tentatively propose polarization-dependent two-ion couplings as their origin........ The axial anisotropy is found to depend sensitively on the orientation of the magnetic moments in the basal plane. This behavior is shown to be a convincing indication of considerable two-ion contributions to the magnetic anisotropy at zero wave vector. With the exception of the sixfold basal...

  19. Magnetic fluctuation power near proton temperature anisotropy instability thresholds in the solar wind

    CERN Document Server

    Bale, S D; Howes, G G; Quataert, E; Salem, C; Sundkvist, D

    2009-01-01

    The proton temperature anisotropy in the solar wind is known to be constrained by the theoretical thresholds for pressure anisotropy-driven instabilities. Here we use approximately 1 million independent measurements of gyroscale magnetic fluctuations in the solar wind to show for the first time that these fluctuations are enhanced along the temperature anisotropy thresholds of the mirror, proton oblique firehose, and ion cyclotron instabilities. In addition, the measured magnetic compressibility is enhanced at high plasma beta ($\\beta_\\parallel \\gtrsim 1$) along the mirror instability threshold but small elsewhere, consistent with expectations of the mirror mode. The power in this frequency (the 'dissipation') range is often considered to be driven by the solar wind turbulent cascade, an interpretation which should be qualified in light of the present results. In particular, we show that the short wavelength magnetic fluctuation power is a strong function of collisionality, which relaxes the temperature aniso...

  20. Torque magnetometry analysis of magnetic anisotropy distribution in Ni nanowire arrays

    Energy Technology Data Exchange (ETDEWEB)

    Vega, Victor; Prida, Victor M.; Garcia, Jose Angel [Dept. Fisica, Universidad de Oviedo, Asturias (Spain); Vazquez, Manuel [Instituto de Ciencia de Materiales de Madrid, CSIC, Madrid (Spain)

    2011-03-15

    Highly ordered arrays of Ni nanowires have been prepared by pulsed electrochemical deposition into nanopores of anodic alumina membranes (NAAMs) used as templates. They have been experimentally characterized by magnetic torque measurements and vibrating sample magnetometer (VSM) techniques in order to determine the magnetic anisotropy of the hexagonal array of nanowires. A detailed analysis of the experimental data has been performed based on a phenomenological model taking into account the influence of the nanowire shape anisotropy added to the dipolar magnetostatic interactions among them. An overall agreement is obtained between the simulations derived from the model and the experimental magnetic torque anisotropy curves. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  1. Electrodeposition of Fe/Au(1 1 1) ultrathin layers with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Guendel, A. [Laboratoire de Physique de la Matiere Condensee (CNRS UMR 7643), Ecole Polytechnique, F-91128 Palaiseau (France) and Laboratorio de Magnetismo, Instituto de Fisica-UFRGS 91501-970 Porto Alegre RS (Brazil)]. E-mail: gundel@smail.ufsm.br; Devolder, T. [Institut d' Electronique Fondamentale (CNRS UMR 8622) Bat. 220, Universite Paris-Sud, F-91405 Orsay (France); Chappert, C. [Institut d' Electronique Fondamentale (CNRS UMR 8622) Bat. 220, Universite Paris-Sud, F-91405 Orsay (France); Schmidt, J.E. [Laboratorio de Magnetismo, Instituto de Fisica--UFRGS 91501-970 Porto Alegre RS (Brazil); Cortes, R. [Laboratoire de Physique de la Matiere Condensee (CNRS UMR 7643), Ecole Polytechnique, F-91128 Palaiseau (France); Allongue, P. [Laboratoire de Physique de la Matiere Condensee (CNRS UMR 7643), Ecole Polytechnique, F-91128 Palaiseau (France)

    2004-12-31

    The magnetic state of electrodeposited iron on Au(1 1 1) substrates is investigated during the electrodeposition process by means of in situ alternating gradient force magnetometer (AGFM) and in situ perpendicular magneto-optic Kerr effect measurements (PMOKE). A perpendicular magnetic anisotropy (PMA) is observed for a thickness below 2 monolayers (ML). In situ STM observations of the initial stages of iron growth and ex situ EXAFS are used to correlate the structure of films to their magnetic properties.

  2. Structure-induced spin reorientation in magnetic nanostructures

    Science.gov (United States)

    Neumann, Alexander; Frauen, Axel; Vollmers, Julian; Meyer, Andreas; Oepen, Hans Peter

    2016-09-01

    We report on structuring-induced changes of the magnetic anisotropy of cylindrical nanostructures which are carved out of thin Pt/Co/Pt films. The magnetic properties of films and structures with a diameter of about 34 nm were investigated via magneto-optic Kerr effect. The magnetic anisotropy is determined for both films and nanostructures for varying Co thicknesses (0.5-7 nm). In general, the nanostructures exhibit larger perpendicular anisotropy than the films. On thickness increase of the Co layer two spin reorientation transitions at about 2.2 and 5 nm are found. At 2.2 nm the nanostructures exhibit the transition from perpendicular to in-plane orientation of magnetization while at 5 nm the reversed transition is found. The variation of the magnetic anisotropy of the Co nanostructures is not solely caused by the change of shape anisotropy. The net change, corrected for the shape, reveals a reduction of strain in the thinnest Co layers while the increase of the anisotropy of the nanostructures at higher Co thicknesses is caused by a transformation of the Co lattice from fcc to hcp.

  3. Structure and magnetic anisotropy evolution in Au/Co/Au sandwiches upon thermal treatment

    Energy Technology Data Exchange (ETDEWEB)

    Wawro, A.; Kurant, Z.; Baczewski, L.T.; Pankowski, P.; Pelka, J.B.; Maneikis, A. [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw (Poland); Bojko, A.; Zablotskii, V.; Maziewski, A. [Institute of Experimental Physics, University of Bialystok, ul. Lipowa 41, 15-424 Bialystok (Poland)

    2006-01-01

    The correlation between structural and magnetic properties of Au(111)/Co(0001)/Au(111) sandwiches with perpendicular magnetic anisotropy, grown by molecular beam epitaxy, has been studied in details. Thermal treatment in the range between room temperature and 300 C at various stages of samples growth process as well as after its completion is applied as a factor modifying the structure of studied specimens. Annealing at 150 C does not affect substantially either crystalline structure or perpendicular magnetic anisotropy. At 250 C the RHEED pattern of Co layers reveals the loss of the lattice coherence with Au underlayer and the analysis of synchrotron radiation reflectometry leads to the conclusion that the continuity of Co layers is lost. Structural evolution upon thermal treatment is well correlated with changes of magnetic anisotropy studied by magnetooptical Kerr effect. After annealing at 250 C magnetization switches from out-of-plane to in-plane orientation, which is explained in terms of interfacial and magnetoelastic contributions to the sample magnetic anisotropy. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. Magnetic and elastic anisotropy in magnetorheological elastomers using nickel-based nanoparticles and nanochains

    Science.gov (United States)

    Landa, Romina A.; Soledad Antonel, Paula; Ruiz, Mariano M.; Perez, Oscar E.; Butera, Alejandro; Jorge, Guillermo; Oliveira, Cristiano L. P.; Negri, R. Martín

    2013-12-01

    magnetorheological composites with anisotropic properties, with larger anisotropy when using nanochains. For instance, the magnetic remanence, the FMR field, and the elastic response to compression are higher when measured parallel to the needles (about 30% with nanochains as fillers). Analogously, the elastic response is also anisotropic, with larger anisotropy when using nanochains as fillers. Therefore, all experiments performed confirm the high potential of nickel nanochains to induce anisotropic effects in magnetorheological materials.

  5. Anisotropy and Microstructure of High Coercivity Rare Earth Iron Permanent Magnets, List of Papers Published

    Science.gov (United States)

    1989-01-01

    aublattice anisotropy. 1. Introduction The compound Nd2Fe14B is the basic material for the production of high quality Permanent magniets [1, 21. It...the in-plane anisotropy is in disagreement with the observed different magnetiza- tion curves for Nd2Fe14B in the [1001 and [1101 directions [101... Nd2Fe14B based permanent magnets so far. The grain size of the magnets also strongly der ds on the processing technique. The electron micrographs of Fig

  6. Shape anisotropy enhanced optomagnetic measurement for prostate-specific antigen detection via magnetic chain formation

    DEFF Research Database (Denmark)

    Tian, Bo; Wetterskog, Erik; Qiu, Zhen

    2017-01-01

    We demonstrate a homogeneous biosensor for the detection of multivalent targets by combination of magnetic nanoparticle (MNP) chains and a low-cost 405 nm laser-based optomagnetic system. The MNP chains are assembled in a rotating magnetic field and stabilized by multivalent target molecules...... anisotropy), and directly increasing the optomagnetic signal (via optical shape anisotropy). We achieve a limit of detection (LOD) of 5.5 pM (0.82 ng/mL) for the detection of a model multivalent molecule, biotinylated anti-streptavidin, in PBS. For the measurements of prostate-specific antigen (PSA) in 50...

  7. Entanglement and Sources of Magnetic Anisotropy in Radical Pair-Based Avian Magnetoreceptors

    Science.gov (United States)

    Hogben, Hannah J.; Biskup, Till; Hore, P. J.

    2012-11-01

    One of the principal models of magnetic sensing in migratory birds rests on the quantum spin dynamics of transient radical pairs created photochemically in ocular cryptochrome proteins. We consider here the role of electron spin entanglement and coherence in determining the sensitivity of a radical pair-based geomagnetic compass and the origins of the directional response. It emerges that the anisotropy of radical pairs formed from spin-polarized molecular triplets could form the basis of a more sensitive compass sensor than one founded on the conventional hyperfine-anisotropy model. This property offers new and more flexible opportunities for the design of biologically inspired magnetic compass sensors.

  8. Entanglement and Sources of Magnetic Anisotropy in Radical Pair-Based Avian Magnetoreceptors

    CERN Document Server

    Hogben, Hannah J; Hore, P J

    2012-01-01

    One of the principal models of magnetic sensing in migratory birds rests on the quantum spin-dynamics of transient radical pairs created photochemically in ocular cryptochrome proteins. We consider here the role of electron spin entanglement and coherence in determining the sensitivity of a radical pair-based geomagnetic compass and the origins of the directional response. It emerges that the anisotropy of radical pairs formed from spin-polarized molecular triplets could form the basis of a more sensitive compass sensor than one founded on the conventional hyper?ne-anisotropy model. This property offers new and more flexible opportunities for the design of biologically inspired magnetic compass sensors.

  9. Ferromagnetic (Ga,Mn)As layers and nanostructures: control of magnetic anisotropy by strain engineering

    Energy Technology Data Exchange (ETDEWEB)

    Wenisch, Jan

    2008-07-01

    This work studies the fundamental connection between lattice strain and magnetic anisotropy in the ferromagnetic semiconductor (Ga,Mn)As. The first chapters provide a general introduction into the material system and a detailed description of the growth process by molecular beam epitaxy. A finite element simulation formalism is developed to model the strain distribution in (Ga,Mn)As nanostructures is introduced and its predictions verified by high-resolution X-ray diffraction methods. The influence of lattice strain on the magnetic anisotropy is explained by an magnetostatic model. A possible device application is described in the closing chapter. (orig.)

  10. Measurement of magnetic anisotropy of multiwalled carbon nanotubes in nematic host

    Science.gov (United States)

    Cirtoaje, Cristina; Petrescu, Emil

    2016-10-01

    The magnetic anisotropy of multiwalled carbon nanotubes (MWCNT-s) is measured using their dispersion in nematic liquid crystal (NLC). Due to their ability to align themselves with inserted nano-particles, NLC are very useful for the study of the physical properties of MWCNT as well as for other micro or nano-particles. Thus an organized system is obtained from the beginning and the influence of initial random orientation is considerably reduced. The average magnetic anisotropy of MWCNT dispersed in NLC was calculated from the system relaxation time and the obtained value (6.61 ×10-5) was in good agreement with other reported results.

  11. Helicity, anisotropies, and their competition in a multiferroic magnet: Insight from the phase diagram

    Science.gov (United States)

    Gvozdikova, M. V.; Ziman, T.; Zhitomirsky, M. E.

    2016-07-01

    Motivated by the complex phase diagram of MnWO4, we investigate the competition between anisotropy, magnetic field, and helicity for the anisotropic next-nearest-neighbor Heisenberg model. Apart from two competing exchanges, which favor a spiral magnetic structure, the model features the biaxial single-ion anisotropy. The model is treated in the real-space mean-field approximation and the phase diagram containing various incommensurate and commensurate states is obtained for different field orientations. We discuss the similarities and differences of the theoretical phase diagram and the experimental diagram of MnWO4.

  12. Engineering spin-orbit torque in Co/Pt multilayers with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Kuo-Feng; Wang, Ding-Shuo; Lai, Chih-Huang, E-mail: chlai@mx.nthu.edu.tw [Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Lin, Hsiu-Hau [Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan (China)

    2015-12-07

    To address thermal stability issues for spintronic devices with a reduced size, we investigate spin-orbit torque in Co/Pt multilayers with strong perpendicular magnetic anisotropy. Note that the spin-orbit torque arises from the global imbalance of the spin currents from the top and bottom interfaces for each Co layer. By inserting Ta or Cu layers to strengthen the top-down asymmetry, the spin-orbit torque efficiency can be greatly modified without compromised perpendicular magnetic anisotropy. Above all, the efficiency builds up as the number of layers increases, realizing robust thermal stability and high spin-orbit-torque efficiency simultaneously in the multilayers structure.

  13. Engineering spin-orbit torque in Co/Pt multilayers with perpendicular magnetic anisotropy

    Science.gov (United States)

    Huang, Kuo-Feng; Wang, Ding-Shuo; Lin, Hsiu-Hau; Lai, Chih-Huang

    2015-12-01

    To address thermal stability issues for spintronic devices with a reduced size, we investigate spin-orbit torque in Co/Pt multilayers with strong perpendicular magnetic anisotropy. Note that the spin-orbit torque arises from the global imbalance of the spin currents from the top and bottom interfaces for each Co layer. By inserting Ta or Cu layers to strengthen the top-down asymmetry, the spin-orbit torque efficiency can be greatly modified without compromised perpendicular magnetic anisotropy. Above all, the efficiency builds up as the number of layers increases, realizing robust thermal stability and high spin-orbit-torque efficiency simultaneously in the multilayers structure.

