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Sample records for strong perpendicular magnetic

  1. Viscosity of two-dimensional strongly coupled dusty plasma modified by a perpendicular magnetic field.

    Science.gov (United States)

    Feng, Yan; Lin, Wei; Murillo, M S

    2017-11-01

    Transport properties of two-dimensional (2D) strongly coupled dusty plasmas have been investigated in detail, but never for viscosity with a strong perpendicular magnetic field; here, we examine this scenario using Langevin dynamics simulations of 2D liquids with a binary Yukawa interparticle interaction. The shear viscosity η of 2D liquid dusty plasma is estimated from the simulation data using the Green-Kubo relation, which is the integration of the shear stress autocorrelation function. It is found that, when a perpendicular magnetic field is applied, the shear viscosity of 2D liquid dusty plasma is modified substantially. When the magnetic field is increased, its viscosity increases at low temperatures, while at high temperatures its viscosity diminishes. It is determined that these different variational trends of η arise from the different behaviors of the kinetic and potential parts of the shear stress under external magnetic fields.

  2. Magnetotransport properties of Cr1−δTe thin films with strong perpendicular magnetic anisotropy

    Directory of Open Access Journals (Sweden)

    L. Zhou

    2017-12-01

    Full Text Available P-type ferromagnetic Cr1-δTe thin films with the Curie temperature of 170K were epitaxially grown on GaAs substrate. Low-temperature magnetotransport study reveals that the film has a strong perpendicular magnetic anisotropy (PMA and an anisotropic magnetoresistance (AMR ratio up to 8.1%. Furthermore, reduced anomalous Hall effect is observed at low temperatures in Cr1-δTe, suggesting the possible crossover of the contribution to AHE from the intrinsic mechanism to extrinsic skew scattering. Distinctive from conventional transition metal ferromagnets, the AMR ratio is also greatly suppressed at low temperatures. Our work demonstrates that epitaxial Cr1-δTe films are interesting platforms for studying the physics underlying the strong PMA and large AMR.

  3. Strong ion accelerating by collisionless magnetosonic shock wave propagating perpendicular to a magnetic field

    International Nuclear Information System (INIS)

    Ohsawa, Yukiharu.

    1984-12-01

    A 2-1/2 dimensional fully relativistic, fully electromagnetic particle code is used to study a time evolution of nonlinear magnetosonic pulse propagating in the direction perpendicular to a magnetic field. The pulse is excited by an instantaneous piston acceleration, and evolves totally self-consistently. Large amplitude pulse traps some ions and accelerates them parallel to the wave front. They are detrapped when their velocities become of the order of the sum of the ExB drift velocity and the wave phase velocity, where E is the electric field in the direction of wave propagation. The pulse develops into a quasi-shock wave in a collisionless plasma by a dissipation due to the resonant ion acceleration. Simple nonlinear wave theory for a cold plasma well describes the shock properties observed in the simulation except for the effects of resonant ions. In particular, magnitude of an electric potential across the shock region is derived analytically and is found to be in good agreement with our simulations. The potential jump is proportional to B 2 , and hence the ExB drift velocity of the trapped ions is proportional to B. (author)

  4. Strong perpendicular magnetic anisotropy at FeCoB/MgO interface with an ultrathin HfOx insertion layer

    Science.gov (United States)

    Ou, Yongxi; Ralph, Daniel; Buhrman, Robert

    The realization of robust perpendicular magnetic anisotropy (PMA) in heavy metal(HM)/FeCoB/MgO thin-film heterostructures has enabled a pathway for the implementation of high density memory elements based on perpendicularly magnetized tunnel junctions, and also provides a platform for the study and control of domain walls and of novel magnetic chiral structures such as skyrmions in nanowire structures. Here we report on the achievement of more robust PMA in Ta/FeCoB/MgO heterostructures by the insertion of an ultrathin HfOx passivation layer at the FeCoB/MgO interface. This is accomplished by depositing one to two atomic layers of Hf onto the FeCoB before the subsequent rf sputter deposition of the MgO layer, which fully oxidizes the Hf layer as confirmed by X-ray photoelectron spectroscopy measurements. The result is a strong interfacial perpendicular anisotropy energy density as large as 1.7 erg/cm-2 without any post-fabrication annealing treatment. Similar results have been achieved with the use of W and Pt HM base layers. This work broadens the class and enhances the capabilities of PMA HM/FM heterostructures for spintronics research and applications.

  5. Surface-termination-dependent magnetism and strong perpendicular magnetocrystalline anisotropy of an FeRh(001) thin film

    Czech Academy of Sciences Publication Activity Database

    Jekal, S.; Rhim, S.H.; Hong, S.C.; Son, W.-J.; Shick, Alexander

    2015-01-01

    Roč. 92, č. 6 (2015), " 064410-1"-" 064410-6" ISSN 1098-0121 R&D Projects: GA ČR GA15-07172S Institutional support: RVO:68378271 Keywords : magnetic anisotropy * magnetic recording * surface science Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.736, year: 2014

  6. Perpendicular relativistic shocks in magnetized pair plasma

    Science.gov (United States)

    Plotnikov, Illya; Grassi, Anna; Grech, Mickael

    2018-04-01

    Perpendicular relativistic (γ0 = 10) shocks in magnetized pair plasmas are investigated using two dimensional Particle-in-Cell simulations. A systematic survey, from unmagnetized to strongly magnetized shocks, is presented accurately capturing the transition from Weibel-mediated to magnetic-reflection-shaped shocks. This transition is found to occur for upstream flow magnetizations 10-3 10-2, it leaves place to a purely electromagnetic precursor following from the strong emission of electromagnetic waves at the shock front. Particle acceleration is found to be efficient in weakly magnetized perpendicular shocks in agreement with previous works, and is fully suppressed for σ > 10-2. Diffusive Shock Acceleration is observed only in weakly magnetized shocks, while a dominant contribution of Shock Drift Acceleration is evidenced at intermediate magnetizations. The spatial diffusion coefficients are extracted from the simulations allowing for a deeper insight into the self-consistent particle kinematics and scale with the square of the particle energy in weakly magnetized shocks. These results have implications for particle acceleration in the internal shocks of AGN jets and in the termination shocks of Pulsar Wind Nebulae.

  7. Current induced multi-mode propagating spin waves in a spin transfer torque nano-contact with strong perpendicular magnetic anisotropy

    Science.gov (United States)

    Mohseni, S. Morteza; Yazdi, H. F.; Hamdi, M.; Brächer, T.; Mohseni, S. Majid

    2018-03-01

    Current induced spin wave excitations in spin transfer torque nano-contacts are known as a promising way to generate exchange-dominated spin waves at the nano-scale. It has been shown that when these systems are magnetized in the film plane, broken spatial symmetry of the field around the nano-contact induced by the Oersted field opens the possibility for spin wave mode co-existence including a non-linear self-localized spin-wave bullet and a propagating mode. By means of micromagnetic simulations, here we show that in systems with strong perpendicular magnetic anisotropy (PMA) in the free layer, two propagating spin wave modes with different frequency and spatial distribution can be excited simultaneously. Our results indicate that in-plane magnetized spin transfer nano-contacts in PMA materials do not host a solitonic self-localized spin-wave bullet, which is different from previous studies for systems with in plane magnetic anisotropy. This feature renders them interesting for nano-scale magnonic waveguides and crystals since magnon transport can be configured by tuning the applied current.

  8. Write field asymmetry in perpendicular magnetic recording

    Science.gov (United States)

    Li, Zhanjie; Bai, Daniel Z.; Lin, Ed; Mao, Sining

    2012-04-01

    We present a systematic study of write field asymmetry by using micromagnetic modeling for a perpendicular magnetic recording (PMR) writer structure. Parameters investigated include initial magnetization condition, write current amplitude, write current frequency, and initial write current polarity. It is found that the write current amplitude and frequency (data rate) are the dominant factors that impact the field asymmetry. Lower write current amplitude and higher write current frequency will deteriorate the write field asymmetry, causing recording performance (such as bit error rate) degradation.

  9. Tailoring perpendicular magnetic coupling by XMCD

    Directory of Open Access Journals (Sweden)

    Y. U. Idzerda

    2017-05-01

    Full Text Available The elemental perpendicular magnetic anisotropy constants of both elements of a 20 nm bcc Co88Mn12 alloy film grown on MgO(001 and capped with Al, have been determined. By fitting a Stoner-Wohlfarth astroid model to the measured Co and Mn L3 XMCD peak intensities as a function of incidence photon angle with the magnetic field applied co-axially with the photon propagation direction, the elemental perpendicular anisotropy constants were found to be −6.46 x 105 J/m3 and −6.68 x 105 J/m3, respectively. The modeling of the Co and Mn data both result in nearly the same anisotropy constant as expected for a single alloy film.

  10. Recent progress in perpendicularly magnetized Mn-based binary alloy films

    Science.gov (United States)

    Zhu, Li-Jun; Nie, Shuai-Hua; Zhao, Jian-Hua

    2013-11-01

    In this article, we review the recent progress in growth, structural characterizations, magnetic properties, and related spintronic devices of tetragonal MnxGa and MnxAl thin films with perpendicular magnetic anisotropy. First, we present a brief introduction to the demands for perpendicularly magnetized materials in spintronics, magnetic recording, and permanent magnets applications, and the most promising candidates of tetragonal MnxGa and MnxAl with strong perpendicular magnetic anisotropy. Then, we focus on the recent progress of perpendicularly magnetized MnxGa and MnxAl respectively, including their lattice structures, bulk synthesis, epitaxial growth, structural characterizations, magnetic and other spin-dependent properties, and spintronic devices like magnetic tunneling junctions, spin valves, and spin injectors into semiconductors. Finally, we give a summary and a perspective of these perpendicularly magnetized Mn-based binary alloy films for future applications.

  11. Heusler compounds with perpendicular magnetic anisotropy and large tunneling magnetoresistance

    Science.gov (United States)

    Faleev, Sergey V.; Ferrante, Yari; Jeong, Jaewoo; Samant, Mahesh G.; Jones, Barbara; Parkin, Stuart S. P.

    2017-07-01

    In the present work we suggest a recipe for finding tetragonal Heusler compounds with perpendicular magnetic anisotropy (PMA) that also exhibit large tunneling magnetoresistance (TMR) when used as electrodes in magnetic tunnel junction devices with suitable tunneling barrier materials. We performed density-functional theory calculations for 286 Heusler compounds and identified 116 stable tetragonal compounds. Ten of these compounds are predicted to have strong PMA and, simultaneously, exponentially increasing TMR with increasing tunneling barrier thickness due to the so-called Brillouin zone spin filtering effect. Experimental measurements performed for 25 Heusler compounds theoretically identified as tetragonal show that ten of these compounds indeed have tetragonal structure with PMA.

  12. Temperature dependence of microwave oscillations in magnetic tunnel junctions with a perpendicularly magnetized free layer

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Peng; Feng, Jiafeng, E-mail: hxwei@iphy.ac.cn, E-mail: jiafengfeng@iphy.ac.cn; Wei, Hongxiang, E-mail: hxwei@iphy.ac.cn, E-mail: jiafengfeng@iphy.ac.cn; Han, Xiufeng [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Fang, Bin; Zhang, Baoshun; Zeng, Zhongming [Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Ruoshui Road 398, Suzhou 215123 (China)

    2015-01-05

    We experimentally study the temperature dependence of the spin-transfer-torque-induced microwave oscillations in MgO-based magnetic tunnel junction nanopillars with a perpendicularly magnetized free layer. We demonstrate that the oscillation frequency increases rapidly with decreasing temperature, which is mainly ascribed to the temperature dependence of both the saturation magnetization and the perpendicular magnetic anisotropy. We also find that a strong temperature dependence of the output power while a nonmonotonic temperature dependence of spectral linewidth are maintained for a constant dc bias in measured temperature range. Possible mechanisms leading to the different dependences of oscillation frequency, output power, and linewidth are discussed.

  13. Angular dependence of magnetization reversal in epitaxial chromium telluride thin films with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Pramanik, Tanmoy, E-mail: pramanik.tanmoy@utexas.edu; Roy, Anupam, E-mail: anupam@austin.utexas.edu; Dey, Rik, E-mail: rikdey@utexas.edu; Rai, Amritesh; Guchhait, Samaresh; Movva, Hema C.P.; Hsieh, Cheng-Chih; Banerjee, Sanjay K.

    2017-09-01

    Highlights: • Perpendicular magnetic anisotropy in epitaxial Cr{sub 2}Te{sub 3} has been investigated. • Presence of a relatively strong second order anisotropy contribution is observed. • Magnetization reversal is explained quantitatively using a 1D defect model. • Relative roles of nucleation and pinning in magnetization reversal are discussed. • Domain structures and switching process are visualized by micromagnetic simulation. - Abstract: We investigate magnetic anisotropy and magnetization reversal mechanism in chromium telluride thin films grown by molecular beam epitaxy. We report existence of strong perpendicular magnetic anisotropy in these thin films, along with a relatively strong second order anisotropy contribution. The angular variation of the switching field observed from the magnetoresistance measurement is explained quantitatively using a one-dimensional defect model. The model reveals the relative roles of nucleation and pinning in the magnetization reversal, depending on the applied field orientation. Micromagnetic simulations are performed to visualize the domain structure and switching process.

  14. Properties of a Bound Polaron under a Perpendicular Magnetic Field

    International Nuclear Information System (INIS)

    Liu Jia; Chen Ziyu; Xiao Jinglin; Huo Shufen

    2007-01-01

    We investigate the influence of a perpendicular magnetic field on a bound polaron near the interface of a polar-polar semiconductor with Rashba effect. The external magnetic field strongly changes the ground state binding energy of the polaron and the Rashba spin-orbit (SO) interaction originating from the inversion asymmetry in the heterostructure splits the ground state binding energy of the bound polaron. In this paper, we have shown how the ground state binding energy will be with the change of the external magnetic field, the location of a single impurity, the wave vector of the electron and the electron areal density, taking into account the SO coupling. Due to the presence of the phonons, whose energy gives negative contribution to the polaron's, the spin-splitting states of the bound polaron are more stable, and we find that in the condition of week magnetic field, the Zeeaman effect can be neglected.

  15. NON-AXISYMMETRIC PERPENDICULAR DIFFUSION OF CHARGED PARTICLES AND THEIR TRANSPORT ACROSS TANGENTIAL MAGNETIC DISCONTINUITIES

    Energy Technology Data Exchange (ETDEWEB)

    Strauss, R. D.; Engelbrecht, N. E.; Dunzlaff, P. [Center for Space Research, North-West University, Potchefstroom, 2522 (South Africa); Roux, J. A. le [Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, AL 3585 (United States); Ruffolo, D., E-mail: dutoit.strauss@nwu.ac.za [Department of Physics, Faculty of Science, Mahidol University, Bangkok 10400 (Thailand)

    2016-07-01

    We investigate the transport of charged particles across magnetic discontinuities, focusing specifically on stream interfaces associated with co-rotating interaction regions in the solar wind. We argue that the magnetic field fluctuations perpendicular to the magnetic discontinuity, and usually also perpendicular to the mean magnetic field, are strongly damped in the vicinity of such a magnetic structure, leading to anisotropic perpendicular diffusion. Assuming that perpendicular diffusion arises from drifts in a turbulent magnetic field, we adopt a simplified approach to derive the relevant perpendicular diffusion coefficient. This approach, which we believe gives the correct principal dependences as expected from more elaborate calculations, allows us to investigate transport in different turbulent geometries, such as longitudinal compressional turbulence that may be present near the heliopause. Although highly dependent on the (possibly anisotropic) perpendicular length scales and turbulence levels, we generally find perpendicular diffusion to be strongly damped at magnetic discontinuities, which may in turn provide an explanation for the large particle gradients associated with these structures.

  16. Tailoring perpendicular magnetic anisotropy with graphene oxide membranes

    KAUST Repository

    Ning, Keyu

    2017-11-15

    Graphene oxide (GO) membranes have been widely explored for their excellent physical and chemical properties, and abundant functional groups. In this work, we report the improvement of the perpendicular magnetic anisotropy (PMA) of CoFeB thin films by applying a coating of GO membranes. We observe that the PMA of the CoFeB/MgAl–O stacks is strongly enhanced by the coating of GO membranes and even reaches 0.6 mJ m−2 at room temperature after an annealing process. The critical thickness of the membrane-coated CoFeB for switching the magnetization from the out-of-plane to the in-plane axis exceeds 1.6 nm. First-principle calculations are performed to investigate the contribution of the GO membranes to the magnetic anisotropy energy (MAE). Due to changes in the hybridization of 3d orbitals, varying the location of the C atomic layer with Co changes the contribution of the Co–C stacks to PMA. Thus, the large PMA achieved with GO membranes can be attributed to the orbital hybridization of the C and O atoms with the Co orbitals. These results provide a comprehensive understanding of the PMA and point towards opportunities to achieve multifunctional graphene-composite spintronic devices.

  17. Magnetic and transport properties of single and double perpendicular magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Cuchet, Lea

    2015-01-01

    Due to their advantageous properties in terms of data retention, storage density and critical current density for Spin Transfer Torque (STT) switching, the magnetic tunnel junctions with perpendicular anisotropy have become predominant in the developments for MRAM applications. The aim of this thesis is to improve the anisotropy and transport properties of such structures and to realize even more complex stacks such as perpendicular double junctions. Studies on the magnetic properties and Tunnel Magnetoresistance (TMR) measurements showed that to optimize the performances of the junctions, all the thicknesses of the different layers constituting the stack have to be adapted. To guaranty both a large TMR as well a strong perpendicular anisotropy, compromises are most of the time needed. Studies as a function of magnetic thickness enabled to extract the saturation magnetization, the critical thickness and the magnetic dead layer thickness both in the bottom reference and the top storage layer in structures capped with Ta. This type of junction could be tested electrically after patterning the sample into nano-pillars. Knowing that perpendicular anisotropy mostly arises at the metal/oxide interface, the Ta capping layer was replaced by a MgO one, leading to a huge increase in the anisotropy of the free layer. A second top reference was then added on such a stack to create functional perpendicular double junctions. CoFeB/insertion/CoFeB synthetic antiferromagnetic storage layers could be developed and were proved to be stable enough to replace the standard Co/Pt-based reference layers. (author) [fr

  18. Interaction of Mutually Perpendicular Magnetic Fields in HTSC

    Directory of Open Access Journals (Sweden)

    Vasilyev Aleksandr Fedorovich

    2015-11-01

    Full Text Available In this article a problem of interaction of the crossed magnetic fields in superconductors is considered. Superconducting materials have nonlinear magnetic properties. It allows using a non-linear magnetic susceptibility for measurement of feeble magnetic fields. We place a wire of superconducting material in a constant parallel uniform magnetic field. Then we let through a wire the alternating current leak. Interaction of mutual and perpendicular variation magnetic fields, with adequate accuracy is described by Ginzburg-Landau's equations. Approximate solution of the written equations is received. The component of a magnetic field parallel to a wire contains a variable component. Frequency of a variable component of the magnetic field is equal to the doubled current frequency. Amplitude of the variable component of the magnetic field is proportional to strength of the constant magnetic field. The experimental installation for research of interaction of mutually perpendicular magnetic fields is created. The cylinder from HTSC of ceramics of the YBa2Cu3O7-x was used as a sensor. Dependence of amplitude of the second harmonica of a variation magnetic field on strength of a constant magnetic field is received.

  19. Highly tunable perpendicularly magnetized synthetic antiferromagnets for biotechnology applications

    OpenAIRE

    Vemulkar, T; Mansell, Rhodri; Petit, Dorothee Celine; Cowburn, Russell Paul; Lesniak, MS

    2015-01-01

    Magnetic micro and nanoparticles are increasingly used in biotechnological applications due to the ability to control their behavior through an externally applied field. We demonstrate the fabrication of particles made from ultrathin perpendicularly magnetized CoFeB/Pt layers with antiferromagnetic interlayer coupling. The particles are characterized by zero moment at remanence, low susceptibility at low fields, and a large saturated moment created by the stacking of the basic coupled bilayer...

  20. Origin of perpendicular magnetic anisotropy in Co/Ni multilayers

    Science.gov (United States)

    Arora, M.; Hübner, R.; Suess, D.; Heinrich, B.; Girt, E.

    2017-07-01

    We studied the variation in perpendicular magnetic anisotropy of (111) textured Au /N ×[Co /Ni ]/Au films as a function of the number of bilayer repeats N . The ferromagnetic resonance and superconducting quantum interference device magnetometer measurements show that the perpendicular magnetic anisotropy of Co/Ni multilayers first increases with N for N ≤10 and then moderately decreases for N >10 . The model we propose reveals that the decrease of the anisotropy for N reduction in the magnetoelastic and magnetocrystalline anisotropies. A moderate decrease in the perpendicular magnetic anisotropy for N >10 is due to the reduction in the magnetocrystalline and the surface anisotropies. To calculate the contribution of magnetoelastic anisotropy in the Co/Ni multilayers, in-plane and out-of-plane x-ray diffraction measurements are performed to determine the spacing between Co/Ni (111) and (220) planes. The magnetocrystalline bulk anisotropy is estimated from the difference in the perpendicular and parallel g factors of Co/Ni multilayers that are measured using the in-plane and out-of-plane ferromagnetic resonance measurements. Transmission electron microscopy has been used to estimate the multilayer film roughness. These values are used to calculate the roughness-induced surface and magnetocrystalline anisotropy coefficients as a function of N .

  1. Non-Uniform Switching of the Perpendicular Magnetization in a Spin-Torque Magnetic Nanopillar

    Energy Technology Data Exchange (ETDEWEB)

    Bernstein, David

    2011-06-01

    Time-resolved scanning transmission x-ray microscopy (STXM) measurements were performed to study the current-induced magnetization switching mechanism in nanopillars exhibiting strong perpendicular magnetic anisotropy (PMA). This technique provides both short time (70 ps) and high spatial (25 nm) resolution. Direct imaging of the magnetization demonstrates that, after an incubation time of {approx} 1.3 ns, a 100 x 300 nm{sup 2} ellipsoidal device switches in {approx} 1 ns via a central domain nucleation and opposite propagation of two domain walls towards the edges. High domain wall velocities on the order of 100m/s are measured. Micromagnetic simulations are shown to be in good agreement with experimental results and provide insight into magnetization dynamics during the incubation and reversal period.

  2. Domain morphology in ultrathin ferromagnetic films with perpendicular magnetization

    Energy Technology Data Exchange (ETDEWEB)

    Kaplan, B. [Department of Secondary Science and Mathematics Education, University of Mersin, Yenisehir Campus, 33169 Mersin (Turkey)]. E-mail: bengukaplan@yahoo.com

    2006-03-15

    We determine the minimal domain structure for the equilibrium thickness of stripes as well as for the minimal energy of the domain configuration in ultrathin films of ferromagnetically coupled spins, where the easy direction of magnetization is perpendicular to the film. It is found that the equilibrium thickness of stripes and walls depend on the exchange energy. The normalized anisotropy, f, depends on interplay between the magnetic and anisotropy energies and is almost independent of the exchange energy inside the wall. The results are compared with the experimental data for thin Ag/Fe/Ag (0 0 1) films and a good coincidence is obtained between both results.

  3. Superparamagnetic perpendicular magnetic tunnel junctions for true random number generators

    Science.gov (United States)

    Parks, Bradley; Bapna, Mukund; Igbokwe, Julianne; Almasi, Hamid; Wang, Weigang; Majetich, Sara A.

    2018-05-01

    Superparamagnetic perpendicular magnetic tunnel junctions are fabricated and analyzed for use in random number generators. Time-resolved resistance measurements are used as streams of bits in statistical tests for randomness. Voltage control of the thermal stability enables tuning the average speed of random bit generation up to 70 kHz in a 60 nm diameter device. In its most efficient operating mode, the device generates random bits at an energy cost of 600 fJ/bit. A narrow range of magnetic field tunes the probability of a given state from 0 to 1, offering a means of probabilistic computing.

  4. Amplification of perpendicular and parallel magnetic fields by cosmic ray currents

    Science.gov (United States)

    Matthews, J. H.; Bell, A. R.; Blundell, K. M.; Araudo, A. T.

    2017-08-01

    Cosmic ray (CR) currents through magnetized plasma drive strong instabilities producing amplification of the magnetic field. This amplification helps explain the CR energy spectrum as well as observations of supernova remnants and radio galaxy hotspots. Using magnetohydrodynamic simulations, we study the behaviour of the non-resonant hybrid (NRH) instability (also known as the Bell instability) in the case of CR currents perpendicular and parallel to the initial magnetic field. We demonstrate that extending simulations of the perpendicular case to 3D reveals a different character to the turbulence from that observed in 2D. Despite these differences, in 3D the perpendicular NRH instability still grows exponentially far into the non-linear regime with a similar growth rate to both the 2D perpendicular and 3D parallel situations. We introduce some simple analytical models to elucidate the physical behaviour, using them to demonstrate that the transition to the non-linear regime is governed by the growth of thermal pressure inside dense filaments at the edges of the expanding loops. We discuss our results in the context of supernova remnants and jets in radio galaxies. Our work shows that the NRH instability can amplify magnetic fields to many times their initial value in parallel and perpendicular shocks.

  5. Channel modeling, signal processing and coding for perpendicular magnetic recording

    Science.gov (United States)

    Wu, Zheng

    With the increasing areal density in magnetic recording systems, perpendicular recording has replaced longitudinal recording to overcome the superparamagnetic limit. Studies on perpendicular recording channels including aspects of channel modeling, signal processing and coding techniques are presented in this dissertation. To optimize a high density perpendicular magnetic recording system, one needs to know the tradeoffs between various components of the system including the read/write transducers, the magnetic medium, and the read channel. We extend the work by Chaichanavong on the parameter optimization for systems via design curves. Different signal processing and coding techniques are studied. Information-theoretic tools are utilized to determine the acceptable region for the channel parameters when optimal detection and linear coding techniques are used. Our results show that a considerable gain can be achieved by the optimal detection and coding techniques. The read-write process in perpendicular magnetic recording channels includes a number of nonlinear effects. Nonlinear transition shift (NLTS) is one of them. The signal distortion induced by NLTS can be reduced by write precompensation during data recording. We numerically evaluate the effect of NLTS on the read-back signal and examine the effectiveness of several write precompensation schemes in combating NLTS in a channel characterized by both transition jitter noise and additive white Gaussian electronics noise. We also present an analytical method to estimate the bit-error-rate and use it to help determine the optimal write precompensation values in multi-level precompensation schemes. We propose a mean-adjusted pattern-dependent noise predictive (PDNP) detection algorithm for use on the channel with NLTS. We show that this detector can offer significant improvements in bit-error-rate (BER) compared to conventional Viterbi and PDNP detectors. Moreover, the system performance can be further improved by

  6. 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.

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

    International Nuclear Information System (INIS)

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

    2007-01-01

    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

  8. 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.

  9. Bound states in a strong magnetic field

    International Nuclear Information System (INIS)

    Machado, C. S.; Navarra, F. S.; Noronha, J.; Oliveira, E. G.; Ferreira Filho, L. G.

    2013-01-01

    We expect a strong magnetic field to be produced in the perpendicular direction to the reaction plane, in a noncentral heavy-ion collision . The strength of the magnetic field is estimated to be eB∼m 2 π ∼ 0.02 GeV 2 at the RHIC and eB∼ 15m 2 π ∼ 0.3 GeV 2 at the LHC. We investigate the effects of the magnetic field on B 0 and D 0 mesons, focusing on the changes of the energy levels and of the mass of the bound states.

  10. Frictional Coulomb drag in strong magnetic fields

    DEFF Research Database (Denmark)

    Bønsager, Martin Christian; Flensberg, Karsten; Hu, Ben Yu-Kuang

    1997-01-01

    A treatment of frictional Coulomb drag between two two-dimensional electron layers in a strong perpendicular magnetic field, within the independent electron picture, is presented. Assuming fully resolved Landau levels, the linear response theory expression for the transresistivity rho(21) is eval......A treatment of frictional Coulomb drag between two two-dimensional electron layers in a strong perpendicular magnetic field, within the independent electron picture, is presented. Assuming fully resolved Landau levels, the linear response theory expression for the transresistivity rho(21......) is evaluated using diagrammatic techniques. The transresistivity is given by an integral over energy and momentum transfer weighted by the product of the screened interlayer interaction and the phase space for scattering events. We demonstrate, by a numerical analysis of the transresistivity, that for well...

  11. Analytical calculation of the torque exerted between two perpendicularly magnetized magnets

    Science.gov (United States)

    Allag, H.; Yonnet, J.-P.; Latreche, M. E. H.

    2011-04-01

    Analytical expressions of the torque on cuboidal permanent magnets are given. The only hypothesis is that the magnetizations are rigid, uniform, and perpendicularly oriented. The analytical calculation is made by replacing magnetizations by distributions of magnetic charges on the magnet poles. The torque expressions are obtained using the Lorentz force method. The results are valid for any relative magnet position, and the torque can be obtained with respect to any reference point. Although these expressions seem rather complicated, they enable an extremely fast and accurate torque calculation on a permanent magnet in the presence of a magnetic field of another permanent magnet.

  12. Relaxation dynamics of magnetization transitions in synthetic antiferromagnet with perpendicular anisotropy

    Science.gov (United States)

    Talantsev, A.; Lu, Y.; Fache, T.; Lavanant, M.; Hamadeh, A.; Aristov, A.; Koplak, O.; Morgunov, R.; Mangin, S.

    2018-04-01

    Two synthetic antiferromagnet bilayer systems with strong perpendicular anisotropy CoFeB/Ta/CoFeB and Pt/Co/Ir/Co/Pt have been grown using sputtering techniques. For both systems two types of magnetization transitions have been studied. The first one concerns transitions from a state where magnetizations of the two magnetic layers are parallel (P state) to a state where magnetizations of the two layers are aligned antiparallel (AP state). The second one concerns transitions between the two possible antiparallel alignments (AP+  to AP-). For both systems and both transitions after-effect measurements can be understood in the frame of nucleation—propagation model. Time derivative analysis of magnetic relaxation curves and mapping of the first order reversal curves at different temperature allowed us to demonstrate the presence of different pinning centers, which number can be controlled by magnetic field and temperature.

  13. Magnetic Thin Films for Perpendicular Magnetic Recording Systems

    Science.gov (United States)

    Sugiyama, Atsushi; Hachisu, Takuma; Osaka, Tetsuya

    In the advanced information society of today, information storage technology, which helps to store a mass of electronic data and offers high-speed random access to the data, is indispensable. Against this background, hard disk drives (HDD), which are magnetic recording devices, have gained in importance because of their advantages in capacity, speed, reliability, and production cost. These days, the uses of HDD extend not only to personal computers and network servers but also to consumer electronics products such as personal video recorders, portable music players, car navigation systems, video games, video cameras, and personal digital assistances.

  14. Spin-torque oscillation in large size nano-magnet with perpendicular magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Linqiang, E-mail: LL6UK@virginia.edu [Department of Physics, University of Virginia, Charlottesville, VA 22904 (United States); Kabir, Mehdi [Department of Electrical & Computer Engineering, University of Virginia, Charlottesville, VA 22904 (United States); Dao, Nam; Kittiwatanakul, Salinporn [Department of Materials Science & Engineering, University of Virginia, Charlottesville, VA 22904 (United States); Cyberey, Michael [Department of Electrical Engineering, University of Virginia, Charlottesville, VA 22904 (United States); Wolf, Stuart A. [Department of Physics, University of Virginia, Charlottesville, VA 22904 (United States); Department of Materials Science & Engineering, University of Virginia, Charlottesville, VA 22904 (United States); Institute of Defense Analyses, Alexandria, VA 22311 (United States); Stan, Mircea [Department of Electrical & Computer Engineering, University of Virginia, Charlottesville, VA 22904 (United States); Lu, Jiwei [Department of Materials Science & Engineering, University of Virginia, Charlottesville, VA 22904 (United States)

    2017-06-15

    Highlights: • 500 nm size nano-pillar device was fabricated by photolithography techniques. • A magnetic hybrid structure was achieved with perpendicular magnetic fields. • Spin torque switching and oscillation was demonstrated in the large sized device. • Micromagnetic simulations accurately reproduced the experimental results. • Simulations demonstrated the synchronization of magnetic inhomogeneities. - Abstract: DC current induced magnetization reversal and magnetization oscillation was observed in 500 nm large size Co{sub 90}Fe{sub 10}/Cu/Ni{sub 80}Fe{sub 20} pillars. A perpendicular external field enhanced the coercive field separation between the reference layer (Co{sub 90}Fe{sub 10}) and free layer (Ni{sub 80}Fe{sub 20}) in the pseudo spin valve, allowing a large window of external magnetic field for exploring the free-layer reversal. A magnetic hybrid structure was achieved for the study of spin torque oscillation by applying a perpendicular field >3 kOe. The magnetization precession was manifested in terms of the multiple peaks on the differential resistance curves. Depending on the bias current and applied field, the regions of magnetic switching and magnetization precession on a dynamical stability diagram has been discussed in details. Micromagnetic simulations are shown to be in good agreement with experimental results and provide insight for synchronization of inhomogeneities in large sized device. The ability to manipulate spin-dynamics on large size devices could be proved useful for increasing the output power of the spin-transfer nano-oscillators (STNOs).