  14. Anatomy and Giant Enhancement of the Perpendicular Magnetic Anisotropy of Cobalt-Graphene Heterostructures.

    Science.gov (United States)

    Yang, Hongxin; Vu, Anh Duc; Hallal, Ali; Rougemaille, Nicolas; Coraux, Johann; Chen, Gong; Schmid, Andreas K; Chshiev, Mairbek

    2016-01-13

    We report strongly enhanced perpendicular magnetic anisotropy (PMA) of Co films by graphene coating from both first-principles and experiments. Our calculations show that graphene can dramatically boost the surface anisotropy of Co films up to twice the value of its pristine counterpart and can extend the out-of-plane effective anisotropy up to unprecedented thickness of 25 Å. These findings are supported by our experiments on graphene coating on Co films grown on Ir substrate. Furthermore, we report layer-resolved and orbital-hybridization-resolved anisotropy analysis, which help understanding of the physical mechanisms of PMA and more practically can help design structures with giant PMA. As an example, we propose superexchange stabilized Co-graphene heterostructures with a robust constant effective PMA and linearly increasing interfacial anisotropy as a function of film thickness. These findings point toward possibilities to engineer graphene/ferromagnetic metal heterostructures with giant magnetic anisotropy more than 20-times larger compared to conventional multilayers, which constitutes a hallmark for future graphene and traditional spintronic technologies.

  15. Anatomy and Giant Enhancement of the Perpendicular Magnetic Anisotropy of Cobalt-Graphene Heterostructures

    Science.gov (United States)

    Yang, Hongxin; Vu, Anh Duc; Hallal, Ali; Rougemaille, Nicolas; Coraux, Johann; Chen, Gong; Schmid, Andreas K.; Chshiev, Mairbek

    2016-01-01

    We report strongly enhanced perpendicular magnetic anisotropy (PMA) of Co films by graphene coating from both first-principles and experiments. Our calculations show that graphene can dramatically boost the surface anisotropy of Co films up to twice the value of its pristine counterpart and can extend the out-of-plane effective anisotropy up to unprecedented thickness of 25~\\AA. These findings are supported by our experiments on graphene coating on Co films grown on Ir substrate. Furthermore, we report layer-resolved and orbital-hybridization-resolved anisotropy analysis which help understanding the physical mechanisms of PMA and more practically can help design structures with giant PMA. As an example, we propose super-exchange stabilized Co-graphene heterostructures with a robust out-of-plane constant effective PMA and linearly increasing interfacial anisotropy as a function of film thickness. These findings point towards possibilities to engineer graphene/ferromagnetic metal heterostructures with giant magnetic anisotropy more than 20 times larger compared to conventional multilayers, which constitutes a hallmark for future graphene and traditional spintronic technologies.

  16. Unusually large magnetic anisotropy in electrochemically deposited Co-rich Co-Pt films.

    Science.gov (United States)

    Sirtori, V; Cavallotti, P L; Rognoni, R; Xu, X; Zangari, G; Fratesi, G; Trioni, M I; Bernasconi, M

    2011-06-01

    Co-rich Co-Pt films grown by electrodeposition from an amino-nitrite/citrate/glycine electrolyte onto Au(111) substrates apparently grow with a hexagonal structure, with its c-axis directed perpendicular to the surface. The films exhibit a perpendicular magnetic anisotropy (MCA) of the same order of magnitude as the shape anisotropy. Experimental estimates of the MCA result in a higher anisotropy than that reported for bulk materials of the same composition, but similar to values measured in films grown by vacuum methods at relatively high temperature, which partly consist of a high anisotropy, metastable orthorhombic Pmm2 phase. Comparison of valence band X-ray photoelectron spectroscopy measurements on electrodeposited films with density functional theory simulations of the electronic structure of the various reported Co(3)Pt structures support the notion that the films may consist of a mixture of the hexagonal and the Pmm2 structure.

  17. Precision ESR measurements of transverse anisotropy in the single-molecule magnet Ni4

    Science.gov (United States)

    Collett, Charles A.; Allão Cassaro, Rafael A.; Friedman, Jonathan R.

    2016-12-01

    We present a method for precisely measuring the tunnel splitting in single-molecule magnets (SMMs) using electron-spin resonance, and use these measurements to precisely and independently determine the underlying transverse anisotropy parameter, given a certain class of transitions. By diluting samples of the SMM Ni4 via cocrystallization in a diamagnetic isostructural analog we obtain markedly narrower resonance peaks than are observed in undiluted samples. Using custom loop-gap resonators we measure the transitions at several frequencies, allowing a precise determination of the tunnel splitting. Because the transition under investigation occurs at zero field, and arises due to a first-order perturbation from the transverse anisotropy, we can determine the magnitude of this anisotropy independent of any other Hamiltonian parameters. This method can be applied to other SMMs with tunnel splittings arising from first-order transverse anisotropy perturbations.

  18. Temperature dependence of perpendicular magnetic anisotropy in CoFeB thin films

    Science.gov (United States)

    Fu, Yu; Barsukov, I.; Li, Jing; Gonçalves, A. M.; Kuo, C. C.; Farle, M.; Krivorotov, I. N.

    2016-04-01

    We study perpendicular magnetic anisotropy in thin films of Ta/Co20Fe60B20/MgO by ferromagnetic resonance and find a linear temperature dependence for the first and second order uniaxial terms from 5 to 300 K. Our data suggest the possible hybridization of Fe-O orbitals at the CoFeB/MgO interface for the origin of the first order anisotropy. However, we also find that non-interfacial contributions to the anisotropy are present. An easy-cone anisotropy is found for the entire temperature range in the narrow region of film thicknesses around the spin reorientation transition 1.2-1.35 nm.

  19. Perpendicular magnetic anisotropy in epitaxially strained cobalt-ferrite (001) thin films

    Energy Technology Data Exchange (ETDEWEB)

    Yanagihara, H., E-mail: yanagiha@bk.tsukuba.ac.jp; Utsumi, Y.; Niizeki, T., E-mail: t-niizeki@imr.tohoku.ac.jp; Inoue, J.; Kita, Eiji [Institute of Applied Physics, University of Tsukuba, Tsukuba 305-8573 (Japan)

    2014-05-07

    We investigated the dependencies of both the magnetization characteristics and the perpendicular magnetic anisotropy of Co{sub x}Fe{sub 3–x}O{sub 4}(001) epitaxial films (x = 0.5 and 0.75) on the growth conditions of the reactive magnetron sputtering process. Both saturation magnetization and the magnetic uniaxial anisotropy constant K{sub u} are strongly dependent on the reactive gas (O{sub 2}) flow rate, although there is little difference in the surface structures for all samples observed by reflection high-energy electron diffraction. In addition, certain dead-layer-like regions were observed in the initial stage of the film growth for all films. Our results suggest that the magnetic properties of Co{sub x}Fe{sub 3–x}O{sub 4} epitaxial films are governed by the oxidation state and the film structure at the vicinity of the interface.

  20. CoxC nanorod magnets: Highly magnetocrystalline anisotropy with lower Curie temperature for potential applications

    Energy Technology Data Exchange (ETDEWEB)

    El-Gendy, AA; Almugaiteeb, T; Carpenter, EE

    2013-12-01

    Magnetic CoxC nanorods with larger magnetocrystalline anisotropy of 5 x 10(5) J/m(3) as well as larger coercivity and lower Curie temperature are introduced. The particles have an average diameter of 8 nm and shows three different magnetic behaviors. The sample shows ferromagnetism up to 400 K, superparamagnetism at temperature > 400 K and magnets, magnetic sensors and contract agent for magnetic resonance imaging. (c) 2013 Elsevier B.V. All rights reserved.

  1. Perpendicular magnetic anisotropy in composite MgO/CoFeB/Ta/[Co/Pd]n structures

    Science.gov (United States)

    Garcia-Vazquez, Valentin; Chang, Yao-Jen; Canizo-Cabrera, A.; Garzon-Roman, Abel; Wu, Te-ho

    2016-02-01

    The impact of a non-magnetic Ta spacer layer on the perpendicular magnetic anisotropy (PMA) of composite magnetic structures constituted by ultra-thin Co/Pd multilayers (MLs) and MgO/CoFeB was studied. Composite structures lacking a Ta layer present in-plane magnetic anisotropy. The strong perpendicular anisotropy observed in sole Co/Pd MLs is not sufficient to pull the magnetic moment out of the film plane, not even after annealing at 300 or 350 °C. PMA with squareness values close to unity and annealing stability up to 350 °C is observed after the insertion of an ultra-thin Ta layer. Our study demonstrates that Ta layer is essential for obtaining perpendicular magnetic axis in MgO/CoFeB/Ta/[Co/Pd]6. The exchange coupling between the MgO/CoFeB bilayer and the Co/Pd MLs is ferromagnetic with sharp switching characteristics. Perpendicular composite structures with sharp magnetization reversal and annealing stability are relevant in perpendicular CoFeB-based magnetic tunnel junctions for the development of gigabit-scale nonvolatile memory.

  2. The perpendicular magnetic anisotropy of CoPt/Au multilayer films

    Energy Technology Data Exchange (ETDEWEB)

    Yokota, T. [Department of Physics and Astronomy and Center for Materials Research and Analysis, University of Nebraska, Lincoln, Nebraska 68588-0111 (United States); Gao, L. [Department of Physics and Astronomy and Center for Materials Research and Analysis, University of Nebraska, Lincoln, Nebraska 68588-0111 (United States); Zhang, R. [Department of Physics and Astronomy and Center for Materials Research and Analysis, University of Nebraska, Lincoln, Nebraska 68588-0111 (United States); Nicholl, L. [Department of Physics and Astronomy and Center for Materials Research and Analysis, University of Nebraska, Lincoln, Nebraska 68588-0111 (United States); Yan, M.L. [Department of Physics and Astronomy and Center for Materials Research and Analysis, University of Nebraska, Lincoln, Nebraska 68588-0111 (United States); Sellmyer, D.J. [Department of Physics and Astronomy and Center for Materials Research and Analysis, University of Nebraska, Lincoln, Nebraska 68588-0111 (United States); Liou, S.H. [Department of Physics and Astronomy and Center for Materials Research and Analysis, University of Nebraska, Lincoln, Nebraska 68588-0111 (United States)]. E-mail: sliou@unl.edu

    2005-02-01

    We have studied the magnetic properties of Au (2 nm)/Co{sub 50}Pt{sub 50} (3 nm)/Au (2 nm) multilayer films prepared on amorphous Al{sub 2}O{sub 3}/Si and (0 0 1) MgO substrates. The as-deposited films on both substrates are magnetically soft with an FCC structure and exhibit a perpendicular anisotropy. After annealing at 500 deg. C, the sample on the Al{sub 2}O{sub 3}/Si substrate has become magnetically isotropic but the sample on the MgO substrate still has perpendicular anisotropy with FCT structure. This film deposited on the MgO substrate did not show a strong perpendicular anisotropy due to the diffusion of the Au and the (1 1 1) nucleation of initial Au layer. We can obtain a perpendicular anisotropy in the multilayer films without an initial Au layer on a (0 0 1) MgO substrate. After annealing at 400 deg. C, these films have L1{sub 0} phase with (0 0 1) texture and strong perpendicular anisotropy.

  3. Out-of-plane magnetic anisotropy in columnar grown Fe-Ni films

    Science.gov (United States)

    Pires, M. J. M.; Araújo Filho, M. S.; Tedesco, J. C. G.; Ardisson, J. D.; Macedo, W. A. A.

    2014-10-01

    Polycrystalline thin films usually present magnetic anisotropy resulting from a conjunction of textures, residual stresses, surface effects, and magnetic dipole distribution. The shape anisotropy, which is caused by the magnetic dipole distribution, is dominant in most of the cases, and it forces the occurrence of in-plane easy axes for the magnetization. Contrary to this common expectation, we have found predominant out-of-plane easy axes in a series of Fe-Ni thin films produced by DC sputtering. Films with different thicknesses, from 40 to 1000 nm, and different deposition temperatures have been tested and show similar results. These unusual characteristics are results of a particular columnar structure formed during the films growth. The magnetic characterization of the samples has been done by Mössbauer spectroscopy, magnetometry, and ferromagnetic resonance. The unusual anisotropy observed is not believed to be uniform along the film thickness. This interpretation comes from the comparison of the experimental results with hysteresis obtained by micromagnetic simulations. Five distinct configurations for the anisotropies have been simulated for this comparison.

  4. RKKY-like contributions to the magnetic anisotropy energy: 3 d adatoms on Pt(111) surface

    Science.gov (United States)

    Bouhassoune, Mohammmed; Dias, Manuel dos Santos; Zimmermann, Bernd; Dederichs, Peter H.; Lounis, Samir

    2016-09-01

    The magnetic anisotropy energy defines the energy barrier that stabilizes a magnetic moment. Utilizing density-functional-theory-based simulations and analytical formulations, we establish that this barrier is strongly modified by long-range contributions very similar to Friedel oscillations and Rudermann-Kittel-Kasuya-Yosida interactions. Thus, oscillations are expected and observed, with different decaying factors and highly anisotropic in realistic materials, which can switch nontrivially the sign of the magnetic anisotropy energy. This behavior is general, and for illustration we address the transition-metal adatoms, Cr, Mn, Fe, and Co deposited on a Pt(111) surface. We explain, in particular, the mechanisms leading to the strong site dependence of the magnetic anisotropy energy observed for Fe adatoms on a Pt(111) surface as revealed previously via first-principles-based simulations and inelastic scanning tunneling spectroscopy [A. A. Khajetoorians et al., Phys. Rev. Lett. 111, 157204 (2013), 10.1103/PhysRevLett.111.157204]. The same mechanisms are probably active for the site dependence of the magnetic anisotropy energy obtained for Fe adatoms on Pd or Rh(111) surfaces and for Co adatoms on a Rh(111) surface [P. Blonski et al., Phys. Rev. B 81, 104426 (2010), 10.1103/PhysRevB.81.104426].

  5. Observation of Various and Spontaneous Magnetic Skyrmionic Bubbles at Room Temperature in a Frustrated Kagome Magnet with Uniaxial Magnetic Anisotropy

    KAUST Repository

    Hou, Zhipeng

    2017-06-07

    The quest for materials hosting topologically protected skyrmionic spin textures continues to be fueled by the promise of novel devices. Although many materials have demonstrated the existence of such spin textures, major challenges remain to be addressed before devices based on magnetic skyrmions can be realized. For example, being able to create and manipulate skyrmionic spin textures at room temperature is of great importance for further technological applications because they can adapt to various external stimuli acting as information carriers in spintronic devices. Here, the first observation of skyrmionic magnetic bubbles with variable topological spin textures formed at room temperature in a frustrated kagome Fe3 Sn2 magnet with uniaxial magnetic anisotropy is reported. The magnetization dynamics are investigated using in situ Lorentz transmission electron microscopy, revealing that the transformation between different magnetic bubbles and domains is via the motion of Bloch lines driven by an applied external magnetic field. These results demonstrate that Fe3 Sn2 facilitates a unique magnetic control of topological spin textures at room temperature, making it a promising candidate for further skyrmion-based spintronic devices.