  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.

    2015-12-01

    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.

  16. Looking back at perpendicular magnetic recording R and D in NEC

    International Nuclear Information System (INIS)

    Tagami, Katsumichi

    2012-01-01

    This paper reports perpendicular magnetic recording (PMR) circumstances and the results based on the reference published by NEC. The PMR flexible disks using Co-Cr-Ta films were investigated. Pass wear durability of Co-Cr-Ta film strongly depends on the base film surface roughness and Young's modulus values of Co-Cr-Ta films. Pass wear durability, more than 10 million passes, was confirmed under a high temperature (60 deg. C) and a high humidity (80% RH) condition, as well as a low temperature (5 deg. C) condition. The read/write characteristics for double-layered PMR media were examined by using a combination of a single-pole-type (SPT) write head and a magnetoresistive (MR) read head, and a conventional merged ring type inductive (ID) write head/MR read head. By differential equalization of the reproduced voltage, the bit error rate less than 10 -6 at 3 Gb/in. 2 was obtained for the SPT/MR head combination. The antenna effect for PMR realization was analyzed using the merged ring type ID/MR head. In order to increase the magnetic circuit resistance from the ID head pole to the soft underlayer, we developed the sendust (FeAlSi) soft underlayer with low magnetic permeability. We confirmed that the recorded signal has better stability under the ID/MR head-loaded condition than the SPT head-loaded condition. These results show that there are the head and media solutions to realize PMR. We had confidence that we could use the basic structure of the commercial ID/MR head for the PMR head. - Research highlights: → The guideline and our thought of NEC perpendicular magnetic recording R and D were described. → More than 10 million pass wear for Co-Cr film flexible disk was confirmed. → ID/MR head can be available for perpendicular magnetic head. → Antenna effect in PMR was investigated.

  17. Temperature dependence of interlayer coupling in perpendicular magnetic tunnel junctions with GdOX barriers

    Science.gov (United States)

    Newhouse-Illige, T.; Xu, Y. H.; Liu, Y. H.; Huang, S.; Kato, H.; Bi, C.; Xu, M.; LeRoy, B. J.; Wang, W. G.

    2018-02-01

    Perpendicular magnetic tunnel junctions with GdOX tunneling barriers have shown a unique voltage controllable interlayer magnetic coupling effect. Here, we investigate the quality of the GdOX barrier and the coupling mechanism in these junctions by examining the temperature dependence of the tunneling magnetoresistance and the interlayer coupling from room temperature down to 11 K. The barrier is shown to be of good quality with the spin independent conductance only contributing a small portion, 14%, to the total room temperature conductance, similar to AlOX and MgO barriers. The interlayer coupling, however, shows an anomalously strong temperature dependence including sign changes below 80 K. This non-trivial temperature dependence is not described by previous models of interlayer coupling and may be due to the large induced magnetic moment of the Gd ions in the barrier.

  18. Magnetic ground and remanent states of synthetic metamagnets with perpendicular anisotropy

    International Nuclear Information System (INIS)

    Kiselev, N S; Roessler, U K; Bogdanov, A N; Hellwig, O

    2011-01-01

    In this work, we summarize our theoretical results within a phenomenological micromagnetic approach for magnetic ground state and nonequilibrium states as topological magnetic defects in multilayers with strong perpendicular anisotropy and antiferromagnetic (AF) interlayer exchange coupling (IEC), e.g. [Co/Pt(Pd)]/Ru(Ir, NiO). We give detailed analysis of our model together with the most representative results which elucidate common features of such systems. We discuss phase diagrams of the magnetic ground state, and compare solutions of our model with experimental data. A model to assess the stability of so-called tiger tail patterns is presented. It is found that these modulated topological defect cannot be stabilized by an interplay between magnetostatic and IEC energies only. It is argued that tiger tail patterns arise as nuclei of ferro-stripe structure in AF domain walls and that they are stabilized by domain wall pinning.

  19. 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.

  20. Perpendicular magnetic anisotropy of ultrathin FeCo alloy films on Pd(0 0 1) surface: First principles study

    International Nuclear Information System (INIS)

    Kim, Dongyoo; Hong, Jisang

    2009-01-01

    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 2.36μ B . Besides, the calculated X-ray magnetic circular dichroism (XMCD) has been presented.

  1. Strain induced enhancement of perpendicular magnetic anisotropy in Co/graphene and Co/BN heterostructures

    Science.gov (United States)

    Yang, B. S.; Zhang, J.; Jiang, L. N.; Chen, W. Z.; Tang, P.; Zhang, X.-G.; Yan, Y.; Han, X. F.

    2017-05-01

    Perpendicular magnetic tunnel junctions in the next-generation magnetic memory using current induced magnetization switching will likely rely on a material design that can enhance the perpendicular magnetic anisotropy of heterojunctions containing only light elements. Using first-principles calculations, we investigated the effect of compressive and tensile strain on the perpendicular magnetic anisotropy of light element heterostructures of Co films, Co/graphene, and Co/BN. We found that the perpendicular magnetic anisotropy of Co/graphene is greatly enhanced compared to the Co films, while that of Co/BN is reduced compared to the Co films. In addition, tensile strain can further enhance perpendicular magnetic anisotropy of Co/graphene and Co/BN heterojunctions by 48.5% and 80.8%, respectively, compared to the unstrained systems. A density of state analysis, combined with layer and orbital magnetic anisotropy contributions obtained from a second-order perturbation theory of the spin-orbit coupling, reveals that the tensile strain effect arises from the increase of the hybridization between same spin dx y and dx2-y2 states of the surface Co film. Our results suggest that strain engineering is an effective approach to enhance the perpendicular magnetic anisotropy of light element heterostructures.

  2. Probing structure-property relationships in perpendicularly magnetized Fe/Cu(001) using MXLD and XPD

    Energy Technology Data Exchange (ETDEWEB)

    Cummins, T.R.; Waddill, G.D. [Univ. of Missouri, Rolla, MO (United States); Goodman, K.W. [Lawrence Berkeley National Lab., CA (United States)] [and others

    1997-04-01

    Magnetic X-ray Linear Dichroism (MXLD) in Photoelectron Spectroscopy and X-Ray Photoelectron Diffraction (XPD) of the Fe 3p core level have been used to probe the magnetic structure-property relationships of perpendicularly magnetized Fe/Cu(001), in an element-specific fashion. A strong MEXLD effect was observed in the high resolution photoelectron spectroscopy of the Fe 3p at {open_quotes}normal{close_quotes} emission and was used to follow the loss of perpendicular ferromagnetic ordering as the temperature was raised toward room temperature. In parallel with this, {open_quotes}Forward Focussing{close_quotes} in XPD was used as a direct measure of geometric structure in the overlayer. These results and the implications of their correlation will be discussed. Additionally, an investigation of the effect of Mn doping of the Fe/Cu(001) will be described. These measurements were performed at the Spectromicroscopy Facility (Beamline 7.0.1) of the Advanced Light Source.

  3. Methods for characterizing magnetic footprints of perpendicular magnetic recording writer heads

    International Nuclear Information System (INIS)

    Li, Shaoping; Lin, Ed; George, Zach; Terrill, Dave; Mendez, H.; Santucci, J.; Yie, Derek

    2014-01-01

    In this work, the magnetic footprints, along with some of its dynamic features in recording process, of perpendicular magnetic recording writer heads have been characterized by using three different techniques. Those techniques are the spin-stand stationary footprint technique, the spin-stand dynamic footprint technique, and the coherent writing technique combined with magnetic force microscope imaging method. The characteristics of those techniques have been compared to one another. It was found experimentally that the spin-stand stationary method could not precisely catch some peculiar recording dynamics of the write heads in certain conditions. The advantages and disadvantages among all those techniques are also examined and discussed in detail

  4. Read/write characteristics of focused-ion-beam-etched heads for perpendicular magnetic recording media

    International Nuclear Information System (INIS)

    Tsuboi, S.; Matsutera, H.; Ishi, T.; Ishiwata, N.; Ohashi, K.

    2001-01-01

    The read/write characteristics for perpendicular magnetic recording media of focused-ion-beam (FIB)-etched recording heads were investigated. It was found that the trailing edge of an FIB-etched head produces a higher gradient in the magnetic field perpendicular to the medium than a head which has not been etched. The signal-to-noise ratio of the medium increased with the FIB-etched write gap. A high-Bs and thin pole increased the magnetic field's gradient in the perpendicular direction, resulting in excellent read/write characteristics

  5. 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.

  6. Influence of domain structure induced coupling on magnetization reversal of Co/Pt/Co film with perpendicular anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Matczak, Michał [Institute of Molecular Physics, Polish Academy of Sciences, M. Smoluchowskiego 17, 60-179 Poznań (Poland); NanoBioMedical Centre, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań (Poland); Schäfer, Rudolf [Leibniz Institute for Solid State and Materials Research (IFW) Dresden, Institute for Metallic Materials, PO 270116, D-01171 Dresden (Germany); Dresden University of Technology, Institute for Materials Science, D-01062 Dresden (Germany); Urbaniak, Maciej; Kuświk, Piotr; Szymański, Bogdan; Schmidt, Marek; Aleksiejew, Jacek [Institute of Molecular Physics, Polish Academy of Sciences, M. Smoluchowskiego 17, 60-179 Poznań (Poland); Stobiecki, Feliks, E-mail: Feliks.Stobiecki@ifmpan.poznan.pl [Institute of Molecular Physics, Polish Academy of Sciences, M. Smoluchowskiego 17, 60-179 Poznań (Poland); NanoBioMedical Centre, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań (Poland)

    2017-01-15

    A magnetic multilayer of substrate/Pt-15 nm/Co-0.8 nm/Pt-wedge 0–7 nm/Co-0.6 nm/Pt-2 nm structure is characterized by a perpendicular anisotropy of the Co layers and by graded interlayer coupling between them. Using magnetooptical Kerr microscopy we observed a distinct influence of magnetic domains in one Co layer on the nucleation field and positions of nucleation sites of reversed domains in the second Co layer. For sufficiently strong interlayer coupling a replication of magnetic domains from the magnetically harder layer to the magnetically softer layer is observed. - Highlights: • Co/Pt-wedge/Co layered film is characterized by a gradient of interlayer coupling. • Magnetic field controls propagation of straight domain wall. • Replication of magnetic domains in multilayers with strong ferromagnetic coupling. • Coupling induced by domains influences magnetization reversal of spin valves.

  7. Electronic properties of bilayer phosphorene quantum dots in the presence of perpendicular electric and magnetic fields

    Science.gov (United States)

    Li, L. L.; Moldovan, D.; Xu, W.; Peeters, F. M.

    2017-10-01

    Using the tight-binding approach, we investigate the electronic properties of bilayer phosphorene (BLP) quantum dots (QDs) in the presence of perpendicular electric and magnetic fields. Since BLP consists of two coupled phosphorene layers, it is of interest to examine the layer-dependent electronic properties of BLP QDs, such as the electronic distributions over the two layers and the so-produced layer-polarization features, and to see how these properties are affected by the magnetic field and the bias potential. We find that in the absence of a bias potential only edge states are layer polarized while the bulk states are not, and the layer-polarization degree (LPD) of the unbiased edge states increases with increasing magnetic field. However, in the presence of a bias potential both the edge and bulk states are layer polarized, and the LPD of the bulk (edge) states depends strongly (weakly) on the interplay of the bias potential and the interlayer coupling. At high magnetic fields, applying a bias potential renders the bulk electrons in a BLP QD to be mainly distributed over the top or bottom layer, resulting in layer-polarized bulk Landau levels (LLs). In the presence of a large bias potential that can drive a semiconductor-to-semimetal transition in BLP, these bulk LLs exhibit different magnetic-field dependences, i.e., the zeroth LLs exhibit a linearlike dependence on the magnetic field while the other LLs exhibit a square-root-like dependence.

  8. Magnetic Reversal and Thermal Stability of CoFeB Perpendicular Magnetic Tunnel Junction Arrays Patterned by Block Copolymer Lithography

    KAUST Repository

    Tu, Kun-Hua

    2018-04-10

    Dense arrays of pillars, with diameters of 64 and 25 nm, were made from a perpendicular CoFeB magnetic tunnel junction thin film stack using block copolymer lithography. While the soft layer and hard layer in the 64 nm pillars reverse at different fields, the reversal of the two layers in the 25 nm pillars could not be distinguished, attributed to the strong interlayer magnetostatic coupling. First order reversal curves were used to identify the steps that occur during switching, and the thermal stability and effective switching volume were determined from scan rate dependent hysteresis measurements.

  9. Enhancement of perpendicular magnetic anisotropy and anomalous hall effect in Co/Ni multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yiwei; Zhang, Jingyan, E-mail: jyzhang@ustb.edu.cn; Jiang, Shaolong; Liu, Qianqian; Li, Xujing; Yu, Guanghua, E-mail: ghyu@mater.ustb.edu.cn

    2016-12-15

    The perpendicular magnetic anisotropy (PMA) and the anomalous Hall effect (AHE) in Co/Ni multilayer were optimized by manipulating its interface structure (inducing HfO{sub 2} capping layer and Pt insertion) and post-annealing treatment. A strong PMA can be obtained in Co/Ni multilayers with HfO{sub 2} 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 HfO{sub 2} 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. - Highlights: • The perpendicular magnetic anisotropy and anomalous Hall effect of Co/Ni multilayer films were studied. • The PMA thermal stability of the Co/Ni ML can be enhanced by HfO{sub 2} capping layer and Pt insertion. • The anomalous Hall resistivity of Co/Ni ML covered by HfO{sub 2} was enhanced by post-annealing treatment.

  10. Perpendicular magnetization of CoFeB on top of an amorphous buffer layer

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Dongseok; Jung, K.Y. [Department of Display and Semiconductor Physics, Korea University, Sejong 339-700 (Korea, Republic of); Joo, Sungjung [Department of Display and Semiconductor Physics, Korea University, Sejong 339-700 (Korea, Republic of); Center for Electricity and Magnetism, Korea Research Institute of Standard and Science, Daejeon 305-340 (Korea, Republic of); Jang, Youngjae; Hong, Jinki [Department of Display and Semiconductor Physics, Korea University, Sejong 339-700 (Korea, Republic of); Lee, B.C.; You, C.Y.; Cho, J.H. [Department of Physics, Inha University, Incheon 402-751 (Korea, Republic of); Kim, M.Y. [Department of Nano Physics, Sookmyung Women' s University, Seoul 140-742 (Korea, Republic of); Rhie, K., E-mail: krhie@korea.ac.kr [Department of Display and Semiconductor Physics, Korea University, Sejong 339-700 (Korea, Republic of)

    2015-01-15

    Perpendicular magnetic anisotropy was observed in sputtered FeZr/CoFeB/MgO multilayers. A thin paramagnetic amorphous FeZr layer was used as a buffer layer and perpendicular anisotropy was obtained by annealing the samples without an external magnetic field. The critical CoFeB thickness for perpendicular anisotropy was 1.8 nm; the anisotropy changes from out-of-plane to in-plane as the CoFeB thickness increases beyond this point. Perpendicular anisotropy was also enhanced when a Ta layer was capped on top of the MgO layer. The amorphous buffer provided better perpendicular anisotropy than previously reported Ta buffer, and it may be applied to perpendicular magnetization MRAM devices where good uniformity of tunnel junctions is required. - Highlights: • Perpendicular magnetic anisotropy (PMA) of buffer/CoFeB/MgO was investigated. • The PMA was enhanced by using an amorphous buffer. • The PMA of the CoFeB layer was maintained up to 1.8 nm. • Ta capping layer further improved the PMA by 40%.

  11. Magnetic Force Microscopy Observation of Perpendicular Recording Head Remanence

    Science.gov (United States)

    Dilekrojanavuti, P.; Saengkaew, K.; Cheowanish, I.; Damrongsak, B.

    2017-09-01

    In this work, magnetic force microscopy (MFM) was utilized to observe the magnetic write head remanence, which is the remaining out-of-plane magnetic field on magnetic write heads after a write current is turned off. This remnant field can write unwanted tracks or erase written tracks on a magnetic media. The write head remanence can also occur from device and slider fabrication, either by applying current to the write coil during the inspection or biasing the external magnetic field to magnetic recording heads. This remanence can attract magnetic nanoparticles, which is suspended in cleaning water or surrounding air, and cause device contamination. MFM images were used to examine locations of the remnant field on the surface of magnetic recording heads. Experimental results revealed that the remanence occurred mostly on the shield and is dependent on the initial direction of magnetic moments. In addition, we demonstrated a potential use of MFM imaging to investigate effects of different etching gases on the head remanence.

  12. Electric-field control of magnetic domain-wall velocity in ultrathin cobalt with perpendicular magnetization.

    Science.gov (United States)

    Chiba, D; Kawaguchi, M; Fukami, S; Ishiwata, N; Shimamura, K; Kobayashi, K; Ono, T

    2012-06-06

    Controlling the displacement of a magnetic domain wall is potentially useful for information processing in magnetic non-volatile memories and logic devices. A magnetic domain wall can be moved by applying an external magnetic field and/or electric current, and its velocity depends on their magnitudes. Here we show that the applying an electric field can change the velocity of a magnetic domain wall significantly. A field-effect device, consisting of a top-gate electrode, a dielectric insulator layer, and a wire-shaped ferromagnetic Co/Pt thin layer with perpendicular anisotropy, was used to observe it in a finite magnetic field. We found that the application of the electric fields in the range of ± 2-3 MV cm(-1) can change the magnetic domain wall velocity in its creep regime (10(6)-10(3) m s(-1)) by more than an order of magnitude. This significant change is due to electrical modulation of the energy barrier for the magnetic domain wall motion.

  13. Liquid-metal flow through a thin-walled elbow in a plane perpendicular to a uniform magnetic field

    International Nuclear Information System (INIS)

    Walker, J.S.

    1986-04-01

    This paper presents analytical solutions for the liquid-metal flow through two straight pipes connected by a smooth elbow with the same inside radius. The pipes and the elbow lie in a plane which is perpendicular to a uniform, applied magnetic field. The strength of the magnetic field is assumed to be sufficiently strong that inertial and viscous effects are negligible. This assumption is appropriate for the liquid-lithium flow in the blanket of a magnetic confinement fusion reactor, such as a tokamak. The pipes and the elbow have thin metal walls

  14. Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures

    Science.gov (United States)

    Peng, Shouzhong; Wang, Mengxing; Yang, Hongxin; Zeng, Lang; Nan, Jiang; Zhou, Jiaqi; Zhang, Youguang; Hallal, Ali; Chshiev, Mairbek; Wang, Kang L.; Zhang, Qianfan; Zhao, Weisheng

    2015-12-01

    Spin-transfer-torque magnetic random access memory (STT-MRAM) attracts extensive attentions due to its non-volatility, high density and low power consumption. The core device in STT-MRAM is CoFeB/MgO-based magnetic tunnel junction (MTJ), which possesses a high tunnel magnetoresistance ratio as well as a large value of perpendicular magnetic anisotropy (PMA). It has been experimentally proven that a capping layer coating on CoFeB layer is essential to obtain a strong PMA. However, the physical mechanism of such effect remains unclear. In this paper, we investigate the origin of the PMA in MgO/CoFe/metallic capping layer structures by using a first-principles computation scheme. The trend of PMA variation with different capping materials agrees well with experimental results. We find that interfacial PMA in the three-layer structures comes from both the MgO/CoFe and CoFe/capping layer interfaces, which can be analyzed separately. Furthermore, the PMAs in the CoFe/capping layer interfaces are analyzed through resolving the magnetic anisotropy energy by layer and orbital. The variation of PMA with different capping materials is attributed to the different hybridizations of both d and p orbitals via spin-orbit coupling. This work can significantly benefit the research and development of nanoscale STT-MRAM.

  15. Perpendicular magnetic anisotropy at transition metal/oxide interfaces and applications

    Science.gov (United States)

    Dieny, B.; Chshiev, M.

    2017-04-01

    Spin electronics is a rapidly expanding field stimulated by a strong synergy between breakthrough basic research discoveries and industrial applications in the fields of magnetic recording, magnetic field sensors, nonvolatile memories [magnetic random access memories (MRAM) and especially spin-transfer-torque MRAM (STT-MRAM)]. In addition to the discovery of several physical phenomena (giant magnetoresistance, tunnel magnetoresistance, spin-transfer torque, spin-orbit torque, spin Hall effect, spin Seebeck effect, etc.), outstanding progress has been made on the growth and nanopatterning of magnetic multilayered films and nanostructures in which these phenomena are observed. Magnetic anisotropy is usually observed in materials that have large spin-orbit interactions. However, in 2002 perpendicular magnetic anisotropy (PMA) was discovered to exist at magnetic metal/oxide interfaces [for instance Co (Fe )/alumina ]. Surprisingly, this PMA is observed in systems where spin-orbit interactions are quite weak, but its amplitude is remarkably large—comparable to that measured at Co /Pt interfaces, a reference for large interfacial anisotropy (anisotropy˜1.4 erg /cm2=1.4 mJ /m2 ). Actually, this PMA was found to be very common at magnetic metal/oxide interfaces since it has been observed with a large variety of amorphous or crystalline oxides, including AlOx, MgO, TaOx, HfOx, etc. This PMA is thought to be the result of electronic hybridization between the oxygen and the magnetic transition metal orbit across the interface, a hypothesis supported by ab initio calculations. Interest in this phenomenon was sparked in 2010 when it was demonstrated that the PMA at magnetic transition metal/oxide interfaces could be used to build out-of-plane magnetized magnetic tunnel junctions for STT-MRAM cells. In these systems, the PMA at the CoFeB /MgO interface can be used to simultaneously obtain good memory retention, thanks to the large PMA amplitude, and a low write current

  16. 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.

  17. Magnetic stripes and holes: Complex domain patterns in perforated films with weak perpendicular anisotropy

    Science.gov (United States)

    Valdés-Bango, F.; Vélez, M.; Alvarez-Prado, L. M.; Alameda, J. M.; Martín, J. I.

    2017-05-01

    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. A Charged Particle in Perpendicular Electric and Magnetic Fields

    Indian Academy of Sciences (India)

    http://www.ias.ac.in/article/fulltext/reso/021/11/1043-1045. Keywords. Relativity, electric and magnetic fields, cycloid, Lorentz transformation. Abstract. Author Affiliations. B A Bhargava1 Adithi Udupa1 P Jayanth Vyasanakere2. BSc III Year, St. Joseph's College, Bengaluru 560 027. Department of Physics, University College ...

  19. MnGa-based fully perpendicular magnetic tunnel junctions with ultrathin Co2MnSi interlayers

    Science.gov (United States)

    Mao, Siwei; Lu, Jun; Zhao, Xupeng; Wang, Xiaolei; Wei, Dahai; Liu, Jian; Xia, Jianbai; Zhao, Jianhua

    2017-02-01

    Because tetragonal structured MnGa alloy has intrinsic (not interface induced) giant perpendicular magnetic anisotropy (PMA), ultra-low damping constant and high spin polarization, it is predicted to be a kind of suitable magnetic electrode candidate in the perpendicular magnetic tunnel junction (p-MTJ) for high density spin transfer torque magnetic random access memory (STT-MRAM) applications. However, p-MTJs with both bottom and top MnGa electrodes have not been achieved yet, since high quality perpendicular magnetic MnGa films can hardly be obtained on the MgO barrier due to large lattice mismatch and surface energy difference between them. Here, a MnGa-based fully p-MTJ with the structure of MnGa/Co2MnSi/MgO/Co2MnSi/MnGa is investigated. As a result, the multilayer is with high crystalline quality, and both the top and bottom MnGa electrodes show well PMA. Meanwhile, a distinct tunneling magnetoresistance (TMR) ratio of 65% at 10 K is achieved. Ultrathin Co2MnSi films are used to optimize the interface quality between MnGa and MgO barrier. A strong antiferromagnetic coupling in MnGa/Co2MnSi bilayer is confirmed with the interfacial exchange coupling constant of -5erg/cm2. This work proposes a novel p-MTJ structure for the future STT-MRAM progress.

  20. Exploration of perpendicular magnetic anisotropy material system for application in spin transfer torque - Random access memory

    Science.gov (United States)

    Natarajarathinam, Anusha

    Perpendicular magnetic anisotropy (PMA) materials have unique advantages when used in magnetic tunnel junctions (MTJ) which are the most critical part of spin-torque transfer random access memory devices (STT-RAMs) that are being researched intensively as future non-volatile memory technology. They have high magnetoresistance which improves their sensitivity. The STT-RAM has several advantages over competing technologies, for instance, low power consumption, non-volatility, ultra-fast read and write speed and high endurance. In personal computers, it can replace SRAM for high-speed applications, Flash for non-volatility, and PSRAM and DRAM for high-speed program execution. The main aim of this research is to identify and optimize the best perpendicular magnetic anisotropy (PMA) material system for application to STT-RAM technology. Preliminary search for perpendicular magnetic anisotropy (PMA) materials for pinned layer for MTJs started with the exploration and optimization of crystalline alloys such as Co50Pd50 alloy, Mn50Al50 and amorphous alloys such as Tb21Fe72Co7 and are first presented in this work. Further optimization includes the study of Co/[Pd/Pt]x multilayers (ML), and the development of perpendicular synthetic antiferromagnets (SAF) utilizing these multilayers. Focused work on capping and seed layers to evaluate interfacial perpendicular anisotropy in free layers for pMTJs is then discussed. Optimization of the full perpendicular magnetic tunnel junction (pMTJ) includes the CoFeB/MgO/CoFeB trilayer coupled to a pinned/pinning layer with perpendicular Co/[Pd/Pt]x SAF and a thin Ta seeded CoFeB free layer. Magnetometry, simulations, annealing studies, transport measurements and TEM analysis on these samples will then be presented.

  1. Tunable exchange bias-like effect in patterned hard-soft two-dimensional lateral composites with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Hierro-Rodriguez, A., E-mail: ahierro@fc.up.pt; Alvarez-Prado, L. M.; Martín, J. I.; Alameda, J. M. [Departamento de Física, Universidad de Oviedo, C/Calvo Sotelo S/N, 33007 Oviedo (Spain); Centro de Investigación en Nanomateriales y Nanotecnología—CINN (CSIC—Universidad de Oviedo—Principado de Asturias), Parque Tecnológico de Asturias, 33428 Llanera (Spain); Teixeira, J. M. [IN-IFIMUP, Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua Campo Alegre 687, 4169-007 Porto (Portugal); Vélez, M. [Departamento de Física, Universidad de Oviedo, C/Calvo Sotelo S/N, 33007 Oviedo (Spain)

    2014-09-08

    Patterned hard-soft 2D magnetic lateral composites have been fabricated by e-beam lithography plus dry etching techniques on sputter-deposited NdCo{sub 5} thin films with perpendicular magnetic anisotropy. Their magnetic behavior is strongly thickness dependent due to the interplay between out-of-plane anisotropy and magnetostatic energy. Thus, the spatial modulation of thicknesses leads to an exchange coupled system with hard/soft magnetic regions in which rotatable anisotropy of the thicker elements provides an extra tool to design the global magnetic behavior of the patterned lateral composite. Kerr microscopy studies (domain imaging and magneto-optical Kerr effect magnetometry) reveal that the resulting hysteresis loops exhibit a tunable exchange bias-like shift that can be switched on/off by the applied magnetic field.

  2. Light scattering of rectangular slot antennas: parallel magnetic vector vs perpendicular electric vector.

    Science.gov (United States)

    Lee, Dukhyung; Kim, Dai-Sik

    2016-01-07

    We study light scattering off rectangular slot nano antennas on a metal film varying incident polarization and incident angle, to examine which field vector of light is more important: electric vector perpendicular to, versus magnetic vector parallel to the long axis of the rectangle. While vector Babinet's principle would prefer magnetic field along the long axis for optimizing slot antenna function, convention and intuition most often refer to the electric field perpendicular to it. Here, we demonstrate experimentally that in accordance with vector Babinet's principle, the incident magnetic vector parallel to the long axis is the dominant component, with the perpendicular incident electric field making a small contribution of the factor of 1/|ε|, the reciprocal of the absolute value of the dielectric constant of the metal, owing to the non-perfectness of metals at optical frequencies.

  3. Ab initio theory of perpendicular transport in layered magnetic systems

    Czech Academy of Sciences Publication Activity Database

    Kudrnovský, Josef; Drchal, Václav; Turek, Ilja; Dederichs, P. H.; Weinberger, P.; Bruno, P.

    2002-01-01

    Roč. 240, - (2002), s. 177-179 ISSN 0304-8853 R&D Projects: GA AV ČR IAA1010829; GA ČR GA202/00/0122; GA MŠk OC P5.30; GA MŠk OC P3.40; GA MŠk OC P3.70 Institutional research plan: CEZ:AV0Z1010914 Keywords : magnetoresistance -theory * ferromagnetic multilayers * disorder-alloys * electronic structure Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.046, year: 2002

  4. Perpendicularly magnetized Mn x Ga films: promising materials for future spintronic devices, magnetic recording and permanent magnets

    Science.gov (United States)

    Zhu, Lijun; Zhao, Jianhua

    2013-05-01

    In this article, we review the recent progress in synthesis, characterization and related spintronic devices of tetragonal Mn x Ga alloys with L10 or D022 ordering. After a brief introduction to the growing demands for perpendicularly magnetized materials and the prospective candidate of Mn x Ga, we focus on lattice structures and synthesis of Mn x Ga bulks, and epitaxial growth, structural characterization and magnetic properties of Mn x Ga films. Then we discuss effective ways to tailor and improve the structure and magnetism for possible applications in spintronics, magnetic recording and permanent magnets. Finally, we outline the recent progress in spin polarization, magnetic damping, magneto-optical and magneto-transport behaviors and thermal and chemical stability of Mn x Ga films and related spintronic devices like magnetic tunneling junctions, spin valves and spin injectors into semiconductors.

  5. Magnetic skyrmions without the skyrmion Hall effect in a magnetic nanotrack with perpendicular anisotropy.

    Science.gov (United States)

    Zhang, Yue; Luo, Shijiang; Yan, Baiqian; Ou-Yang, Jun; Yang, Xiaofei; Chen, Shi; Zhu, Benpeng; You, Long

    2017-07-27

    Magnetic skyrmions have potential applications in novel information devices with excellent energy efficiency. However, the skyrmion Hall effect (SkHE) could cause skyrmions moving in a nanotrack to get annihilated at the track edge. In this work, we discovered that the SkHE is depressed by modifying the magnetic structure at the edge of a track, and thus the skyrmion can move in almost a straight line at a high speed. Unlike the inner part of a track with perpendicular magnetic anisotropy, the edge layer exhibits in-plane magnetic anisotropy, and the orientation of edge moments is opposite that at the perimeter of skyrmions nearby. As a result, an enhanced repulsive force acts on the skyrmion to oppose the Magnus force that causes the SkHE. Additionally, the Dzyaloshinskii-Moriya interaction (DMI) constant of the edge layer also matters. When there is no DMI at the edge layer, the transverse displacement of the skyrmion can be depressed effectively when the width of the edge layer is sufficiently large. However, when the inner part and the edge share the same DMI constant, non-monotonically varied transverse displacement occurs because of the Néel-wall-like structure at the edge layer.

  6. Magnetization switching diagram of a perpendicular synthetic ferrimagnet CoFeB/Ta/CoFeB bilayer

    Energy Technology Data Exchange (ETDEWEB)

    Koplak, O. [Immanuel Kant Baltic Federal University, 236041 Kaliningrad (Russian Federation); Institute of Problems of Chemical Physics, 142432 Chernogolovka, Moscow (Russian Federation); Talantsev, A. [Institute of Problems of Chemical Physics, 142432 Chernogolovka, Moscow (Russian Federation); Lu, Y.; Hamadeh, A.; Pirro, P.; Hauet, T. [Institut Jean Lamour, UMR 7198 CNRS, Université de Lorraine (France); Morgunov, R., E-mail: morgunov2005@yandex.ru [Institute of Problems of Chemical Physics, 142432 Chernogolovka, Moscow (Russian Federation); Tambov State Technical University, 392000 Tambov (Russian Federation); Mangin, S. [Institut Jean Lamour, UMR 7198 CNRS, Université de Lorraine (France)

    2017-07-01

    Highlights: • Anisotropy, Zeeman and exchange energy determine sequence of magnetic transitions. • Three temperature ranges manifest different shapes of the hysteresis loop. • The critical transition fields are temperature dependent. - Abstract: Magnetic configurations in synthetic ferrimagnet CoFeB/Ta/CoFeB bilayer with strong perpendicular anisotropy have been systematically studied. Magnetization versus field hysteresis loop has been measured for different temperature ranging from 5 to 300 K. The applied field – temperature (H-T) magnetization switching diagram has been constructed by extracting the different switching fields as a function of temperature. This switching diagram can be well explained by considering the competition between energy barrier of layer’s magnetization reversal, interlayer exchange coupling, and Zeeman energy.