  6. Determination of the in-plane anisotropy field in hexagonal systems via rotational magnetization: Theoretical model and Monte Carlo simulations

    Institute of Scientific and Technical Information of China (English)

    WANG AiMin; PANG Hua

    2009-01-01

    The magnetic anisotropy field in thin films with in-plane uniaxial anisotropy can be deduced from the VSM magnetization curves measured in magnetic fields of constant magnitudes. This offers a new possibility of applying rotational magnetization curves to determine the first- and second-order ani-aotropy constant in these films. In this paper we report a theoretical derivation of rotational magnetiza-tion curve in hexagonal crystal system with easy-plane anisotropy based on the principle of the minimum total energy. This model is applied to calculate and analyze the rotational magnetization process for magnetic spherical particles with hexagonal easy-plane anisotropy when rotating the external magnetic field in the basal plane. The theoretical calculations are consistent with Monte Carlo simulation results. It is found that to well reproduce experimental curves, the effect of coercive force on the magnetization reversal process should be fully considered when the intensity of the ex-ternal field is much weaker than that of the anisotropy field. Our research proves that the rotational magnetization curve from VSM measurement provides an effective access to analyze the in-plane anisotropy constant K3 in hexagonal compounds, and the suitable experimental condition to measure K3 is met when the ratio of the magnitude of the external field to that of the anisotropy field is around 0.2.

  7. Failure Analysis in Magnetic Tunnel Junction Nanopillar with Interfacial Perpendicular Magnetic Anisotropy

    Directory of Open Access Journals (Sweden)

    Weisheng Zhao

    2016-01-01

    Full Text Available Magnetic tunnel junction nanopillar with interfacial perpendicular magnetic anisotropy (PMA-MTJ becomes a promising candidate to build up spin transfer torque magnetic random access memory (STT-MRAM for the next generation of non-volatile memory as it features low spin transfer switching current, fast speed, high scalability, and easy integration into conventional complementary metal oxide semiconductor (CMOS circuits. However, this device suffers from a number of failure issues, such as large process variation and tunneling barrier breakdown. The large process variation is an intrinsic issue for PMA-MTJ as it is based on the interfacial effects between ultra-thin films with few layers of atoms; the tunneling barrier breakdown is due to the requirement of an ultra-thin tunneling barrier (e.g., <1 nm to reduce the resistance area for the spin transfer torque switching in the nanopillar. These failure issues limit the research and development of STT-MRAM to widely achieve commercial products. In this paper, we give a full analysis of failure mechanisms for PMA-MTJ and present some eventual solutions from device fabrication to system level integration to optimize the failure issues.

  8. First-principles study of electric field and structural strain impact on perpendicular magnetic anisotropy of Fe/MgO interfaces

    Science.gov (United States)

    Ibrahim, Fatima; Yang, Hongxin; Dieny, Bernard; Chshiev, Mairbek

    2015-03-01

    Electric-field (EF) control of magnetic anisotropy is promising in the context of establishing low-energy consumption memory devices since it allows EF-assisted switching of magnetization in magnetic tunnel junctions with perpendicular magnetic anisotropy (PMA). Using first-principles calculations, we demonstrate that both the EF and structural strain induce changes of the PMA in Fe/MgO interfaces which originally exhibit strong PMA. Namely, we find that the PMA change in response to strain is much larger than that induced by applied EF. This suggests that the EF control of PMA is caused not only by charge accumulation and depletion mechanism but rather mediated by structural modifications occurring at the interface in agreement with recent experimental reports. In addition, using atomic and orbital-resolved analysis of PMA, we elucidate the effect of both the EF and structural strain on PMA showing in particular that it extends beyond the interfacial layer.

  9. The effect of crystalline and shape anisotropy on the magnetic properties of Co and Ni nanowires

    Directory of Open Access Journals (Sweden)

    R. Golipour

    2007-06-01

    Full Text Available   Co and Ni magnetic nanowires with different diameter and deposition time were fabricated into the alumina template using ac electrodeposition. For Ni nanowires with 30 nm diameter the coercivity initially increased then dropped with deposition time, while it only increased with deposition time for all the other diameters. In general, the results showed that the coercivity reduced with diameter. The maximum coercivity was obtained for the Co nanowire made with 30 nm diameter and 30 s deposition time and further electrodeposition time causes a reduction of the coercivity. The effect of crystal and shape anisotropy on the magnetic properties were investigated and the results revealed that the crystal anisotropy has a dominant role on the coercive field of Co nanowires, while there is a competitive effect between both the anisotropies for the Ni nanowires changing the coercivity.

  10. Anisotropies of anhysteretic remanence and magnetic susceptibility of marly clays from Central Italy

    Directory of Open Access Journals (Sweden)

    L. Sagnotti

    1994-06-01

    Full Text Available Marly clays from an Upper Pliocene unit at Valle Ricca (Rorne were investigated for their Anisotropy of Anhysteretic Remanence (AAR and Anisotropy of Magnetic Susceptibility (AMS. The study of AAR was accomplished for the first time in ltaly, developing a suitable laboratory technique and adapting a standard statistical procedure. The comparison between anhysteretic remanence and magnetic susceptibility anisotropies discriminates the fabric of the ferromagnetic fraction from that of the paramagnetic matrix of the rock. The separation of fabric components was applied to distinguish subsequent geological processes that affected the total rock fabric. The results indicate that the clayey units are particularly suitable for the empirical investigation of fabric to strain relationship in weakly deformed rocks.

  11. Magnetic anisotropy, damping, and interfacial spin transport in Pt/LSMO bilayers

    Directory of Open Access Journals (Sweden)

    H. K. Lee

    2016-05-01

    Full Text Available We report ferromagnetic resonance measurements of magnetic anisotropy and damping in epitaxial La0.7Sr0.3MnO3 (LSMO and Pt capped LSMO thin films on SrTiO3 (001 substrates. The measurements reveal large negative perpendicular magnetic anisotropy and a weaker uniaxial in-plane anisotropy that are unaffected by the Pt cap. The Gilbert damping of the bare LSMO films is found to be low α = 1.9(1 × 10−3, and two-magnon scattering is determined to be significant and strongly anisotropic. The Pt cap increases the damping by 50% due to spin pumping, which is also directly detected via inverse spin Hall effect in Pt. Our work demonstrates efficient spin transport across the Pt/LSMO interface.

  12. Magnetic anisotropy in Ta/CoFeB/MgO investigated by x-ray magnetic circular dichroism and first-principles calculation

    Energy Technology Data Exchange (ETDEWEB)

    Kanai, Shun [Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Tsujikawa, Masahito; Shirai, Masafumi [Center for Spintronics Integrated Systems, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Miura, Yoshio [Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Department of Electronics and Information Science, Kyoto Institute of Technology, Kyoto (Japan); Matsukura, Fumihiro, E-mail: f-matsu@wpi-aimr.tohoku.ac.jp; Ohno, Hideo [Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); WPI-Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan)

    2014-12-01

    We study the spin and orbital magnetic moments in Ta/Co{sub 0.4}Fe{sub 0.4}B{sub 0.2}/MgO by x-ray magnetic circular dichroism measurements as well as first-principles calculations, in order to clarify the origin of the perpendicular magnetic anisotropy. Both experimental and theoretical results show that orbital magnetic moment of Fe is more anisotropic than that of Co with respect to the magnetization direction. The anisotropy is larger for thinner CoFeB, indicating that Fe atoms at the interface with MgO contribute more than Co to the observed perpendicular magnetic anisotropy.

  13. Perpendicular magnetic anisotropy, unconventional magnetization texture and extraordinary gradual spin reorientation transition of cobalt films in contact with graphene (Conference Presentation)

    Science.gov (United States)

    Rougemaille, Nicolas; Vu, Anh Duc; Chen, Gong; N'Diaye, Alpha T.; Schmid, Andreas K.; Coraux, Johann

    2016-10-01

    Owing to its peculiar electronic band structure, high carrier mobility and long spin diffusion length, graphene is a promising two-dimensional material for microelectronics and spintronics. Graphene also shows interesting magnetic properties when in contact with a ferromagnetic metal (FM). For instance, graphene carries a net magnetic moment when deposited on Fe/Ni(111), and a significant spin splitting can be induced in graphene due to proximity with a heavy element. While these results illustrate potential advantages of integrating graphene within a magnetic stack, the influence of graphene on the magnetic properties of a FM is still largely unexplored. In particular, non-magnetic overlayers generally affect the magnetic anisotropy energy (MAE) of thin layers, where interfaces play an important role. We can then wonder how an interface with graphene would influence the MAE of a thin FM film. Using spin-polarized low-energy electron microscopy, we study how a graphene overlayer affects the magnetic properties of atomically flat, nm-thick Co films grown on Ir(111). In this contribution, we report several astonishing magnetic properties of graphene-covered Co films: 1) Perpendicular magnetic anisotropy is favored over an unusually large thickness range, 2) Vectorial magnetic imaging reveals an extraordinarily gradual thickness-dependent spin reorientation transition (SRT), 3) During the SRT, cobalt films are characterized by an unconventional spin texture, 4) Spectroscopy measurements indicate that incident spin-polarized electrons do not suffer substantial spin-dependent collisions a few electron-Volts above the vacuum level. These properties strikingly differ from those of pristine cobalt films and could open new prospects in surface magnetism and spintronics.

  14. FePtCu alloy thin films: Morphology, L1{sub 0} chemical ordering, and perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Brombacher, C.; Schletter, H.; Daniel, M.; Matthes, P.; Joehrmann, N.; Makarov, D.; Hietschold, M.; Albrecht, M. [Institute of Physics, Chemnitz University of Technology, D-09107 Chemnitz (Germany); Maret, M. [Laboratory of Science and Engineering of Materials and Processes (SIMaP), INP-Grenoble/CNRS/UJF, F-38402 Saint-Martin d' Heres (France)

    2012-10-01

    Rapid thermal annealing was applied to transform sputter-deposited Fe{sub 51}Pt{sub 49}/Cu bilayers into L1{sub 0} chemically ordered ternary (Fe{sub 51}Pt{sub 49}){sub 100-x}Cu{sub x} alloys with (001) texture on amorphous SiO{sub 2}/Si substrates. It was found that for thin film samples, which were processed at 600 Degree-Sign C for 30 s, the addition of Cu strongly favors the L1{sub 0} ordering and (001) texture formation. Furthermore, it could be revealed by transmission electron microscopy and electron backscatter diffraction that the observed reduction of the ordering temperature with Cu content is accompanied by an increased amount of nucleation sites forming L1{sub 0} ordered grains. The change of the structural properties with Cu content and annealing temperature is closely related to the magnetic properties. While an annealing temperature of 800 Degree-Sign C induces strong perpendicular magnetic anisotropy (PMA) in binary Fe{sub 51}Pt{sub 49} films, the addition of Cu systematically reduces the PMA. However, due to the enhancement of both the A1-L1{sub 0} phase transformation and the development of the (001) texture with increasing Cu content, lowering of the annealing temperature leads to a shift of the maximum perpendicular magnetic anisotropy towards alloys with higher Cu content. Thus, for an annealing temperature of 600 Degree-Sign C, the highest perpendicular magnetic anisotropy energy is found for the (Fe{sub 51}Pt{sub 49}){sub 91}Cu{sub 9} alloy. The smooth surface morphology, adjustable PMA, and high degree of intergranular exchange coupling make these films suitable for post-processing required for specific applications such as for sensorics or magnetic data storage.

  15. Origin of Perpendicular Magnetic Anisotropy and Large Orbital Moment in Fe Atoms on MgO.

    Science.gov (United States)

    Baumann, S; Donati, F; Stepanow, S; Rusponi, S; Paul, W; Gangopadhyay, S; Rau, I G; Pacchioni, G E; Gragnaniello, L; Pivetta, M; Dreiser, J; Piamonteze, C; Lutz, C P; Macfarlane, R M; Jones, B A; Gambardella, P; Heinrich, A J; Brune, H

    2015-12-04

    We report on the magnetic properties of individual Fe atoms deposited on MgO(100) thin films probed by x-ray magnetic circular dichroism and scanning tunneling spectroscopy. We show that the Fe atoms have strong perpendicular magnetic anisotropy with a zero-field splitting of 14.0±0.3  meV/atom. This is a factor of 10 larger than the interface anisotropy of epitaxial Fe layers on MgO and the largest value reported for Fe atoms adsorbed on surfaces. The interplay between the ligand field at the O adsorption sites and spin-orbit coupling is analyzed by density functional theory and multiplet calculations, providing a comprehensive model of the magnetic properties of Fe atoms in a low-symmetry bonding environment.

  16. Origin of Perpendicular Magnetic Anisotropy and Large Orbital Moment in Fe Atoms on MgO

    Science.gov (United States)

    Baumann, S.; Donati, F.; Stepanow, S.; Rusponi, S.; Paul, W.; Gangopadhyay, S.; Rau, I. G.; Pacchioni, G. E.; Gragnaniello, L.; Pivetta, M.; Dreiser, J.; Piamonteze, C.; Lutz, C. P.; Macfarlane, R. M.; Jones, B. A.; Gambardella, P.; Heinrich, A. J.; Brune, H.

    2015-12-01

    We report on the magnetic properties of individual Fe atoms deposited on MgO(100) thin films probed by x-ray magnetic circular dichroism and scanning tunneling spectroscopy. We show that the Fe atoms have strong perpendicular magnetic anisotropy with a zero-field splitting of 14.0 ±0.3 meV /atom . This is a factor of 10 larger than the interface anisotropy of epitaxial Fe layers on MgO and the largest value reported for Fe atoms adsorbed on surfaces. The interplay between the ligand field at the O adsorption sites and spin-orbit coupling is analyzed by density functional theory and multiplet calculations, providing a comprehensive model of the magnetic properties of Fe atoms in a low-symmetry bonding environment.

  17. Perpendicular magnetic anisotropy of Co/Pt bilayers on ALD HfO2

    Science.gov (United States)

    Vermeulen, Bart F.; Wu, Jackson; Swerts, Johan; Couet, Sebastien; Linten, Dimitri; Radu, Iuliana P.; Temst, Kristiaan; Rampelberg, Geert; Detavernier, Christophe; Groeseneken, Guido; Martens, Koen

    2016-10-01

    Perpendicular Magnetic Anisotropy (PMA) is a key requirement for state of the art Magnetic Random Access Memories (MRAM). Currently, PMA has been widely reported in standard Magnetic Tunnel Junction material stacks using MgO as a dielectric. In this contribution, we present the first report of PMA at the interface with a high-κ dielectric grown by Atomic Layer Deposition, HfO2. The PMA appears after annealing a HfO2/Co/Pt/Ru stack in N2 with the Keff of 0.25 mJ/m2 as determined by Vibrating Sample Magnetometry. X-Ray Diffraction and Transmission Electron Microscopy show that the appearance of PMA coincides with interdiffusion and the epitaxial ordering of the Co/Pt bilayer. High-κ dielectrics are especially interesting for Voltage Control of Magnetic Anisotropy applications and are of potential interest for low-power MRAM and spintronics technologies.

  18. Room-temperature perpendicular magnetic anisotropy of MgO/Fe/MgO ultrathin films

    Energy Technology Data Exchange (ETDEWEB)

    Kozioł-Rachwał, A.; Ślęzak, T.; Przewoźnik, J. [Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, al. Mickiewicza 30, 30-059 Kraków (Poland); Skowroński, W.; Stobiecki, T. [Department of Electronics, AGH University of Science and Technology, al. Mickiewicza 30, 30-059 Kraków (Poland); Wilgocka-Ślęzak, D. [Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 8, 30-239 Kraków (Poland); Qin, Q. H.; Dijken, S. van [NanoSpin, Department of Applied Physics, Aalto University School of Science, P.O. Box 15100, FI-00076 Aalto (Finland); Korecki, J. [Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, al. Mickiewicza 30, 30-059 Kraków (Poland); Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 8, 30-239 Kraków (Poland)

    2013-12-14

    We used the anomalous Hall effect to study the magnetic properties of MgO/Fe(t)/MgO(001) structures in which the Fe thickness t ranged from 4 Å to 14 Å. For the iron deposited at 140 K, we obtained perpendicular magnetization at room temperature below the critical thickness of t{sub c} = (9 ± 1) Å. In the vicinity of t{sub c}, the easy magnetization axis switched from an out-of-plane orientation to an in-plane orientation, and the observed spin-reorientation transition was considered in terms of the competition among different anisotropies. The perpendicular magnetization direction was attributed to magnetoelastic anisotropy. Finally, the temperature-dependent spin-reorientation transition was analyzed for Fe thicknesses close to t{sub c}.

  19. Model of Electron Pressure Anisotropy in the Process of Magnetic Reconnection

    Science.gov (United States)

    Divin, A. V.; Lapenta, G.; Markidis, S.

    2009-12-01

    In our work we use particle-in-cell simulations of plasma for the study of magnetic reconection. Details of the diffusive process inside electron diffusion region (EDR) are explored. Reconnection is considered in two-dimensional antiparallel approach and pressure anisotropy is well-known to provide for collisionless dissipation in such configurations. We identify particles of different trajectories near X-point and their contribution to the pressure tensor anisotropy. Electrons are magnetized far from X-point (gyrotropic particle distribution) but gyrotropy is lost as the magnetic field vanishes near the X-point and electrons behave non-adiabaticly. The transition between inflow distribution and accelerated particles manifests itself as a tilt of distribution function, which creates pressure anisotropy and renders electron pressure divergency to be non-zero. Assuming stationarity of the reconnection process, next we apply test particle approach and trace particles back in time over characteristic meandering time. It allows for the separation between different populations of particles: those particles which meander in the vicinity of X-point are accelerating and trapped, whereas magnetized particles display drift motion and stay inside the inflow region. Model of electron pressure anisotropy is proposed, based on such bi-Maxwellian origin of the distribution function inside EDR. Equating reconnection electric field and divergency of pressure tensor at the X-point, we obtain scalings for the elecron flow velocity, width and total electron current within EDR.

  20. On the single-ion Magnetic Anisotropy of the Rare-Earth Metals

    DEFF Research Database (Denmark)

    Kolmakova, N.P.; Tishin, A.M.; Bohr, Jakob

    1996-01-01

    The temperature dependences of the single-ion magnetic anisotropy constants for Tb and Dy metals are calculated in terms of the multipole moments of the rare-earth ions utilizing the available crystal-field parameters. The results are compared with the existing experimental data....

  1. Perpendicular magnetic anisotropy in TbFeGa ternary alloys grown by cosputtering

    Energy Technology Data Exchange (ETDEWEB)

    Ranchal, R., E-mail: rociran@fis.ucm.es; Gutiérrez-Díez, V.

    2013-05-01

    In this work we have studied the magnetic anisotropy of as-grown TbFeGa ternary alloys with a Ga doping between 10 and 16% and a Tb content between 9 and 12%. The samples were deposited by cosputtering at room temperature in the oblique incidence from two targets with a TbFe{sub 2} and Fe{sub 3}Ga nominal composition. Samples with different compositions were achieved keeping constant the DC growth power at 100 W in the TbFe{sub 2} and modifying the pulsed power between 60 and 120 W in the Fe{sub 3}Ga target, respectively. The X-ray diffraction patterns indicate the presence of crystalline TbFe{sub 2}-based phases. It has been obtained perpendicular magnetic anisotropy in all the samples except when the pulsed power increases up to 120 W that corresponds to a 16% of Ga. The existence of perpendicular magnetic anisotropy seems to be related to the presence of TbFe{sub 2}-based phases with a composition close to the TbFe{sub 2}. - Highlights: ► TbFeGa ternary alloys were cosputtered from TbFe{sub 2} and Fe{sub 3}Ga targets. ► The studied alloys exhibit a structure close to the cubic TbFe{sub 2} Laves phase. ► Perpendicular magnetic anisotropy seems to be related to TbFe{sub 2}-based phases.

  2. Coupled Néel domain wall motion in sandwiched perpendicular magnetic anisotropy nanowires

    OpenAIRE

    Purnama, I.; Kerk, I. S.; Lim, G J; Lew, W. S.

    2015-01-01

    The operating performance of a domain wall-based magnetic device relies on the controlled motion of the domain walls within the ferromagnetic nanowires. Here, we report on the dynamics of coupled Néel domain wall in perpendicular magnetic anisotropy (PMA) nanowires via micromagnetic simulations. The coupled Néel domain wall is obtained in a sandwich structure, where two PMA nanowires that are separated by an insulating layer are stacked vertically. Under the application of high current densit...

  3. Microwave Magnetic Properties of Nd2Fe17N3-δ with Planar Anisotropy

    Institute of Scientific and Technical Information of China (English)

    LI Fa-Shen; WEN Fu-Sheng; ZHOU Dong; QIAO Liang; ZUO Wen-Liang

    2008-01-01

    @@ Microwave magnetic properties are studied for rhombohedral structure Nd2Fe17N3-δ with planar magnetic anisotropy.Its resin composites show the permeability μ'0 = 4.15 at low frequency,the natural resonance frequency fr = 1.71 GHz and the resonance bandwidth 6.66 GHz.The calculated static permeability of Nd2Fe17N3-δ reaches 133.

  4. Four-fold magnetic anisotropy in a Co film on MgO(0 0 1)

    Energy Technology Data Exchange (ETDEWEB)

    Pires, M.J.M., E-mail: manoeljmp@gmail.co [Servico de Nanotecnologia, Centro de Desenvolvimento da Tecnologia Nuclear, 31270-901 Belo Horizonte, MG (Brazil); Cotta, A.A.C.; Martins, M.D.; Silva, A.M.A.; Macedo, W.A.A. [Servico de Nanotecnologia, Centro de Desenvolvimento da Tecnologia Nuclear, 31270-901 Belo Horizonte, MG (Brazil)

    2011-03-15

    The development of devices based on magnetic tunnel junctions has raised new interests on the structural and magnetic properties of the interface Co/MgO. In this context, we have grown ultrathin Co films ({<=}30 A) by molecular-beam epitaxy on MgO(0 0 1) substrates kept at different temperatures (T{sub S}). Their structural and magnetic properties were correlated and discussed in the context of distinct magnetic anisotropies for Co phases reported in the literature. The sample characterization has been done by reflection high energy electron diffraction, magneto-optical Kerr effect and ferromagnetic resonance. The main focus of the work is on a sample deposited at T{sub S}=25 {sup o}C, as its particular way of growth has enabled a bct Co structure to settle on the substrate, where it is not normally obtained without specific seed layers. This sample presented the best crystallinity, softer magnetic properties and a four-fold in-plane magnetic anisotropy with Co<1 1 0> easy directions. Concerning the samples prepared at T{sub S}=200 and 500{sup o} C, they show fcc and polycrystalline structures, respectively and more intricate magnetic anisotropy patterns. - Research highlights: > Results suggest the lattice is already after the Bain transformation for T{sub S}=25 {sup o}C, and the Co film has a bct structure instead of an fct one. > For deposition temperature of T{sub S}=25 {sup o}C, a four-fold in-plane magnetic anisotropy with Co<1 1 0> easy directions has been obtained. > The growth mode of Co on MgO single crystals at different temperatures resulted in bct Co at T{sub S}=25 {sup o}C, fcc Co at T{sub S}=200 {sup o}C and polycrystalline Co at T{sub S}=500 {sup o}C.

  5. Magnetization, Magnetocrystalline Anisotropy and the Crystalline Electric Field in Rare-Earth Al2 Compounds

    DEFF Research Database (Denmark)

    Purwins, H. -G.; Walker, E.; Barbara, B.;

    1974-01-01

    Magnetization measurements are reported for single crystals of PrAl2 in the range from 4.2K to 30K for magnetic fields up to 150 kOe applied in the (100), (110) and (111) directions. For these measurements, together with the magnetization results obtained earlier for TbAl2 the authors give...... a quantitative quantum mechanical description of the magnetization and the related magnetocrystalline anisotropy in terms of a cubic crystalline electric field and an isotropic exchange interaction. The parameters used in this description can be unified to good approximation to all REAl2 intermetallic compounds...

  6. Search for giant magnetic anisotropy in transition-metal dimers on defected hexagonal boron nitride sheet

    Science.gov (United States)

    Li, J.; Wang, H.; Hu, J.; Wu, R. Q.

    2016-05-01

    Structural and magnetic properties of many transition-metal dimers embedded in a defected hexagonal boron nitride monolayer are investigated through density functional calculations to search for systems with magnetic anisotropy energies (MAEs) larger than 30meV. In particular, Ir-Ir@Dh-BN is found to have both large MAE (˜126 meV) and high structural stability against dissociation and diffusion, and it hence can serve as magnetic unit in spintronics and quantum computing devices. This giant MAE mainly results from the spin orbit coupling and the magnetization of the upper Ir atom, which is in a rather isolated environment.

  7. Magnetic anisotropy of Co/Pt/FeMn multilayers grown on polystyrene nanospheres

    Energy Technology Data Exchange (ETDEWEB)

    Martins, A., E-mail: alessandro.martins@pq.cnpq.br [Universidade Federal de Goias, Campus de Jatai, 75800 000 Jatai (Brazil); Pelegrini, F. [Universidade Federal de Goias, Instituto de Fisica, 74001 970 Goiania (Brazil); Soares, M.M. [Universidade Federal de Pernambuco, Departamento de Fisica, 50670 901 Recife (Brazil); Garcia, F. [Laboratorio Nacional de Luz Sincrotron, Campinas (Brazil)

    2013-02-15

    The magnetic anisotropy of Co/Pt/FeMn multilayers grown onto two-dimensional arrays of nanospherical polystyrene particles is studied at room temperature using Ferromagnetic Resonance measurements with X-band microwave frequency. The in-plane and out-of-plane resonance spectra display two uniform absorption modes due to two distinct magnetic phases, revealing an inhomogeneous magnetization profile through the thickness and at the top and the equator of the magnetic caps. The in-plane measurements of the angular dependence of the two absorption fields reveal that the distinct magnetic phases exhibit the effects of twofold and fourfold magnetic anisotropy fields. Out-of-plane measurements show that the magnetization of each magnetic phase depends on the structure of the multilayer and is oriented at a specific direction oblique to the plane of the film. - Highlights: Black-Right-Pointing-Pointer The multilayers investigated in this work were grown at room temperature by dc sputtering. Black-Right-Pointing-Pointer The FMR data were taken at room temperature with X-band microwave system (9.6 GHz). Black-Right-Pointing-Pointer We report distinct magnetic phases in the multilayer's. Black-Right-Pointing-Pointer The magnetic phase depends on the structure and is oriented at a specific direction.

  8. Comparison of Theories of Anisotropy in Transformer Oil-Based Magnetic Fluids

    Directory of Open Access Journals (Sweden)

    Jozef Kudelcik

    2013-01-01

    Full Text Available The external magnetic field in transformer oil-based magnetic fluids leads to the aggregation of magnetic nanoparticles and formation of clusters. These aggregations are the result of the interaction between the external magnetic field and the magnetic moments of the nanoparticles occurs. However, the temperature of magnetic fluids has also very important influence on the structural changes because the mechanism of thermal motion acts against the cluster creation. The acoustic spectroscopy was used to study the anisotropy of transformer oil-based magnetic fluids upon the effect of an external magnetic field and temperature. In present the anisotropy of the magnetic fluids can be described by two theories. Taketomi theory assumes the existence of spherical clusters. These clusters form long chains, aligned in a magnetic field direction. Shliomis in his theory supposed that only nanoparticles formed chains. A comparison of the experimental results with the predictions of the Taketomi theory allowed a determination of the cluster radius and the number density of the colloidal particles. The proportions of the acoustic wave energy used for excitation of the translational and rotational motion were determined.

  9. Conversion of magnetic anisotropy in electrodeposited Co–Ni alloy nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Samardak, A.S., E-mail: samardak.as@dvfu.ru [School of Natural Sciences, Far Eastern Federal University, Vladivostok (Russian Federation); Nasirpouri, F., E-mail: nasirpouri@sut.ac.ir [Faculty of Materials Engineering, Sahand University of Technology, Tabriz (Iran, Islamic Republic of); Nadi, M. [Faculty of Materials Engineering, Sahand University of Technology, Tabriz (Iran, Islamic Republic of); Sukovatitsina, E.V.; Ognev, A.V.; Chebotkevich, L.A. [School of Natural Sciences, Far Eastern Federal University, Vladivostok (Russian Federation); Komogortsev, S.V. [Institute of Physics, SB Russian Academy of Sciences, Krasnoyarsk (Russian Federation)

    2015-06-01

    In this paper, the influence of alternating current (ac) electrodeposition frequency and waveform is reported on chemical composition, microstructure and consequently magnetic properties of Co–Ni binary alloy nanowire arrays embedded in an alumina template. For sinusoidal and square electrodeposition waveforms the easy axis of magnetization rotates from being parallel to perpendicular orientation to nanowire long axis as the deposition frequency increases from 200 to 800 Hz. The reason for the drastic change of magnetic anisotropy in nanowires is attributed to the increase of cobalt content and the crystal structure phase transformation from fcc–hcp mixture at high Ni content to hcp at high Co content. We explain the conversion of magnetic behavior of nanowire arrays in terms of a competition between the shape and magnetocrystalline anisotropies. - Highlights: • Electrodeposition frequency variation leads to change of atomic percentage of Co and Ni in Co–Ni alloy nanowires. • Rising in the frequency assists to increase of Co content leading to significant changes in the crystal structure. • Rotation of the easy axis of magnetization from being parallel to the perpendicular direction to nanowire long axis is result of the competition between the magnetocrystalline and the shape magnetic anisotropies.