  7. Magnetization switching diagram of a perpendicular synthetic ferrimagnet CoFeB/Ta/CoFeB bilayer

    International Nuclear Information System (INIS)

    Koplak, O.; Talantsev, A.; Lu, Y.; Hamadeh, A.; Pirro, P.; Hauet, T.; Morgunov, R.; Mangin, S.

    2017-01-01

    Highlights: • Anisotropy, Zeeman and exchange energy determine sequence of magnetic transitions. • Three temperature ranges manifest different shapes of the hysteresis loop. • The critical transition fields are temperature dependent. - Abstract: Magnetic configurations in synthetic ferrimagnet CoFeB/Ta/CoFeB bilayer with strong perpendicular anisotropy have been systematically studied. Magnetization versus field hysteresis loop has been measured for different temperature ranging from 5 to 300 K. The applied field – temperature (H-T) magnetization switching diagram has been constructed by extracting the different switching fields as a function of temperature. This switching diagram can be well explained by considering the competition between energy barrier of layer’s magnetization reversal, interlayer exchange coupling, and Zeeman energy.

  8. Size Dependence of Magnetic Properties of Nanoscale CoFeB-MgO Magnetic Tunnel Junctions with Perpendicular Magnetic Easy Axis Observed by Ferromagnetic Resonance

    Science.gov (United States)

    Mizunuma, Kotaro; Yamanouchi, Michihiko; Sato, Hideo; Ikeda, Shoji; Kanai, Shun; Matsukura, Fumihiro; Ohno, Hideo

    2013-06-01

    The junction diameter D dependence of effective magnetic fields in a recording layer of CoFeB-MgO magnetic tunnel junctions with perpendicular magnetic easy axis is evaluated by ferromagnetic resonance measurements using the homodyne detection technique. The effective perpendicular magnetic field increases with decreasing D, which reflects mainly the reduction of the demagnetizing factor normal to the film plane. The stray field from a reference layer also increases with reducing D, which is in agreement with the D dependence of the shift field of the center of minor resistance versus perpendicular magnetic field curves with respect to zero magnetic field.

  9. Influence of mechanical scratch on the recorded magnetization stability of perpendicular recording media

    International Nuclear Information System (INIS)

    Nagano, Katsumasa; Sasaki, Syota; Futamoto, Masaaki

    2010-01-01

    Stability of recorded magnetization of hard disk drives (HDDs) is influenced by external environments, such as temperature, magnetic field, etc. Small scratches are frequently formed on HDD medium surface upon contacts with the magnetic head. Influence of temperature and mechanical scratch on the magnetization structure stability of perpendicular recording media was investigated by using a magnetic force microscope. The magnetic bit shape started to change at around 300 0 C for an area with no scratches, whereas for the area near a shallow mechanical scratch it started to change at a lower temperature around 250 0 C. An analysis of magnetization structure under an influence of temperature and mechanical scratch is carried out for the magnetization structure variation and recorded magnetization strength.

  10. Heating of charged particles by electrostatic wave propagating perpendicularly to uniform magnetic field

    International Nuclear Information System (INIS)

    Niu, Keishiro; Shimojo, Takashi.

    1978-02-01

    Increase in kinetic energy of a charged particle, affected by an electrostatic wave propagating perpendicularly to a uniform magnetic field, is obtained for both the initial and later stages. Detrapping time of the particle from the potential dent of the electrostatic wave and energy increase during trapping of the particle is analytically derived. Numerical simulations are carried out to support theoretical results. (auth.)

  11. 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.

  12. 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., 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.

  13. Tailoring magnetism in CoNi films with perpendicular anisotropy by ion irradiation

    International Nuclear Information System (INIS)

    Stanescu, D.; Ravelosona, D.; Mathet, V.; Chappert, C.; Samson, Y.; Beigne, C.; Vernier, N.; Ferre, J.; Gierak, J.; Bouhris, E.; Fullerton, E. E.

    2008-01-01

    This paper reports on the influence of ion irradiation on the magnetic properties of Co/Ni multilayers with perpendicular magnetic anisotropy (PMA). This material is a very promising candidate for ultrahigh density spintronic applications since it exhibits high polarization and low damping parameters. We show that PMA can be tailored in a controlled way by using uniform He + ion irradiation or focused Ga + ion beam

  14. Wave packet revivals in a graphene quantum dot in a perpendicular magnetic field

    International Nuclear Information System (INIS)

    Torres, J. J.; Romera, E.

    2010-01-01

    We study the time evolution of localized wave packets in graphene quantum dots in a perpendicular magnetic field, focusing on the quasiclassical and revival periodicities, for different values of the magnetic field intensities in a theoretical framework. We have considered contributions of the two inequivalent points in the Brillouin zone. The revival time has been found as an observable that shows the break valley degeneracy.

  15. Enhanced current quantization in high-frequency electron pumps in a perpendicular magnetic field

    International Nuclear Information System (INIS)

    Wright, S. J.; Blumenthal, M. D.; Gumbs, Godfrey; Thorn, A. L.; Pepper, M.; Anderson, D.; Jones, G. A. C.; Nicoll, C. A.; Ritchie, D. A.; Janssen, T. J. B. M.; Holmes, S. N.

    2008-01-01

    We present experimental results of high-frequency quantized charge pumping through a quantum dot formed by the electric field arising from applied voltages in a GaAs/AlGaAs system in the presence of a perpendicular magnetic field B. Clear changes are observed in the quantized current plateaus as a function of applied magnetic field. We report on the robustness in the length of the quantized plateaus and improvements in the quantization as a result of the applied B field

  16. Influence of thermal agitation on the electric field induced precessional magnetization reversal with perpendicular easy axis

    Directory of Open Access Journals (Sweden)

    Hongguang Cheng

    2013-12-01

    Full Text Available We investigated the influence of thermal agitation on the electric field induced precessional magnetization switching probability with perpendicular easy axis by solving the Fokker-Planck equation numerically with finite difference method. The calculated results show that the thermal agitation during the reversal process crucially influences the switching probability. The switching probability can be achieved is only determined by the thermal stability factor Δ of the free layer, it is independent on the device dimension, which is important for the high density device application. Ultra-low error rate down to the order of 10−9 can be achieved for the device of thermal stability factor Δ of 40. Low damping factor α material should be used for the free layer for high reliability device applications. These results exhibit potential of electric field induced precessional magnetization switching with perpendicular easy axis for ultra-low power, high speed and high density magnetic random access memory (MRAM applications.

  17. Influence of thermal agitation on the electric field induced precessional magnetization reversal with perpendicular easy axis

    Energy Technology Data Exchange (ETDEWEB)

    Cheng, Hongguang, E-mail: chenghg7932@gmail.com; Deng, Ning [Institute of Microelectronics, Tsinghua University, Beijing 100084 (China)

    2013-12-15

    We investigated the influence of thermal agitation on the electric field induced precessional magnetization switching probability with perpendicular easy axis by solving the Fokker-Planck equation numerically with finite difference method. The calculated results show that the thermal agitation during the reversal process crucially influences the switching probability. The switching probability can be achieved is only determined by the thermal stability factor Δ of the free layer, it is independent on the device dimension, which is important for the high density device application. Ultra-low error rate down to the order of 10{sup −9} can be achieved for the device of thermal stability factor Δ of 40. Low damping factor α material should be used for the free layer for high reliability device applications. These results exhibit potential of electric field induced precessional magnetization switching with perpendicular easy axis for ultra-low power, high speed and high density magnetic random access memory (MRAM) applications.

  18. Perpendicular magnetic tunnel junction with enhanced anisotropy obtained by utilizing an Ir/Co interface

    Science.gov (United States)

    Yakushiji, Kay; Kubota, Hitoshi; Fukushima, Akio; Yuasa, Shinji

    2016-01-01

    A highly scalable perpendicularly magnetized storage layer of a spin-torque-switching magnetic random-access memory (STT-MRAM) was developed. This storage layer attains a perpendicular magnetic anisotropy (PMA) of above 0.9 erg/cm2 at a thickness of 2 nm. Such high PMA is suitable for pushing STT-MRAM technology beyond the 20 nm node. The key was to realize dual interfacial PMA at both the Ir/Co and FeB/MgO interfaces in the united structure of the storage layer. While a high PMA was retained, a high magnetoresistance ratio (100%) and a low resistance-area product (3.0 Ω µm2) were also achieved.

  19. Competing effect of spin-orbit torque terms on perpendicular magnetization switching in structures with multiple inversion asymmetries

    OpenAIRE

    Yu, Guoqiang; Akyol, Mustafa; Upadhyaya, Pramey; Li, Xiang; He, Congli; Fan, Yabin; Montazeri, Mohammad; Alzate, Juan G.; Lang, Murong; Wong, Kin L.; Khalili Amiri, Pedram; Wang, Kang L.

    2016-01-01

    Current-induced spin-orbit torques (SOTs) in structurally asymmetric multilayers have been used to efficiently manipulate magnetization. In a structure with vertical symmetry breaking, a damping-like SOT can deterministically switch a perpendicular magnet, provided an in-plane magnetic field is applied. Recently, it has been further demonstrated that the in-plane magnetic field can be eliminated by introducing a new type of perpendicular field-like SOT via incorporating a lateral structural a...

  20. Study of the electric Held in HTS tape caused by perpendicular AC magnetic field

    International Nuclear Information System (INIS)

    Roiberg, V; Kopansky, F.

    2004-01-01

    Full Text: In a previous work we studied the influence of AC magnetic fields on voltage-currents (V-I) characteristics of high temperature superconducting (HTS) multi filament BSCC0-2223 tapes. It was found that AC magnetic fields perpendicular to the ab plane (the wide surface of the tape) cause a linear decrease of the critical current (IC) with amplitude of the AC magnetic field. The degradation of IC in .AC field was explained by the geometrical model according to which the transport current floe: is confined to the central zone of the tape where .AC field does not penetrate. For deeper understanding of the observed phenomena we carried out a study of the time dependence of the electric field during the cycle of AC field. At the same time we expanded the frequency range to low frequencies down to 1 Hz. The main results of the work are as following. 1. The time modulation of the electric field E in the HTS tape carrying transport DC current has the double frequency relating to AC magnetic field. 2. In field amplitudes less than 70 G the electric field modulation decreases with increasing frequency in opposite to its well-pronounced increase in higher AC field amplitudes. Alcove 70 G, the electric field increases with increasing the frequency of the external magnetic field. The wave forms of the electric field are different in both amplitudes ranges. 3. E-I curves of the tape in low amplitudes are frequency independent and coincide with E-l curves in AC field with intensity equal to the AC field amplitude. 4. In high AC field amplitudes, a strong dependence of the E-I curves on frequency is observed in the frequency range of 1-40 Hz and no dependence is observed in higher frequencies. Our results suggest that a combination of the geometrical model with flux creep concepts is necessary for a better understanding of the electric field behavior in our measurement conditions

  1. Tailoring of Perpendicular Magnetic Anisotropy in Dy13Fe87 Thin Films with Hexagonal Antidot Lattice Nanostructure

    Directory of Open Access Journals (Sweden)

    Mohamed Salaheldeen

    2018-04-01

    Full Text Available In this article, the magnetic properties of hexagonally ordered antidot arrays made of Dy13Fe87 alloy are studied and compared with corresponding ones of continuous thin films with the same compositions and thicknesses, varying between 20 nm and 50 nm. Both samples, the continuous thin films and antidot arrays, were prepared by high vacuum e-beam evaporation of the alloy on the top-surface of glass and hexagonally self-ordered nanoporous alumina templates, which serve as substrates, respectively. By using a highly sensitive magneto-optical Kerr effect (MOKE and vibrating sample magnetometer (VSM measurements an interesting phenomenon has been observed, consisting in the easy magnetization axis transfer from a purely in-plane (INP magnetic anisotropy to out-of-plane (OOP magnetization. For the 30 nm film thickness we have measured the volume hysteresis loops by VSM with the easy magnetization axis lying along the OOP direction. Using magnetic force microscopy measurements (MFM, there is strong evidence to suggest that the formation of magnetic domains with OOP magnetization occurs in this sample. This phenomenon can be of high interest for the development of novel magnetic and magneto-optic perpendicular recording patterned media based on template-assisted deposition techniques.

  2. In-plane anisotropy of a nano-scaled magnetic tunnel junction with perpendicular magnetic easy axis

    Science.gov (United States)

    Hirayama, Eriko; Kanai, Shun; Sato, Koji; Yamanouchi, Michihiko; Sato, Hideo; Ikeda, Shoji; Matsukura, Fumihiro; Ohno, Hideo

    2015-04-01

    We investigate magnetic properties of a 100-nm-diameter CoFeB/MgO magnetic tunnel junction (MTJ) with perpendicular magnetic easy axis by homodyne-detected ferromagnetic resonance (FMR) and junction resistance measurements. The resonant frequency depends clearly on the direction of the in-plane magnetic field, which is also the case for the angle dependence of the junction resistance. A good correspondence between the two independent measurements indicates the presence of unintentionally introduced in-plane magnetic anisotropy in the present MTJ.

  3. Thickness dependence of magnetic properties in La–Co substituted strontium hexaferrite films with perpendicular anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Hui, Yajuan [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074 (China); Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074 (China); Cheng, Weiming, E-mail: wmcheng@mail.hust.edu.cn [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074 (China); Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074 (China); Yan, Peng [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074 (China); Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074 (China); Chen, Jincai [Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074 (China); Miao, Xiangshui [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074 (China); Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074 (China); Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074 (China)

    2015-09-15

    The thickness dependence of magnetization reversal and coercivity behavior for La–Co substituted strontium hexaferrite (Sr-M) films was investigated. It is found that perpendicular anisotropy appears only when film thickness (t) is above 110 nm. With increasing t, perpendicular anisotropy energy (K{sub u⊥}) increases gradually to its maximum of 1.76×10{sup 6} erg/cm{sup 3} at t=300 nm, but turns to decrease when t>300 nm. Moreover, when t>110 nm, those films exhibit domains pinning or Stoner–Wohlfarth reversal model, present large K{sub u⊥} values and a rapid increase in H{sub c⊥}. However, while t≤110 nm, Sr-M films show nucleation model of magnetization reversal and perform low coercivity. The origin of the coercivity varying with thickness should be correlated with the grain size and preferred orientations in Sr-M films. - Highlights: • Thickness dependence in submicro-scale bulk system is investigated for La–Sr–Co–Fe–O films. • (0 0 1) preferred orientation gradually increases until t=300 nm and then declines. • The magnetization reversal presents different models with thickness. • Perpendicular anisotropy energy increases to maximum value of 1.76×10{sup 6} erg/cm{sup 3} at t=300 nm. • The coercivity varying with thickness is correlated with the grain size and preferred orientation.

  4. Perpendicularly magnetized Mn-based binary films compatible with semiconductor in structure and technique

    Science.gov (United States)

    Zhu, Lijun; Nie, Shuaihua; Zhao, Xupeng; Mao, Siwei; Xiao, Jiaxing; Lu, Jun; Zhao, Jianhua

    Ferromagnetic films with both high perpendicular anisotropy and good compatibility with semiconductors have great potential not only in semiconductor spintronic devices, but also in high-density integration of metallic spintronic functional devices like nonvolatile MRAM on semiconductor circuits. Recently, we have grown the high-quality L10-MnGa and L10-MnAl films on GaAs by MBE, which show giant perpendicular magnetic anisotropy. Moreover, annealing studies revealed the thermal stability of them up to at least 350C, indicating its compatible with current semiconductor industry technique. Here, we will present the orbital two-channel Kondo (2CK) effect observed in ferromagnetic L10-MnAl and L10-MnGa, which provide the first evidence for the presence of 2CK effect in a ferromagnet. The tunneling magnetic resistivity of L10-MnGa-based perpendicularly magnetic tunnel junctions will also be mentioned. This work was supported partly by MOST of China (Grant No. 2015CB921503) and NSFC (Grant No. 61334006).

  5. Characterization of rf-SSET in both in-plane and perpendicular magnetic fields

    Science.gov (United States)

    Tang, Chunyang; Yang, Zhen; Yuan, Mingyun; Rimberg, A. J.; Savage, D. E.; Eriksson, M. A.; Rimberg Team; Eriksson Collaboration

    2013-03-01

    Previous success in coupling an aluminum radio-frequency superconducting single electron transistor (rf-SSET) to quantum dots (QDs) has demonstrated use of the rf-SSET as an ultra-sensitive and fast charge sensor. Since a magnetic field is usually necessary for quantum dot qubit manipulation, it is important to understand the effect of magnetic fields, either in-plane or perpendicular, on the performance of any charge sensor near the QDs. Here we report characterization of rf-SSETs in both in-plane and perpendicular magnetic fields. The rf-SSET works well in an in-plane fields up to 1 Tesla at a temperature of 30 mK. At 0.3K, in a perpendicular field generated by a stripline located 700 nm away, the rf-SSET charge sensitivity even shows improvement for up to 2.1 mA current through the stripline (corresponding roughly to a field of 6 Gauss). This work was supported by NSA, LPS and ARO

  6. Magnetic force microscopy image of Co-Cr-Ta layer in perpendicular magnetic tape at high linear recording density

    Science.gov (United States)

    Ishikawa, K.; Taguchi, R.; Miyashita, E.; Numazawa, J.; Ohshima, H.

    1997-04-01

    In this study, magnetic force microscopy (MFM) was used to investigate the recording capability of a perpendicular magnetic tape at a higher linear recording density. Perpendicular magnetic tapes with polyimide base sheets 10 μm thick were fabricated by a facing-target sputtering system [H. Yoshimoto, K. Kuga, Y. Yoneda, and J. Numazawa, J. Magn. Magn. Mater. 148, 357 (1995)]. A Co-Cr-Ta (200 nm) monolayered tape with a base sheet of excellent surface roughness was fabricated. A complete recorded bit pattern of 250 kfci was observed as a MFM image on the tape. A recorded bit pattern of 300 kfci was also observed. A Co-Cr-Ta/Ni-Fe (150/50 nm) multilayered tape was also fabricated. The remnant magnetization state on this tape at 50 kfci was improved by the presence of an underlayer (Ni-Fe) only 50 nm thick. The MFM image at 250 kfci was the same as with a monolayered tape.

  7. Dipole-exchange spin waves in perpendicularly magnetized discs: Role of the Oersted field

    Science.gov (United States)

    Arias, R. E.; Mills, D. L.

    2007-06-01

    We develop the theory of the exchange dipole spin waves in thin circular discs for the case where the magnetization is nominally perpendicular to the plane. Our interest is in the circumstance where a transport current is injected into the disc, with current also perpendicular to the plane of the disc. Such a current creates an azimuthal magnetic field, referred to often as the Oersted field. We develop the theory of the influence of the Oersted field on the spin-wave spectrum of the disc. This field produces a vortex state. We suggest that this vortex state is stable down to zero applied field. If the external applied field H0 is in the +z direction, perpendicular to the plane of the disc, the vortex state has magnetization at the center of the disc also parallel to +z always. This is the case even when H0<4πMS , where the magnetization at the center of the disc is antiparallel to the local field H0-4πMS there. We present calculations of the current dependence of spin-wave frequencies of several modes as a function of applied magnetic field. We also address an issue overlooked in previous studies of spin waves in thin discs. This is that for quantitative purposes, it is not sufficient to describe internal dipole fields generated by the spin motions simply by adding an effective internal field -4πmzẑ to the equations of motion, with mz the component of dynamic magnetization normal to the surface. For samples of present interest, we derive terms we call gradient corrections, and these play a role quantitatively comparable to exchange itself in the analysis of the spin-wave frequencies. Quantitative studies of spin dynamics in such samples thus must include the gradient corrections.

  8. Spin-transfer-torque efficiency enhanced by edge-damage of perpendicular magnetic random access memories

    Energy Technology Data Exchange (ETDEWEB)

    Song, Kyungmi [KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 136-713 (Korea, Republic of); Lee, Kyung-Jin, E-mail: kj-lee@korea.ac.kr [KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 136-713 (Korea, Republic of); Department of Materials Science and Engineering, Korea University, Seoul 136-713 (Korea, Republic of)

    2015-08-07

    We numerically investigate the effect of magnetic and electrical damages at the edge of a perpendicular magnetic random access memory (MRAM) cell on the spin-transfer-torque (STT) efficiency that is defined by the ratio of thermal stability factor to switching current. We find that the switching mode of an edge-damaged cell is different from that of an undamaged cell, which results in a sizable reduction in the switching current. Together with a marginal reduction of the thermal stability factor of an edge-damaged cell, this feature makes the STT efficiency large. Our results suggest that a precise edge control is viable for the optimization of STT-MRAM.

  9. Spin-transfer-torque efficiency enhanced by edge-damage of perpendicular magnetic random access memories

    Science.gov (United States)

    Song, Kyungmi; Lee, Kyung-Jin

    2015-08-01

    We numerically investigate the effect of magnetic and electrical damages at the edge of a perpendicular magnetic random access memory (MRAM) cell on the spin-transfer-torque (STT) efficiency that is defined by the ratio of thermal stability factor to switching current. We find that the switching mode of an edge-damaged cell is different from that of an undamaged cell, which results in a sizable reduction in the switching current. Together with a marginal reduction of the thermal stability factor of an edge-damaged cell, this feature makes the STT efficiency large. Our results suggest that a precise edge control is viable for the optimization of STT-MRAM.

  10. Perpendicular Magnetic Anisotropy in FePt Patterned Media Employing a CrV Seed Layer

    Directory of Open Access Journals (Sweden)

    Chun Dong

    2011-01-01

    Full Text Available Abstract A thin FePt film was deposited onto a CrV seed layer at 400°C and showed a high coercivity (~3,400 Oe and high magnetization (900–1,000 emu/cm3 characteristic of L10 phase. However, the magnetic properties of patterned media fabricated from the film stack were degraded due to the Ar-ion bombardment. We employed a deposition-last process, in which FePt film deposited at room temperature underwent lift-off and post-annealing processes, to avoid the exposure of FePt to Ar plasma. A patterned medium with 100-nm nano-columns showed an out-of-plane coercivity fivefold larger than its in-plane counterpart and a remanent magnetization comparable to saturation magnetization in the out-of-plane direction, indicating a high perpendicular anisotropy. These results demonstrate the high perpendicular anisotropy in FePt patterned media using a Cr-based compound seed layer for the first time and suggest that ultra-high-density magnetic recording media can be achieved using this optimized top-down approach.

  11. Transport Theory for Plasmas that are Strongly Magnetized and Strongly Coupled

    Science.gov (United States)

    Baalrud, Scott; Daligault, Jerome

    2016-10-01

    Plasmas with components that are magnetized, strongly coupled, or both arise in a variety of frontier plasma physics experiments including magnetized dusty plasmas, nonneutral plasmas, magnetized ICF concepts, as well as from self-generated fields in ICF. Here, a species is considered strongly magnetized if the gyroradius is smaller than the spatial scale over which Coulomb interactions occur. A theory for transport properties is described that treats a wide range of both coupling and magnetization strengths. The approach is based on an extension of the recent effective potential transport theory to include a strong magnetic field. The underlying kinetic theory is based on an extension of the Boltzmann equation to include a strong magnetic field in the dynamics of binary scattering events. Corresponding magnetohydrodynamic equations are derived by solving the kinetic equation using a Chapman-Enskog like spectral method. Results are compared with classical molecular dynamics simulations of self-diffusion of the one component plasmas, and with simulations of parallel to perpendicular temperature equilibration of an initially anisotropic distribution. This material is based upon work supported by AFOSR Award FA9550-16-1-0221 and DOE OFES Award DE-SC0016159.

  12. Electric field-induced magnetization reversal in a perpendicular-anisotropy CoFeB-MgO magnetic tunnel junction

    Science.gov (United States)

    Kanai, S.; Yamanouchi, M.; Ikeda, S.; Nakatani, Y.; Matsukura, F.; Ohno, H.

    2012-09-01

    The electric field-induced ˜180° magnetization reversal is realized for a sputtered CoFeB/MgO-based magnetic tunnel junction with perpendicular magnetic easy axis in a static external magnetic field. Application of bias voltage with nanoseconds duration results in a temporal change of magnetic easy axis in the free layer CoFeB to in-plane, which induces precessional motion of magnetization in the free layer. The magnetization reversal takes place when the bias voltage pulse duration is adjusted to a half period of the precession. We show that the back and forth magnetization reversal can be observed by using successive application of half-period voltage pulses.

  13. Imaginary potential in strongly coupled N = 4 SYM plasma in a magnetic field

    Science.gov (United States)

    Zhang, Zi-qiang; Hou, De-fu

    2018-03-01

    We study the effect of a constant magnetic field on the imaginary part of a quarkonia potential in a strongly-coupled N = 4 SYM plasma. We consider the pair axis to be aligned perpendicularly and parallel to the magnetic field, respectively. For both cases, we find that the presence of the magnetic field tends to enhance the imaginary potential thus decreasing the thermal width. In addition, the magnetic field has a stronger effect on the imaginary potential when the pair axis is perpendicular to the magnetic field rather than parallel.

  14. Spin-Orbit Torque-Assisted Switching in Magnetic Insulator Thin Films with Perpendicular Magnetic Anisotropy

    Science.gov (United States)

    Wu, Mingzhong

    As an in-plane charge current flows in a heavy metal film with spin-orbit coupling, it produces a torque that can induce magnetization switching in a neighboring 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. This presentation reports the SOT-assisted switching in heavy metal/magnetic insulator systems.1 The experiments made use of Pt/BaFe12O19 bi-layered structures. Thanks to its strong spin-orbit coupling, Pt has been widely used to produce pure spin currents in previous studies. BaFe12O19 is an M-type barium hexagonal ferrite and is often referred as BaM. It is one of the few magnetic insulators with strong magneto-crystalline anisotropy and shows an effective uniaxial anisotropy field of about 17 kOe. It's found that the switching response in the BaM film strongly depends on the charge current applied to the Pt film. When a constant magnetic field is applied in the film plane, the charge current in the Pt film can switch the normal component of the magnetization (M⊥) in the BaM film between the up and down states. The current also dictates the up and down states of the remnant magnetization when the in-plane field is reduced to zero. When M⊥ is measured by sweeping an in-plane field, the response manifests itself as a hysteresis loop, which evolves in a completely opposite manner if the sign of the charge current is flipped. When the coercivity is measured by sweeping an out-of-plane field, its value can be reduced or increased by as much as about 500 Oe if an appropriate charge current is applied. 1. P. Li, T. Liu, H. Chang, A. Kalitsov, W. Zhang, G. Csaba, W. Li, D. Richardson, A. Demann, G. Rimal, H. Dey, J. S. Jiang, W. Porod, S. Field, J. Tang, M. C. Marconi, A. Hoffmann, O. Mryasov, and M. Wu, Nature Commun. 7:12688 doi: 10.1038/ncomms12688 (2016).

  15. 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.

  16. Quantifying angular dependence of spin-orbit torques in Ta/CoFeB/MgO trilayers with perpendicular magnetic anisotropy

    Science.gov (United States)

    Chen, Yunpeng; Celik, Halise; Wang, Tao; Kannan, Harsha; Krivorotov, Ilya N.; Xiao, John Q.

    2017-04-01

    The spin-orbit interactions in heavy-metal/ferromagnet heterostructures have attracted considerable attention because they provide an efficient way to manipulate the magnetization with strong current-driven spin-orbit torques (SOTs) via the spin Hall effect in the heavy metal or Rashba effect due to the symmetry breaking at the interface. Theoretical calculations predict no dependence of the SOTs on the out-of-plane angle of magnetization due to spin Hall effect, but Rashba effect induces a nontrivial angular dependence of SOTs. Quantitative measurements with adiabatic harmonic Hall technique have observed the angular dependence in Ta/CoFeB/MgO or Pt /Co /Al Ox with perpendicular magnetic anisotropy. However, this method is complicated because the signal consists of both anomalous and planar Hall contributions. In addition, the fitting of the measurement data is sensitive to the fitting parameters, particularly to the perpendicular anisotropy, in a certain angle region (40-70°). To avoid this uncertainty, we have developed a scheme to quantify the angular dependence of SOTs based on the magneto-optic Kerr effect with field calibration. Without fitting procedures, we precisely determine the SOTs and their angle dependence on the magnetization orientation. We observe a strong angular dependence that is different from the previous experimental observations. Based on this strong dependence, we conclude that a Rashba effect at the same interface, that is responsible for the perpendicular magnetic anisotropy, is the dominant mechanism for the current-driven SOTs in this system.

  17. Perpendicular magnetic tunnel junction with a strained Mn-based nanolayer

    Science.gov (United States)

    Suzuki, K. Z.; Ranjbar, R.; Okabayashi, J.; Miura, Y.; Sugihara, A.; Tsuchiura, H.; Mizukami, S.

    2016-07-01

    A magnetic tunnel junction with a perpendicular magnetic easy-axis (p-MTJ) is a key device for spintronic non-volatile magnetoresistive random access memory (MRAM). Co-Fe-B alloy-based p-MTJs are being developed, although they have a large magnetisation and medium perpendicular magnetic anisotropy (PMA), which make it difficult to apply them to a future dense MRAM. Here, we demonstrate a p-MTJ with an epitaxially strained MnGa nanolayer grown on a unique CoGa buffer material, which exhibits a large PMA of more than 5 Merg/cm3 and magnetisation below 500 emu/cm3 these properties are sufficient for application to advanced MRAM. Although the experimental tunnel magnetoresistance (TMR) ratio is still low, first principles calculations confirm that the strain-induced crystal lattice distortion modifies the band dispersion along the tetragonal c-axis into the fully spin-polarised state; thus, a huge TMR effect can be generated in this p-MTJ.

  18. High tunneling magnetoresistance ratio in perpendicular magnetic tunnel junctions using Fe-based Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yu-Pu, E-mail: Vicky-sg1015@hotmail.com [Department of Electrical and Computer Engineering, National University of Singapore (Singapore); Data Storage Institute, Agency for Science, Technology and Research - A*STAR (Singapore); Lim, Sze-Ter; Han, Gu-Chang, E-mail: HAN-Guchang@dsi.a-star.edu.sg [Data Storage Institute, Agency for Science, Technology and Research - A*STAR (Singapore); Teo, Kie-Leong, E-mail: eleteokl@nus.edu.sg [Department of Electrical and Computer Engineering, National University of Singapore (Singapore)

    2015-12-21

    Heulser alloys Fe{sub 2}Cr{sub 1−x}Co{sub x}Si (FCCS) with different Co compositions x have been predicted to have high spin polarization. High perpendicular magnetic anisotropy (PMA) has been observed in ultra-thin FCCS films with magnetic anisotropy energy density up to 2.3 × 10{sup 6 }erg/cm{sup 3}. The perpendicular magnetic tunnel junctions (p-MTJs) using FCCS films with different Co compositions x as the bottom electrode have been fabricated and the post-annealing effects have been investigated in details. An attractive tunneling magnetoresistance ratio as high as 51.3% is achieved for p-MTJs using Fe{sub 2}CrSi (FCS) as the bottom electrode. The thermal stability Δ can be as high as 70 for 40 nm dimension devices using FCS, which is high enough to endure a retention time of over 10 years. Therefore, Heusler alloy FCS is a promising PMA candidate for p-MTJ application.

  19. Micromagnetic study of skyrmion stability in confined magnetic structures with perpendicular anisotropy

    Science.gov (United States)

    Novak, R. L.; Garcia, F.; Novais, E. R. P.; Sinnecker, J. P.; Guimarães, A. P.

    2018-04-01

    Skyrmions are emerging topological spin structures that are potentially revolutionary for future data storage and spintronics applications. The existence and stability of skyrmions in magnetic materials is usually associated to the presence of the Dzyaloshinskii-Moriya interaction (DMI) in bulk magnets or in magnetic thin films lacking inversion symmetry. While some methods have already been proposed to generate isolated skyrmions in thin films with DMI, a thorough study of the conditions under which the skyrmions will remain stable in order to be manipulated in an integrated spintronic device are still an open problem. The stability of such structures is believed to be a result of ideal combinations of perpendicular magnetic anisotropy (PMA), DMI and the interplay between geometry and magnetostatics. In the present work we show some micromagnetic results supporting previous experimental observations of magnetic skyrmions in spin-valve stacks with a wide range of DMI values. Using micromagnetic simulations of cobalt-based disks, we obtain the magnetic ground state configuration for several values of PMA, DMI and geometric parameters. Skyrmion numbers, corresponding to the topological charge, are calculated in all cases and confirm the occurrence of isolated, stable, axially symmetric skyrmions for several combinations of DMI and anisotropy constant. The stability of the skyrmions in disks is then investigated under magnetic field and spin-polarized current, in finite temperature, highlighting the limits of applicability of these spin textures in spintronic devices.

  20. Free- and reference-layer magnetization modes versus in-plane magnetic field in a magnetic tunnel junction with perpendicular magnetic easy axis

    Science.gov (United States)

    Mazraati, Hamid; Le, Tuan Q.; Awad, Ahmad A.; Chung, Sunjae; Hirayama, Eriko; Ikeda, Shoji; Matsukura, Fumihiro; Ohno, Hideo; Åkerman, Johan

    2016-09-01

    We study the magnetodynamic modes of a magnetic tunnel junction with perpendicular magnetic easy axis (p-MTJ) in in-plane magnetic fields using device-level ferromagnetic resonance spectroscopy. We compare our experimental results to those of micromagnetic simulations of the entire p-MTJ. Using an iterative approach to determine the material parameters that best fit our experiment, we find excellent agreement between experiments and simulations in both the static magnetoresistance and magnetodynamics in the free and reference layers. From the micromagnetic simulations, we determine the spatial mode profiles, the localization of the modes and, as a consequence, their distribution in the frequency domain due to the inhomogeneous internal field distribution inside the p-MTJ under different applied field regimes. We also conclude that the excitation mechanism is a combination of the microwave voltage modulated perpendicular magnetic anisotropy, the microwave Oersted field, and the spin-transfer torque generated by the microwave current.

  1. Oxygen control of perpendicular magnetic anisotropy and spin-orbit torques in Ta/ CoFeB/ MgO trilayer

    Science.gov (United States)

    Kannan, Harsha; Chen, Yunpeng; Haughey, Kevin; Xiao, John

    Current-induced magnetization switching allows the integration of magnetic capabilities into electric circuits. The spin-orbit interaction in heavy-metal/ferromagnetic heterostructures are of profound interest, since they provide an efficient way to manipulate the magnetization, via strong current driven spin orbital torques (SOTs). Materials possessing perpendicular magnetic anisotropy (PMA) are the preferred choice for the fabrication of memory devices since its magnetization can be switched with a small current density. Here we present the Oxygen control of perpendicular magnetic anisotropy of Ta/ CoFeB/ MgO, which is accomplished by fabricating a thin wedge layer of Al on top of the MgO layer followed by oxidation in Oxygen plasma. Thinner end of the Al wedge will be over oxidized and the thicker end will be under oxidized, hence degree of oxidation varies from thinner to the thicker end. This in effect provides a means to control the Oxygen content at the CoFeB/ MgO interface and to control the perpendicular magnetic anisotropy. We will further discuss the dependence of SOTs, measured with adiabatic harmonic Hall technique on varying PMA.

  2. THz-driven demagnetization with perpendicular magnetic anisotropy: towards ultrafast ballistic switching

    Science.gov (United States)

    Polley, Debanjan; Pancaldi, Matteo; Hudl, Matthias; Vavassori, Paolo; Urazhdin, Sergei; Bonetti, Stefano

    2018-02-01

    We study THz-driven spin dynamics in thin CoPt films with perpendicular magnetic anisotropy. Femtosecond magneto-optical Kerr effect measurements show that demagnetization amplitude of about 1% can be achieved with a peak THz electric field of 300 kV cm‑1, and a corresponding peak magnetic field of 0.1 T. The effect is more than an order of magnitude larger than observed in samples with easy-plane anisotropy irradiated with the same field strength. We also utilize finite-element simulations to design a meta-material structure that can enhance the THz magnetic field by more than an order of magnitude, over an area of several tens of square micrometers. Magnetic fields exceeding 1 Tesla, generated in such meta-materials with the available laser-based THz sources, are expected to produce full magnetization reversal via ultrafast ballistic precession driven by the THz radiation. Our results demonstrate the possibility of table-top ultrafast magnetization reversal induced by THz radiation.

  3. Strong and superstrong pulsed magnetic fields generation

    CERN Document Server

    Shneerson, German A; Krivosheev, Sergey I

    2014-01-01

    Strong pulsed magnetic fields are important for several fields in physics and engineering, such as power generation and accelerator facilities. Basic aspects of the generation of strong and superstrong pulsed magnetic fields technique are given, including the physics and hydrodynamics of the conductors interacting with the field as well as an account of the significant progress in generation of strong magnetic fields using the magnetic accumulation technique. Results of computer simulations as well as a survey of available field technology are completing the volume.

  4. Confinement and αs in a strong magnetic field

    Directory of Open Access Journals (Sweden)

    Yu.A. Simonov

    2015-07-01

    Full Text Available Hadron decay widths are shown to increase in strong magnetic fields as Γ(eB∼eBκΓ(0. The same mechanism is shown to be present in the production of the sea quark pair inside the confining string, which decreases the string tension with the growing eB parallel to the string. On the other hand, the average energy of the qq¯ holes in the string world sheet increases, when the direction of B is perpendicular to the sheet. These two effects stipulate the spectacular picture of the B dependent confinement and αs, discovered on the lattice.

  5. Perpendicular magnetic anisotropy in Co{sub X}Pd{sub 100−X} alloys for magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Clark, B.D.; Natarajarathinam, A.; Tadisina, Z.R. [Center for Materials for Information Technology, University of Alabama, Tuscaloosa, AL 35487 (United States); Chen, P.J.; Shull, R.D. [National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States); Gupta, S., E-mail: Sgupta@eng.ua.edu [Center for Materials for Information Technology, University of Alabama, Tuscaloosa, AL 35487 (United States)

    2017-08-15

    Highlights: • CoPd alloy perpendicular anisotropy dependent on composition and thickness. • CIPT results show that TMR tracks with PMA of CoPd. • Potential replacement for Co/Pd multilayers. - Abstract: 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 L1{sub 0} alloy, or an overly complex multilayered synthetic antiferromagnet (SyAF). We report a compositional study of perpendicular Co{sub x}Pd alloy-pinned Co{sub 20}Fe{sub 60}B{sub 20}/MgO based MTJ stacks, grown at moderate temperatures in a planetary deposition system. The perpendicular anisotropy of the Co{sub x}Pd 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 Co{sub x}Pd MTJ stacks. The Co{sub x}Pd alloy becomes fully perpendicular at approximately x = 30% (atomic fraction) Co. Full-film MTJ stacks of Si/SiO{sub 2}/MgO (13)/Co{sub X}Pd{sub 100−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.

  6. A New Circuit Model for Spin-Torque Oscillator Including Perpendicular Torque of Magnetic Tunnel Junction

    Directory of Open Access Journals (Sweden)

    Hyein Lim

    2013-01-01

    Full Text Available Spin-torque oscillator (STO is a promising new technology for the future RF oscillators, which is based on the spin-transfer torque (STT effect in magnetic multilayered nanostructure. It is expected to provide a larger tunability, smaller size, lower power consumption, and higher level of integration than the semiconductor-based oscillators. In our previous work, a circuit-level model of the giant magnetoresistance (GMR STO was proposed. In this paper, we present a physics-based circuit-level model of the magnetic tunnel junction (MTJ-based STO. MTJ-STO model includes the effect of perpendicular torque that has been ignored in the GMR-STO model. The variations of three major characteristics, generation frequency, mean oscillation power, and generation linewidth of an MTJ-STO with respect to the amount of perpendicular torque, are investigated, and the results are applied to our model. The operation of the model was verified by HSPICE simulation, and the results show an excellent agreement with the experimental data. The results also prove that a full circuit-level simulation with MJT-STO devices can be made with our proposed model.

  7. Stochastic simulation of thermally assisted magnetization reversal in sub-100 nm dots with perpendicular anisotropy

    International Nuclear Information System (INIS)

    Purnama, Budi; Koga, Masashi; Nozaki, Yukio; Matsuyama, Kimihide

    2009-01-01

    Thermally assisted magnetization reversal of sub-100 nm dots with perpendicular anisotropy has been investigated using a micromagnetic Langevin model. The performance of the two different reversal modes of (i) a reduced barrier writing scheme and (ii) a Curie point writing scheme are compared. For the reduced barrier writing scheme, the switching field H swt decreases with an increase in writing temperature but is still larger than that of the Curie point writing scheme. For the Curie point writing scheme, the required threshold field H th , evaluated from 50 simulation results, saturates at a value, which is not simply related to the energy barrier height. The value of H th increases with a decrease in cooling time owing to the dynamic aspects of the magnetic ordering process. Dependence of H th on material parameters and dot sizes has been systematically studied

  8. Increased magnetic damping in ultrathin films of Co2FeAl with perpendicular anisotropy

    Science.gov (United States)

    Takahashi, Y. K.; Miura, Y.; Choi, R.; Ohkubo, T.; Wen, Z. C.; Ishioka, K.; Mandal, R.; Medapalli, R.; Sukegawa, H.; Mitani, S.; Fullerton, E. E.; Hono, K.

    2017-06-01

    We estimated the magnetic damping constant α of Co2FeAl (CFA) Heusler alloy films of different thicknesses with an MgO capping layer by means of time-resolved magneto-optical Kerr effect and ferromagnetic resonance measurements. CFA films with thicknesses of 1.2 nm and below exhibited perpendicular magnetic anisotropy arising from the presence of the interface with MgO. While α increased gradually with decreasing CFA film thickness down to 1.2 nm, it was increased substantially when the thickness was reduced further to 1.0 nm. Based on the microstructure analyses and first-principles calculations, we attributed the origin of the large α in the ultrathin CFA film primarily to the Al deficiency in the CFA layer, which caused an increase in the density of states and thereby in the scatterings of their spins.

  9. Asymmetric driven dynamics of Dzyaloshinskii domain walls in ultrathin ferromagnetic strips with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Sánchez-Tejerina, L. [Dpto. Electricidad y Electrónica, Facultad de Ciencias, Universidad de Valladolid, 47011 Valladolid (Spain); Alejos, Ó., E-mail: oscaral@ee.uva.es [Dpto. Electricidad y Electrónica, Facultad de Ciencias, Universidad de Valladolid, 47011 Valladolid (Spain); Martínez, E. [Dpto. Física Aplicada, Facultad de Ciencias, Universidad de Salamanca, 37011 Salamanca (Spain); Muñoz, J.M. [Dpto. Electricidad y Electrónica, Facultad de Ciencias, Universidad de Valladolid, 47011 Valladolid (Spain)

    2016-07-01

    The dynamics of domain walls in ultrathin ferromagnetic strips with perpendicular magnetic anisotropy is studied from both numerical and analytical micromagnetics. The influence of a moderate interfacial Dzyaloshinskii–Moriya interaction associated to a bi-layer strip arrangement has been considered, giving rise to the formation of Dzyaloshinskii domain walls. Such walls possess under equilibrium conditions an inner magnetization structure defined by a certain orientation angle that make them to be considered as intermediate configurations between Bloch and Néel walls. Two different dynamics are considered, a field-driven and a current-driven dynamics, in particular, the one promoted by the spin torque due to the spin-Hall effect. Results show an inherent asymmetry associated with the rotation of the domain wall magnetization orientation before reaching the stationary regime, characterized by a constant terminal speed. For a certain initial DW magnetization orientation at rest, the rotation determines whether the reorientation of the DW magnetization prior to reach stationary motion is smooth or abrupt. This asymmetry affects the DW motion, which can even reverse for a short period of time. Additionally, it is found that the terminal speed in the case of the current-driven dynamics may depend on either the initial DW magnetization orientation at rest or the sign of the longitudinally injected current. - Highlights: • The asymmetric response of domain walls in bilayer strips with PMA is studied. • Out-of-plane fields and SHE longitudinal currents are applied. • The response is associated to the rotation of the domain wall inner magnetization. • Clockwise and counter-clockwise magnetization rotations are not equivalent. • The asymmetry results in different travelled distances and/or terminal speeds.

  10. First-principles investigation of the very large perpendicular magnetic anisotropy at Fe | MgO and Co | MgO interfaces

    KAUST Repository

    Yang, H. X.

    2011-08-01

    The perpendicular magnetic anisotropy (PMA) arising at the interface between ferromagnetic transition metals and metallic oxides was investigated via first-principles calculations. In this work very large values of PMA, up to 3 erg/cm2, at Fe|MgO interfaces are reported, in agreement with recent experiments. The origin of PMA is attributed to overlap between O-pz and transition metal dz2 orbitals hybridized with dxz(yz) orbitals with stronger spin-orbit coupling-induced splitting around the Fermi level for perpendicular magnetization orientation. Furthermore, it is shown that the PMA value weakens in the case of over- or underoxidation due to the fact that oxygen pz and transition metal dz2 orbital overlap is strongly affected by disorder, in agreement with experimental observations in magnetic tunnel junctions.

  11. Perpendicular magnetic anisotropy in amorphous NdxCo1 -x thin films studied by x-ray magnetic circular dichroism

    Science.gov (United States)

    Cid, R.; Alameda, J. M.; Valvidares, S. M.; Cezar, J. C.; Bencok, P.; Brookes, N. B.; Díaz, J.

    2017-06-01

    The origin of perpendicular magnetic anisotropy (PMA) in amorphous NdxCo1 -x thin films is investigated using x-ray magnetic circular dichroism (XMCD) spectroscopy at the Co L2 ,3 and Nd M4 ,5 edges. The magnetic orbital and spin moments of the 3 d cobalt and 4 f neodymium electrons were measured as a function of the magnetic field orientation, neodymium concentration, and temperature. In all the studied samples, the magnetic anisotropy of the neodymium subnetwork is always oriented perpendicular to the plane, whereas the anisotropy of the orbital moment of cobalt is in the basal plane. The ratio Lz/Sz of the neodymium 4 f orbitals changes with the sample orientation angle, being higher and closer to the atomic expected value at normal orientation and smaller at grazing angles. This result is well explained by assuming that the 4 f orbital is distorted by the effect of an anisotropic crystal field when it is magnetized along its hard axis, clearly indicating that the 4 f states are not rotationally invariant. The magnetic anisotropy energy associated to the neodymium subnetwork should be proportional to this distortion, which we demonstrate is accessible by applying the XMCD sum rules for the spin and intensity at the Nd M4 ,5 edges. The analysis unveils a significant portion of neodymium atoms magnetically uncoupled to cobalt, i.e., paramagnetic, confirming the inhomogeneity of the films and the presence of a highly disordered neodymium rich phase already detected by extended x-ray-absorption fine structure (EXAFS) spectroscopy. The presence of these inhomogeneities is inherent to the evaporation preparation method when the chosen concentration in the alloy is far from its eutectic concentrations. An interesting consequence of the particular way in which cobalt and neodymium segregates in this system is the enhancement of the cobalt spin moment which reaches 1.95 μB in the sample with the largest segregation.

  12. Thermodynamical instabilities under strong magnetic fields

    Science.gov (United States)

    Chen, Y. J.

    2017-03-01

    The thermodynamical instabilities of low densities in the n p matter and n p e matter are studied within several relativistic nuclear models under some values of magnetic fields. The results are compared between each other and the effects of the symmetry energy slope at saturation density on the instability are investigated. The instability regions can exhibit bands due to the presence of Landau levels for very strong magnetic fields of the order of 1017 G, while for weaker magnetic fields, the bands are replaced by many diffused or scattered pieces. It also shows that the proton fraction in the inner crust of neutron stars may be complex under strong magnetic fields.

  13. Nano-patterning of perpendicular magnetic recording media by low-energy implantation of chemically reactive ions

    International Nuclear Information System (INIS)

    Martin-Gonzalez, M.S.; Briones, F.; Garcia-Martin, J.M.; Montserrat, J.; Vila, L.; Faini, G.; Testa, A.M.; Fiorani, D.; Rohrmann, H.

    2010-01-01

    Magnetic nano-patterning of perpendicular hard disk media with perpendicular anisotropy, but preserving disk surface planarity, is presented here. Reactive ion implantation is used to locally modify the chemical composition (hence the magnetization and magnetic anisotropy) of the Co/Pd multilayer in irradiated areas. The procedure involves low energy, chemically reactive ion irradiation through a resist mask. Among N, P and As ions, P are shown to be most adequate to obtain optimum bit density and topography flatness for industrial Co/Pd multilayer media. The effect of this ion contributes to isolate perpendicular bits by destroying both anisotropy and magnetic exchange in the irradiated areas. Low ion fluences are effective due to the stabilization of atomic displacement levels by the chemical effect of covalent impurities.

  14. Nano-patterning of perpendicular magnetic recording media by low-energy implantation of chemically reactive ions

    Energy Technology Data Exchange (ETDEWEB)

    Martin-Gonzalez, M.S., E-mail: marisol@imm.cnm.csic.e [Instituto de Microelectronica de Madrid, IMM (CNM-CSIC) C/Isaac Newton, 8 (PTM) 28760 Tres Cantos, Madrid (Spain); Briones, F.; Garcia-Martin, J.M. [Instituto de Microelectronica de Madrid, IMM (CNM-CSIC) C/Isaac Newton, 8 (PTM) 28760 Tres Cantos, Madrid (Spain); Montserrat, J. [Instituto de Microelectronica de Barcelona, IMB (CNM-CSIC), Campus Universitat Autonoma Barcelona, E-08193 Bellaterra (Spain); Vila, L.; Faini, G. [Laboratoire de Photonique et de Nanostructures LPN-CNRS, Route de Nozay, 91460 Marcoussis (France); Testa, A.M.; Fiorani, D. [Istituto di Struttura della Materia, Area della Ricerca di Roma-CNR, C.P. 10, 00016 Monterotondo Scalo, Roma (Italy); Rohrmann, H. [Oerlikon Systems, Iramali 18, FL-9496 Balzers (Liechtenstein)

    2010-09-15

    Magnetic nano-patterning of perpendicular hard disk media with perpendicular anisotropy, but preserving disk surface planarity, is presented here. Reactive ion implantation is used to locally modify the chemical composition (hence the magnetization and magnetic anisotropy) of the Co/Pd multilayer in irradiated areas. The procedure involves low energy, chemically reactive ion irradiation through a resist mask. Among N, P and As ions, P are shown to be most adequate to obtain optimum bit density and topography flatness for industrial Co/Pd multilayer media. The effect of this ion contributes to isolate perpendicular bits by destroying both anisotropy and magnetic exchange in the irradiated areas. Low ion fluences are effective due to the stabilization of atomic displacement levels by the chemical effect of covalent impurities.

  15. 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.

  16. 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.

  17. Giant interfacial perpendicular magnetic anisotropy in MgO/CoFe/capping layer structures

    Science.gov (United States)

    Peng, Shouzhong; Zhao, Weisheng; Qiao, Junfeng; Su, Li; Zhou, Jiaqi; Yang, Hongxin; Zhang, Qianfan; Zhang, Youguang; Grezes, Cecile; Amiri, Pedram Khalili; Wang, Kang L.

    2017-02-01

    Magnetic tunnel junction based on the CoFeB/MgO/CoFeB structures is of great interest due to its application in the spin-transfer-torque magnetic random access memory (STT-MRAM). Large interfacial perpendicular magnetic anisotropy (PMA) is required to achieve high thermal stability. Here, we use the first-principles calculations to investigate the magnetic anisotropy energy (MAE) of the MgO/CoFe/capping layer structures, where the capping materials include 5d metals Hf, Ta, Re, Os, Ir, Pt, and Au and 6p metals Tl, Pb, and Bi. We demonstrate that it is feasible to enhance PMA by using proper capping materials. Relatively large PMA is found in the structures with the capping materials of Hf, Ta, Os, Ir, and Pb. More importantly, the MgO/CoFe/Bi structure gives rise to giant PMA (6.09 mJ/m2), which is about three times larger than that of the MgO/CoFe/Ta structure. The origin of the MAE is elucidated by examining the contributions to MAE from each atomic layer and orbital. These findings provide a comprehensive understanding of the PMA and point towards the possibility to achieve the advanced-node STT-MRAM with high thermal stability.

  18. Perpendicular magnetic anisotropy of CoFeB\\Ta bilayers on ALD HfO2

    Directory of Open Access Journals (Sweden)

    Bart F. Vermeulen

    2017-05-01

    Full Text Available Perpendicular magnetic anisotropy (PMA is an essential condition for CoFe thin films used in magnetic random access memories. Until recently, interfacial PMA was mainly known to occur in materials stacks with MgO\\CoFe(B interfaces or using an adjacent crystalline heavy metal film. Here, PMA is reported in a CoFeB\\Ta bilayer deposited on amorphous high-κ dielectric (relative permittivity κ=20 HfO2, grown by atomic layer deposition (ALD. PMA with interfacial anisotropy energy Ki up to 0.49 mJ/m2 appears after annealing the stacks between 200°C and 350°C, as shown with vibrating sample magnetometry. Transmission electron microscopy shows that the decrease of PMA starting from 350°C coincides with the onset of interdiffusion in the materials. High-κ dielectrics are potential enablers for giant voltage control of magnetic anisotropy (VCMA. The absence of VCMA in these experiments is ascribed to a 0.6 nm thick magnetic dead layer between HfO2 and CoFeB. The results show PMA can be easily obtained on ALD high-κ dielectrics.

  19. Magneto-Seebeck effect in magnetic tunnel junctions with perpendicular anisotropy

    Directory of Open Access Journals (Sweden)

    Keyu Ning

    2017-01-01

    Full Text Available As one invigorated filed of spin caloritronics combining with spin, charge and heat current, the magneto-Seebeck effect has been experimentally and theoretically studied in spin tunneling thin films and nanostructures. Here we analyze the tunnel magneto-Seebeck effect in magnetic tunnel junctions with perpendicular anisotropy (p-MTJs under various measurement temperatures. The large tunnel magneto-Seebeck (TMS ratio up to −838.8% for p-MTJs at 200 K is achieved, with Seebeck coefficient S in parallel and antiparallel states of 6.7 mV/K and 62.9 mV/K, respectively. The temperature dependence of the tunnel magneto-Seebeck can be attributed to the contributing transmission function and electron states at the interface between CoFeB electrode and MgO barrier.

  20. Scalable and thermally robust perpendicular magnetic tunnel junctions for STT-MRAM

    Energy Technology Data Exchange (ETDEWEB)

    Gottwald, M. [QUALCOMM Europe Incorporated, Kapeldreef 75, 3001 Heverlee (Belgium); Kan, J. J.; Lee, K.; Zhu, X.; Park, C.; Kang, S. H. [Corporate Research and Development, Qualcomm Technologies Incorporated, San Diego, California 92121-1714 (United States)

    2015-01-19

    Thermal budget, stack thickness, and dipolar offset field control are crucial for seamless integration of perpendicular magnetic junctions (pMTJ) into semiconductor integrated circuits to build scalable spin-transfer-torque magnetoresistive random access memory. This paper is concerned with materials and process tuning to deliver thermally robust (400 °C, 30 min) and thin (i.e., fewer layers and integration-friendly) pMTJ utilizing Co/Pt-based bottom pinned layers. Interlayer roughness control is identified as a key enabler to achieve high thermal budgets. The dipolar offset fields of the developed film stacks at scaled dimensions are evaluated by micromagnetic simulations. This paper shows a path towards achieving sub-15 nm-thick pMTJ with tunneling magnetoresistance ratio higher than 150% after 30 min of thermal excursion at 400 °C.

  1. Theory of ferromagnetic resonance in perpendicularly magnetized nanodisks: Excitation by the Oersted field

    Science.gov (United States)

    Arias, R. E.; Mills, D. L.

    2009-04-01

    We present theoretical studies of ferromagnetic resonance in perpendicularly magnetized nanodisks, wherein spin waves are excited through the ac modulation of the dc transport current injected into the disk. We have nanopillars in mind in our analysis, where spin-polarized current is injected from a metallic ferromagnet elsewhere in the structure. We argue that in a limit described, the modulation of the Oersted field generated by the transport current is the dominant spin-wave excitation mechanism, and our studies explore this limit. We calculate the critical current above which the nominal ferromagnetic state becomes unstable through studies of the linewidth of the lowest spin-wave mode, which vanishes when the critical current is reached. We find that as the applied Zeeman field H0 is decreased from values above 4πMS , the critical current has a minimum when H0˜4πMS to increase for values of the external field below this value.

  2. Spin wave propagation in perpendicularly magnetized nm-thick yttrium iron garnet films

    Science.gov (United States)

    Chen, Jilei; Heimbach, Florian; Liu, Tao; Yu, Haiming; Liu, Chuanpu; Chang, Houchen; Stückler, Tobias; Hu, Junfeng; Zeng, Lang; Zhang, Youguang; Liao, Zhimin; Yu, Dapeng; Zhao, Weisheng; Wu, Mingzhong

    2018-03-01

    Magnonics offers a new way for information transport that uses spin waves (SWs) and is free of charge currents. Unlike Damon-Eshbach SWs, the magneto-static forward volume SWs offer the reciprocity configuration suitable for SW logic devices with low power consumption. Here, we study forward volume SW propagation in yttrium iron garnet (YIG) thin films with an ultra-low damping constant α = 8 ×10-5 . We design different integrated microwave antenna with different k-vector excitation distributions on YIG thin films. Using a vector network analyzer, we measured SW transmission with the films magnetized in perpendicular orientation. Based on the experimental results, we extract the group velocity as well as the dispersion relation of SWs and directly compare the power efficiency of SW propagation in YIG using coplanar waveguide and micro stripline for SW excitation and detection.

  3. Spin wave propagation in perpendicular magnetized 20 nm Yttrium Iron Garnet with different antenna design

    Science.gov (United States)

    Chen, Jilei; Stueckler, Tobias; Zhang, Youguang; Zhao, Weisheng; Yu, Haiming; Chang, Houchen; Liu, Tao; Wu, Mingzhong; Liu, Chuanpu; Liao, Zhimin; Yu, Dapeng; Fert Beijing research institute Team; Colorado State University Team; Peking University Collaboration

    Magnonics offers a new way to transport information using spin waves free of charge current and could lead to a new paradigm in the area of computing. Forward volume (FV) mode spin wave with perpendicular magnetized configuration is suitable for spin wave logic device because it is free of non-reciprocity effect. Here, we study FV mode spin wave propagation in YIG thin film with an ultra-low damping. We integrated differently designed antenna i.e., coplanar waveguide and micro stripline with different dimensions. The k vectors of the spin waves defined by the design of the antenna are calculated using Fourier transform. We show FV mode spin wave propagation results by measuring S12 parameter from vector network analyzer and we extract the group velocity of the FV mode spin wave as well as its dispersion relations.

  4. Current-induced magnetization switching in atom-thick tungsten engineered perpendicular magnetic tunnel junctions with large tunnel magnetoresistance.

    Science.gov (United States)

    Wang, Mengxing; Cai, Wenlong; Cao, Kaihua; Zhou, Jiaqi; Wrona, Jerzy; Peng, Shouzhong; Yang, Huaiwen; Wei, Jiaqi; Kang, Wang; Zhang, Youguang; Langer, Jürgen; Ocker, Berthold; Fert, Albert; Zhao, Weisheng

    2018-02-14

    Perpendicular magnetic tunnel junctions based on MgO/CoFeB structures are of particular interest for magnetic random-access memories because of their excellent thermal stability, scaling potential, and power dissipation. However, the major challenge of current-induced switching in the nanopillars with both a large tunnel magnetoresistance ratio and a low junction resistance is still to be met. Here, we report spin transfer torque switching in nano-scale perpendicular magnetic tunnel junctions with a magnetoresistance ratio up to 249% and a resistance area product as low as 7.0 Ω µm 2 , which consists of atom-thick W layers and double MgO/CoFeB interfaces. The efficient resonant tunnelling transmission induced by the atom-thick W layers could contribute to the larger magnetoresistance ratio than conventional structures with Ta layers, in addition to the robustness of W layers against high-temperature diffusion during annealing. The critical switching current density could be lower than 3.0 MA cm -2 for devices with a 45-nm radius.

  5. Laser-driven, magnetized quasi-perpendicular collisionless shocks on the Large Plasma Device

    Energy Technology Data Exchange (ETDEWEB)

    Schaeffer, D. B., E-mail: dschaeffer@physics.ucla.edu; Everson, E. T.; Bondarenko, A. S.; Clark, S. E.; Constantin, C. G.; Vincena, S.; Van Compernolle, B.; Tripathi, S. K. P.; Gekelman, W.; Niemann, C. [Department of Physics and Astronomy, University of California - Los Angeles, Los Angeles, California 90095 (United States); Winske, D. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

    2014-05-15

    The interaction of a laser-driven super-Alfvénic magnetic piston with a large, preformed magnetized ambient plasma has been studied by utilizing a unique experimental platform that couples the Raptor kJ-class laser system [Niemann et al., J. Instrum. 7, P03010 (2012)] to the Large Plasma Device [Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)] at the University of California, Los Angeles. This platform provides experimental conditions of relevance to space and astrophysical magnetic collisionless shocks and, in particular, allows a detailed study of the microphysics of shock formation, including piston-ambient ion collisionless coupling. An overview of the platform and its capabilities is given, and recent experimental results on the coupling of energy between piston and ambient ions and the formation of collisionless shocks are presented and compared to theoretical and computational work. In particular, a magnetosonic pulse consistent with a low-Mach number collisionless shock is observed in a quasi-perpendicular geometry in both experiments and simulations.

  6. Collective coordinate models of domain wall motion in perpendicularly magnetized systems under the spin hall effect and longitudinal fields

    Energy Technology Data Exchange (ETDEWEB)

    Nasseri, S. Ali, E-mail: ali.nasseri@isi.it [ISI Foundation - Via Alassio 11/c –10126 Torino (Italy); Politecnico di Torino - Corso Duca degli Abruzzi 24, 10129 Torino (Italy); Moretti, Simone; Martinez, Eduardo [University of Salamanca - Cardenal Plá y Deniel, 22, 37008 Salamanca (Spain); Serpico, Claudio [ISI Foundation - Via Alassio 11/c –10126 Torino (Italy); University of Naples Federico II - Via Claudio 21, 80125 Napoli (Italy); Durin, Gianfranco [ISI Foundation - Via Alassio 11/c –10126 Torino (Italy); Istituto Nazionale di Ricerca Metrologica (INRIM) - Strada delle Cacce 91, 10135 Torino (Italy)

    2017-03-15

    Recent studies on heterostructures of ultrathin ferromagnets sandwiched between a heavy metal layer and an oxide have highlighted the importance of spin-orbit coupling (SOC) and broken inversion symmetry in domain wall (DW) motion. Specifically, chiral DWs are stabilized in these systems due to the Dzyaloshinskii-Moriya interaction (DMI). SOC can also lead to enhanced current induced DW motion, with the Spin Hall effect (SHE) suggested as the dominant mechanism for this observation. The efficiency of SHE driven DW motion depends on the internal magnetic structure of the DW, which could be controlled using externally applied longitudinal in-plane fields. In this work, micromagnetic simulations and collective coordinate models are used to study current-driven DW motion under longitudinal in-plane fields in perpendicularly magnetized samples with strong DMI. Several extended collective coordinate models are developed to reproduce the micromagnetic results. While these extended models show improvements over traditional models of this kind, there are still discrepancies between them and micromagnetic simulations which require further work. - Highlights: • Moving DWs in PMA material maintain their structure under longitudinal in-plane fields. • As a result of longitudinal fields, magnetization in the domains becomes canted. • A critical longitudinal field was identified and correlated with the DMI strength. • A canted collective coordinate model was developed for DW motion under in-plane fields.

  7. Magnetization reversal induced by in-plane current in Ta/CoFeB/MgO structures with perpendicular magnetic easy axis

    Science.gov (United States)

    Zhang, C.; Yamanouchi, M.; Sato, H.; Fukami, S.; Ikeda, S.; Matsukura, F.; Ohno, H.

    2014-05-01

    We investigate in-plane current-induced magnetization reversal under an in-plane magnetic field in Hall bar shaped devices composed of Ta/CoFeB/MgO structures with perpendicular magnetic easy axis. The observed relationship between the directions of current and magnetization switching and Ta thickness dependence of magnetization switching current are accordance with those for magnetization reversal by spin transfer torque originated from the spin Hall effect in the Ta layer.

  8. Highly controlled orientation of CaBi4Ti4O15 using a strong magnetic field

    Science.gov (United States)

    Suzuki, Tohru S.; Kimura, Masahiko; Shiratsuyu, Kosuke; Ando, Akira; Sakka, Yoshio; Sakabe, Yukio

    2006-09-01

    The texture of feeble magnetic ceramics can be controlled by a strong magnetic field. When the magnetic susceptibility of the c axis is smaller than that of the other axes, the c axis aligns perpendicular to the magnetic field; however, the direction is randomly oriented on the plane perpendicular to the magnetic field. The authors demonstrate in this letter that a highly controlled texture in bismuth titanate, which has a c-axis susceptibility smaller than the other axes, can be achieved using a two-step magnetic field procedure. This highly controlled orientation is effective for improving the electromechanical coupling coefficient.