  10. Interlayer exchange coupling between layers with perpendicular and easy-plane magnetic anisotropies

    Science.gov (United States)

    Fallarino, Lorenzo; Sluka, Volker; Kardasz, Bartek; Pinarbasi, Mustafa; Berger, Andreas; Kent, Andrew D.

    2016-08-01

    Interlayer exchange coupling between layers with perpendicular and easy-plane magnetic anisotropies separated by a non-magnetic spacer is studied using ferromagnetic resonance. The samples consist of a Co/Ni multilayer with perpendicular magnetic anisotropy and a CoFeB layer with easy-plane anisotropy separated by a variable thickness Ru layer. At a fixed frequency, we show that there is an avoided crossing of layer ferromagnetic resonance modes providing direct evidence for interlayer coupling. The mode dispersions for different Ru thicknesses are fit to a Heisenberg-type model to determine the interlayer exchange coupling strength and layer properties. The resulting interlayer exchange coupling varies continuously from antiferromagnetic to ferromagnetic as a function of the Ru interlayer thickness. These results show that the magnetic layer single domain ground state consists of magnetizations that can be significantly canted with respect to the layer planes and the canting can be tuned by varying the Ru thickness and the layer magnetic characteristics, a capability of interest for applications in spin-transfer torque devices.

  11. Influence of the shielding currents lengthscale and anisotropy effects on the magnetic flux profiles of high-temperature superconductors

    Science.gov (United States)

    Vanderbemden, P.; Lovchinov, V.

    2012-12-01

    The so-called "magnetic flux profile" AC inductive technique is a powerful method for determining the critical current density Jc of bulk superconductors. In this work we aim at reporting analytical expressions for magnetic flux profiles of superconducting rectangular samples exhibiting a critical current density anisotropy. The results are used for examining the error resulting from approximating a rectangular cross-section by an "infinite cylinder" or "infinite slab" geometry. It is found that such approximations can lead to an artificial curvature of the flux profiles and errors of 10%-20% in the determination of Jc. Next, the effects of how planar defects (cracks, platelet boundaries,...) affect the magnetic flux profile signal are discussed. It is found that the magnetic flux profiles are much sensitive to the lengthscale of shielding currents, thereby providing means of investigation of the typical size of induced current loops in bulk superconductors. Finally some illustrative flux profile data measured on a bulk, large grain melt-processed YBCO single domain exhibiting Jc anisotropy are presented and discussed in relation with theoretical predictions.

  12. Magnetic anisotropy and magneto optical property of Fe/Co/Cu(001): role of the interface alloy

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Dongyoo; Yang, Jeonghwa; Hong, Jisang [Pukyong National University, Busan (Korea, Republic of)

    2010-01-15

    Using the full potential linearized augmented plane wave (FLAPW) method, we have investigated the role of interface alloy type on the thickness dependent magnetic properties of ultrathin Fe/Co/Cu(001) films. We have observed that the Co underlayer induces an antiferromagnetic (AFM) state in Fe/Co/Cu(001) film, but the position of AFM layer is strongly sensitive to both Fe and Co coverage. It is found that the magnetic anisotropy of Fe/Co/Cu alloy films is significantly influenced by the alloy type and the Fe film thickness. For instance, a thickness-dependent spin reorientation transition from in-plane to perpendicular to the film surface or vice versa is observed in CoFe alloy configuration whereas the perpendicular magnetization is always achieved in CuCo alloy. In particular, a large perpendicular magnetic anisotropy energy (MAE) about 270 {mu}eV /atom at 4 ML Fe thickness is observed in the CuCo alloy. In addition, we find that the magnitude of Kerr rotation angle in the presence of antiferromagnetic layer is greatly suppressed compared with that of fully ferromagnetic films.

  13. Optimizing magnetic anisotropy of La1-xSrxMnO3 nanoparticles for hyperthermia applications

    Science.gov (United States)

    Rashid, Amin ur; Manzoor, Sadia

    2016-12-01

    Maximizing the magnetothermal response of magnetic nanoparticles (MNP's) for hyperthermia applications is a complex problem, because it depends sensitively upon interrelated magnetic and structural parameters. The task is somewhat simpler for systems with fixed composition, e.g. Fe3O4 or CoFe2O4, in which the particle size is the only means of modifying the magnetic anisotropy, and hence the magnetothermal response. In the La1-xSrxMnO3 system however, the magnetic interactions as well as the particle size both change with the Sr concentration x, which makes it a much more complex system for which to optimize the hyperthermia response. We have investigated the effect of magnetic anisotropy on the magnetothermal response of La1-xSrxMnO3 nanoparticles as a function of the particle size as well as the Sr concentration x where 0.20≤x≤0.45. The optimum particle size range is 25-30 nm for all concentrations, where the specific absorption rate (SAR) has a maximum. The linear response theory (LRT) has been applied to this system and good agreement has been found between the experimental and theoretically determined values of the SAR for samples lying in the single domain regime and having large enough anisotropy energies. The agreement is much better for the intermediate concentrations of 0.27 and 0.33, because of their large anisotropy as compared to other concentrations. It is concluded that the LRT can be successfully used to predict the SAR of these nanoparticles, provided they possess large enough effective anisotropies. Values of the ILP have been obtained for these samples and found to be comparable to those of magnetite and some commercial ferrofluids.

  14. Effects of the applied magnetic field and anisotropy on the spin wave gap in ultrathin magnetic films at zero temperature

    Energy Technology Data Exchange (ETDEWEB)

    Kaplan, B., E-mail: bengukaplan@yahoo.com; Kaplan, R.

    2014-12-15

    We investigate the calculated spin wave gap of two-dimensional magnetic films under the combined influence of the in-plane direction of the applied magnetic field and different kinds of magnetic anisotropies. We also compute the spin wave gap as a function of the applied magnetic field at zero temperature. We discuss the results in connection with experimental data reported for epitaxial Fe-deficient yttrium garnet (YIG) films grown by pulsed laser deposition (PLD) technique onto the different faces of the Gd{sub 3}Ga{sub 5}O{sub 12} single crystal. - Highlights: • The spin wave gap as a function of the applied field is calculated. • The influence of in-plane anisotropy on the spin wave gap is discussed. • The results are compared in connection with experimental data.

  15. Magnetic properties of a Pt/Co2FeAl/MgO structure with perpendicular magnetic anisotropy

    Science.gov (United States)

    Li, Xiao-Qi; Xu, Xiao-Guang; Wang, Sheng; Wu, Yong; Zhang, De-Lin; Miao, Jun; Jiang, Yong

    2012-10-01

    Microstructures and magnetic properties of Ta/Pt/Co2FeAl (CFA)/MgO multilayers are studied to understand perpendicular magnetic anisotropy (PMA) of half-metallic full-Heusler alloy films. PMA is realized in a 2.5-nm CFA film with B2-ordered structure observed by a high resolution transmission electron microscope. It is demonstrated that a high quality interface between the ferromagnetic layer and oxide layer is not essential for PMA. The conversions between in-plane anisotropy and PMA are investigated to study the dependence of magnetic moment on temperature. At the intersection points, the decreasing slope of the saturation magnetization (Ms) changes because of the conversions. The dependence of Ms on the annealing temperature and MgO thickness is also studied.

  16. Thickness dependence of the magnetic properties of high-coercive Pr-Fe-B thin films with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Yang, F. [Shenyang National Laboratory for Materials Science, Institute of Metal Research and International Centre for Materials Physics, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang Liaoning 110016 (China); Liu, W. [Shenyang National Laboratory for Materials Science, Institute of Metal Research and International Centre for Materials Physics, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang Liaoning 110016 (China)], E-mail: wliu@imr.ac.cn; Cui, W.B.; Feng, J.N.; Zhang, Y.Q.; Zhang, Z.D [Shenyang National Laboratory for Materials Science, Institute of Metal Research and International Centre for Materials Physics, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang Liaoning 110016 (China)

    2008-10-01

    The magnetic properties of Pr-Fe-B films with perpendicular magnetic anisotropy have been studied as a function of thickness varying from 10 to 1200 nm. The crucial thickness for forming the Pr{sub 2}Fe{sub 14}B phase is estimated to be about 25 nm in our study, and the perpendicular anisotropy shows a trend to vanish for thick films. The coercivity of the films initially increases with increasing film thickness, gradually reaching a value which is near the value for bulk material. The magnetic domain size increases with increasing thickness. The surface morphology, the roughness and the domain structure of the films have been investigated by means of atomic-force microscopy and magnetic-force microscopy.

  17. Magnetic properties of a Pt/Co2FeAl/MgO structure with perpendicular magnetic anisotropy

    Institute of Scientific and Technical Information of China (English)

    Li Xiao-Qi; Xu Xiao-Guang; Wang Sheng; Wu Yong; Zhang De-Lin; Miao Jun; Jiang Yong

    2012-01-01

    Microstructures and magnetic properties of Ta/Pt/Co2FeAl (CFA)/MgO multilayers are studied to understand perpendicular magnetic anisotropy (PMA) of half-metallic full-Heusler alloy films.PMA is realized in a 2.5-nm CFA film with B2-ordered structure observed by a high resolution transmission electron microscope.It is demonstrated that a high quality interface between the ferromagnetic layer and oxide layer is not essential for PMA.The conversions between in-plane anisotropy and PMA are investigated to study the dependence of magnetic moment on temperature.At the intersection points,the decreasing slope of the saturation magnetization (Ms) changes because of the conversions.The dependence of Ms on the annealing temperature and MgO thickness is also studied.

  18. Nonlinear dynamic behaviour of a rotor-foundation system coupled through passive magnetic bearings with magnetic anisotropy - Theory and experiment

    DEFF Research Database (Denmark)

    Enemark, Søren; Santos, Ilmar F.

    2016-01-01

    In this work, the nonlinear dynamic behaviour of a vertical rigid rotor interacting with a flexible foundation by means of two passive magnetic bearings is quantified and evaluated. The quantification is based on theoretical and experimental investigation of the non-uniformity (anisotropy) of the...

  19. Crystallographic origin of perpendicular magnetic anisotropy in CoPt film: polarized x-ray absorption study

    Energy Technology Data Exchange (ETDEWEB)

    Pandey, K.K.M.; Chen, J.S.; Liu, T.; Sun, C.J.; Chow, G.M.; (NU Sinapore); (ORNL)

    2009-09-17

    Crystallographic structure, growth induced miscibility gap and strain in Ta/Co{sub 100-x}Pt{sub x} (0 {le} x {le} 43 at%)/Ru/Ta/glass films deposited at ambient temperature were investigated using polarized x-ray absorption spectroscopy to clarify the origin of observed perpendicular magnetic anisotropy (PMA) in Co{sub 72}Pt{sub 28} film. Extended x-ray absorption fine structure spectroscopy data at Co K-edge showed that Co has a similar local atomic environment and averaged interatomic distance in the in-plane and out-of-plane polarization geometries for Co{sub 72}Pt{sub 28}, ruling out the contribution of magneto-elastic anisotropy and growth induced structural anisotropy as the origin of PMA. A large PMA in Co{sub 72}Pt{sub 28} film was attributed to the preferred hexagonal close-packed stacking as observed using the x-ray absorption near-edge structure spectroscopy.

  20. Detection of the Magnetic Easy Direction in Steels Using Induced Magnetic Fields

    Directory of Open Access Journals (Sweden)

    Edgard M. Silva

    2016-12-01

    Full Text Available Conventional manufacturing processes cause plastic deformation that leads to magnetic anisotropy in processed materials. A deeper understanding of materials characterization under rotational magnetization enables engineers to optimize the overall volume, mass, and performance of devices such as electrical machines in industry. Therefore, it is important to find the magnetic easy direction of the magnetic domains in a simple and straightforward manner. The Magnetic easy direction can be obtained through destructive tests such as the Epstein frame method and the Single Sheet Tester by taking measurements in regions of irreversible magnetization usually called domains. In the present work, samples of rolled SAE 1045 steel (formed by perlite and ferrite microstructures were submitted to induced magnetic fields in the reversibility region of magnetic domains to detect the magnetic easy direction. The magnetic fields were applied to circular samples with different thicknesses and angles varying from 0° to 360° with steps of 45°. A square sample with a fixed thickness was also tested. The results showed that the proposed non-destructive approach is promising to evaluate the magnetic anisotropy in steels independently of the geometry of the sample. The region studied presented low induction losses and was affected by magnetic anisotropy, which did not occur in other works that only took into account regions of high induction losses.

  1. Rock magnetic and anisotropy of magnetic susceptibility(AMS) of earthquake affected soft sediments: Examples from Shillong and Latur (Deccan Trap), India.

    Science.gov (United States)

    Lakshmi, B. V., ,, Dr.; Gawali, Mr. Praveen B.; Deenadayalan, K., ,, Dr.; Ramesh, D. S., ,, Prof.

    2017-04-01

    Rock magnetic and anisotropy of magnetic susceptibility (AMS) of earthquake affected soft sediments: Examples from Shillong and Latur (Deccan Trap), India. B.V.Lakshmi, Praveen B.Gawali, K.Deenadayalan and D.S.Ramesh Indian Institute of Geomagnetism, plot 5, sector 18, Near Kalamboli Highway, New Panvel(W), Navi Mumbai 410218 Combined rock magnetism and anisotropy of magnetic susceptibility (AMS) studies on earthquake induced soft and non-soft sediments from Shillong and Latur, India have thrown up interesting results. The morphology of hysteresis loops, the pattern of isothermal remanent magnetization (IRM) acquisition, and temperature dependence of susceptibility indicate that titano-magnetite/magnetite is the main magnetic carrier in these sediments. We also analyzed the anisotropy of magnetic susceptibility (AMS) of liquefaction features within the seismically active Dauki fault, Shillong Plateau. We discovered that host sediments (non-liquefied), are characterized by an oblate AMS ellipsoid and liquefied sediment are characterized by a triaxial AMS ellipsoid, well grouped maximum susceptibility axis K1 (NNW-SSE trend). Field evidence and AMS analysis indicate that most of these features were emplaced by injection inferred to be due to seismically triggered fluidization. Anisotropy of magnetic susceptibility (AMS) of deformed and undeformed unconsolidated clay samples of Deccan Trap terrain from the 2000-year-old paleoearthquake site of Ther village, Maharashtra, India, was also studied. Such deposits are rare in the compact basaltic terrain because of which the results acquired are very important. The undeformed clay samples exhibit typical sedimentary fabric with an oblate AMS ellipsoid, whereas the deformed samples are tightly grouped in the inferred compression direction, probably effected by an earthquake, exhibiting prolate as well as oblate AMS ellipsoids. Rock magnetic and AMS methodology can help understand the behavior of different sediments to the

  2. Controlled pinning and depinning of domain walls in nanowires with perpendicular magnetic anisotropy.

    Science.gov (United States)

    Gerhardt, Theo; Drews, André; Meier, Guido

    2012-01-18

    We investigate switching and field-driven domain wall motion in nanowires with perpendicular magnetic anisotropy comprising local modifications of the material parameters. Intentional nucleation and pinning sites with various geometries inside the nanowires are realized via a local reduction of the anisotropy constant. Micromagnetic simulations and analytical calculations are employed to determine the switching fields and to characterize the pinning potentials and the depinning fields. Nucleation sites in the simulations cause a significant reduction of the switching field and are in excellent agreement with analytical calculations. Pinning potentials and depinning fields caused by the pinning sites strongly depend on their shapes and are well explained by analytical calculations.