  9. Hydrogen atoms in a strong magnetic field

    International Nuclear Information System (INIS)

    Santos, R.R. dos.

    1975-07-01

    The energies and wave functions of the 14 lowest states of a Hydrogen atom in a strong magnetic field are calculated, using a variational scheme. The equivalence between the atomic problem and the problems related with excitons and impurities in semiconductors in the presence of a strong magnetic field are shown. The calculations of the energies and wave functions have been divided in two regions: the first, for the magnetic field ranging between zero and 10 9 G; in the second the magnetic field ranges between 10 9 and 10 11 G. The results have been compared with those obtained by previous authors. The computation time necessary for the calculations is small. Therefore this is a convenient scheme to obtain the energies and wave functions for the problem. Transition probabilities, wavelengths and oscillator strengths for some allowed transitions are also calculated. (Author) [pt

  10. 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...

  11. Interfacial contributions to perpendicular magnetic anisotropy in Pd/Co2MnSi/MgO trilayer films

    Science.gov (United States)

    Fu, Huarui; You, Caiyin; Li, Yunlong; Wang, Ke; Tian, Na

    2016-05-01

    Heusler alloy Co2MnSi is widely selected as the ferromagnetic layer to achieve a giant tunneling magnetic resistance (TMR). It is also one of the most promising materials for potential spintronic applications of magnetic random access memory (MRAM) due to the high spin polarization, in which the configuration of perpendicular magnetic anisotropy (PMA) possesses great advantages over the in-plane ones. Therefore, it is highly desirable to investigate the PMA effects of the Co2MnSi layer with a suitable stack structure. In this work, a strong PMA (1.61  ×  106 erg cm-3) is demonstrated in the system of Pd/Co2MnSi/MgO trilayer films. The contributions of the interfaces beside the ferromagnetic Co2MnSi layer were quantitatively clarified. The interfacial anisotropy K s,MgO of 0.79 erg cm-2 at the Co2MnSi/MgO interface is larger than the K s,Pd value of 0.26 erg cm-2 at the Pd/Co2MnSi interface. Due to the dual interfacial effects, the strong PMA can be sustained at the high annealing temperature with a thick Co2MnSi layer of about 4.9 nm, which is favorable to the potential spintronic application. The Mn-O bonding was also found to be enriched at the Co2MnSi/MgO interface for the annealed Pd/Co2MnSi (3.4 nm)/MgO film with the large PMA, showing an experimental evidence for the theoretical results of the Mn-O bonding contribution to PMA.

  12. Thick CoFeB with perpendicular magnetic anisotropy in CoFeB-MgO based magnetic tunnel junction

    Directory of Open Access Journals (Sweden)

    V. B. Naik

    2012-12-01

    Full Text Available We have investigated the effect of an ultra-thin Ta insertion in the CoFeB (CoFeB/Ta/CoFeB free layer (FL on magnetic and tunneling magnetoresistance (TMR properties of a CoFeB-MgO system with perpendicular magnetic anisotropy (PMA. It is found that the critical thickness (tc to sustain PMA is doubled (tc = 2.6 nm in Ta-inserted CoFeB FL as compared to single CoFeB layer (tc = 1.3 nm. While the effective magnetic anisotropy is found to increase with Ta insertion, the saturation magnetization showed a slight reduction. As the CoFeB thickness increasing, the thermal stability of Ta inserted structure is significantly increased by a factor of 2.5 for total CoFeB thickness less than 2 nm. We have observed a reasonable value of TMR for a much thicker CoFeB FL (thickness = 2-2.6 nm with Ta insertion, and without significant increment in resistance-area product. Our results reveal that an ultra-thin Ta insertion in CoFeB might pay the way towards developing the high-density memory devices with enhanced thermal stability.

  13. Theory of Ferromagnetic Resonance in Perpendicularly Magnetized Nanodiscs; Excitation by Injected AC Current

    Science.gov (United States)

    Arias, Rodrigo; Mills, Douglas

    2008-03-01

    Recent experiments explore the ferromagnetic resonance (FR) response of nanodiscs incorporated into nanopillars, where a DC spin torque current has a small AC component superimposed. For such a circular perpendicularly magnetized disc, we develop the theory of the FR response via AC current. Earlier we discussed the vortex state induced by the DC Oersted field in such a sample, and the nature of the spin waves in the presence of the vortex^2. The present study explores the linear response of the disc, when a small AC current is superimposed on the DC current. A Green's function approach allows us to describe the linear response of the system. We argue that the AC component of the Oersted field is responsible for spin wave excitation; the modes excited thus differ from those observed in ferromagnetic resonance studies via microwaves. We shall present calculations which explore the spectrum and eigenvectors of modes excited by modulation of the DC current, their width as a function of DC current, and their intensity. ^2R. E. Arias and D. L. Mills, Phys. Rev. B75, 214404 (2007).

  14. In Situ TEM Scratch Testing of Perpendicular Magnetic Recording Multilayers with a Novel MEMS Tribometer

    Science.gov (United States)

    Hintsala, Eric D.; Stauffer, Douglas D.; Oh, Yunje; Asif, S. A. Syed

    2017-01-01

    Utilizing a newly developed two-dimensional (2D) transducer designed for in situ transmission electron microscope (TEM) nanotribology, deformation mechanisms of a perpendicular magnetic recording film stack under scratch loading conditions were evaluated. These types of films are widely utilized in storage devices, and loss of data by grain reorientation in the recording layers is of interest. The observed deformation was characterized by a stick-slip mechanism, which was induced by a critical ratio of lateral to normal force regardless of normal force. At low applied normal forces, the diamond-like carbon (DLC) coating and asperities in the recording layer were removed during scratching, while, at higher applied forces, grain reorientation and debonding of the recording layer was observed. As the normal force and displacement were increased, work for stick-slip deformation and contact stress were found to increase based upon an Archard's Law analysis. These experiments also served as an initial case study demonstrating the capabilities of this new transducer.

  15. Nonlinear Electron Waves in Strongly Magnetized Plasmas

    DEFF Research Database (Denmark)

    Pécseli, Hans; Juul Rasmussen, Jens

    1980-01-01

    Weakly nonlinear dispersive electron waves in strongly magnetized plasma are considered. A modified nonlinear Schrodinger equation is derived taking into account the effect of particles resonating with the group velocity of the waves (nonlinear Landau damping). The possibility of including the ion...

  16. Weak and strong nonlinearities in magnetic bearings

    Czech Academy of Sciences Publication Activity Database

    Půst, Ladislav

    2004-01-01

    Roč. 39, č. 7 (2004), s. 779-795 ISSN 0094-114X R&D Projects: GA ČR GA101/00/1471; GA AV ČR IBS2076301 Institutional research plan: CEZ:AV0Z2076919 Keywords : weak nonlinearitiy * strong nonlinearity * magnetics bearings Subject RIV: BI - Acoustics Impact factor: 0.605, year: 2004

  17. Mechanics of magnetic fluid column in strong magnetic fields

    International Nuclear Information System (INIS)

    Polunin, V.M.; Ryapolov, P.A.; Platonov, V.B.

    2017-01-01

    Elastic-and magnetic properties of magnetic fluid confined by ponderomotive force in a tube fixed in horizontal position are considered. The system is placed in a strong magnetic field under the influence of external static and dynamic perturbations. An experimental setup has been developed. A theoretical basis of the processes of magnetic colloid elastic deformation has been proposed. The values of the static ponderomotive elasticity coefficient and the elasticity coefficient under dynamic action are experimentally determined. The calculations of the saturation magnetization for two magnetic fluid samples, carried out according to the equation containing the dynamic elasticity coefficient, are in good agreement with the experimental magnetization curve. The described method is of interest when studying magnetophoresis and aggregation of nanoparticles in magnetic colloids.

  18. Neutrino oscillations in strong magnetic fields

    International Nuclear Information System (INIS)

    Likhachev, G.G.; Studenikin, A.I.

    1994-07-01

    Neutrino conversion processes between two neutrino species and the corresponding oscillations induced by strong magnetic fields are considered. The value of the critical strength of magnetic field B cr as a function of characteristics of neutrinos in vacuum (Δm 2 ν , mixing angle θ), effective particle density of matter n eff , neutrino (transition) magnetic moment μ-tilde and energy E is introduced. It is shown that the neutrino conversion and oscillations effects induced by magnetic fields B ≥ B cr are important and may result in the depletion of the initial type of ν's in the bunch. A possible increase of these effects in the case when neutrinos pass through a sudden decrease of density of matter (''cross-boundary effect'') and applications to neutrinos from neutron stars and supernova are discussed. (author). 25 refs

  19. Annealing effect on magnetic property and recording performance of [FePt/MgO]n perpendicular magnetic recording media

    International Nuclear Information System (INIS)

    Suzuki, Takao; Zhang, Zhengang; Singh, Amarendra K.; Yin, Jinhua; Perumal, A.; Osawa, Hiroshi

    2005-01-01

    Granular-type FePt perpendicular magnetic recording media with (001)-texture, obtained by annealing FePt/MgO multilayer films, are fabricated onto 2.5-in glass discs. For the sake of spin-stand testing, the coercivity of FePt films is carefully modulated by controlling the annealing conditions. With annealing, exchange coupling between FePt grains is decreased, indicated by the reductions in α value and activation volume. FePt ordering process is dependent on initial FePt/MgO multilayer structures, which governs the optimum annealing condition regarding coercivities and α(=4π(dM/dH)H=Hc). The SNR ratio exhibits a sensitive dependence on initial FePt/MgO multilayer structures as well as annealing conditions

  20. Influence of hydrogen patterning gas on electric and magnetic properties of perpendicular magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Jeong, J. H., E-mail: juno@fris.tohoku.ac.jp [Graduate School of Engineering, Tohoku University, Sendai (Japan); Semiconductor R and D Center, Samsung Electronics Co., Ltd., Hwasung (Korea, Republic of); Endoh, T. [Graduate School of Engineering, Tohoku University, Sendai (Japan); Center for Innovative Integrated Electronic Systems, Tohoku University, Sendai (Japan); Kim, Y.; Kim, W. K.; Park, S. O. [Semiconductor R and D Center, Samsung Electronics Co., Ltd., Hwasung (Korea, Republic of)

    2014-05-07

    To identify the degradation mechanism in magnetic tunnel junctions (MTJs) using hydrogen, the properties of the MTJs were measured by applying an additional hydrogen etch process and a hydrogen plasma process to the patterned MTJs. In these studies, an additional 50 s hydrogen etch process caused the magnetoresistance (MR) to decrease from 103% to 14.7% and the resistance (R) to increase from 6.5 kΩ to 39 kΩ. Moreover, an additional 500 s hydrogen plasma process decreased the MR from 103% to 74% and increased R from 6.5 kΩ to 13.9 kΩ. These results show that MTJs can be damaged by the hydrogen plasma process as well as by the hydrogen etch process, as the atomic bonds in MgO may break and react with the exposed hydrogen gas. Compounds such as MgO hydrate very easily. We also calculated the damaged layer width (DLW) of the patterned MTJs after the hydrogen etching and plasma processes, to evaluate the downscaling limitations of spin-transfer-torque magnetic random-access memory (STT-MRAM) devices. With these calculations, the maximum DLWs at each side of the MTJ, generated by the etching and plasma processes, were 23.8 nm and 12.8 nm, respectively. This result validates that the hydrogen-based MTJ patterning processes cannot be used exclusively in STT-MRAMs beyond 20 nm.

  1. L10-Ordered Thin Films with High Perpendicular Magnetic Anisotropy for STT-MRAM Applications

    Science.gov (United States)

    Huang, Efrem Yuan-Fu

    The objective of the research conducted herein was to develop L10-ordered materials and thin film stack structures with high perpendicular magnetic anisotropy (PMA) for spin-transfertorque magnetoresistive random access memory (STT-MRAM) applications. A systematic approach was taken in this dissertation, culminating in exchange coupled L1 0-FePt and L10- MnAl heterogeneous structures showing great promise for developing perpendicular magnetic tunnel junctions (pMTJs) with both high thermal stability and low critical switching current. First, using MgO underlayers on Si substrates, sputtered MnAl films were systematically optimized, ultimately producing a Si substrate/MgO (20 nm)/MnAl (30)/Ta (5) film stack with a high degree of ordering and large PMA. Next, noting the incompatibility of insulating MgO underlayers with industrial-scale CMOS processes, attention was turned to using conductive underlayers. TiN was found to excel at promoting growth of L10-MnAl, with optimized films showing improved magnetic properties over those fabricated on MgO underlayers. The use of different post-annealing processes was then studied as an alternative to in situ annealing. Rapid thermal annealing (RTA) was found to produce PMA in films at lower annealing temperatures than tube furnace annealing, but tube furnace annealing produced films with higher maximum PMA than RTA. While annealed samples had lower surface roughness than those ordered by high in situ deposition temperatures, relying solely on annealing to achieve L10-ordering resulted drastically reduced PMA. Finally, heterogeneous L10-ordered FePt/MgO/MnAl film stacks were explored for pMTJs. Film stacks with MgO barrier layers thinner than 2 nm showed significant interdiffusion between the FePt and MnAl, while film stacks with thicker MgO barrier layers exhibited good ordering and high PMA in both the FePt and MnAl films. It is believed that this limitation is caused by the roughness of the underlying FePt, which was thicker

  2. Interfacial perpendicular magnetic anisotropy and electric field effect in Ta/CoFeB/Mg1-xTixO heterostructures

    Science.gov (United States)

    Ikhtiar, Mukaiyama, K.; Kasai, S.; Hono, K.

    2017-11-01

    The barrier thickness dependence of perpendicular magnetic anisotropy (PMA) of CoFeB thin films is distinctly different for MgO and Mg0.95Ti0.05O barriers. The electric field effects measured using orthogonal magnetic tunnel junctions show that the coefficient of electric field control of PMA for Ta/CoFeB/Mg0.95Ti0.05O magnetic tunnel junction (MTJ) is around 51 fJ/V m, which is the same order of magnitude as that of Ta/CoFeB/MgO. This indicates that Mg0.95Ti0.05O is a promising barrier material for p-MTJs for voltage controlled magnetic random access memory (MRAM). The perpendicular magnetic anisotropy energy and the electric field effect for the Ta/CoFeB/Mg1-xTixO (x = 0 and 0.05) heterostructures have a strong correlation, suggesting the scalability of voltage controlled MRAM.

  3. Magnetic properties of strongly asymmetric nuclear matter

    International Nuclear Information System (INIS)

    Kutschera, M.; Wojcik, W.

    1988-01-01

    We investigate stability of neutron matter containing a small proton admixture with respect to spin fluctuations. We establish conditions under which strongly asymmetric nuclear matter could acquire a permanent magnetization. It is shown that if the protons are localized, the system becomes unstable to spin fluctuations for arbitrarily weak proton-neutron spin interactions. For non-localized protons there exists a threshold value of the spin interaction above which the system can develop a spontaneous polarization. 12 refs., 2 figs. (author)

  4. Ambipolar diffusion regulated collapse of filaments threaded by perpendicular magnetic fields

    Science.gov (United States)

    Burge, C. A.; Van Loo, S.; Falle, S. A. E. G.; Hartquist, T. W.

    2016-11-01

    Context. In giant molecular clouds (GMCs), the fractional ionisation is low enough that the neutral and charged particles are weakly coupled. A consequence of this is that the magnetic flux redistributes within the cloud, allowing an initially magnetically supported region to collapse. Aims: We aim to elucidate the effects of ambipolar diffusion on the evolution of infinitely long filaments and the effect of decaying turbulence on that evolution. Methods: First, in ideal magnetohydrodynamics (MHD), a two-dimensional cylinder of an isothermal magnetised plasma with initially uniform density was allowed to evolve to an equilibrium state. Then, the response of the filament to ambipolar diffusion was followed using an adaptive mesh refinement multifluid MHD code. Various ambipolar resistivities were chosen to reflect different ratios of Jeans length to ambipolar diffusion length scale. To study the effect of turbulence on the ambipolar diffusion rate, we perturbed the equilibrium filament with a turbulent velocity field quantified by a rms sonic Mach number, Mrms, of 10, 3 or 1. Results: We numerically reproduce the density profiles for filaments that are in magnetohydrostatic and pressure equilibrium with their surroundings obtained in a published model and show that these equilibria are dynamically stable. If the effect of ambipolar diffusion is considered, these filaments lose magnetic support initiating cloud collapse. The filaments do not lose magnetic flux. Rather the magnetic flux is redistributed within the filament from the dense centre towards the diffuse envelope. The rate of the collapse is inversely proportional to the fractional ionisation and two gravitationally-driven ambipolar diffusion regimes for the collapse are observed as predicted in a published model. For high values of the ionisation coefficient, that is X ≥ 10-7, the gas is strongly coupled to the magnetic field and the Jeans length is larger than the ambipolar diffusion length scale. Then

  5. Super-strong Magnetic Field in Sunspots

    Science.gov (United States)

    Okamoto, Takenori J.; Sakurai, Takashi

    2018-01-01

    Sunspots are the most notable structure on the solar surface with strong magnetic fields. The field is generally strongest in a dark area (umbra), but sometimes stronger fields are found in non-dark regions, such as a penumbra and a light bridge. The formation mechanism of such strong fields outside umbrae is still puzzling. Here we report clear evidence of the magnetic field of 6250 G, which is the strongest field among Stokes I profiles with clear Zeeman splitting ever observed on the Sun. The field was almost parallel to the solar surface and located in a bright region sandwiched by two opposite-polarity umbrae. Using a time series of spectral data sets, we discuss the formation process of the super-strong field and suggest that this strong field region was generated as a result of compression of one umbra pushed by the horizontal flow from the other umbra, such as the subduction of the Earth’s crust in plate tectonics.

  6. Origin of the collapse of tunnel magnetoresistance at high annealing temperature in CoFeB/MgO perpendicular magnetic tunnel junctions

    Science.gov (United States)

    Gan, H. D.; Sato, H.; Yamanouchi, M.; Ikeda, S.; Miura, K.; Koizumi, R.; Matsukura, F.; Ohno, H.

    2011-12-01

    We have investigated a tunnel magnetoresistance (TMR) ratio of CoFeB/MgO perpendicular magnetic tunnel junctions (p-MTJs) with a 40 nm diameter as a function of an annealing temperature Ta. The TMR ratio at room temperature (RT) increases with increasing Ta and reaches 149% at Ta = 350 °C, and further increase of Ta results in a strong reduction of the TMR ratio, i.e., 2% at Ta = 400 °C. The temperature dependence of the junction resistance versus magnetic field loops reveals that the reduced TMR ratio at RT is due to the disappearance of a stable antiparallel magnetization configuration. We find that reduction of dipole coupling restores the TMR ratio.

  7. Fabrication of perpendicular magnetic recording tape media with a data capacity of over-50TB using Si/NiFe/FeCoB soft magnetic underlayers

    Science.gov (United States)

    Gomi, S.; Mashiko, Y.; Hirata, K.; Matsunuma, S.; Inoue, T.; Doi, T.; Watanabe, T.; Nakagawa, S.

    C-axis orientations of Ru intermediate layer (IML) and CoPtCr-SiO2 recording layer (RL) are attained by using crystalline FeCoB soft magnetic underlayer (SUL). Better (110) orientation of FeCo improves not only (001) orientation of Ru IML but also that of CoPtCr RL. This leads better perpendicular magnetic anisotropy in the RL suitable for perpendicular magnetic recording media. In order to control the (110) orientation in FeCoB layer, various seed layers are prepared beneath the FeCoB layers. Ru and Si/NiFe seed layers gives FeCoB layer a large in-plane magnetic anisotropy that is effective to suppress spike noise from SUL. The laminated FeCoB SUL causes more improvement of Ru (001) texure and leads to better perpendicular magnetic anisotropy of RL. Ru/CoPtCr-SiO2 bilayer deposited on laminated FeCoB SUL on Aramid tape substrate has good perpendicular magnetic properties and reduces the noise from SUL. PACS: Type pacs here, separated by semicolons;

  8. Interfacial magnetic domain wall formation in perpendicular-anisotropy, exchange-spring films

    OpenAIRE

    watson , S.M.; Hauet , Thomas; Borchers , J. A.; Mangin , S; Fullerton , Eric E.

    2008-01-01

    International audience; Using magnetometry and polarized neutron reflectometry ͑PNR͒, we have mapped the reversal processes of the antiferromagnetically coupled, hard/soft system, TbFeCo/ ͓Co/ Pd͑t Pd ͔͒ 15 , with perpendicular anisotropy. The magnitude of the exchange coupling within the ͓Co/ Pd͔ layer can be tuned by varying Pd thickness. Since PNR is insensitive to moments perpendicular to the plane, a scattering geometry with polarization parallel to the scattering vector was used to isol...

  9. Co-containing spinel ferrite thin-film perpendicular magnetic recording media with Mn-Zn ferrite backlayer

    OpenAIRE

    Yamamoto, Setsuo; Kuniki, Hirofumi; Kurisu, Hiroki; Matsuura, Mitsuru

    2003-01-01

    Co-containing ferrite thin-film/Mn-Zn ferrite thin-film double-layered perpendicular media were prepared using reactive ECR sputtering and magnetron sputtering methods, and their magnetic and structural properties and recording characteristics were studied. The Mn-Zn ferrite thin-film backlayer had saturation magnetization of 3.5 kG and coercivity of 60 Oe. Reproduced voltage for the Co-containing ferrite thin-film/Mn-Zn ferrite thin-film double-layered medium was about twice of that for the ...

  10. 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.

  11. Perpendicular magnetic anisotropy in Ta|Co40Fe40B20|MgAl2O4 structures and perpendicular CoFeB|MgAl2O4|CoFeB magnetic tunnel junction

    KAUST Repository

    Tao, B. S.

    2014-09-08

    Magnetic properties of Co40Fe40B20(CoFeB) thin films sandwiched between Ta and MgAl2O4layers have been systematically studied. For as-grown state, Ta/CoFeB/MgAl2O4structures exhibit good perpendicular magnetic anisotropy (PMA) with interface anisotropy Ki=1.22erg/cm2, which further increases to 1.30erg/cm2after annealing, while MgAl2O4/CoFeB/Ta multilayer shows in-plane magnetic anisotropy and must be annealed in order to achieve PMA. For bottom CoFeB layer, the thickness window for PMA is from 0.6 to 1.0nm, while that for top CoFeB layer is between 0.8 and 1.4nm. Perpendicular magnetic tunnel junctions (p-MTJs) with a core structure of CoFeB/MgAl2O4/CoFeB have also been fabricated and tunneling magnetoresistance ratio of about 36% at room temperature and 63% at low temperature have been obtained. The intrinsic excitations in the p-MTJs have been identified by inelastic electron-tunneling spectroscopy.

  12. Anisotropic shear viscosity of a strongly coupled non-Abelian plasma from magnetic branes

    Science.gov (United States)

    Critelli, R.; Finazzo, S. I.; Zaniboni, M.; Noronha, J.

    2014-09-01

    Recent estimates for the electromagnetic fields produced in the early stages of noncentral ultrarelativistic heavy ion collisions indicate the presence of magnetic fields B ˜O(0.1-15mπ2), where mπ is the pion mass. It is then of special interest to study the effects of strong (Abelian) magnetic fields on the transport coefficients of strongly coupled non-Abelian plasmas, such as the quark-gluon plasma formed in heavy ion collisions. In this paper we study the anisotropy in the shear viscosity induced by an external magnetic field in a strongly coupled N =4 super Yang-Mills (SYM) plasma. Due to the spatial anisotropy created by the magnetic field, the most general viscosity tensor of a magnetized plasma has five shear viscosity coefficients and two bulk viscosities. We use the holographic correspondence to evaluate two of the shear viscosities, η⊥≡ηxyxy (perpendicular to the magnetic field) and η∥≡ηxzxz=ηyzyz (parallel to the field). When B ≠0 the shear viscosity perpendicular to the field saturates the viscosity bound η⊥/s=1/(4π), while in the direction parallel to the field the bound is violated since η∥/s<1/(4π). However, the violation of the bound in the case of strongly coupled SYM is minimal even for the largest value of B that can be reached in heavy ion collisions.

  13. Double-layered perpendicular magnetic recording media of granular-type FePt-MgO films

    International Nuclear Information System (INIS)

    Zhang Zhengang; Singh, Amarendra K.; Yin Jinhua; Perumal, A.; Suzuki, Takao

    2005-01-01

    The recording performance of double-layered granular-type FePt-MgO perpendicular magnetic recording media fabricated onto glass discs by sputtering is investigated. The (0 0 1)-textured FePt granular films are obtained by annealing FePt/MgO multilayers. Three different multilayer structures are compared in their magnetic properties and recording SNR performances. To evaluate thermal stability property of these granular-type FePt disks, the time-dependent magnetic force microscope (MFM) signal from the written bits on one of these disks is recorded in the temperature range 25-200 degree sign C. The signal decay at high observation temperature is interpreted based on the temperature dependence of magnetic anisotropy (K u )

  14. C-axis oriented Ba-ferrite thin film with small grain for perpendicular magnetic recording

    International Nuclear Information System (INIS)

    Morisako, A.; Shams, N.N.; Miura, Y.; Matsumoto, M.; Gee, S.H.; Park, M.H.; Hong, Y.K.

    2004-01-01

    Hexagonal Ba-ferrite(BaM) thin films with amorphous AlO(a-AlO) under-layer were prepared by a facing targets sputtering system. The grain size of c-axis perpendicularly oriented BaM/a-AlO films is about 20 nm at the thickness of 20 nm for BaM layer. The perpendicular coercivity is about 3.5-4.3 kOe with BaM layer thickness in the range from 80 to 30 nm and 2.3 kOe for BaM layer thickness of 20 nm.The in-plane coercivity for BaM/a-AlO films was less than 0.1 kOe at the thickness ranging from 20 to 80 nm

  15. A structural study of effects of NiP seed layer on the magnetic properties of CoCrPt/Ti/NiP perpendicular magnetic films

    CERN Document Server

    Sun, C J; Wang, J P; Soo, E W; Noh, D Y; Je, J H; Hwu, Y K

    2003-01-01

    The CoCrPt/Ti/NiP films for perpendicular magnetic recording were studied using X-ray scattering and anomalous X-ray scattering. When the NiP seed layer was used, the long range order of the texture peak of the magnetic film decreased and less Co was associated with this Bragg order. The structural results were consistent with the observed increased coercivity and decreased magnetization due to the increased magnetic grain isolation caused by the presence of NiP seed layer.

  16. Magnetic-field-angle dependence of coercivity in CoFeB/MgO magnetic tunnel junctions with perpendicular easy axis

    Science.gov (United States)

    Igarashi, J.; Llandro, J.; Sato, H.; Matsukura, F.; Ohno, H.

    2017-09-01

    We investigate the magnetization-reversal mode in CoFeB/MgO magnetic tunnel junctions with perpendicular easy axis from the magnetic-field-angle dependence of coercivity. The reversal in a free layer with diameter of ˜20 nm is found to be in a good agreement with coherent reversal mode for a device with a reference layer much larger than the free layer. However, the reversal mode is quite different in a junction in which the two layers are almost the same size. From micromagnetic simulation, the difference is attributed to the reduction of the magnetic anisotropy in the vicinity of the device edge.

  17. Single-pole recording head design for 100 Gbpsi perpendicular magnetic recording

    International Nuclear Information System (INIS)

    Yamakawa, Kiyoshi; Taguchi, Kaori; Ise, Kazuyuki; Honda, Naoki; Ouchi, Kazuhiro

    2001-01-01

    In developing a perpendicular recording head, writability, head induced erasure and head skew problem are major concerns for achieving 100 Gbpsi recording. Sufficient overwrite performance of the single-pole head with a trackwidth down to 0.26 μm and clear MFM images of 0.16 μm recorded signals were obtained. Furthermore, high stray field robustness was realized with a newly designed head accompanied by a high head efficiency

  18. Energy spectrum of carriers in Kaner-type semiconductors in magnetic field of constant direction with trigonometric depending variation perpendicular to the field

    International Nuclear Information System (INIS)

    Babanly, A.M.; Babanly, A.M.; Huner, V.

    2010-01-01

    It was presented compact analytical solutions for the energy spectrum and wave functions of carriers in two-dimensional Kaner-type semiconductors in a magnetic field of constant direction with trigonometric depending variation perpendicular to the field direction

  19. Perpendicular Magnetic Anisotropy and Spin Glass-like Behavior in Molecular Beam Epitaxy Grown Chromium Telluride Thin Films.

    Science.gov (United States)

    Roy, Anupam; Guchhait, Samaresh; Dey, Rik; Pramanik, Tanmoy; Hsieh, Cheng-Chih; Rai, Amritesh; Banerjee, Sanjay K

    2015-04-28

    Reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy (STM), vibrating sample magnetometry, and other physical property measurements are used to investigate the structure, morphology, magnetic, and magnetotransport properties of (001)-oriented Cr2Te3 thin films grown on Al2O3(0001) and Si(111)-(7×7) surfaces by molecular beam epitaxy. Streaky RHEED patterns indicate flat smooth film growth on both substrates. STM studies show the hexagonal arrangements of surface atoms. Determination of the lattice parameter from the atomically resolved STM image is consistent with the bulk crystal structures. Magnetic measurements show the film is ferromagnetic, having a Curie temperature of about 180 K, and a spin glass-like behavior was observed below 35 K. Magnetotransport measurements show the metallic nature of the film with a perpendicular magnetic anisotropy along the c-axis.

  20. Temperature dependence of energy barrier in CoFeB-MgO magnetic tunnel junctions with perpendicular easy axis

    Science.gov (United States)

    Takeuchi, Y.; Sato, H.; Fukami, S.; Matsukura, F.; Ohno, H.

    2015-10-01

    We investigate an energy barrier E that determines the thermal stability factor of nanoscale CoFeB-MgO magnetic tunnel junctions (MTJs) with a perpendicular easy axis as a function of temperature between 298 and 393 K. For the MTJs with a junction diameter above 43 nm, Ε is much smaller and less sensitive to the temperature than the magnetic anisotropy energy of the total recording volume. For the MTJ with a diameter of 33 nm, E and the anisotropy energy take about the same value and show similar temperature dependence. The results can be explained by considering a crossover of magnetization reversal mode from nucleation type to single-domain like type, as the device dimensions reduce.

  1. Effect of annealing conditions on the perpendicular magnetic anisotropy of Ta/CoFeB/MgO multilayers

    Directory of Open Access Journals (Sweden)

    Yan Liu

    2016-04-01

    Full Text Available Films with a structure of Ta (5 nm/Co20Fe60B20 (0.8–1.5 nm/MgO (1 nm/Ta (1 nm were deposited on Corning glass substrates by magnetron sputtering. The as-deposited films with CoFeB layer thickness from 0.8 to 1.3 nm show perpendicular magnetic anisotropy (PMA. After annealing at a proper temperature, the PMA of the films can be enhanced remarkably. A maximum effective anisotropy field of up to 9 kOe was obtained for 1.0- and 1.1-nm-thick CoFeB layers annealed at an optimum temperature of 300 °C. A 4-kOe magnetic field was applied during annealing to study its effect on the PMA of the CoFeB layers. The results confirmed that applying a perpendicular magnetic field during annealing did not improve the maximum PMA of the films, but it did enhance the PMA of the thinner films at a lower annealing temperature.

  2. Studies of current-perpendicular-to-plane magnetoresistance (CPP-MR) and current-induced magnetization switching (CIMS)

    Science.gov (United States)

    Kurt, Huseyin

    2005-08-01

    We present two CPP-MR studies of spin-valves based upon ferromagnetic/nonmagnetic/ferromagnetic (F/N/F) trilayers. We measure the spin-diffusion lengths of N = Pd, Pt, and Au at 4.2K, and both the specific resistances (sample area A times resistance R) and spin-memory-loss of N/Cu interfaces. Pd, Pt and Au are of special device interest because they give perpendicular anisotropy when sandwiching very thin Co layers. Comparing our spin-memory-loss data at Pd/Cu and Pt/Cu interfaces with older data for Nb/Cu and W/Cu gives insight into the importance of spin-orbit coupling in producing such loss. We reproduce and extend prior studies by Eid of 'magnetic activity' at the interface of Co and N-metals (or combinations of N-metals), when the other side of the N-metal contacts a superconductor (S). Our data suggest that magnetic activity may require strong spin-flipping at the N/S interface. We present five studies of a new phenomenon, CIMS, in F1/N/F2 trilayers, with F1 a thick 'polarizing' layer and F2 a thin 'switching' layer. In all prior studies of CIMS, positive current caused the magnetization of F2 to switch from parallel (P) to anti-parallel (AP) to that of F1- 'normal' switching. By judicious addition of impurities to F-metals, we are able to controllably produce both 'normal' and 'inverse' switching- where positive current switches the magnetization of F2 from AP to P to that of F1. In the samples studied, whether the switching is normal or inverse is set by the 'net polarization' produced by F1 and is independent of the properties of F2. As scattering in the bulk of F1 and F2 is essential to producing our results, these results cannot be described by ballistic models, which allow scattering only at interfaces. Most CIMS experiments use Cu as the N-layer due to its low resistivity and long spin-diffusion length. We show that Ag and Au have low enough resistivities and long enough spin-diffusion lengths to be useful alternatives to Cu for some devices. While

  3. Unusual negative magnetoresistance in Bi2Se3-ySy topological insulator under perpendicular magnetic field

    Science.gov (United States)

    Singh, Rahul; Gangwar, Vinod K.; Daga, D. D.; Singh, Abhishek; Ghosh, A. K.; Kumar, Manoranjan; Lakhani, A.; Singh, Rajeev; Chatterjee, Sandip

    2018-03-01

    The magneto-transport properties of Bi2Se3-ySy were investigated. Magnetoresistance (MR) decreases with an increase in the S content, and finally, for 7% (i.e., y = 0.21) S doping, the magnetoresistance becomes negative. This negative MR is unusual as it is observed when a magnetic field is applied in the perpendicular direction to the plane of the sample. The magneto-transport behavior shows the Shubnikov-de Haas (SdH) oscillation, indicating the coexistence of surface and bulk states. The negative MR has been attributed to the non-trivial bulk conduction.

  4. Strongly Interacting Matter in Magnetic Field

    Science.gov (United States)

    Mao, Shijun; Wu, Youjia; Zhuang, Pengfei

    Inverse magnetic catalysis effect on the chiral phase transition is investigated in the frame of SU(2) NJL model with Pauli-Villars regularization scheme. We consider two scenarios, the chiral chemical potential μ5 caused by sphalerons and magnetic inhibition of mesons π0. With different chiral chemical potential, we always obtain magnetic catalysis in the mean field calculation, due to the enhancement of Fermi surface of the pairing fermions by μ5. On the other hand, when going beyond the mean field approximation by including the feed-down from mesons to quarks, the competition between the magnetic catalysis effect of quarks and magnetic inhibition effect of mesons leads to the transition from inverse magnetic catalysis to delayed magnetic catalysis with increasing magnetic field.

  5. 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.

  6. Junction size effect on switching current and thermal stability in CoFeB/MgO perpendicular magnetic tunnel junctions

    Science.gov (United States)

    Sato, H.; Yamanouchi, M.; Miura, K.; Ikeda, S.; Gan, H. D.; Mizunuma, K.; Koizumi, R.; Matsukura, F.; Ohno, H.

    2011-07-01

    Junction size dependence of critical current (IC0) for spin transfer torque switching and thermal stability factor (E/kBT) was examined in CoFeB/MgO perpendicular magnetic tunnel junctions (p-MTJs). The IC0 increased with increasing recording layer area (Srec). On the other hand, the E/kBT showed almost constant values even though the Srec was increased from ˜1500 nm2 (44 nmφ) to ˜5000 nm2 (76 nmφ). Both IC0 and E/kBT behavior can be explained with assuming that the nucleation type magnetization reversal takes place in CoFeB/MgO p-MTJs.

  7. Fabrication and characterization of nano-particulate PtCo media for ultra-high density perpendicular magnetic recording

    International Nuclear Information System (INIS)

    Newman, Dave M; Wears, M Lesley; Jollie, Michael; Choo, Desmond

    2007-01-01

    The year-on-year growth in areal recording density maintained now for half a century by the hard disk industry has required a corresponding reduction in the size of the magnetic grains comprising the storage media employed. Grain dimensions are now such that the performance of materials which thus far have served the industry well can no longer be maintained as further reduction in their volume risks breaching the superparamagnetic limit with the attendant loss of data integrity. The high magnetocrystalline anisotropy of the Ll 0 phase of PtCo allows particles as small as 4 nm diameter to remain magnetically stable in the elevated temperature environment typical of disk drive systems. A non-interacting dispersion of nanomagnetic particles suspended in an inert non-magnetic host such that each has its anisotropy axis directed perpendicular to the surface of the medium now constitutes the new ideal for a recording medium. Fabrication by a novel combination of conventional sputtering and thermal processing technologies of a medium closely approximating this ideal is demonstrated. An optimized two-stage fabrication process produces a near mono-dispersion of particles with magnetic activation volumes centred about 5 x 10 23 and crystallized in the L1 0 phase with an orientated tetragonal structure. The characteristics of this medium are discussed as a function of composition and crystalline structure. In the absence of a thermally assisted recording head, experiments are conducted on a degraded form of the medium that is shown to support perpendicular recording at linear densities in excess of 240 kfci (D50 point)

  8. Zero-field spin transfer oscillators based on magnetic tunnel junction having perpendicular polarizer and planar free layer

    Directory of Open Access Journals (Sweden)

    Bin Fang

    2016-12-01

    Full Text Available We experimentally studied spin-transfer-torque induced magnetization oscillations in an asymmetric MgO-based magnetic tunnel junction device consisting of an in-plane magnetized free layer and an out-of-plane magnetized polarizer. A steady auto-oscillation was achieved at zero magnetic field and room temperature, with an oscillation frequency that was strongly dependent on bias currents, with a large frequency tunability of 1.39 GHz/mA. Our results suggest that this new structure has a high potential for new microwave device designs.

  9. Microwave absorption of a 2D electron system in spatially varying perpendicular magnetic field

    Science.gov (United States)

    Magill, B. A.; Polyanskii, A. A.; Engel, L. W.; Lilly, M. P.; Simmons, J. A.; Reno, J. L.

    2010-03-01

    We report on microwave measurements of a two dimensional electron system (2DES) in a spatially varying magnetic field, Bz, provided by a ferromagnet in proximity to the sample in a homogenous external field, Bz0. Dy, permalloy, and neodymium iron boron ferromagnets are used in two configurations, rods and plates with holes in them. The radius, rm, of the rods or holes ranges from 0.125 mm to 0.5 mm. The microwave transmission of the 2DES exhibits a resonance which decreases in peak frequency as Bz0 is increased. We observe peak frequencies from ˜ 9.5 GHz to150 MHz for external magnetic fields in a range from .02 Telsa to 1.5 Tesla. We will interpret the data in terms of plasma excitations similar to edge magnetoplasmons [1] but confined along the magnetic field inhomogeneity by the large magnetic field gradients there. The interpretation of the data will utilize profiles of the spatially varying magnetic field obtained by magneto optical imaging using iron garnet indicator films with an in-plane magnetization.

  10. THE EFFECT OF LARGE-SCALE MAGNETIC TURBULENCE ON THE ACCELERATION OF ELECTRONS BY PERPENDICULAR COLLISIONLESS SHOCKS

    International Nuclear Information System (INIS)

    Guo Fan; Giacalone, Joe

    2010-01-01

    We study the physics of electron acceleration at collisionless shocks that move through a plasma containing large-scale magnetic fluctuations. We numerically integrate the trajectories of a large number of electrons, which are treated as test particles moving in the time-dependent electric and magnetic fields determined from two-dimensional hybrid simulations (kinetic ions and fluid electron). The large-scale magnetic fluctuations effect the electrons in a number of ways and lead to efficient and rapid energization at the shock front. Since the electrons mainly follow along magnetic lines of force, the large-scale braiding of field lines in space allows the fast-moving electrons to cross the shock front several times, leading to efficient acceleration. Ripples in the shock front occurring at various scales will also contribute to the acceleration by mirroring the electrons. Our calculation shows that this process favors electron acceleration at perpendicular shocks. The current study is also helpful in understanding the injection problem for electron acceleration by collisionless shocks. It is also shown that the spatial distribution of energetic electrons is similar to in situ observations. The process may be important to our understanding of energetic electrons in planetary bow shocks and interplanetary shocks, and explaining herringbone structures seen in some type II solar radio bursts.

  11. Phase-resolved detection of the spin Hall angle by optical ferromagnetic resonance in perpendicularly magnetized thin films

    Science.gov (United States)

    Capua, Amir; Wang, Tianyu; Yang, See-Hun; Rettner, Charles; Phung, Timothy; Parkin, Stuart S. P.

    2017-02-01

    The conversion of charge current to spin current by the spin Hall effect is of considerable current interest from both fundamental and technological perspectives. Measurement of the spin Hall angle, especially for atomically thin systems with large magnetic anisotropies, is not straightforward. Here we demonstrate a hybrid phase-resolved optical-electrical ferromagnetic resonance method that we show can robustly determine the spin Hall angle in heavy-metal/ferromagnet bilayer systems with large perpendicular magnetic anisotropy. We present an analytical model of the ferromagnetic resonance spectrum in the presence of the spin Hall effect, in which the spin Hall angle can be directly determined from the changes in the amplitude response as a function of the spin current that is generated from a dc charge current passing through the heavy-metal layer. Increased sensitivity to the spin current is achieved by operation under conditions for which the magnetic potential is shallowest at the "Smit point." Study of the phase response reveals that the spin Hall angle can be reliably extracted from a simplified measurement that does not require scanning over time or magnetic field but rather only on the dc current. The method is applied to the Pt-Co/Ni/Co system whose spin Hall angle was to date characterized only indirectly and that is especially relevant for spin-orbit torque devices.

  12. Termination layer compensated tunnelling magnetoresistance in ferrimagnetic Heusler compounds with high perpendicular magnetic anisotropy.

    Science.gov (United States)

    Jeong, Jaewoo; Ferrante, Yari; Faleev, Sergey V; Samant, Mahesh G; Felser, Claudia; Parkin, Stuart S P

    2016-01-18

    Although high-tunnelling spin polarization has been observed in soft, ferromagnetic, and predicted for hard, ferrimagnetic Heusler materials, there has been no experimental observation to date of high-tunnelling magnetoresistance in the latter. Here we report the preparation of highly textured, polycrystalline Mn3Ge films on amorphous substrates, with very high magnetic anisotropy fields exceeding 7 T, making them technologically relevant. However, the small and negative tunnelling magnetoresistance that we find is attributed to predominant tunnelling from the lower moment Mn-Ge termination layers that are oppositely magnetized to the higher moment Mn-Mn layers. The net spin polarization of the current reflects the different proportions of the two distinct termination layers and their associated tunnelling matrix elements that result from inevitable atomic scale roughness. We show that by engineering the spin polarization of the two termination layers to be of the same sign, even though these layers are oppositely magnetized, high-tunnelling magnetoresistance is possible.

  13. The Effect of Rotating a Faraday Disc Perpendicular to an Applied Magnetic Field Theory and Experiment

    Science.gov (United States)

    Mazuruk, Konstantin; Grugel, Richard N.

    2003-01-01

    A magnetohydrodynamic model that examines the effect of rotating an electrically conducting cylinder with a uniform external magnetic field applied orthogonal to its axis is presented. Noting a simple geometry, it can be classified as a fundamental dynamo problem. For the case of an infinitely long cylinder, an analytical solution is obtained and analyzed in detail. A semi-analytical model was developed that considers a finite cylinder. Experimental data from a spinning brass wheel in the presence of Earth's magnetic field were compared to the proposed theory and found to fit well.

  14. Neutron Depolarization Studies of CoCr to study the perpendicular magnetic domain structure

    NARCIS (Netherlands)

    Kraan, W.H.; Rekveldt, M.Th.; Hemmes, K.; Lodder, J.C.

    1986-01-01

    Polarised neutrons (l=0.47 nm) are transmitted through sputtered CoCr films. From the measured diagonal elements of the depolarisation matrix it appears that the effective thickness heff of the films is about 50% of the actual thickness. When a soft magnetic NiFe film is deposited before or after

  15. Neutron depolarisation in CoCr layers to study the perpendicular magnetic domain structure

    NARCIS (Netherlands)

    Kraan, W.H.; Rekveldt, M.Th.; Hemmes, K.; Lodder, J.C.

    1985-01-01

    Polarised neutrons (λ = 0.47 nm) are transmitted through sputtered CoCr films. From the measured diagonal elements of the depolarisation matrix it appears that the effective thickness heff of the films is about 50% of the actual thickness. When a soft magnetic NiFe film is deposited before or after

  16. Equation of state of strange quark matter in a strong magnetic field

    International Nuclear Information System (INIS)

    Isayev, A.A.; Yang, J.

    2012-01-01

    Thermodynamic properties of strange quark matter (SQM) in strong magnetic fields H up to 10 20 G are considered at zero temperature within the MIT bag model. The effects of the pressure anisotropy, exhibiting in the difference between the pressures along and perpendicular to the field direction, become essential at H>H t h , with the estimate 10 17 t h 18 G. The longitudinal pressure vanishes in the critical field H c , which can be somewhat less or larger than 10 18 G, depending on the total baryon number density and bag pressure. As a result, the longitudinal instability occurs in strongly magnetized SQM. The appearance of such instability sets the upper bound on the magnetic field strength which can be reached in the interior of a neutron star with the quark core. The longitudinal and transverse pressures as well as the anisotropic equation of state of SQM are determined under the conditions relevant for the cores of magnetars

  17. Tunnel magnetoresistance properties and annealing stability in perpendicular anisotropy MgO-based magnetic tunnel junctions with different stack structures

    Science.gov (United States)

    Mizunuma, K.; Ikeda, S.; Sato, H.; Yamanouchi, M.; Gan, H. D.; Miura, K.; Yamamoto, H.; Hayakawa, J.; Matsukura, F.; Ohno, H.

    2011-04-01

    We have investigated the effect of stack structures on tunnel magnetoresistance (TMR) properties in perpendicular anisotropy MgO-based magnetic tunnel junctions (p-MTJs) with CoFe/Pd multilayer and CoFeB insertion. By adopting Ta and Ru cap-layers, the TMR ratios of 113 and 106% are obtained at annealing temperature (Ta) of 325 °C, respectively. Particularly, the Ru cap-layer is effective in realizing a TMR ratio of 100% at Ta = 350 °C. By replacing (Co25Fe75)80B20 with (Co25Fe75)85B15, the TMR ratio increased quickly at low Ta, reaching a maximum of 120% at Ta = 300 °C.

  18. Electric-field tunable perpendicular magnetic anisotropy in tetragonal Fe4N/BiFeO3 heterostructures

    Science.gov (United States)

    Yin, Li; Wang, Xiaocha; Mi, Wenbo

    2017-07-01

    Electric field control on perpendicular magnetic anisotropy (PMA) is indispensable for spintronic devices. Herewith, in tetragonal Fe4N/BiFeO3 heterostructures with the FeAFeB/Fe-O2 interface, PMA in each Fe4N layer, not merely interfacial layers, is modulated by the electric field, which is attributed to the broken spin screening of the electric field in highly spin-polarized Fe4N. Moreover, the periodical dx y+dy z+dz2 and dx y+dx2-y2 orbital-PMA oscillation enhances the interactions between adjacent FeAFeB and (FeB)2N atomic layers, which benefits the electric field modulation on PMA in the whole Fe4N atomic layers. The electric-field control on PMA in Fe4N/BiFeO3 heterostructures is favored by the electric-field-lifted potential in Fe4N.

  19. Mechanism and Simulation of Generating Pulsed Strong Magnetic Field

    Science.gov (United States)

    Yang, Xian-Jun; Wang, Shuai-Chuang; Deng, Ai-Dong; Gu, Zhuo-Wei; Luo, Hao

    2014-10-01

    A strong magnetic field (over 1000 T) was recently experimentally produced at the Academy of Engineering Physics in China. The theoretical methods, which include a simple model and MHD code, are discussed to investigate the physical mechanism and dynamics of generating the strong magnetic field. The analysis and simulation results show that nonlinear magnetic diffusion contributes less as compared to the linear magnetic diffusion. This indicates that the compressible hydrodynamic effect and solid imploding compression may have a large influence on strong magnetic field generation.

  20. Study on the mechanism of perpendicular magnetic anisotropy in Ta/CoFeB/MgO system

    Science.gov (United States)

    Lou, Yongle; Zhang, Yuming; Guo, Hui; Xu, Daqing; Yimen, Zhang

    2017-06-01

    The mechanism of perpendicular magnetic anisotropy (PMA) in a MgO-based magnetic tunnel junction (MTJ) has been studied in this article. By comparing the magnetic properties and elementary composition analysis for different CoFeB-based structures, such as Ta/CoFeB/MgO, Ta/CoFeB/Ta and Ru/CoFeB/MgO structures, it is found that a certain amount of Fe-oxide existing at the interface of CoFeB/MgO is helpful to enhance the PMA and the PMA is originated from the interface of CoFeB/MgO. In addition, Ta film plays an important role to enhance the PMA in Ta/CoFeB/MgO structure. Project supported by the National Defense Advance Research Foundation (No. 9140A08XXXXXX0DZ106), the Basic Research Program of Ministry of Education, China (No. JY10000925005), the Scientific Research Program Funded by Shaanxi Provincial Education Department (No.11JK0912), the Scientific Research Foundation of Xi’an University of Science and Technology (No. 2010011), the Doctoral Research Startup Fund of Xi’an University of Science and Technology (No. 2010QDJ029).

  1. Bias-voltage dependence of perpendicular spin-transfer torque in asymmetric MgO-based magnetic tunnel junctions

    KAUST Repository

    Oh, Se Chung

    2009-10-25

    Spin-transfer torque (STT) allows the electrical control of magnetic states in nanostructures. The STT in magnetic tunnel junctions (MTJs) is of particular importance owing to its potential for device applications. It has been demonstrated that the MTJ has a sizable perpendicular STT (, field-like torque), which substantially affects STT-driven magnetization dynamics. In contrast to symmetric MTJs where the bias dependence of is quadratic, it is theoretically predicted that the symmetry breaking of the system causes an extra linear bias dependence. Here, we report experimental results that are consistent with the predicted linear bias dependence in asymmetric MTJs. The linear contribution is quite significant and its sign changes from positive to negative as the asymmetry is modified. This result opens a way to design the bias dependence of the field-like term, which is useful for device applications by allowing, in particular, the suppression of the abnormal switching-back phenomena. © 2009 Macmillan Publishers Limited. All rights reserved.

  2. Design of high-throughput and low-power true random number generator utilizing perpendicularly magnetized voltage-controlled magnetic tunnel junction

    Directory of Open Access Journals (Sweden)

    Hochul Lee

    2017-05-01

    Full Text Available A true random number generator based on perpendicularly magnetized voltage-controlled magnetic tunnel junction devices (MRNG is presented. Unlike MTJs used in memory applications where a stable bit is needed to store information, in this work, the MTJ is intentionally designed with small perpendicular magnetic anisotropy (PMA. This allows one to take advantage of the thermally activated fluctuations of its free layer as a stochastic noise source. Furthermore, we take advantage of the voltage dependence of anisotropy to temporarily change the MTJ state into an unstable state when a voltage is applied. Since the MTJ has two energetically stable states, the final state is randomly chosen by thermal fluctuation. The voltage controlled magnetic anisotropy (VCMA effect is used to generate the metastable state of the MTJ by lowering its energy barrier. The proposed MRNG achieves a high throughput (32 Gbps by implementing a 64×64 MTJ array into CMOS circuits and executing operations in a parallel manner. Furthermore, the circuit consumes very low energy to generate a random bit (31.5 fJ/bit due to the high energy efficiency of the voltage-controlled MTJ switching.

  3. Effective magnetic moment of neutrinos in strong magnetic fields

    CERN Document Server

    Pérez, A; Masood, S S; Gaitan, R; Rodríguez, S

    2002-01-01

    In this paper we compute the effective magnetic moment of neutrinos propagating in dense high magnetized medium. Taking typical values of magnetic field and densities of astrophysical objects (such as the cores of supernovae and neutron stars) we obtain an effective type of dipole magnetic moment in agreement with astrophysical and cosmological bounds. (Author)

  4. Negative magnetoresistance in perpendicular of the superlattices axis weak magnetic field at scattering of impurity ions

    International Nuclear Information System (INIS)

    Askerov, B. M.; Figarova, R.; Guseynov, G.I.

    2012-01-01

    Full Text : The transverse magnetoresistance in superlattices with the cosine dispersion law of conduction electrons in a case, when a weak magnetic field in plane of layer at scattering of the charge carriers of impurity ions has been studied. It has been shown that in a quasi-two-dimensional case the magnetoresistance was positive, while in a quasi-three-dimensional case can become negative depending of a degree of mini-band filling. Such behavior of magnetoresistance, apparently, has been related to presence in a mini-band of region with the negative effective mass

  5. Perpendicularly magnetized CoFeB multilayers with tunable interlayer exchange for synthetic ferrimagnets

    Science.gov (United States)

    Pirro, P.; Hamadeh, A.; Lavanant-Jambert, M.; Meyer, T.; Tao, B.; Rosario, E.; Lu, Y.; Hehn, M.; Mangin, S.; Petit Watelot, S.

    2017-06-01

    A study of the multilayer system MgO/CoFeB(1.1 nm)/Ta(t)/CoFeB(0.8 nm)/MgO is presented, where the two CoFeB layers are separated by a Ta interlayer of varying thickness t. The magnetization properties deduced from complementary techniques such as superconducting quantum interference magnetometry, ferromagnetic resonance frequency measurements and Brillouin light scattering spectroscopy can be tuned by changing the Ta thickness between t = 0.25 nm, 0.5 nm and 0.75 nm. For t = 0.5 nm, a ferromagnetic coupling is observed, whereas for t = 0.75 nm, the antiferromagnetic coupling needed to construct a synthetic ferrimagnet is realized. In the latter case, the shape of magnetic domain walls between two ferrimagnetic alignments or between a ferro- and a ferrimagnetic alignment is very different. This behavior can be interpreted as a result of the change in dipolar as well as interlayer exchange energy and domain wall pinning, which is an important conclusion for the realization of data storage devices based on synthetic ferri- and antiferromagnets.

  6. Perpendicularly magnetized CoFeB multilayers with tunable interlayer exchange for synthetic ferrimagnets

    Energy Technology Data Exchange (ETDEWEB)

    Pirro, P., E-mail: ppirro@physik.uni-kl.de [Institut Jean Lamour, Université de Lorraine, UMR 7198 CNRS, 54506 Vandoeuvre-lés-Nancy (France); Hamadeh, A.; Lavanant-Jambert, M. [Institut Jean Lamour, Université de Lorraine, UMR 7198 CNRS, 54506 Vandoeuvre-lés-Nancy (France); Meyer, T. [Fachbereich Physik and Landesforschungszentrum OPTIMAS, Technische Universität Kaiserslautern, 67663 Kaiserslautern (Germany); Tao, B.; Rosario, E.; Lu, Y.; Hehn, M.; Mangin, S.; Petit Watelot, S. [Institut Jean Lamour, Université de Lorraine, UMR 7198 CNRS, 54506 Vandoeuvre-lés-Nancy (France)

    2017-06-15

    Highlights: • MgO/CoFeB/Ta/CoFeB/MgO multilayers as synthetic ferrimagnets. • Comprehensive characterization by measurement of static and dynamic properties. • Different pinning for domain walls with different alignment of the individual layers. - Abstract: A study of the multilayer system MgO/CoFeB(1.1 nm)/Ta(t)/CoFeB(0.8 nm)/MgO is presented, where the two CoFeB layers are separated by a Ta interlayer of varying thickness t. The magnetization properties deduced from complementary techniques such as superconducting quantum interference magnetometry, ferromagnetic resonance frequency measurements and Brillouin light scattering spectroscopy can be tuned by changing the Ta thickness between t = 0.25 nm, 0.5 nm and 0.75 nm. For t = 0.5 nm, a ferromagnetic coupling is observed, whereas for t = 0.75 nm, the antiferromagnetic coupling needed to construct a synthetic ferrimagnet is realized. In the latter case, the shape of magnetic domain walls between two ferrimagnetic alignments or between a ferro- and a ferrimagnetic alignment is very different. This behavior can be interpreted as a result of the change in dipolar as well as interlayer exchange energy and domain wall pinning, which is an important conclusion for the realization of data storage devices based on synthetic ferri- and antiferromagnets.

  7. Enhancement in the interfacial perpendicular magnetic anisotropy and the voltage-controlled magnetic anisotropy by heavy metal doping at the Fe/MgO interface

    Directory of Open Access Journals (Sweden)

    Takayuki Nozaki

    2018-02-01

    Full Text Available We investigated the influence of heavy metal doping at the Fe/MgO interface on the interfacial perpendicular magnetic anisotropy (PMA and the voltage-controlled magnetic anisotropy (VCMA in magnetic tunnel junctions prepared by sputtering-based deposition. The interfacial PMA was increased by tungsten doping and a maximum intrinsic interfacial PMA energy, Ki,0 of 2.0 mJ/m2 was obtained. Ir doping led to a large increase in the VCMA coefficient by a factor of 4.7 compared with that for the standard Fe/MgO interface. The developed technique provides an effective approach to enhancing the interfacial PMA and VCMA properties in the development of voltage-controlled spintronic devices.

  8. A strong angular dependence of magnetic properties of magnetosome chains: Implications for rock magnetism and paleomagnetism

    Science.gov (United States)

    Li, Jinhua; Ge, Kunpeng; Pan, Yongxin; Williams, Wyn; Liu, Qingsong; Qin, Huafeng

    2013-10-01

    Single-domain magnetite particles produced by magnetotactic bacteria (magnetosomes) and aligned in chains are of great interest in the biosciences and geosciences. Here, we investigated angular variation of magnetic properties of aligned Magnetospirillum magneticum AMB-1 cells, each of which contains one single fragmental chain of magnetosomes. With measurements at increasing angles from the chain direction, we observed that (i) the hysteresis loop gradually changes from nearly rectangular to a ramp-like shape (e.g., Bc and remanence decrease), (ii) the acquisition and demagnetization curves of IRM shift toward higher fields (e.g., Bcr increases), and (iii) the FORC diagram shifts toward higher coercivity fields (e.g., Bc,FORC increases). For low-temperature results, compared to unoriented samples, the samples containing aligned chains have a much lower remanence loss of field-cooled (δFC) and zero-field-cooled (δZFC) remanence upon warming through the Verwey transition, higher δ-ratio (δ = δFC/δZFC) for the measurement parallel to the chain direction, and lower δ-ratio, larger δFC and δZFC values for the perpendicular measurement. Micromagnetic simulations confirm the experimental observations and reveal that the magnetization reversal of magnetosome chain appears to be noncoherent at low angles and coherent at high angles. The simulations also demonstrate that the angular dependence of magnetic properties is related to the dispersion degree of individual chains, indicating that effects of anisotropy need to be accounted for when using rock magnetism to identify magnetosomes or magnetofossils once they have been preserved in aligned chains. Additionally, this study experimentally demonstrates an empirical correspondence of the parameter Bc,FORC to Bcr rather than Bc, at least for magnetite chains with strong shape anisotropy. This suggests FORC analysis is a good discriminant of magnetofossils in sediments and rocks.

  9. Dynamic resistance of a high-T c coated conductor wire in a perpendicular magnetic field at 77 K

    Science.gov (United States)

    Jiang, Zhenan; Toyomoto, Ryuki; Amemiya, Naoyuki; Zhang, Xingyou; Bumby, Chris W.

    2017-03-01

    Superconducting high-T c coated conductor (CC) wires comprise a ceramic thin film with a large aspect ratio. This geometry can lead to significant dissipative losses when exposed to an alternating magnetic field. Here we report experimental measurements of the ‘dynamic resistance’ of commercially available SuperPower and Fujikura CC wires in an AC perpendicular field. The onset of dynamic resistance occurs at a threshold field amplitude, which is determined by the total DC transport current and the penetration field of the conductor. We show that the field-dependence of the normalised magnetisation loss provides an unambiguous value for this threshold field at zero transport current. From this insight we then obtain an expression for the dynamic resistance in perpendicular field. This approach implies a linear relationship between dynamic resistance and applied field amplitude, and also between threshold field and transport current and this is consistent with our experimental data. The analytical expression obtained yields values that closely agree with measurements obtained across a wide range of frequencies and transport currents, and for multiple CC wires produced by different wire manufacturers and with significantly differing dimensions and critical currents. We further show that at high transport currents, the measured DC resistance includes an additional nonlinear term which is due to flux-flow resistance incurred by the DC transport current. This occurs once the field-dependent critical current of the wire falls below the DC transport current for part of each field cycle. Our results provide an effective and simple approach to calculating the dynamic resistance of a CC wire, at current and field magnitudes consistent with those expected in superconducting machines.

  10. Energy density and energy flow of surface waves in a strongly magnetized graphene

    Science.gov (United States)

    Moradi, Afshin

    2018-01-01

    General expressions for the energy density and energy flow of plasmonic waves in a two-dimensional massless electron gas (as a simple model of graphene) are obtained by means of the linearized magneto-hydrodynamic model and classical electromagnetic theory when a strong external magnetic field perpendicular to the system is present. Also, analytical expressions for the energy velocity, wave polarization, wave impedance, transverse and longitudinal field strength functions, and attenuation length of surface magneto-plasmon-polariton waves are derived, and numerical results are prepared.

  11. Activity of Strongly Magnetized Neutron Stars

    Science.gov (United States)

    Beloborodov, Andrei

    This proposal is the continuation of a previous 3-year project that focused on modeling the nonthermal emission from magnetars and pulsars and testing the models against new observations, in particular by NuSTAR. The proposed project develops in two directions: (1) First-principle simulations of the magnetospheric electron-positron discharge using our code APERTURE (based on the particle-in-cell method), which is specifically designed for this purpose. Its performance is demonstrated by the first application to rotation-powered pulsars, and it can significantly advance our understanding of the magnetospheric activity of magnetars and pulsars. Our simulations involve a detailed implementation of radiative processes, tracking the emission and propagation of gammarays and production of electron-positron pairs. The results will provide new theoretical foundation for interpreting emission from the twisted magnetospheres of neutron stars. They will clarify, in particular, the radiative mechanism of magnetar bursts and persistent emission. (2) Investigation of magnetic field evolution inside neutron stars, which is ultimately responsible for driving the magnetospheric activity of magnetars and their surface heating. Our recent results suggest two novel phenomena in the solid crust of an active magnetar: thermoplastic waves and Hall-mediated avalanches. We propose to investigate scenarios for the global magnetic field evolution in the core and the crust, and its observables including (a) twisting of the external magnetosphere and the resulting nonthermal activity, (b) subsurface heating, and (c) sudden changes of the rotation rate. We will use our models and the rich accumulated data to disentangle the key dynamic processes inside magnetars. This analysis can constrain the magnetic fields hidden inside magnetars, the state of their core matter and its possible superfluidity.

  12. Strong permanent magnet-assisted electromagnetic undulator

    Science.gov (United States)

    Halbach, Klaus

    1988-01-01

    This invention discloses an improved undulator comprising a plurality of electromagnet poles located along opposite sides of a particle beam axis with alternate north and south poles on each side of the beam to cause the beam to wiggle or undulate as it travels generally along the beam axis and permanent magnets spaced adjacent the electromagnetic poles on each side of the axis of said particle beam in an orientation sufficient to reduce the saturation of the electromagnet poles whereby the field strength of the electromagnet poles can be increased beyond the normal saturation levels of the electromagnetic poles.

  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. Enhanced thermal photon and dilepton production in strongly coupled = 4 SYM plasma in strong magnetic field

    Science.gov (United States)

    Mamo, Kiminad A.

    2013-08-01

    We calculate the DC conductivity tensor of strongly coupled = 4 super-Yang-Mills (SYM) plasma in a presence of a strong external magnetic field B ≫ T 2 by using its gravity dual and employing both the RG flow approach and membrane paradigm which give the same results. We find that, since the magnetic field B induces anisotropy in the plasma, different components of the DC conductivity tensor have different magnitudes depending on whether its components are in the direction of the magnetic field B. In particular, we find that a component of the DC conductivity tensor in the direction of the magnetic field B increases linearly with B while the other components (which are not in the direction of the magnetic field B) are independent of it. These results are consistent with the lattice computations of the DC conductivity tensor of the QCD plasma in an external magnetic field B. Using the DC conductivity tensor, we calculate the soft or low-frequency thermal photon and dilepton production rates of the strongly coupled = 4 SYM plasma in the presence of the strong external magnetic field B ≫ T 2. We find that the strong magnetic field B enhances both the thermal photon and dilepton production rates of the strongly coupled = 4 SYM plasma in a qualitative agreement with the experimentally observed enhancements at the heavy-ion collision experiments.

  15. Electrostatic turbulence in strongly magnetized plasmas

    International Nuclear Information System (INIS)

    Nielsen, A.H.