  3. Effects of the applied magnetic field and anisotropy on the spin wave gap in ultrathin magnetic films at zero temperature

    Science.gov (United States)

    Kaplan, B.; Kaplan, R.

    2014-12-01

    We investigate the calculated spin wave gap of two-dimensional magnetic films under the combined influence of the in-plane direction of the applied magnetic field and different kinds of magnetic anisotropies. We also compute the spin wave gap as a function of the applied magnetic field at zero temperature. We discuss the results in connection with experimental data reported for epitaxial Fe-deficient yttrium garnet (YIG) films grown by pulsed laser deposition (PLD) technique onto the different faces of the Gd3Ga5O12 single crystal.

  4. The formation of linear aggregates in magnetic hyperthermia: implications on specific absorption rate and magnetic anisotropy.

    Science.gov (United States)

    Saville, Steven L; Qi, Bin; Baker, Jonathon; Stone, Roland; Camley, Robert E; Livesey, Karen L; Ye, Longfei; Crawford, Thomas M; Mefford, O Thompson

    2014-06-15

    The design and application of magnetic nanoparticles for use as magnetic hyperthermia agents has garnered increasing interest over the past several years. When designing these systems, the fundamentals of particle design play a key role in the observed specific absorption rate (SAR). This includes the particle's core size, polymer brush length, and colloidal arrangement. While the role of particle core size on the observed SAR has been significantly reported, the role of the polymer brush length has not attracted as much attention. It has recently been reported that for some suspensions linear aggregates form in the presence of an applied external magnetic field, i.e. chains of magnetic particles. The formation of these chains may have the potential for a dramatic impact on the biomedical application of these materials, specifically the efficiency of the particles to transfer magnetic energy to the surrounding cells. In this study we demonstrate the dependence of SAR on magnetite nanoparticle core size and brush length as well as observe the formation of magnetically induced colloidal arrangements. Colloidally stable magnetic nanoparticles were demonstrated to form linear aggregates in an alternating magnetic field. The length and distribution of the aggregates were dependent upon the stabilizing polymer molecular weight. As the molecular weight of the stabilizing layer increased, the magnetic interparticle interactions decreased therefore limiting chain formation. In addition, theoretical calculations demonstrated that interparticle spacing has a significant impact on the magnetic behavior of these materials. This work has several implications for the design of nanoparticle and magnetic hyperthermia systems, while improving understanding of how colloidal arrangement affects SAR.

  5. In-plane magnetic anisotropy and temperature dependence of switching field in (Ga, Mn) as ferromagnetic semiconductors.

    Science.gov (United States)

    Kamara, S; Terki, F; Dumas, R; Dehbaoui, M; Sadowski, J; Galéra, R M; Tran, Q-H; Charar, S

    2012-06-01

    We explore the magnetic anisotropy of GaMnAs ferromagnetic semiconductor by Planar Hall Effect (PHE) measurements. Using low magnitude of applied magnetic field (i.e., when the magnitude H is smaller than both cubic Hc and uniaxial Hu anisotropy field), we have observed various shapes of applied magnetic field direction dependence of Planar Hall Resistance (PHR). In particular, in two regions of temperature. At T Tc/2, the "square-shape" signal and at T > Tc/2 the "zigzag-shape" signal of PHR. They reflect different magnetic anisotropy and provide information about magnetization reversal process in GaMnAs ferromagnetic semiconductor. The theoretical model calculation of PHR based on the free energy density reproduces well the experimental data. We report also the temperature dependence of anisotropy constants and magnetization orientations. The transition of easy axis from biaxial to uniaxiale axes has been observed and confirmed by SQUID measurements.

  6. Engineering the magnetic anisotropy of atomic-scale nanostructure under electric field

    Science.gov (United States)

    Zhu, Wanjiao; Ding, Hang-Chen; Tong, Wen-Yi; Gong, Shi-Jing; Wan, Xiangang; Duan, Chun-Gang

    2015-02-01

    Atomic-scale magnetic nanostructures are promising candidates for future information processing devices. Utilizing external electric field to manipulate their magnetic properties is an especially thrilling project. Here, by carefully identifying the different contributions of each atomic orbital to the magnetic anisotropy energy (MAE) of the ferromagnetic metal films, we argue that it is possible to engineer both the MAE and the magnetic response to the electric field of atomic-scale magnetic nanostructures. Taking the iron monolayer as a matrix, we propose several interesting iron nanostructures with dramatically different magnetic properties. Such nanostructures could exhibit a strong magnetoelectric effect. Our work may open new avenues to the artificial design of electrically controlled magnetic devices.

  7. Abnormal effect of substrate temperature on perpendicular magnetic anisotropy in sputter-deposited NdFeCo films on silicon substrates

    Energy Technology Data Exchange (ETDEWEB)

    Tong, Liuniu, E-mail: lntong@ahut.edu.cn [Anhui Key Laboratory of Metal Materials and Processing, School of Materials Science and Engineering, Anhui University of Technology, Ma-An-Shan, 243002 Anhui (China); Deng, Peng [Anhui Key Laboratory of Metal Materials and Processing, School of Materials Science and Engineering, Anhui University of Technology, Ma-An-Shan, 243002 Anhui (China); He, Xian-Mei [School of Mathematics and Physics, Anhui University of Technology, Ma-An-Shan, 243002 Anhui (China); Li, Tingting [Anhui Key Laboratory of Metal Materials and Processing, School of Materials Science and Engineering, Anhui University of Technology, Ma-An-Shan, 243002 Anhui (China)

    2014-07-01

    The effect of substrate temperature on the perpendicular magnetic anisotropy (PMA) in sputtered NdFeCo films on Si(111) has been studied. A strong PMA is observed in the NdFeCo films deposited at 310 °C, while the room temperature (RT) deposited films show an in-plane dominated anisotropy. The microstructure reveals a stratified microstructure along film thickness due to diffusion occurring at Si(111)/NdFeCo interface of the films deposited at 310 °C. Nd{sub 2}(FeCo){sub 17} nano-crystals and Nd{sub 2}(FeCo){sub 14}Si{sub 3} and/or Nd{sub 6}(FeCo){sub 13}Si intermetallic compounds in nano-size appear in the films deposited at 310 °C, while the RT deposited NdFeCo films are in amorphous state. Annealing at 300 °C results in atomic relaxation and thus ordering of the stripe domains. The distinguishing dependence of the micro/magnetic structure and magnetic characteristics of the NdFeCo films on substrate temperature and annealing temperature is presented. It is concluded that the strong PMA is mainly from the magnetoelastic anisotropy caused by the induced interfacial stress due to the opposite thermal expansion behavior between the NdFeCo layer and Si-doped interfacial layer. - Highlights: • NdFeCo films were deposited on Si substrate at 25 and 310 °C, respectively. • The films deposited at 310 °C show a large perpendicular magnetic anisotropy (PMA). • The films deposited at 25 °C have an in-plane dominated anisotropy. • The PMA is mainly from the magnetoelastic anisotropy induced by interfacial stress.

  8. Finite size effects on the magnetocrystalline anisotropy energy in Fe magnetic nanowires from first principles

    Energy Technology Data Exchange (ETDEWEB)

    Munoz, F. [Max-Planck-Institute fuer Mikrostrukturphysik (Germany); Romero, A. H. [CINVESTAV, Unidad Queretaro (Mexico); Mejia-Lopez, J., E-mail: jmejia@puc.cl [Facultad de Fisica, Pontificia Universidad Catolica de Chile (Chile); Moran-Lopez, J. L. [Universidad Nacional Autonoma de Mexico, Laboratorio Interdisciplinario, Departamento de Fisica, Facultad de Ciencias (Mexico)

    2013-04-15

    The geometric and the electronic structures, the magnetic moments, and the magnetocrystalline anisotropy energy of bcc-Fe nanowires with z-axis along the (110) direction are calculated in the framework of ab initio theories. In particular, we report a systematic study of free standing nanowires with geometries and sizes ranging from diatomic to 1 nm wide with 31 atoms per unit cell. We found that for nanowires with less than 14 atoms per unit cell, the ground-state structure is body-centered tetragonal. We also calculated the contributions of the dipolar magnetic energy to the magnetic anisotropy energy and found that in some cases, this contribution overcomes the magnetocrystalline part, determining thereby the easy axis direction. These results emphasize the importance and competition between both contributions in low dimensional systems.

  9. Size and voltage dependence of effective anisotropy in sub-100-nm perpendicular magnetic tunnel junctions

    Science.gov (United States)

    Piotrowski, Stephan K.; Bapna, Mukund; Oberdick, Samuel D.; Majetich, Sara A.; Li, Mingen; Chien, C. L.; Ahmed, Rizvi; Victora, R. H.

    2016-07-01

    Magnetic tunnel junctions with perpendicular magnetic anisotropy are investigated using a conductive atomic force microscope. The 1.23 -nm Co40Fe40B20 recording layer coercivity exhibits a size dependence which suggests single-domain behavior for diameters ≤100 nm. Focusing on devices with diameters smaller than 100 nm, we determine the effect of voltage and size on the effective device anisotropy Keff using two different techniques. Keff is extracted both from distributions of the switching fields of the recording and reference layers and from measurement of thermal fluctuations of the recording layer magnetization when a field close to the switching field is applied. The results from both sets of measurements reveal that Keff increases monotonically with decreasing junction diameter, consistent with the size dependence of the demagnetization energy density. We demonstrate that Keff can be controlled with a voltage down to the smallest size measured, 64 nm.

  10. Three-terminal magnetic tunneling junction device with perpendicular anisotropy CoFeB sensing layer

    Energy Technology Data Exchange (ETDEWEB)

    Honjo, H., E-mail: hr-honjou@aist.go.jp; Nebashi, R.; Tokutome, K.; Miura, S.; Sakimura, N.; Sugibayashi, T. [Green Platform Research Laboratories, NEC Corporation, Tsukuba (Japan); Fukami, S.; Kinoshita, K.; Murahata, M.; Kasai, N. [Center for Spintronics Integrated Systems, Tohoku University, Sendai (Japan); Ishihara, K. [Smart Energy Research Laboratories, NEC Corporation, Tsukuba (Japan); Ohno, H. [Center for Spintronics Integrated Systems, Tohoku University, Sendai (Japan); Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, Sendai (Japan); WPI Advanced Institute for Materials Research, Tohoku University, Sendai (Japan)

    2014-05-07

    We demonstrated read and write characteristics of a three terminal memory device with a perpendicular anisotropy-free layer of a strip of [Co/Ni] and a low-switching perpendicular-anisotropy CoFeB/MgO sensing layer. This new design of the cell results in a small cell area. The switching magnetic field of the sensing layer can be decreased by changing sputtering gas for the Ta-cap from Ar to Kr. An electron energy-loss spectroscopy analysis of the cross-section of the magnetic tunneling junction (MTJ) revealed that the boron content in CoFeB with a Kr-sputtered Ta-cap was smaller than that with an Ar-sputtered one. A change in resistance for the MTJ was observed that corresponded to the magnetic switching of the Co/Ni wire and its magnetoresistance ratio and critical current were 90% and 0.8 mA, respectively.

  11. Magnetic anisotropy in the incommensurate ScFe{sub 4}Al{sub 8} system

    Energy Technology Data Exchange (ETDEWEB)

    Rećko, K., E-mail: k.recko@uwb.edu.pl [Faculty of Physics, University of Białystok, K. Ciołkowskiego 1L, 15-245 Białystok (Poland); Dobrzyński, L. [National Centre for Nuclear Research, A. Soltan 7, 05-400 Otwock-Świerk (Poland); Waliszewski, J.; Szymański, K. [Faculty of Physics, University of Białystok, K. Ciołkowskiego 1L, 15-245 Białystok (Poland)

    2015-08-15

    Neutron scattering and magnetization data are used for estimation of the spin ordering in ScFe{sub 4}Al{sub 8}. Results of experimental measurements are compared with the ground state configurations obtained by simulated annealing algorithms. The origins of the magnetocrystalline anisotropy of the scandium intermetallic alloy and the conditions of the coexistence of two different magnetic modulations as a function of the exchange integrals are discussed. The influence of the dipolar interactions for the noncollinearity and incommensurability in ScFe{sub 4}Al{sub 8} was determined. - Highlights: • We found dipolar and DM interactions as the anisotropy origins of 3d–3d–3p alloy. • We covered the explanation of incommensurability and noncollinearity of ScFe{sub 4}Al{sub 8}. • We discussed the magnetism resulting from competitiveness of exchange effects.

  12. CPO-induced seismic anisotropy in UHP eclogites

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Ultrahigh-pressure (UHP) eclogites often show strong plastic deformation and anisotropy of seismic properties. We report in this paper the seismic velocity and anisotropy of eclogite calculated from the crystallographic preferred orientations (CPOs) of constituent minerals (garnet, omphacite, quartz and rutile) and single crystal elastic properties. We also compared the calculated results with the measured results in similar eclogites. Our results suggest that (1) Except that garnet is a seismically quasi-isotropic mineral, omphacite, quartz, coesite and rutile all have strong seismic anisotropies (AVp = 23.0%―40.9%, Max. AVs = 18.5%―47.1%). They are the major sources for anisotropy in eclogite. The average seismic velocities are fast in garnet and rutile, moderate in omphacite and coesite, and slow in quartz. (2) The deformed eclogites have the maximum Vp (8.33―8.75 km/s) approximately parallel to foliation and lineation, the minimum Vp (8.25―8.62 km/s) approximately normal to foliation and lineation and the Vp anisotropies of 1.0―1.7%. Their Vs are 4.93―4.97 km/s. The corresponding maximum anisotropies (0.73%―1.78%) of Vs are at 45° to both foliation and lineation and the minimum anisotropies at positions normal to lineation on the foliation plane. The Vs1 polarization planes are approximately parallel to foliation. The mean Vp and Vs of eclogite under UHP peak metamorphism conditions (P = 3―5 GPa, T = 900―1100℃) are estimated to be 3.4%―7.2% and 6.3%―12.1% higher than those at ambient pressure and temperature conditions, respectively. (3) Omphacite component dominates the anisotropy of eclogite while garnet component reduces the anisotropy and increases the seismic velocities. Quartz component has a small effect on the anisotropy but reduces the seismic velocities of eclogite. The effect of rutile component is negligible on seismic properties of eclogite due to its trivial volume fraction. (4) The increase of volume fraction of omphacite

  13. Orbital anisotropy of the field-induced moments in chromium and vanadium

    CERN Document Server

    Brown, P J; Ziebeck, K R A

    2003-01-01

    The dependence of the cross-section for magnetic scattering of neutrons on the angle theta sub k between the field direction and the scattering vector has been used to study the orbital contribution to magnetic scattering from the moments aligned by a magnetic field in chromium and vanadium. The results lend support to band structure calculations which predict very high ratios of orbital to spin moments. The magnetic scattering from the moments induced in Cr and V by a 9.5 T field applied parallel to (110), in sets of crystallographically equivalent reflections having different values of theta sub k , has been determined from polarized neutron flipping ratio measurements. The results have been analysed using the tensor operator formalism. The results do not show the equatorial anisotropy predicted by a simple atomic model in which the orbital moment arises from mixing between empty e sub g and filled t sub 2 sub g states. The azimuthal variation observed suggests that the major part of the orbital moment is d...