    1993-01-01

    Turbulence in plasmas has been investigated experimentally and numerically. On the experimental side the turbulent nature of the Kelvin-Helmholtz instability has been studied in a single-ended Q-machine. The development of coherent structures in the background of the turbulent flow has been demonstrated and the capability of structures of transporting plasma across the magnetic field-lines is explained in detail. The numerical investigations are divided into two parts: Numerical simulations of the dynamics from the Q-machine experiments using spectral methods to solve the two-dimensional Navier-Stokes equations in a cylindrical geometry. A numerical study of the Eulerian-Lagrangian transformation in a two-dimensional flow. Here the flow is made up by a large number of structures, where each individual structure is convected by the superposed flow field of all the others. (au) (33 ills., 67 refs.)

  16. Operating a magnetic nozzle helicon thruster with strong magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Takahashi, Kazunori, E-mail: kazunori@ecei.tohoku.ac.jp; Komuro, Atsushi; Ando, Akira [Department of Electrical Engineering, Tohoku University, Sendai 980-8579 (Japan)

    2016-03-15

    A pulsed axial magnetic field up to ∼2.8 kG is applied to a 26-mm-inner-diameter helicon plasma thruster immersed in a vacuum chamber, and the thrust is measured using a pendulum target. The pendulum is located 30-cm-downstream of the thruster, and the thruster rf power and argon flow rate are fixed at 1 kW and 70 sccm (which gives a chamber pressure of 0.7 mTorr). The imparted thrust increases as the applied magnetic field is increased and saturates at a maximum value of ∼9.5 mN for magnetic field above ∼2 kG. At the maximum magnetic field, it is demonstrated that the normalized plasma density, and the ion flow energy in the magnetic nozzle, agree within ∼50% and of 10%, respectively, with a one-dimensional model that ignores radial losses from the nozzle. This magnetic nozzle model is combined with a simple global model of the thruster source that incorporates an artificially controlled factor α, to account for radial plasma losses to the walls, where α = 0 and 1 correspond to zero losses and no magnetic field, respectively. Comparison between the experiments and the model implies that the radial losses in the thruster source are experimentally reduced by the applied magnetic field to about 10% of that obtained from the no magnetic field model.

  17. Perpendicular spin transfer torque magnetic random access memories with high spin torque efficiency and thermal stability for embedded applications (invited)

    Energy Technology Data Exchange (ETDEWEB)

    Thomas, Luc, E-mail: luc.thomas@headway.com; Jan, Guenole; Zhu, Jian; Liu, Huanlong; Lee, Yuan-Jen; Le, Son; Tong, Ru-Ying; Pi, Keyu; Wang, Yu-Jen; Shen, Dongna; He, Renren; Haq, Jesmin; Teng, Jeffrey; Lam, Vinh; Huang, Kenlin; Zhong, Tom; Torng, Terry; Wang, Po-Kang [TDK-Headway Technologies, Inc., Milpitas, California 95035 (United States)

    2014-05-07

    Magnetic random access memories based on the spin transfer torque phenomenon (STT-MRAMs) have become one of the leading candidates for next generation memory applications. Among the many attractive features of this technology are its potential for high speed and endurance, read signal margin, low power consumption, scalability, and non-volatility. In this paper, we discuss our recent results on perpendicular STT-MRAM stack designs that show STT efficiency higher than 5 k{sub B}T/μA, energy barriers higher than 100 k{sub B}T at room temperature for sub-40 nm diameter devices, and tunnel magnetoresistance higher than 150%. We use both single device data and results from 8 Mb array to demonstrate data retention sufficient for automotive applications. Moreover, we also demonstrate for the first time thermal stability up to 400 °C exceeding the requirement of Si CMOS back-end processing, thus opening the realm of non-volatile embedded memory to STT-MRAM technology.

  18. Spiraling contaminant electrons increase doses to surfaces outside the photon beam of an MRI-linac with a perpendicular magnetic field.

    Science.gov (United States)

    Hackett, Sara L; van Asselen, Bram; Wolthaus, Jochem W H; Bluemink, J J; Ishakoglu, Kübra; Kok, Jan G M; Lagendijk, Jan J W; Raaymakers, Bas W

    2018-03-29

    The transverse magnetic field of an MRI-linac sweeps contaminant electrons away from the radiation beam. Films oriented perpendicular to the magnetic field and 5cm from the radiation beam edge show a projection of the divergent beam, indicating that contaminant electrons spiral along magnetic field lines and deposit dose on surfaces outside the primary beam perpendicular to the magnetic field. These spiraling contaminant electrons (SCE) could increase skin doses to protruding regions of the patient along the cranio-caudal axis. This study investigated doses from SCE for an MRI-linac comprising a 7MV linac and a 1.5T MRI scanner. Surface doses to films perpendicular to the magnetic field and 5cm from the radiation beam edge showed increased dose within the projection of the primary beam, whereas films parallel to the magnetic field and 5cm from the beam edge showed no region of increased dose. However, the dose from contaminant electrons is absorbed within a few millimeters. For large fields, the SCE dose is within the same order of magnitude as doses from scattered and leakage photons. Doses for both SCE and scattered photons decrease rapidly with decreasing beam size and increasing distance from the beam edge. © 2018 Institute of Physics and Engineering in Medicine.

  19. The low-field peak in magnetization loops of uniform and granular superconductors in perpendicular magnetic fields

    Czech Academy of Sciences Publication Activity Database

    Johansen, T. H.; Shantsev, D. V.; Koblischka, M. R.; Galperin, Y. M.; Nálevka, Petr; Jirsa, Miloš

    341-348, - (2000), s. 1443-1444 ISSN 0921-4534. [International Conference on Materials and Mechanism of Superconductivity High Temperature Superconductors /4./. Houston , 20.02.2000-25.02.2000] Institutional research plan: CEZ:AV0Z1010914 Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.489, year: 2000

  20. Electromagnetic modes in cold magnetized strongly coupled plasmas

    OpenAIRE

    Tkachenko, I. M.; Ortner, J.; Rylyuk, V. M.

    1999-01-01

    The spectrum of electromagnetic waves propagating in a strongly coupled magnetized fully ionized hydrogen plasma is found. The ion motion and damping being neglected, the influence of the Coulomb coupling on the electromagnetic spectrum is analyzed.

  1. Electron cyclotron maser instability (ECMI in strong magnetic guide field reconnection

    Directory of Open Access Journals (Sweden)

    R. A. Treumann

    2017-08-01

    Full Text Available The ECMI model of electromagnetic radiation from electron holes is shown to be applicable to spontaneous magnetic reconnection. We apply it to reconnection in strong current-aligned magnetic guide fields. Such guide fields participate only passively in reconnection, which occurs in the antiparallel components to both sides of the guide-field-aligned current sheets with current carried by kinetic Alfvén waves. Reconnection generates long (the order of hundreds of electron inertial scales electron exhaust regions at the reconnection site X point, which are extended perpendicular to the current and the guide fields. Exhausts contain a strongly density-depleted hot electron component and have properties similar to electron holes. Exhaust electron momentum space distributions are highly deformed, exhibiting steep gradients transverse to both the reconnecting and guide fields. Such properties suggest application of the ECMI mechanism with the fundamental ECMI X-mode emission beneath the nonrelativistic guide field cyclotron frequency in localized source regions. An outline of the mechanism and its prospects is given. Potential applications are the kilometric radiation (AKR in auroral physics, solar radio emissions during flares, planetary emissions and astrophysical scenarios (radiation from stars and compact objects involving the presence of strong magnetic fields and field-aligned currents. Drift of the exhausts along the guide field maps the local field and plasma properties. Escape of radiation from the exhaust and radiation source region still poses a problem. The mechanism can be studied in 2-D particle simulations of strong guide field reconnection which favours 2-D, mapping the deformation of the electron distribution perpendicular to the guide field, and using it in the numerical calculation of the ECMI growth rate. The mechanism suggests also that reconnection in general may become a source of the ECMI with or without guide fields. This is

  2. Electron cyclotron maser instability (ECMI) in strong magnetic guide field reconnection

    Science.gov (United States)

    Treumann, Rudolf A.; Baumjohann, Wolfgang

    2017-08-01

    The ECMI model of electromagnetic radiation from electron holes is shown to be applicable to spontaneous magnetic reconnection. We apply it to reconnection in strong current-aligned magnetic guide fields. Such guide fields participate only passively in reconnection, which occurs in the antiparallel components to both sides of the guide-field-aligned current sheets with current carried by kinetic Alfvén waves. Reconnection generates long (the order of hundreds of electron inertial scales) electron exhaust regions at the reconnection site X point, which are extended perpendicular to the current and the guide fields. Exhausts contain a strongly density-depleted hot electron component and have properties similar to electron holes. Exhaust electron momentum space distributions are highly deformed, exhibiting steep gradients transverse to both the reconnecting and guide fields. Such properties suggest application of the ECMI mechanism with the fundamental ECMI X-mode emission beneath the nonrelativistic guide field cyclotron frequency in localized source regions. An outline of the mechanism and its prospects is given. Potential applications are the kilometric radiation (AKR) in auroral physics, solar radio emissions during flares, planetary emissions and astrophysical scenarios (radiation from stars and compact objects) involving the presence of strong magnetic fields and field-aligned currents. Drift of the exhausts along the guide field maps the local field and plasma properties. Escape of radiation from the exhaust and radiation source region still poses a problem. The mechanism can be studied in 2-D particle simulations of strong guide field reconnection which favours 2-D, mapping the deformation of the electron distribution perpendicular to the guide field, and using it in the numerical calculation of the ECMI growth rate. The mechanism suggests also that reconnection in general may become a source of the ECMI with or without guide fields. This is of particular

  3. Spectral confinement and current for atoms in strong magnetic fields

    DEFF Research Database (Denmark)

    Fournais, Søren

    2007-01-01

    e study confinement of the ground state of atoms in strong magnetic fields to different subspaces related to the lowest Landau band. Using the results on confinement we can calculate the quantum current in the entire semiclassical region B<3......e study confinement of the ground state of atoms in strong magnetic fields to different subspaces related to the lowest Landau band. Using the results on confinement we can calculate the quantum current in the entire semiclassical region B

  4. Radial oscillations of neutron stars in strong magnetic fields

    Indian Academy of Sciences (India)

    The eigen frequencies of radial pulsations of neutron stars are calculated in a strong magnetic field. At low densities we use the magnetic BPS equation of state (EOS) similar to that obtained by Lai and Shapiro while at high densities the EOS obtained from the relativistic nuclear mean field theory is taken and extended to ...

  5. Radial oscillations of neutron stars in strong magnetic fields

    Indian Academy of Sciences (India)

    Abstract. The eigen frequencies of radial pulsations of neutron stars are calculated in a strong magnetic field. At low densities we use the magnetic BPS equation of state (EOS) similar to that obtained by Lai and Shapiro while at high densities the EOS obtained from the relativistic nuclear mean field theory is taken and ...

  6. Spin-dependent electronic transport characteristics in Fe4N/BiFeO3/Fe4N perpendicular magnetic tunnel junctions

    Science.gov (United States)

    Yin, Li; Wang, Xiaocha; Mi, Wenbo

    2018-01-01

    Perpendicular magnetic tunnel junctions (MTJs) have attracted increasing attention owing to the low energy consumption and wide application prospects. Herewith, against Julliere's formula, an inverse tunnel magnetoresistance (TMR) appears in tetragonal Fe4N/BiFeO3/Fe4N perpendicular MTJs, which is attributed to the binding between the interface resonant tunneling state and central (bordered) hot spots. Especially, antiferromagnetic BiFeO3 shows an extra spin-polarized resonant state in the barrier, which provides a magnetic-barrier factor to affect the tunneling transport in MTJs. Meanwhile, due to the spin-polarized transport in Fe4N/BiFeO3/Fe4N MTJs, the sign of TMR can be tuned by the applied bias. The tunable TMR and resonant magnetic barrier effect pave the way for clarifying the tunneling transport in other junctions and spintronic devices.

  7. Weak-field precession of nano-pillar spin-torque oscillators using MgO-based perpendicular magnetic tunnel junction

    Science.gov (United States)

    Zhang, Changxin; Fang, Bin; Wang, Bochong; Zeng, Zhongming

    2018-04-01

    This paper presents a steady auto-oscillation in a spin-torque oscillator using MgO-based magnetic tunnel junction (MTJ) with a perpendicular polarizer and a perpendicular free layer. As the injected d.c. current varied from 1.5 to 3.0 mA under a weak magnetic field of 290 Oe, the oscillation frequency decreased from 1.85 to 1.3 GHz, and the integrated power increased from 0.1 to 74 pW. A narrow linewidth down to 7 MHz corresponding to a high Q factor of 220 was achieved at 2.7 mA, which was ascribed to the spatial coherent procession of the free layer magnetization. Moreover, the oscillation frequency was quite sensitive to the applied field, about 3.07 MHz/Oe, indicating the potential applications as a weak magnetic field detector. These results suggested that the MgO-based MTJ with perpendicular magnetic easy axis could be helpful for developing spin-torque oscillators with narrow-linewidth and high sensitive.

  8. Magnetic separation technique for environmental water purification by strong magnetic field generator loading HTS bulk magnets

    International Nuclear Information System (INIS)

    Oka, T.; Tanaka, K.; Kimura, T.; Mimura, D.; Fukui, S.; Ogawa, J.; Sato, T.; Ooizumi, M.; Yokoyama, K.; Yamaguchi, M.

    2010-01-01

    The magnetic separation technique in combination with high temperature superconducting bulk magnets has been investigated to purify the ground water which has been used in the coolant system for the incinerator furnace to cool the burning gas. The experiment has been operated by means of the newly-built alternating channel type magnetic separating device. The separation ratios of ferromagnetic flocks including fine magnetite powder have been estimated by means of the high gradient magnetic separation method with small iron balls filled in the water channels. As the magnetic force acting on the magnetic particle is given by the product of a magnetization of the material and a gradient of magnetic field, and as the ferromagnetic stainless steel balls yield the steep gradient of magnetic field around them in a strong magnetic field, the system has exhibited a quite excellent performance with respect to the separation ratios. The separation ratios of the flocks which contain the magnetite powder with the values more than 50 ppm have remained over 80% for under the flow rates less than 5 L/min.

  9. Magnetic separation technique for environmental water purification by strong magnetic field generator loading HTS bulk magnets

    Science.gov (United States)

    Oka, T.; Tanaka, K.; Kimura, T.; Mimura, D.; Fukui, S.; Ogawa, J.; Sato, T.; Ooizumi, M.; Yokoyama, K.; Yamaguchi, M.

    2010-11-01

    The magnetic separation technique in combination with high temperature superconducting bulk magnets has been investigated to purify the ground water which has been used in the coolant system for the incinerator furnace to cool the burning gas. The experiment has been operated by means of the newly-built alternating channel type magnetic separating device. The separation ratios of ferromagnetic flocks including fine magnetite powder have been estimated by means of the high gradient magnetic separation method with small iron balls filled in the water channels. As the magnetic force acting on the magnetic particle is given by the product of a magnetization of the material and a gradient of magnetic field, and as the ferromagnetic stainless steel balls yield the steep gradient of magnetic field around them in a strong magnetic field, the system has exhibited a quite excellent performance with respect to the separation ratios. The separation ratios of the flocks which contain the magnetite powder with the values more than 50 ppm have remained over 80% for under the flow rates less than 5 L/min.

  10. Ideal magnetohydrodynamic simulations of low beta compact toroid injection into a hot strongly magnetized plasma

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Wei [Los Alamos National Laboratory; Hsu, Scott [Los Alamos National Laboratory; Li, Hui [Los Alamos National Laboratory

    2009-01-01

    We present results from three-dimensional ideal magnetohydrodynamic simulations of low {beta} compact toroid (CT) injection into a hot strongly magnetized plasma, with the aim of providing insight into CT fueling of a tokamak with parameters relevant for ITER (International Thermonuclear Experimental Reactor). A regime is identified in terms of CT injection speed and CT-to-background magnetic field ratio that appears promising for precise core fueling. Shock-dominated regimes, which are probably unfavorable for tokamak fueling, are also identified. The CT penetration depth is proportional to the CT injection speed and density. The entire CT evolution can be divided into three stages: (1) initial penetration, (2) compression in the direction of propagation and reconnection, and (3) coming to rest and spreading in the direction perpendicular to injection. Tilting of the CT is not observed due to the fast transit time of the CT across the background plasma.

  11. 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}.

  12. Nonlinear waves and solitons propagating perpendicular to the magnetic field in bi-ion plasma with finite plasma pressure

    Directory of Open Access Journals (Sweden)

    E. M. Dubinin

    2002-01-01

    Full Text Available We investigate the nature of nonlinear waves propagating transverse to the magnetic field in a bi-ion plasma including plasma pressure. By using the conservation laws derived from the multi-ion fluid equations the system may be described by a single order differential equation whose properties control the structure of the flow and the magnetic field. Compressive solitons exist in specific ranges of the characteristic Mach numbers. Various features of solitons differ in different existence "windows". For example, there are solitons that contain a strong proton rarefaction core embedded in the main compressional structure. Compressive solitons are found in a wide range of flow parameters. Finite ion pressure introduces critical Mach numbers. In contrast to a plasma consisting only of protons and electrons these singular points are reached where a specific combination of ion and electron speeds lies on particular locii, in multi-parameter space, which corresponds to the generalized "sonic point" of the compound system.

  13. Ion Motion in a Plasma Interacting with Strong Magnetic Fields

    International Nuclear Information System (INIS)

    Weingarten, A.; Grabowski, C.; Chakrabarti, N.; Maron, Y.; Fruchtmant, A.

    1999-01-01

    The interaction of a plasma with strong magnetic fields takes place in many laboratory experiments and astrophysical plasmas. Applying a strong magnetic field to the plasma may result in plasma displacement, magnetization, or the formation of instabilities. Important phenomena in plasma, such as the energy transport and the momentum balance, take a different form in each case. We study this interaction in a plasma that carries a short-duration (80-ns) current pulse, generating a magnetic field of up to 17 kG. The evolution of the magnetic field, plasma density, ion velocities, and electric fields are determined before and during the current pulse. The dependence of the plasma limiting current on the plasma density and composition are studied and compared to theoretical models based on the different phenomena. When the plasma collisionality is low, three typical velocities should be taken into consideration: the proton and heavier-ion Alfven velocities (v A p and v A h , respectively) and the EMHD magnetic-field penetration velocity into the plasma (v EMHD ). If both Alfven velocities are larger than v EMHD the plasma is pushed ahead of the magnetic piston and the magnetic field energy is dissipated into ion kinetic energy. If v EMHD is the largest of three velocities, the plasma become magnetized and the ions acquire a small axial momentum only. Different ion species may drift in different directions along the current lines. In this case, the magnetic field energy is probably dissipated into electron thermal energy. When vs > V EMHD > vi, as in the case of one of our experiments, ion mass separation occurs. The protons are pushed ahead of the piston while the heavier-ions become magnetized. Since the plasma electrons are unmagnetized they cannot cross the piston, and the heavy ions are probably charge-neutralized by electrons originating from the cathode that are 'born' magnetized

  14. Orientation of glutaraldehyde-fixed erythrocytes in strong static magnetic fields.

    Science.gov (United States)

    Higashi, T; Sagawa, S; Ashida, N; Takeuchi, T

    1996-01-01

    In a uniform static magnetic field up to 8 Telsa, glutaraldehyde-fixed erythrocytes showed an orientation in which their disk plane was perpendicular to the magnetic field. The paramagnetism of membrane-bound hemoglobin was through to contribute significantly to this orientation. The observation of magnetic orientation is directed toward understanding the fundamental microstructural aspects of the erythrocyte.

  15. Perpendicular magnetic tunnel junction with tunneling magnetoresistance ratio of 64% using MgO (100) barrier layer prepared at room temperature

    International Nuclear Information System (INIS)

    Ohmori, Hideto; Hatori, Tomoya; Nakagawa, Shigeki

    2008-01-01

    MgO (100) textured films can be prepared by reactive facing targets sputtering at room temperature without postdeposition annealing process when they were deposited on (100) oriented Fe buffer layers. This method allows fabrication of perpendicular magnetic tunnel junction (p-MTJ) with MgO (100) tunneling barrier layer and rare-earth transition metal (RE-TM) alloy thin films as perpendicularly magnetized free and pinned layers. The 3-nm-thick MgO tunneling barrier layer in p-MTJ multilayer prepared on glass substrate revealed (100) crystalline orientation. Extraordinary Hall effect measurement clarified that the perpendicular magnetic components of 3-nm-thick Fe buffer layers on the two ends of MgO tunneling barrier layer were increased by exchange coupling with RE-TM alloy layers. The RA of 35 kΩ μm 2 and tunneling magnetoresistance ratio of 64% was observed in the multilayered p-MTJ element by current-in-plane-tunneling

  16. Strong uniaxial magnetic anisotropy in Co films on highly ordered grating-like nanopatterned Ge surfaces

    Science.gov (United States)

    Alam Mollick, Safiul; Singh, Ranveer; Kumar, Mohit; Bhattacharyya, Satyaranjan; Som, Tapobrata

    2018-03-01

    We present a systematic investigation on uniaxial magnetic anisotropy (UMA) in Co thin films induced by high aspect ratio nanopatterned anisotropic substrates. Self-organized long grating-like nanostructures, with extreme regularities, are fabricated on Ge surfaces using Au-ion implantation at room temperature. Subsequently deposition of Co films are carried out on the same at two different angles. Magneto-optical Kerr effect measurements show strong UMA in Co films grown on ion-patterned Ge substrates, fabricated under different ion fluences, along and perpendicular to the direction of the patterns (long grating-like nanostructures). Magnetic force microscopy measurements under different externally applied magnetic fields reveal an easy domain wall motion when the field is applied along the grating-like nanostructures. On the other hand, high amplitude grating-like nanostructures hinder the spin rotation when the field is applied along the hard axis. The present study will be useful for magnetic recording media and ultra-small magnetic field sensors.

  17. Vortex-lattice states at strong magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Akera, H.; MacDonald, A.H.; Girvin, S.M. (Department of Physics, Indiana University, Bloomington, Indiana (USA)); Norman, M.R. (Materials Science Division, Argonne National Laboratory, Argonne, Illinois (USA))

    1991-10-21

    At strong magnetic fields, Landau quantization invalidates the semiclassical approximations which underly the Ginzburg-Landau (GL) theory of the mixed states of type-II superconductors. We have solved the {ital microscopic} mean-field equations for the case of a two-dimensional electron system in the strong magnetic-field limit. For delta-function attractive interactions there exist {ital n}+1 pairing channels in the {ital n}th Landau level. For {ital n}{gt}0, two channels share the maximum {ital T}{sub {ital c}}, and the order parameter differs markedly from expectations based on GL theory.

  18. Electrical-field and spin-transfer torque effects in CoFeB/MgO-based perpendicular magnetic tunnel junction

    Energy Technology Data Exchange (ETDEWEB)

    Yoshida, Chikako, E-mail: cyoshida@jp.fujitsu.com; Noshiro, Hideyuki; Yamazaki, Yuichi; Sugii, Toshihiro [Fujitsu limited, 10-1 Morinosato-Wakamiya, Atsugi, Kanagawa, 243-0197 (Japan); Furuya, Atsushi; Ataka, Tadashi; Tanaka, Tomohiro; Uehara, Yuji [Fujitsu limited, 4-1-1 Kamikodanaka, Nakahara-ku, Kawasaki, Kanagawa, 211-8588 (Japan)

    2016-05-15

    The electric-field (E) dependence of the magnetoresistance (RH) loops for top-pinned perpendicular CoFeB/MgO-based magnetic tunnel junctions (MTJs) in the presence of a spin-transfer torque (STT)-current was measured. The E effects were distinguished from the STT-current effects using a micromagnetic simulation. The coercive field (H{sub c}) decreased and the RH loop shifted as both the positive and negative bias E increased owing to the STT current. Furthermore, E-assisted switching for an MTJ with a diameter of 20 nm, which exhibited a nearly coherent magnetization reversal, was demonstrated using micromagnetic simulation.

  19. Strain relaxation and enhanced perpendicular magnetic anisotropy in BiFeO3:CoFe2O4 vertically aligned nanocomposite thin films

    Science.gov (United States)

    Zhang, Wenrui; Jian, Jie; Chen, Aiping; Jiao, Liang; Khatkhatay, Fauzia; Li, Leigang; Chu, Frank; Jia, Quanxi; MacManus-Driscoll, Judith L.; Wang, Haiyan

    2014-02-01

    Self-assembled BiFeO3:CoFe2O4 (BFO:CFO) vertically aligned nanocomposite thin films have been fabricated on SrTiO3 (001) substrates using pulsed laser deposition. The strain relaxation mechanism between BFO and CFO with a large lattice mismatch has been studied by X-ray diffraction and transmission electron microscopy. The as-prepared nanocomposite films exhibit enhanced perpendicular magnetic anisotropy as the BFO composition increases. Different anisotropy sources have been investigated, suggesting that spin-flop coupling between antiferromagnetic BFO and ferrimagnetic CFO plays a dominant role in enhancing the uniaxial magnetic anisotropy.

  20. Perpendicular magnetic tunnel junctions with a synthetic storage or reference layer: A new route towards Pt- and Pd-free junctions

    Science.gov (United States)

    Cuchet, Léa; Rodmacq, Bernard; Auffret, Stéphane; Sousa, Ricardo C.; Prejbeanu, Ioan L.; Dieny, Bernard

    2016-02-01

    We report here the development of Pt and Pd-free perpendicular magnetic tunnel junctions (p-MTJ) for STT-MRAM applications. We start by studying a p-MTJ consisting of a bottom synthetic Co/Pt reference layer and a synthetic FeCoB/Ru/FeCoB storage layer covered with an MgO layer. We first investigate the evolution of RKKY coupling with Ru spacer thickness in such a storage layer. The coupling becomes antiferromagnetic above 0.5 nm and its strength decreases monotonously with increasing Ru thickness. This contrasts with the behavior of Co-based systems for which a maximum in interlayer coupling is generally observed around 0.8 nm. A thin Ta insertion below the Ru spacer considerably decreases the coupling energy, without basically changing its variation with Ru thickness. After optimization of the non-magnetic and magnetic layer thicknesses, it appears that such a FeCoB/Ru/FeCoB synthetic storage layer sandwiched between MgO barriers can be made stable enough to actually be used as hard reference layer in single or double magnetic tunnel junctions, the storage layer being now a single soft FeCoB layer. Finally, we realize Pt- or Pd-free robust perpendicular magnetic tunnel junctions, still keeping the advantage of a synthetic reference layer in terms of reduction of stray fields at small pillar sizes.

  1. A soft magnetic underlayer with negative uniaxial magnetocrystalline anisotropy for suppression of spike noise and wide adjacent track erasure in perpendicular recording media

    Science.gov (United States)

    Hashimoto, Atsushi; Saito, Shin; Takahashi, Migaku

    2006-04-01

    The suppression of spike noise and wide adjacent track erasure (WATE) are important technical issues in the development of a perpendicular recording medium (PRM). As a solution to both of these problems, this paper presents a type of soft magnetic underlayer (SUL) with negative uniaxial perpendicular magnetic anisotropy. The magnetic anisotropy is achieved by employing a material with negative uniaxial magnetocrystalline anisotropy (Kugrain). WATE is suppressed in the SUL by realizing wide distribution of magnetic flux below the edge of the return yoke, while spike noise is eliminated by ensuring the formation of a Néel wall instead of a Bloch wall in SUL domains. CoIr with the disordered hcp structure is selected as a negative Kugrain material, and c-plane-oriented CoIr films with various Ir contents are prepared for experimental evaluation. Among the films tested, the CoIr film with 22 at. % Ir is found to provide the minimum Kugrain value of -6×106 ergs/cm3. Under a field applied parallel to the film plane, this film exhibits soft magnetic properties, attributable to the high crystallographic symmetry of the c-plane sheet texture. A PRM fabricated using the CoIr SUL is confirmed to display substantially lower spike noise and WATE compared to conventional structures.

  2. Dependency of anti-ferro-magnetic coupling strength on Ru spacer thickness of [Co/Pd]{sub n}-synthetic-anti-ferro-magnetic layer in perpendicular magnetic-tunnel-junctions fabricated on 12-inch TiN electrode wafer

    Energy Technology Data Exchange (ETDEWEB)

    Chae, Kyo-Suk [MRAM Center, Department of Electronics, Hanyang University, Seoul 133-791 (Korea, Republic of); Samsung Electronics Co., Ltd., San #16 Banwol-dong, Hwasung-City, Gyeonggi-Do 445-701 (Korea, Republic of); Shim, Tae-Hun; Park, Jea-Gun, E-mail: parkjgL@hanyang.ac.kr [MRAM Center, Department of Electronics, Hanyang University, Seoul 133-791 (Korea, Republic of)

    2014-07-21

    We investigated the Ru spacer-thickness effect on the anti-ferro-magnetic coupling strength (J{sub ex}) of a [Co/Pd]{sub n}-synthetic-anti-ferro-magnetic layer fabricated with Co{sub 2}Fe{sub 6}B{sub 2}/MgO based perpendicular-magnetic-tunneling-junction spin-valves on 12-in. TiN electrode wafers. J{sub ex} peaked at a certain Ru spacer-thickness: specifically, a J{sub ex} of 0.78 erg/cm{sup 2} at 0.6 nm, satisfying the J{sub ex} criteria for realizing the mass production of terra-bit-level perpendicular-spin-transfer-torque magnetic-random-access-memory. Otherwise, J{sub ex} rapidly degraded when the Ru spacer-thickness was less than or higher than 0.6 nm. As a result, the allowable Ru thickness variation should be controlled less than 0.12 nm to satisfy the J{sub ex} criteria. However, the Ru spacer-thickness did not influence the tunneling-magneto-resistance (TMR) and resistance-area (RA) of the perpendicular-magnetic-tunneling-junction (p-MTJ) spin-valves since the Ru spacer in the synthetic-anti-ferro-magnetic layer mainly affects the anti-ferro-magnetic coupling efficiency rather than the crystalline linearity of the Co{sub 2}Fe{sub 6}B{sub 2} free layer/MgO tunneling barrier/Co{sub 2}Fe{sub 6}B{sub 2} pinned layer, although Co{sub 2}Fe{sub 6}B{sub 2}/MgO based p-MTJ spin-valves ex-situ annealed at 275 °C achieved a TMR of ∼70% at a RA of ∼20 Ω μm{sup 2}.

  3. Confinining properties of QCD in strong magnetic backgrounds

    Directory of Open Access Journals (Sweden)

    Bonati Claudio

    2017-01-01

    Full Text Available Strong magnetic backgrounds are known to modify QCD properties at a nonperturbative level. We discuss recent lattice results, obtained for Nf = 2 + 1 QCD with physical quark masses, concerning in particular the modifications and the anisotropies induced at the level of the static quark-antiquark potential, both at zero and finite temperature.

  4. Theory of Spin Waves in Strongly Anisotropic Magnets

    DEFF Research Database (Denmark)

    Lindgård, Per-Anker; Cooke, J. F.

    1976-01-01

    A new infinite-order perturbation approach to the theory of spin waves in strongly anisotropic magnets is introduced. The system is transformed into one with effective two-ion anisotropy and considerably reduced ground-state corrections. A general expression for the spin-wave energy, valid to any...

  5. Resonances of the helium atom in a strong magnetic field

    DEFF Research Database (Denmark)

    Lühr, Armin Christian; Al-Hujaj, Omar-Alexander; Schmelcher, Peter

    2007-01-01

    We present an investigation of the resonances of a doubly excited helium atom in a strong magnetic field covering the regime B=0–100  a.u. A full-interaction approach which is based on an anisotropic Gaussian basis set of one-particle functions being nonlinearly optimized for each field strength...

  6. Quantifying data retention of perpendicular spin-transfer-torque magnetic random access memory chips using an effective thermal stability factor method

    Energy Technology Data Exchange (ETDEWEB)

    Thomas, Luc, E-mail: luc.thomas@headway.com; Jan, Guenole; Le, Son; Wang, Po-Kang [TDK-Headway Technologies, Inc., 463 S. Milpitas Boulevard, Milpitas, California 95035 (United States)

    2015-04-20

    The thermal stability of perpendicular Spin-Transfer-Torque Magnetic Random Access Memory (STT-MRAM) devices is investigated at chip level. Experimental data are analyzed in the framework of the Néel-Brown model including distributions of the thermal stability factor Δ. We show that in the low error rate regime important for applications, the effect of distributions of Δ can be described by a single quantity, the effective thermal stability factor Δ{sub eff}, which encompasses both the median and the standard deviation of the distributions. Data retention of memory chips can be assessed accurately by measuring Δ{sub eff} as a function of device diameter and temperature. We apply this method to show that 54 nm devices based on our perpendicular STT-MRAM design meet our 10 year data retention target up to 120 °C.