  14. Exposing the intermolecular nature of the second relaxation pathway in a mononuclear cobalt(II) single-molecule magnet with positive anisotropy.

    Science.gov (United States)

    Habib, Fatemah; Korobkov, Ilia; Murugesu, Muralee

    2015-04-14

    The investigation of a pentagonal bipyramidal Co(ii) complex with large positive anisotropy (D ≈ +30 cm(-1)) revealed field induced Single-Molecule Magnet behaviour with Ueff ≈ 50 K at 1.0 kOe. This compound belongs to a group of only a handful of complexes which exhibit this unique magnetic property while possessing easy-plane anisotropy. At high applied fields, a second relaxation process with an intermolecular nature has been exposed using magnetic dilution studies with varying percentages of Zn(ii) analogue. The disappearance of the second relaxation process at low frequency can be followed using magnetically diluted samples at 25%, 10% and 5% Co(ii) concentrations.

  15. Tuning of the nucleation field in nanowires with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Kimling, Judith; Gerhardt, Theo; Kobs, Andre; Vogel, Andreas; Peter Oepen, Hans; Merkt, Ulrich; Meier, Guido [Institut fuer Angewandte Physik und Zentrum fuer Mikrostrukturforschung Hamburg, Universitaet Hamburg, Jungiusstr. 11, 20355 Hamburg (Germany); Wintz, Sebastian [Institut fuer Ionenstrahlphysik und Materialforschung, Helmholtz-Zentrum Dresden-Rossendorf, 01314 Dresden (Germany); Im, Mi-Young; Fischer, Peter [Center for X-ray Optics, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

    2013-04-28

    We report on domain nucleation in nanowires consisting of Co/Pt multilayers with perpendicular magnetic anisotropy that are patterned by electron-beam lithography, sputter deposition, and lift-off processing. It is found that the nucleation field can be tuned by changing the geometry of the wire ends. A reduction of the nucleation field by up to 60% is achieved when the wire ends are designed as tips. This contrasts with the behavior of wires with in-plane anisotropy where the nucleation field increases when triangular-pointed ends are used. In order to clarify the origin of the reduction of the nucleation field, micromagnetic simulations are employed. The effect cannot be explained by the lateral geometrical variation but is attributable to a local reduction of the perpendicular anisotropy caused by shadowing effects due to the resist mask during sputter deposition of the multilayer.

  16. Off-specular polarized neutron reflectometry study of magnetic dots with a strong shape anisotropy

    CERN Document Server

    Temst, K; Moshchalkov, V V; Bruynseraede, Y; Fritzsche, H; Jonckheere, R

    2002-01-01

    We have measured the off-specular polarized neutron reflectivity of a regular array of rectangular magnetic polycrystalline Co dots, which were prepared by a combination of electron-beam lithography, molecular beam deposition, and lift-off processes. The dots have a length-to-width ratio of 4:1 imposing a strong shape anisotropy. The intensity of the off-specular satellite reflection was monitored as a function of the magnetic field applied parallel to the rows of dots and in the plane of the sample, allowing us to analyze the magnetization-reversal process using the four spin-polarized cross sections. (orig.)

  17. Magnetic stripes and holes: Complex domain patterns in perforated films with weak perpendicular anisotropy

    Directory of Open Access Journals (Sweden)

    F. Valdés-Bango

    2017-05-01

    Full Text Available Hexagonal antidot arrays have been patterned on weak perpendicular magnetic anisotropy NdCo films by e-beam lithography and lift off. Domain structure has been characterized by Magnetic Force Microscopy at remanence. On a local length scale, of the order of stripe pattern period, domain configuration is controlled by edge effects within the stripe pattern: stripe domains meet the hole boundary at either perpendicular or parallel orientation. On a longer length scale, in-plane magnetostatic effects dominate the system: clear superdomains are observed in the patterned film with average in-plane magnetization along the easy directions of the antidot array, correlated over several antidot array cells.

  18. Manipulation of superparamagnetic beads on patterned Au/Co/Au multilayers with perpendicular magnetic anisotropy

    Science.gov (United States)

    Jarosz, A.; Holzinger, D.; Urbaniak, M.; Ehresmann, A.; Stobiecki, F.

    2016-08-01

    The magnetophoresis of water-suspended 4 μm-diameter superparamagnetic beads above topographically patterned, sputter deposited Ti(4 nm)/Au(60 nm)/[Co(0.7 nm)/Au(1 nm)] × 3 multilayers with perpendicular magnetic anisotropy was investigated. The results impressively demonstrate that the magnetic stray field landscape above the stripe structure when superimposed with an external, slowly rotating, field enables the directed transport of magnetic beads across the stripe panel with velocities up to 12 μm s-1.

  19. Strong perpendicular magnetic anisotropy in [Co/Pt] n ultrathin superlattices

    Science.gov (United States)

    Liu, Yi; Qiu, Jinjun; Ter Lim, Sze; Li Toh, Suey; Zhu, Zhengyong; Han, Guchang; Zhu, Kaigui

    2017-01-01

    Ultrathin [Co/Pt] n superlattice films consisting of 0.18-0.60-nm-thick Co and Pt sublayers were deposited by sputtering. A large in-plane saturation field (H s) of ˜39 kOe and a very large effective perpendicular magnetic anisotropy (K eff) with a magnitude of 107 erg/cm3 were attained. The highest K eff was ˜1.40 × 107 erg/cm3. These films are promising candidates for the reference layer of the p-MgO magnetic tunnel junction in Gb-scale magnetic random-access memory.

  20. Perpendicular magnetic anisotropy of Au/FePt thin films grown on Si substrates

    CERN Document Server

    Lee, Y W; Kim, C O

    1999-01-01

    FePt thin films show in plane magnetism with a very large coercive force when they are deposited on lattice-mismatched substrates, such as glass or Si In our research, FePt alloy thin films were deposited, using the coevaporation method, on a Au buffer layer which was evaporated onto a Si substrate at 500 .deg. C. The magnetic easy axis of the FePt film changed from the in-plane direction to the normal direction of the film. Therefore, it can be said that a Au buffer layer can enhance the perpendicular magnetic anisotropy of a FePt thin film on a lattice-mismatched substrate.

  1. Rock magnetism and magnetic anisotropy in folded sills and basaltic flows: A case study of volcanics from the Taimyr Peninsula, Northern Russia

    Institute of Scientific and Technical Information of China (English)

    ZHANG ShuWei; J. Harald WALDERHAUG; YANG YueJun

    2008-01-01

    Magnetic measurements were performed on apparently deformed igneous rocks of 23 sites from the southeastern part of the Taimyr Peninsula. Rock magnetism and reflected light microscopy analyses reveal that fine-grained titanomagnetites up to pure magnetites mainly carry the majority of magnetic fabrics in the sills, and that the slightly coarser Ti-poor or-medium titanomagnetites carry most mag-netic fabrics in the basaltic flows. Magnetic anisotropies were determined by applying anisotropy of low-field magnetic susceptibility (AMS) on 180 unheated samples and 128 samples that had been pre-viously heated to 600℃ during a paleomagnetic study to detect heating effects on the anisotropy of magnetic susceptibility (AMS) properties of volcanic rocks. Laboratory heating significantly affects anisotropy variations of these igneous rocks corresponding to the mineralogical changes during the heat treatment.

  2. Edge-modulated perpendicular magnetic anisotropy in [Co/Pd]n and L10-FePt thin film wires

    Science.gov (United States)

    Zhang, Jinshuo; Ho, Pin; Currivan-Incorvia, Jean Anne; Siddiqui, Saima A.; Baldo, Marc A.; Ross, Caroline A.

    2015-11-01

    Thickness modulation at the edges of nanostructured magnetic thin films is shown to have important effects on their perpendicular magnetic anisotropy. Thin film wires with tapered edges were made from [Co/Pd]20 multilayers or L10-FePt films using liftoff with a double-layer resist. The effect of edge taper on the reversal process was studied using magnetic force microscopy and micromagnetic modeling. In [Co/Pd]20, the anisotropy was lower in the tapered edge regions which switched at a lower reverse field compared to the center of the wire. The L10-FePt wires showed opposite behavior with the tapered regions exhibiting higher anisotropy.

  3. Perpendicular magnetic anisotropy of ultrathin FeCo alloy films on Pd(0 0 1) surface: First principles study

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Dongyoo [Department of Physics, Pukyong National University, Busan 608-737 (Korea, Republic of); Hong, Jisang [Department of Physics, Pukyong National University, Busan 608-737 (Korea, Republic of)], E-mail: hongj@pknu.ac.kr

    2009-06-15

    Using the full potential linearized augmented plane wave (FLAPW) method, thickness dependent magnetic anisotropy of ultrathin FeCo alloy films in the range of 1 monolayer (ML) to 5 ML coverage on Pd(0 0 1) surface has been explored. We have found that the FeCo alloy films have close to half metallic state and well-known surface enhancement in thin film magnetism is observed in Fe atom, whereas the Co has rather stable magnetic moment. However, the largest magnetic moment in Fe and Co is found at 1 ML thickness. Interestingly, it has been observed that the interface magnetic moments of Fe and Co are almost the same as those of surface elements. The similar trend exists in orbital magnetic moment. This indicates that the strong hybridization between interface FeCo alloy and Pd gives rise to the large magnetic moment. Theoretically calculated magnetic anisotropy shows that the 1 ML FeCo alloy has in-plane magnetization, but the spin reorientation transition (SRT) from in-plane to perpendicular magnetization is observed above 2 ML thickness with huge magnetic anisotropy energy. The maximum magnetic anisotropy energy for perpendicular magnetization is as large as 0.3 meV/atom at 3 ML film thickness with saturation magnetization of 2.36{mu}{sub B}. Besides, the calculated X-ray magnetic circular dichroism (XMCD) has been presented.

  4. Anisotropy of Anhysteretic Remanent Magnetization: A Tool To Estimate Trm Deviations In Volcanic Rocks

    Science.gov (United States)

    Gattacceca, J.; Rochette, P.

    In order to assess the paleomagnetic direction deviations due to anisotropy in volcanic rocks, we studied the anisotropies of magnetic susceptibility (AMS), of anhysteretic remanent magnetization (AARM) and of thermoremanent magnetization (ATRM) of a set of Miocene pyroclastic rocks from Sardinia (Italy). The main magnetic carrier is pseudo-single domain titanomagnetite. AARM and ATRM were determined with a 3-position measurement scheme. The measurements show that there is no general relation between the degrees of AMS and ATRM (as this relation depends on the ti- tanomagnetite grain size spectrum), while the degree of AARM and ATRM are almost identical. Measuring the AMS is thus nearly irrelevant to quantitatively estimate TRM deviations due to anisotropy in volcanic rocks. Instead, measuring the AARM provides a reliable and relatively fast method to correct paleomagnetic direction deviations in volcanic rocks (inclination shallowing due to horizontal planar fabric in most cases). This is confirmed by a case study on a succession of four welded pyroclastic flows : an apparent paleosecular variation pattern is almost entirely explained by the effect of ATRM.

  5. Magneto-optical investigation of the shape anisotropy of individual micron-sized magnetic elements

    Science.gov (United States)

    Sebastian, T.; Conca, A.; Wolf, G.; Schultheiss, H.; Leven, B.; Hillebrands, B.

    2011-10-01

    In this work, the anisotropy of individual microstructured magnetic elements has been investigated. The investigated elements are of elliptical shape with different sizes and aspect ratios (AR), structured from a 5-nm-thick permalloy (Ni80 Fe20) film. For the measurements, a new magneto-optical Kerr effect (MOKE) magnetometer was used. To allow for the investigation of individual microstructured elements, a micro-focused probing laser beam (spatial resolution ≈1μm) has been combined with a self-stabilizing positioning system of high accuracy, including a rotating unit. Hysteresis loops can be taken for varying orientation of the symmetry axes of the magnetic elements relative to the applied field. For the characterization of the anisotropy, the coercive field as a function of the magnetization direction is extracted from the corresponding hysteresis loops. These results make a quantitative and systematic study of the influence of the shape anisotropy on the magnetic behavior of microstructures possible. The experimental data has been compared to an extended Stoner-Wohlfarth model.

  6. Perpendicular Magnetic Anisotropy of Tb/Fe and Gd/Fe Multilayers Studied with Torque Magnetometer

    Science.gov (United States)

    Chowdhury, Ataur

    Perpendicular magnetic anisotropy (PMA) of multilayers critically depend on the magnetic and structural ordering of the interface. To study the effect of interface on PMA, Tb/Fe and Gd/Fe multilayers with varying Fe (0.8-9.0 nm) and Gd (0.5-2.8 nm) or Tb (0.3-6.3 nm) layer thicknesses were fabricated by planar magnetron sputtering. The magnetometer results of spin orientation clearly reveals that samples with Gd or Tb layer thickness of more than 1.2 nm display no PMA, regardless of the Fe layer thickness. Tb/Fe and Gd/Fe multilayers with thin (<1.2 nm) Tb or Gd layers display large PMA, but no PMA is observed when the Fe layer thickness is increased to 4.0 nm and higher. The bulk magnetization and anisotropy energy constant of the samples are found to increase with increasing Fe layer thickness. Torque measurement also reveals that there are two distinctly different axes of spin alignment at different energy. Tb/Fe and Gd/Fe multilayers with similar composition reveal similar magnetic and structural characteristics, and it may imply that single-ion-anisotropy of rare-earth element, which is quite large for Tb ions and very small for Gd ions, may not be the dominating cause of PMA in Td/Fe and Gd/Fe multilayers. A detailed explanation of the results will be provided based on exchange interaction at the interface.

  7. Engineering the magnetic coupling and anisotropy at the molecule-magnetic surface interface in molecular spintronic devices

    Science.gov (United States)

    Campbell, Victoria E.; Tonelli, Monica; Cimatti, Irene; Moussy, Jean-Baptiste; Tortech, Ludovic; Dappe, Yannick J.; Rivière, Eric; Guillot, Régis; Delprat, Sophie; Mattana, Richard; Seneor, Pierre; Ohresser, Philippe; Choueikani, Fadi; Otero, Edwige; Koprowiak, Florian; Chilkuri, Vijay Gopal; Suaud, Nicolas; Guihéry, Nathalie; Galtayries, Anouk; Miserque, Frederic; Arrio, Marie-Anne; Sainctavit, Philippe; Mallah, Talal

    2016-12-01

    A challenge in molecular spintronics is to control the magnetic coupling between magnetic molecules and magnetic electrodes to build efficient devices. Here we show that the nature of the magnetic ion of anchored metal complexes highly impacts the exchange coupling of the molecules with magnetic substrates. Surface anchoring alters the magnetic anisotropy of the cobalt(II)-containing complex (Co(Pyipa)2), and results in blocking of its magnetization due to the presence of a magnetic hysteresis loop. In contrast, no hysteresis loop is observed in the isostructural nickel(II)-containing complex (Ni(Pyipa)2). Through XMCD experiments and theoretical calculations we find that Co(Pyipa)2 is strongly ferromagnetically coupled to the surface, while Ni(Pyipa)2 is either not coupled or weakly antiferromagnetically coupled to the substrate. These results highlight the importance of the synergistic effect that the electronic structure of a metal ion and the organic ligands has on the exchange interaction and anisotropy occurring at the molecule-electrode interface.

  8. Lattice and magnetic anisotropies in uranium intermetallic compounds

    DEFF Research Database (Denmark)

    Havela, L.; Mašková, S.; Adamska, A.

    2013-01-01

    Examples of UNiAlD and UCoGe illustrate that the soft crystallographic direction coincides quite generally with the shortest U-U links in U intermetallics. Added to existing experimental evidence on U compounds it leads to a simple rule, that the easy magnetization direction and the soft crystall...... crystallographic direction (in the sense of highest compressibility under hydrostatic pressure) must be mutually orthogonal. © (2013) Trans Tech Publications, Switzerland....

  9. Electronic structure and magnetic anisotropy of CrO_2

    OpenAIRE

    Toropova, A.; Kotliar, G.; Savrasov, S. Y.; Oudovenko, V. S.

    2004-01-01

    The problem of importance of strong correlations for the electronic structure, transport and magnetic properties of half--metallic ferromagnetic CrO_2 is addressed by performing density functional electronic structure calculations in the local spin density approximation (LSDA) as well as using the LSDA+U method. It is shown that the corresponding low--temperature experimental data are best fitted without accounting for the Hubbard U corrections. We conclude that the ordered phase of CrO$_2 is...

  10. Magnetic anisotropy and microscopy studies in magnetostrictive Tb-(Fe,Co) thin films

    Science.gov (United States)

    Umadevi, K.; Talapatra, A.; Arout Chelvane, J.; Palit, Mithun; Mohanty, J.; Jayalakshmi, V.

    2017-08-01

    This paper reports the effect of the film thickness on the magnetostrictive behavior of (Fe,Co) rich Tb-(Fe,Co) films grown on Si ⟨100⟩ by electron beam evaporation. Magnetostriction was found to decrease with an increase in film thicknesses. To understand the variation of magnetostriction with the film thickness, detailed structural, microstructural, magnetization, and magnetic microscopy studies were carried out. X-ray diffraction studies indicated the presence of two phases, viz., Tb2 (Fe, Co)17 and Fe-Co phases, for all the films. With the increase in the film thickness, the peak intensity of the Tb2 (Fe, Co)17 phase decreased and that of the Fe-Co phase increased. Magnetization studies showed the presence of strong in-plane anisotropy for all the films. In addition to this, the presence of the out-of-plane component of magnetization was also observed for the films grown with higher thicknesses. This anisotropic behavior was also validated through magnetic microscopy studies carried out along the in-plane and out-of-plane directions employing magneto-optic Kerr microscopy and magnetic force microscopy, respectively. The decrease in magnetostriction was explained on the basis of dual phase formation and complex interplay between the in-plane and out-of-plane magnetic anisotropies present in the film.

  11. Magnetic tunnel junctions using Co/Pt multilayered free layers with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Machida, K; Funabashi, N; Aoshima, K; Kuga, K; Kikuchi, H; Shimidzu, N [Science and Technology Research Labs., Japan Broadcasting Corp. (NHK), 1-10-11 Kinuta, Setagaya-ku, Tokyo 157-8510 (Japan); Furukawa, K; Nakayama, T [Department of Electrical Engineering, Tokyo Denki University, 2-2 Kandanishikicho, Chiyoda-ku, Tokyo 101-8457 (Japan); Ishibashi, T, E-mail: machida.k-ge@nhk.or.jp [Department of Materials Science and Technology, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188 (Japan)

    2011-07-06

    Co/Pt multilayered films with perpendicular magnetic anisotropy have a large magneto-optical Kerr effect. To use the films with a submicron magneto-optical light modulator driven by spin transfer switching, we fabricated two types of magnetic tunnel junctions (MTJs) with Co/Pt multilayered films for the free layers. One is an fcc-based MTJ, another is a bcc-based MTJ with CoFeB/MgO/CoFeB junction. The fcc-based MTJ with a Ag buffer layer on the bottom electrode showed a large coercive force of the pinned layer, a large Kerr rotation angle of 0.3 degree in the free layer and a tunnel magnetoresistance (TMR) ratio of 3.8%. In the CoFeB/MgO/CoFeB junction, an X-ray diffraction pattern of an MgO layer showed a large MgO(002)-orientation. However, the TMR ratio was less than 3 %. An MTJ with a Ta buffer layer between the CoFeB layer and the Co/Pt multilayered films in the free layer was prepared. The Ta buffer was used to alleviate a lattice mismatch between bcc-CoFeB/MgO/CoFeB and fcc-Co/Pt multilayer. The peak intensity of the MgO(002)-orientation was increased up to 2 times. This result suggests that the crystalline texture of the bcc-CoFeB/MgO/CoFeB junction is strongly influenced by the fcc-Co/Pt multilayered films.

  12. Perpendicular Magnetic Anisotropy in Ultrathin Co/Ni Multilayer Films Studies with Ferromagnetic Resonance and Magnetic X-Ray Microspectroscopy

    Science.gov (United States)

    2012-06-28

    Element specific hysteresis measurements for n¼6 obtained at the Fe L3 edge with an out-of-plane applied field, showing a hard axis magnetic response...of the perpendicular magnetic anisotropy in these systems, XMCD spectroscopy and element-specific hysteresis loops were measured at beam line U4B at...Fig. 2(b) and (c) were measured by tuning the photon energy to the L3 edges of Co, Ni, and Fe and sweeping the out-of-plane magnetic field from an

  13. Perpendicular magnetic anisotropy in granular multilayers of CoPd alloyed nanoparticles

    Science.gov (United States)

    Vivas, L. G.; Rubín, J.; Figueroa, A. I.; Bartolomé, F.; García, L. M.; Deranlot, C.; Petroff, F.; Ruiz, L.; González-Calbet, J. M.; Pascarelli, S.; Brookes, N. B.; Wilhelm, F.; Chorro, M.; Rogalev, A.; Bartolomé, J.

    2016-05-01

    Co-Pd multilayers obtained by Pd capping of pre-deposited Co nanoparticles on amorphous alumina are systematically studied by means of high-resolution transmission electron microscopy, x-ray diffraction, extended x-ray absorption fine structure, SQUID-based magnetometry, and x-ray magnetic circular dichroism. The films are formed by CoPd alloyed nanoparticles self-organized across the layers, with the interspace between the nanoparticles filled by the non-alloyed Pd metal. The nanoparticles show atomic arrangements compatible with short-range chemical order of L 10 strucure type. The collective magnetic behavior is that of ferromagnetically coupled particles with perpendicular magnetic anisotropy, irrespective of the amount of deposited Pd. For increasing temperature three magnetic phases are identified: hard ferromagnetic with strong coercive field, soft-ferromagnetic as in an amorphous asperomagnet, and superparamagnetic. Increasing the amount of Pd in the system leads to both magnetic hardness increment and higher transition temperatures. Magnetic total moments of 1.77(4) μB and 0.45(4) μB are found at Co and Pd sites, respectively, where the orbital moment of Co, 0.40(2) μB, is high, while that of Pd is negligible. The effective magnetic anisotropy is the largest in the capping metal series (Pd, Pt, W, Cu, Ag, Au), which is attributed to the interparticle interaction between de nanoparticles, in addition to the intraparticle anisotropy arising from hybridization between the 3 d -4 d bands associated to the Co and Pd chemical arrangement in a L 10 structure type.

  14. Perpendicular magnetic anisotropy in Co2MnGa and its anomalous Hall effect

    Science.gov (United States)

    Ludbrook, B. M.; Ruck, B. J.; Granville, S.

    2017-02-01

    We report perpendicular magnetic anisotropy in the ferromagnetic Heusler alloy Co2MnGa in a MgO/Co2MnGa/Pd trilayer stack for Co2MnGa thicknesses up to 3.5 nm. There is a thickness- and temperature-dependent spin reorientation transition from perpendicular to in-plane magnetic anisotropy, which we study through the anomalous Hall effect. From the temperature dependence of the anomalous Hall effect, we observe the expected scaling of ρx y A H E with ρxx, suggesting that the intrinsic and side-jump mechanisms are largely responsible for the anomalous Hall effect in this material.

  15. Electronic structure and magnetic anisotropy of CrO2

    Science.gov (United States)

    Toropova, A.; Kotliar, G.; Savrasov, S. Y.; Oudovenko, V. S.

    2005-05-01

    The problem of importance of strong correlations for the electronic structure, transport, and magnetic properties of half-metallic ferromagnetic CrO2 is addressed by performing density functional electronic structure calculations in the local spin density approximation (LSDA) as well as using the LSDA+U method. It is shown that the corresponding low-temperature experimental data are best fitted without accounting for the Hubbard U corrections. We conclude that the ordered phase of CrO2 is weakly correlated.

  16. Electric field modulation of magnetic anisotropy and microwave absorption properties in Fe50Ni50/Teflon composite films

    Directory of Open Access Journals (Sweden)

    Zhenjun Xia

    2016-05-01

    Full Text Available Fe50Ni50 nanoparticle films with the size about 6 nm were deposited by a high energetic cluster deposition source. An electric field of about 0 - 40 kV was applied on the sample platform when the films were prepared. The field assisted deposition technique can dramatically induce in-plane magnetic anisotropy. To probe the microwave absorption properties, the Fe50Ni50 nanoparticles were deliberately deposited on the dielectric Teflon sheet. Then the laminated Fe50Ni50/Teflon composites were used to do reflection loss scan. The results prove that the application of electric field is an effective avenue to improve the GHz microwave absorption performance of our magnetic nanoparticles films expressed by the movement of reflection loss peak to high GHz region for the composites.

  17. Electric field modulation of magnetic anisotropy and microwave absorption properties in Fe50Ni50/Teflon composite films

    Science.gov (United States)

    Xia, Zhenjun; He, Jun; Ou, Xiulong; Wang, Yu; He, Shuli; Zhao, Dongliang; Yu, Guanghua

    2016-05-01

    Fe50Ni50 nanoparticle films with the size about 6 nm were deposited by a high energetic cluster deposition source. An electric field of about 0 - 40 kV was applied on the sample platform when the films were prepared. The field assisted deposition technique can dramatically induce in-plane magnetic anisotropy. To probe the microwave absorption properties, the Fe50Ni50 nanoparticles were deliberately deposited on the dielectric Teflon sheet. Then the laminated Fe50Ni50/Teflon composites were used to do reflection loss scan. The results prove that the application of electric field is an effective avenue to improve the GHz microwave absorption performance of our magnetic nanoparticles films expressed by the movement of reflection loss peak to high GHz region for the composites.

  18. Characterization of Residual Stresses in Ferrous Components by Magnetic Anisotropy Measurements Using a Hall Effect Sensor Array Probe

    Science.gov (United States)

    Lo, C. C. H.

    2011-06-01

    A new surface sensor probe comprising an angular array of Hall effect sensors has been developed for characterization of residual stresses in ferrous materials by means of stress-induced magnetic anisotropy measurements. The sensor probe applies a radially spreading ac magnetic field to a test sample, and detects stray fields in different directions simultaneously to determine the principal stress axes. In situ measurements were conducted on a annealed steel plate under four-point bending stresses to evaluate the probe performance. The ratio of stray field signals measured along and perpendicular to the stress axis varies linearly with the surface stress, indicating the possibility of characterizing residual stresses in ferrous components using the sensor array probe.

  19. Spin Hall switching of the magnetization in Ta/TbFeCo structures with bulk perpendicular anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Zhengyang; Jamali, Mahdi; Smith, Angeline K.; Wang, Jian-Ping, E-mail: jpwang@umn.edu [Department of Electrical and Computer Engineering, University of Minnesota, 4-174 200 Union Street SE, Minneapolis, Minnesota 55455 (United States)

    2015-03-30

    Spin-orbit torques are studied in Ta/TbFeCo/MgO patterned structures, where the ferrimagnetic material TbFeCo provides a strong bulk perpendicular magnetic anisotropy (bulk-PMA) independent of the interfaces. The current-induced magnetization switching in TbFeCo is investigated in the presence of a perpendicular, longitudinal, or transverse field. An unexpected partial-switching phenomenon is observed in the presence of a transverse field unique to our bulk-PMA material. It is found that the anti-damping torque related with spin Hall effect is very strong, and a spin Hall angle is determined to be 0.12. The field-like torque related with Rashba effect is unobservable, suggesting that the interface play a significant role in Rashba-like torque.

  20. Dependence of Effective Anisotropy on Grain Size in Nanocrystalline Nd2Fe14B Hard Magnetic Material

    Institute of Scientific and Technical Information of China (English)

    Feng Weicun; Gao Ruwei; Han Guangbing; Zhu Minggang; Li Wei; Sun Guangfei

    2005-01-01

    Taking nanocrystalline Nd2Fe14B as a typical sample, based on Herzer′s random anisotropy theory and the cubic grain model, the partial exchange-coupling interaction model was established and the dependence of effective anisotropy constant Keff on grain size was investigated. Calculation results reveal that the exchange-coupling interaction enhances and the effective anisotropy of material Keff decreases with the reduction of grain size. The variation of Keff is basically the same as that of coercivity. The decrease of effective anisotropy is the main reason of the reduction of coercivity for nanocrystalline Nd2Fe14B permanent magnetic material.