  7. Perpendicular-anisotropy CoFeB-MgO magnetic tunnel junctions with a MgO/CoFeB/Ta/CoFeB/MgO recording structure

    Science.gov (United States)

    Sato, H.; Yamanouchi, M.; Ikeda, S.; Fukami, S.; Matsukura, F.; Ohno, H.

    2012-07-01

    We investigated perpendicular CoFeB-MgO magnetic tunnel junctions (MTJs) with a recording structure consisting of two CoFeB-MgO interfaces, MgO/CoFeB (1.6 nm)/Ta (0.4 nm)/CoFeB (1.0 nm)/MgO. Thermal stability factor of MTJ with the structure having junction size of 70 nmφ was increased by a factor of 1.9 from the highest value of perpendicular MTJs with single CoFeB-MgO interface having the same device structure. On the other hand, intrinsic critical current for spin transfer torque switching of the double- and single-interface MTJs was comparable.

  8. Observation of strong magnetic effects in visible-infrared sum frequency generation from magnetic structures

    NARCIS (Netherlands)

    Kirilyuk, A.; Knippels, G.M.H.; van der Meer, A. F. G.; Renard, S.; Rasing, T.; Heskamp, I. R.; Lodder, J. C.

    2000-01-01

    We have observed very strong magnetization-induced changes of the infrared-visible sum-frequency generation (SFG) intensity from thin magnetic films using a free electron laser as a tunable infrared source. With the help of a magnetic grating a clear resonance is observed due to the excitation of

  9. Macrospin modeling of sub-ns pulse switching of perpendicularly magnetized free layer via spin-orbit torques for cryogenic memory applications

    Energy Technology Data Exchange (ETDEWEB)

    Park, Junbo; Rowlands, G. E.; Lee, O. J.; Buhrman, R. A. [Cornell University, Ithaca, New York 14853 (United States); Ralph, D. C. [Cornell University, Ithaca, New York 14853 (United States); Kavli Institute at Cornell, Ithaca, New York 14853 (United States)

    2014-09-08

    We model, using the macrospin approximation, the magnetic reversal of a perpendicularly magnetized nanostructured free layer formed on a normal, heavy-metal nanostrip, subjected to spin-orbit torques (SOTs) generated by short (≤0.5 ns) current pulses applied to the nanostrip, to examine the potential for SOT-based fast, efficient cryogenic memory. Due to thermal fluctuations, if solely an anti-damping torque is applied, then, for a device with sufficiently low anisotropy (H{sub anis}{sup 0} ∼ 1 kOe) suitable for application in cryogenic memory, a high magnetic damping parameter (α∼0.1−0.2) is required for reliable switching over a significant variation of pulse current. The additional presence of a substantial field-like torque improves switching reliability even for low damping (α≤0.03).

  10. Neutrino-electron processes in a strongly magnetized thermal plasma

    CERN Document Server

    Hardy, S J; Hardy, Stephen J.; Thoma, Markus H.

    2001-01-01

    We present a new method of calculating the rate of neutrino-electron interactions in a strong magnetic field based on finite temperature field theory. Using this method, in which the effect of the magnetic field on the electron states is taken into account exactly, we calculate the rates of all of the lowest order neutrino-electron interactions in a plasma. As an example of the use of this technique, we explicitly calculate the rate at which neutrinos and antineutrinos annihilate in a highly magnetized plasma, and compare that to the rate in an unmagnetized plasma. The most important channel for energy deposition is the gyromagnetic absorption of a neutrino-antineutrino pair on an electron or positron in the plasma ($\

  11. Nonlinear Alfvén waves, discontinuities, proton perpendicular acceleration, and magnetic holes/decreases in interplanetary space and the magnetosphere: intermediate shocks?

    Directory of Open Access Journals (Sweden)

    B. T. Tsurutani

    2005-01-01

    Full Text Available Alfvén waves, discontinuities, proton perpendicular acceleration and magnetic decreases (MDs in interplanetary space are shown to be interrelated. Discontinuities are the phase-steepened edges of Alfvén waves. Magnetic decreases are caused by a diamagnetic effect from perpendicularly accelerated (to the magnetic field protons. The ion acceleration is associated with the dissipation of phase-steepened Alfvén waves, presumably through the Ponderomotive Force. Proton perpendicular heating, through instabilities, lead to the generation of both proton cyclotron waves and mirror mode structures. Electromagnetic and electrostatic electron waves are detected as well. The Alfvén waves are thus found to be both dispersive and dissipative, conditions indicting that they may be intermediate shocks. The resultant 'turbulence' created by the Alfvén wave dissipation is quite complex. There are both propagating (waves and nonpropagating (mirror mode structures and MDs byproducts. Arguments are presented to indicate that similar processes associated with Alfvén waves are occurring in the magnetosphere. In the magnetosphere, the 'turbulence' is even further complicated by the damping of obliquely propagating proton cyclotron waves and the formation of electron holes, a form of solitary waves. Interplanetary Alfvén waves are shown to rapidly phase-steepen at a distance of 1AU from the Sun. A steepening rate of ~35 times per wavelength is indicated by Cluster-ACE measurements. Interplanetary (reverse shock compression of Alfvén waves is noted to cause the rapid formation of MDs on the sunward side of corotating interaction regions (CIRs. Although much has been learned about the Alfvén wave phase-steepening processfrom space plasma observations, many facets are still not understood. Several of these topics are discussed for the interested researcher. Computer simulations and theoretical developments will be particularly useful in making further progress in

  12. Effects of intermediate layers on magnetic properties and read/write performance in CoCrPt perpendicular recording media with an FeHfN soft magnetic underlayer

    International Nuclear Information System (INIS)

    Hong, D.H.; Shin, J.N.; Lee, T.D.; Hong, S.Y.; Lee, H.J.

    2003-01-01

    In this study, the effects of CoCrPtTa and CoCrPtB magnetic intermediate layers (ILs) on the magnetic properties and read/write performance of CoCrPt/soft magnetic layer perpendicular recording media were investigated. Even though the perpendicular coercivity of the media with these ILs was reduced by 500 Oe, these media still showed a low exchange slope of 1.4 and a large negative nucleation field of about -1000 Oe. Additionally, the reduced grain size of the media with these IL was observed by transmission electron microscopy. From the read/write test, these media with ILs showed improved performance of 3-5 dB higher signal-to-noise ratio and overwrite ratio (OW) compared to the media without ILs. These enhancements could be attributed to the reduction of grain size of the magnetic layer and weakening of the intergranular interaction between grains by insertion of the IL

  13. Magnetic properties of metallic impurities with strongly correlated electrons

    Czech Academy of Sciences Publication Activity Database

    Janiš, Václav; Ringel, Matouš

    2009-01-01

    Roč. 115, č. 1 (2009), s. 30-35 ISSN 0587-4246 R&D Projects: GA ČR GA202/07/0644 Institutional research plan: CEZ:AV0Z10100520 Keywords : And erson impurity * strong electron correlations * spin-polarized solution * three-channel parquet equations * magnetic field Subject RIV: BE - Theoretical Physics Impact factor: 0.433, year: 2009 http://przyrbwn.icm.edu.pl/APP/ABSTR/115/a115-1-5.html

  14. Semicalssical quantization of interacting anyons in a strong magnetic field

    International Nuclear Information System (INIS)

    Levit, S.; Sivan, N.

    1992-01-01

    We represent a semiclassical theory of charged interacting anyons in strong magnetic fields. We apply this theory to a number of few anyons systems including two interacting anyons in the presence of an impurity and three interacting anyons. We discuss the dependence of their energy levels on the statistical parameter and find regions in which this dependence follows very different patterns. The semiclassical arguments allow to correlate these patterns with the change in the character of the classical motion of the system. (author)

  15. Strongly Coupled Magnetic and Electronic Transitions in Multivalent Strontium Cobaltites.

    Science.gov (United States)

    Lee, J H; Choi, Woo Seok; Jeen, H; Lee, H-J; Seo, J H; Nam, J; Yeom, M S; Lee, H N

    2017-11-22

    The topotactic phase transition in SrCoO x (x = 2.5-3.0) makes it possible to reversibly transit between the two distinct phases, i.e. the brownmillerite SrCoO 2.5 that is a room-temperature antiferromagnetic insulator (AFM-I) and the perovskite SrCoO 3 that is a ferromagnetic metal (FM-M), owing to their multiple valence states. For the intermediate x values, the two distinct phases are expected to strongly compete with each other. With oxidation of SrCoO 2.5 , however, it has been conjectured that the magnetic transition is decoupled to the electronic phase transition, i.e., the AFM-to-FM transition occurs before the insulator-to-metal transition (IMT), which is still controversial. Here, we bridge the gap between the two-phase transitions by density-functional theory calculations combined with optical spectroscopy. We confirm that the IMT actually occurs concomitantly with the FM transition near the oxygen content x = 2.75. Strong charge-spin coupling drives the concurrent IMT and AFM-to-FM transition, which fosters the near room-T magnetic transition characteristic. Ultimately, our study demonstrates that SrCoO x is an intriguingly rare candidate for inducing coupled magnetic and electronic transition via fast and reversible redox reactions.

  16. Electrical manipulation of perpendicular magnetic anisotropy in a Pt/Co/Pt trilayer grown on PMN-PT(0 1 1) substrate

    Science.gov (United States)

    Xiao, X.; Sun, L.; Luo, Y. M.; Zhang, D.; Liang, J. H.; Wu, Y. Z.

    2018-03-01

    Strain-induced modulation of perpendicular magnetic anisotropy (PMA) is demonstrated in a wedge-shaped Pt/Co/Pt sandwich grown on PMN-PT(0 1 1) substrate using magnetic torque measurements. An anisotropic in-plane strain is generated by applying an electric field across the PMN-PT substrate and transferred to the ferromagnetic Pt/Co/Pt sandwich. The critical thickness of spin reorientation transition is tuned to the thicker region of the Pt/Co/Pt wedge. The strain-induced change of PMA is quantitatively extracted. Only the first order anisotropy term is tuned by the electric field, while the second order anisotropy term has negligible electric field-dependence. Both of the volume and interface contributions of the first order anisotropy term show tunable electric field modulation. These results may benefit the understanding of strain-mediated magnetoelectric coupling effect in artificial multiferroic structures containing a ferromagnetic layer with PMA.

  17. Helium atoms and molecules in strong magnetic fields

    Science.gov (United States)

    Mori, K.

    Recent theoretical studies have shown that the neutron star surface may be composed of helium or heavier elements as hydrogen may be quickly depleted by diffuse nuclear burning Chang Bildsten However while Hydrogen atmospheres have been studied in great details atomic data for helium is available only for He ion Pavlov Bezchastnov 2005 We performed Hartree-Fock type calculation for Helium atom and molecules and computed their binding ionization and dissociation energies in strong magnetic fields B sim10 12 -- 10 15 G We will present ionization balance of Helium atmospheres at typical magnetic field strengths and temperatures to radio-quiet neutron stars and AXPs We will also discuss several implications of helium atmosphere to X-ray data of isolated neutron stars focusing on the detected spectral features

  18. Magnetic Fields in the Massive Dense Cores of the DR21 Filament: Weakly Magnetized Cores in a Strongly Magnetized Filament

    Energy Technology Data Exchange (ETDEWEB)

    Ching, Tao-Chung; Lai, Shih-Ping [Institute of Astronomy and Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Zhang, Qizhou; Girart, Josep M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge MA 02138 (United States); Qiu, Keping [School of Astronomy and Space Science, Nanjing University, 163 Xianlin Avenue, Nanjing 210023 (China); Liu, Hauyu B., E-mail: chingtaochung@gmail.com [European Southern Observatory (ESO), Karl-Schwarzschild-Str. 2, D-85748 Garching (Germany)

    2017-04-01

    We present Submillimeter Array 880 μ m dust polarization observations of six massive dense cores in the DR21 filament. The dust polarization shows complex magnetic field structures in the massive dense cores with sizes of 0.1 pc, in contrast to the ordered magnetic fields of the parsec-scale filament. The major axes of the massive dense cores appear to be aligned either parallel or perpendicular to the magnetic fields of the filament, indicating that the parsec-scale magnetic fields play an important role in the formation of the massive dense cores. However, the correlation between the major axes of the cores and the magnetic fields of the cores is less significant, suggesting that during the core formation, the magnetic fields below 0.1 pc scales become less important than the magnetic fields above 0.1 pc scales in supporting a core against gravity. Our analysis of the angular dispersion functions of the observed polarization segments yields a plane-of-sky magnetic field strength of 0.4–1.7 mG for the massive dense cores. We estimate the kinematic, magnetic, and gravitational virial parameters of the filament and the cores. The virial parameters show that the gravitational energy in the filament dominates magnetic and kinematic energies, while the kinematic energy dominates in the cores. Our work suggests that although magnetic fields may play an important role in a collapsing filament, the kinematics arising from gravitational collapse must become more important than magnetic fields during the evolution from filaments to massive dense cores.

  19. Bound states in strongly correlated magnetic and electronic systems

    International Nuclear Information System (INIS)

    Trebst, S.

    2002-02-01

    A novel strong coupling expansion method to calculate two-particle spectra of quantum lattice models is developed. The technique can be used to study bosonic and fermionic models and in principle it can be applied to systems in any dimension. A number of strongly correlated magnetic and electronic systems are examined including the two-leg spin-half Heisenberg ladder, the dimerized Heisenberg chain with a frustrating next-nearest neighbor interaction, coupled Heisenberg ladders, and the one-dimensional Kondo lattice model. In the various models distinct bound states are found below the two-particle continuum. Quantitative calculations of the dispersion, coherence length and binding energy of these bound states are used to describe spectroscopic experiments on (Ca,La) 14 Cu 24 O 41 and NaV 2 O 5 . (orig.)

  20. Role of substrate bias on the magnetic properties and microstructure of CoCrPt:SiO2 perpendicular recording media

    International Nuclear Information System (INIS)

    Piramanayagam, S. N.; Mah, C. S.; Ong, C. Y.; Shi, J. Z.; Dumaya, Jo Alvin; Onoue, T.; Ishibashi, S.

    2007-01-01

    The role of substrate bias during the sputter deposition of various layers of double-layered CoCrPt-SiO 2 perpendicular recording media has been investigated in order to understand the physical mechanisms behind the various effects observed. Perpendicular recording media with dual Ru intermediate layers were investigated using several magnetic and microstructural characterization techniques. It was observed that, in general, the application of a bias voltage during the deposition of the seedlayer (Ta) and the first intermediate layer (Ru) is helpful in reducing the c-axis dispersion of the recording layer. For the other layers, application of bias voltage leads to deterioration in the magnetic properties. It was also observed that the application of a bias voltage during the deposition of the first intermediate layer (especially Ru) may not enhance the preferred growth of Ru hexagonal-close-packed (00.2) planes parallel to the disk surface, as predicted before. However, the bias voltage on the Ru layer still reduces the c-axis dispersion of the magnetic layer. From the omega-offset x-ray diffraction investigations, it is estimated that the lattice parameter ''a'' of the Ru layer is reduced slightly with bias voltage, which could probably lead to a reduction in the lattice mismatch between the Ru layer and Co-alloy layer. Bias conditions also could lead to improved interface condition. Such an improvement in the lattice matching or interface conditions could probably be the cause of the reduction of c-axis dispersion of the recording layer

  1. Verification of antiferromagnetic exchange coupling at room temperature using polar magneto-optic Kerr effect in thin EuS/Co multilayers with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Goschew, A., E-mail: alexander.goschew@fu-berlin.de; Scott, M.; Fumagalli, P. [Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin (Germany)

    2016-08-08

    We report on magneto-optic Kerr measurements in polar geometry carried out on a series of thin Co/EuS multilayers on suitable Co/Pd-multilayer substrates. Thin Co/EuS multilayers of a few nanometers individual layer thickness usually have their magnetization in plane. Co/Pd multilayers introduce a perpendicular magnetic anisotropy in the Co/EuS layers deposited on top, thus making it possible to measure magneto-optic signals in the polar geometry in remanence in order to study exchange coupling. Magneto-optic Kerr-effect spectra and hysteresis loops were recorded in the visible and ultraviolet photon-energy range at room temperature. The EuS contribution to the magneto-optic signal is extracted at 4.1 eV by combining hysteresis loops measured at different photon energies with polar magneto-optic Kerr-effect spectra recorded in remanence and in an applied magnetic field of 2.2 T. The extracted EuS signal shows clear signs of antiferromagnetic coupling of the Eu magnetic moments to the Co layers. This implies that the ordering temperature of at least a fraction of the EuS layers is above room temperature proving that magneto-optic Kerr-effect spectroscopy can be used here as a quasi-element-specific method.

  2. Dependency of Tunneling-Magnetoresistance Ratio on Nanoscale Spacer Thickness and Material for Double MgO Based Perpendicular-Magnetic-Tunneling-Junction

    Science.gov (United States)

    Lee, Du-Yeong; Hong, Song-Hwa; Lee, Seung-Eun; Park, Jea-Gun

    2016-12-01

    It was found that in double MgO based perpendicular magnetic tunneling junction spin-valves ex-situ annealed at 400 °C, the tunneling magnetoresistance ratio was extremely sensitive to the material and thickness of the nanoscale spacer: it peaked at a specific thickness (0.40~0.53 nm), and the TMR ratio for W spacers (~134%) was higher than that for Ta spacers (~98%). This dependency on the spacer material and thickness was associated with the (100) body-centered-cubic crystallinity of the MgO layers: the strain enhanced diffusion length in the MgO layers of W atoms (~1.40 nm) was much shorter than that of Ta atoms (~2.85 nm) and the shorter diffusion length led to the MgO layers having better (100) body-centered-cubic crystallinity.

  3. Quark-gluon plasma in strong magnetic fields

    International Nuclear Information System (INIS)

    Kalaydzhyan, Tigran

    2013-04-01

    One of the fundamental problems in subatomic physics is the determination of properties of matter at extreme temperatures, densities and electromagnetic fields. The modern ultrarelativistic heavy-ion experiments are able to study such states (the quark-gluon plasma) and indicate that the physics at extreme conditions differs drastically from what is known from the conventional observations. Also the theoretical methods developed mostly within the perturbative framework face various conceptual problems and need to be replaced by a nonperturbative approach. In this thesis we study the physics of the strongly-coupled quark-gluon plasma in external magnetic fields as well as general electromagnetic and topological properties of the QCD and QCD-like systems. We develop and apply various nonperturbative techniques, based on e.g. gauge-gravity correspondence, lattice QCD simulations, relativistic hydrodynamics and condensed-matter-inspired models.

  4. 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.

  5. Quark-gluon plasma in strong magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Kalaydzhyan, Tigran

    2013-04-15

    One of the fundamental problems in subatomic physics is the determination of properties of matter at extreme temperatures, densities and electromagnetic fields. The modern ultrarelativistic heavy-ion experiments are able to study such states (the quark-gluon plasma) and indicate that the physics at extreme conditions differs drastically from what is known from the conventional observations. Also the theoretical methods developed mostly within the perturbative framework face various conceptual problems and need to be replaced by a nonperturbative approach. In this thesis we study the physics of the strongly-coupled quark-gluon plasma in external magnetic fields as well as general electromagnetic and topological properties of the QCD and QCD-like systems. We develop and apply various nonperturbative techniques, based on e.g. gauge-gravity correspondence, lattice QCD simulations, relativistic hydrodynamics and condensed-matter-inspired models.

  6. Anomalous electrodynamics of neutral pion matter in strong magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Brauner, Tomáš [Department of Mathematics and Natural Sciences, University of Stavanger,N-4036 Stavanger (Norway); Kadam, Saurabh V. [Indian Institute of Science Education and Research (IISER),Pune 411008 (India)

    2017-03-03

    The ground state of quantum chromodynamics in sufficiently strong external magnetic fields and at moderate baryon chemical potential is a chiral soliton lattice (CSL) of neutral pions https://arxiv.org/abs/1609.05213. We investigate the interplay between the CSL structure and dynamical electromagnetic fields. Our main result is that in presence of the CSL background, the two physical photon polarizations and the neutral pion mix, giving rise to two gapped excitations and one gapless mode with a nonrelativistic dispersion relation. The nature of this mode depends on the direction of its propagation, interpolating between a circularly polarized electromagnetic wave https://www.doi.org/10.1103/PhysRevD.93.085036 and a neutral pion surface wave, which in turn arises from the spontaneously broken translation invariance. Quite remarkably, there is a neutral-pion-like mode that remains gapped even in the chiral limit, in seeming contradiction to the Goldstone theorem. Finally, we have a first look at the effect of thermal fluctuations of the CSL, showing that even the soft nonrelativistic excitation does not lead to the Landau-Peierls instability. However, it leads to an anomalous contribution to pressure that scales with temperature and magnetic field as T{sup 5/2}(B/f{sub π}){sup 3/2}.

  7. High thermal stability in W/MgO/CoFeB/W/CoFeB/W stacks via ultrathin W insertion with perpendicular magnetic anisotropy

    Science.gov (United States)

    Liu, Yi; Yu, Tao; Zhu, Zhengyong; Zhong, Huicai; Khamis, Khamis Masoud; Zhu, Kaigui

    2016-07-01

    The perpendicular magnetic anisotropy (PMA) of a series of top MgO/CoFeB/W stacks were studied. In these stacks, the thickness of CoFeB is limited in a range of 1.1-2.2 nm. It was found that the stack can still maintain PMA in a 1.9 nm thick CoFeB free layer. Besides, we investigated the thermal stability factor ∆ of a spin transfer torque magnetic random access memory (STT-MRAM) by inserting an ultra-thin W film of 0.8 nm between two CoFeB films. The result shows a clear PMA behavior for the samples with CoFeB thickness up to 2.5 nm, and an in-plane magnetic anisotropy (IMA) when the CoFeB is thicker than 2.5 nm. Moreover, the thermal stability factor ∆ of the CoFeB stack with W insertion is about 132 for a 50 nm size STT-MRAM device, which is remarkably improved compared to 112 for a sample without W insertion. Our results represent an alternative way to realize the endurance at high annealing temperature, high-density and high ∆ in STT-MRAM device by ultra-thin W insertion.

  8. Perpendicular Giant Magnetoresistance and Magnetic Properties of Co/Cu Nanowire Arrays Affected by Period Number and Copper Layer Thickness

    Directory of Open Access Journals (Sweden)

    Juan Han

    2016-01-01

    Full Text Available One-dimensional magnetic nanowires have attracted much attention in the last decades due to their unique physical properties and potential applications in magnetic recording and spintronics. In this work, ordered arrays of Co/Cu multilayered nanowires which can be exploited to develop magnetoresistive sensors were successfully prepared using porous anodic alumina (PAA templates. The structure and morphology of the multilayered nanowire arrays were characterized by transmission electron microscopy and scanning electron microscopy. The nanowire arrays are highly ordered and the average diameter is about 50 nm, which is controlled by the pore diameter of the PAA templates. The influences of period number and Cu layer thickness on the magnetic and the giant magnetoresistance (GMR properties were investigated. The coercivity and remanence ratio increase first and then gradually tend to be stable with the increase of period number and the Cu layer thickness, while the GMR ratio increases first and then decreases with the increase of the period number accompanied by an oscillatory behavior of GMR as the Cu layer thickness changes, which are ascribed to the spin dependence electron scattering in the multilayers. The optimum GMR of −13% appears at Co (50 nm/Cu (5 nm with 200 deposition cycles in our experimental conditions.

  9. Perpendicular magnetic anisotropy in Mo/Co2FeAl0.5Si0.5/MgO/Mo multilayers with optimal Mo buffer layer thickness

    Science.gov (United States)

    Saravanan, L.; Raja, M. Manivel; Prabhu, D.; Pandiyarasan, V.; Ikeda, H.; Therese, H. A.

    2018-05-01

    Perpendicular Magnetic Anisotropy (PMA) was realized in as-deposited Mo(10)/Co2FeAl0.5Si0.5(CFAS)(3)/MgO(0.5)/Mo multilayer stacks with large perpendicular magnetic anisotropy energy (Keff). PMA of this multilayer is found to be strongly dependent on the thickness of the individual CFAS (tCFAS), Mo (tMo) and MgO (tMgO) layers and annealing temperatures. The interactions at the Mo/CFAS/MgO interfaces are critical to induce PMA and are tuned by the interfacial oxidation. The major contribution to PMA is due to iron oxide at the CFAS/MgO interface. X-ray diffraction (XRD) and infrared spectroscopic (FT-IR) studies further ascertain this. However, an adequate oxidation of MgO and the formation of (0 2 4) and (0 1 8) planes of α-Fe2O3 at the optimal Mo buffer layer thickness is mainly inducing PMA in Mo/CFAS/MgO/Mo stack. Microstructural changes in the films are observed by atomic force microscopy (AFM). X-ray photoelectron spectroscopy (XPS) demonstrates the oxidation of CFAS/MgO interface and the formation of Fe-O bonds confirming that the real origin of PMA in Mo/CFAS/MgO is due to hybridization of Fe (3dz2) and O (2pz) orbitals and the resulted spin-orbit interaction at their interface. The half-metallic nature CFAS with Mo layer exhibiting PMA can be a potential candidate as p-MTJs electrodes for the new generation spintronic devices.

  10. Exact Landau levels in two-dimensional electron systems with Rashba and Dresselhaus spin-orbit interactions in a perpendicular magnetic field

    International Nuclear Information System (INIS)

    Zhang Degang

    2006-01-01

    We study a two-dimensional electron system in the presence of both Rashba and Dresselhaus spin-orbit interactions in a perpendicular magnetic field. Defining two suitable boson operators and using the unitary transformations we are able to obtain the exact Landau levels in the range of all the parameters. When the strengths of the Rashba and Dresselhaus spin-orbit interactions are equal, a new analytical solution for the vanishing Zeeman energy is found, where the orbital and spin wavefunctions of the electron are separated. It is also shown that in this case the Zeeman and spin-orbit splittings are independent of the Landau level index n. Due to the Zeeman energy, new crossing between the eigenstates vertical bar n, k, s = 1, σ) and vertical bar n + 1, k, s' = -1, σ') is produced at a certain magnetic field for larger Rashba spin-orbit coupling. This degeneracy leads to a resonant spin Hall conductance if it happens at the Fermi level. (letter to the editor)

  11. Anomalous transport phenomena in Fermi liquids with strong magnetic fluctuations

    Energy Technology Data Exchange (ETDEWEB)

    Kontani, Hiroshi [Department of Physics, Nagoya University, Nagoya 464-8602 (Japan)

    2008-02-15

    In this paper, we present recent developments in the theory of transport phenomena based on the Fermi liquid theory. In conventional metals, various transport coefficients are scaled according to the quasiparticles relaxation time, {tau}, which implies that the relaxation time approximation (RTA) holds well. However, such a simple scaling does not hold in many strongly correlated electron systems. The most famous example would be high-T{sub c} superconductors (HTSCs), where almost all the transport coefficients exhibit a significant deviation from the RTA results. This issue has been one of the most significant unresolved problems in HTSCs for a long time. Similar anomalous transport phenomena have been observed in metals near their antiferromagnetic (AF) quantum critical point (QCP). The main goal of this study is to demonstrate whether the anomalous transport phenomena in HTSC is evidence of a non-Fermi liquid ground state, or just RTA violation in strongly correlated Fermi liquids. Another goal is to establish a unified theory of anomalous transport phenomena in metals with strong magnetic fluctuations. For these purposes, we develop a method for calculating various transport coefficients beyond the RTA by employing field theoretical techniques. In a Fermi liquid, an excited quasiparticle induces other excited quasiparticles by collision, and current due to these excitations is called a current vertex correction (CVC). Landau noticed the existence of CVC first, which is indispensable for calculating transport coefficients in accord with the conservation laws. Here, we develop a transport theory involving resistivity and the Hall coefficient on the basis of the microscopic Fermi liquid theory, by considering the CVC. In nearly AF Fermi liquids, we find that the strong backward scattering due to AF fluctuations induces the CVC with prominent momentum dependence. This feature of the CVC can account for the significant enhancement in the Hall coefficient

  12. Anomalous transport phenomena in Fermi liquids with strong magnetic fluctuations

    International Nuclear Information System (INIS)

    Kontani, Hiroshi

    2008-01-01

    In this paper, we present recent developments in the theory of transport phenomena based on the Fermi liquid theory. In conventional metals, various transport coefficients are scaled according to the quasiparticles relaxation time, τ, which implies that the relaxation time approximation (RTA) holds well. However, such a simple scaling does not hold in many strongly correlated electron systems. The most famous example would be high-T c superconductors (HTSCs), where almost all the transport coefficients exhibit a significant deviation from the RTA results. This issue has been one of the most significant unresolved problems in HTSCs for a long time. Similar anomalous transport phenomena have been observed in metals near their antiferromagnetic (AF) quantum critical point (QCP). The main goal of this study is to demonstrate whether the anomalous transport phenomena in HTSC is evidence of a non-Fermi liquid ground state, or just RTA violation in strongly correlated Fermi liquids. Another goal is to establish a unified theory of anomalous transport phenomena in metals with strong magnetic fluctuations. For these purposes, we develop a method for calculating various transport coefficients beyond the RTA by employing field theoretical techniques. In a Fermi liquid, an excited quasiparticle induces other excited quasiparticles by collision, and current due to these excitations is called a current vertex correction (CVC). Landau noticed the existence of CVC first, which is indispensable for calculating transport coefficients in accord with the conservation laws. Here, we develop a transport theory involving resistivity and the Hall coefficient on the basis of the microscopic Fermi liquid theory, by considering the CVC. In nearly AF Fermi liquids, we find that the strong backward scattering due to AF fluctuations induces the CVC with prominent momentum dependence. This feature of the CVC can account for the significant enhancement in the Hall coefficient, magnetoresistance

  13. The realization of strong, stray static magnetic fields

    Czech Academy of Sciences Publication Activity Database

    Žežulka, Václav; Straka, Pavel

    2012-01-01

    Roč. 9, č. 1 (2012), s. 71-77 ISSN 1214-9705 Institutional research plan: CEZ:AV0Z30460519 Keywords : magnetic fields * magnetic circuits * permanent NdFeB magnets Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.530, year: 2011 http://www.irsm.cas.cz/materialy/acta_content/2012_01/7_Zezulka.pdf

  14. Application of orbital strong magnet in the extraction of deep orbital magnetic foreign bodies

    Directory of Open Access Journals (Sweden)

    Jin-Chen Jia

    2017-12-01

    Full Text Available AIM: To investigate the surgical method and efficacy of extraction of deep orbital magnetic foreign bodies by mean of an orbital strong magnet. METHODS: A retrospective analysis of clinical data of patients with deep orbital magnetic foreign bodies(OMFBin Hebei Eye Hospital from June 2014 to May 2017 was processed. A total of 23 eyes were enrolled, among them, 14 eyes of extraorbital OMFB, 9 eyes of intraorbital OMFB. The rate of extraction of foreign bodies and the postoperative complications were observed. RESULTS: All eyes of intraorbital foreign bodies were successfully extracted with 100% success rate. Twelve of 14 eyes of extraorbital foreign bodies were extracted with 86% success rate. Mild orbital hemorrhage were found in 2 eyes. There was no other obvious complication such as visual loss, orbital massive hemorrhage or limited ocular movement. CONCLUSION: It's an ideal surgical method to extract the deep orbital magnetic foreign bodies by mean of an orbital strong magnet, with mini-injury, high success rate, short duration and few complications.

  15. Ion H2+ can dissociate in a strong magnetic field

    International Nuclear Information System (INIS)

    Turbiner, A.V.; Lopez, J.C.; Flores-Riveros, A.

    2001-01-01

    In framework of a variational method the molecular ion H 2 + in a magnetic field is studied. An optimal form of the vector potential corresponding to a given magnetic field is chosen. It is shown that for any magnetic field strength as well as for any orientation of the molecular axis the system (ppe) possesses a minimum in the potential energy. The stable configuration always corresponds to elongation along the magnetic line. However, for magnetic fields B ≥ 5 x 10 11 G and some orientations the ion H 2 + becomes instable decaying to H-atom + p [ru

  16. High thermal stability in W/MgO/CoFeB/W/CoFeB/W stacks via ultrathin W insertion with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yi; Yu, Tao [School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191 (China); Zhu, Zhengyong; Zhong, Huicai [Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029 (China); Khamis, Khamis Masoud [School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191 (China); Zhu, Kaigui, E-mail: kgzhu@buaa.edu.cn [School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191 (China); Key Laboratory of Micro-Nano Measurement-Manipulation and Physics, Ministry of Education, Beihang University, Beijing 100191 (China)

    2016-07-15

    The perpendicular magnetic anisotropy (PMA) of a series of top MgO/CoFeB/W stacks were studied. In these stacks, the thickness of CoFeB is limited in a range of 1.1–2.2 nm. It was found that the stack can still maintain PMA in a 1.9 nm thick CoFeB free layer. Besides, we investigated the thermal stability factor ∆ of a spin transfer torque magnetic random access memory (STT-MRAM) by inserting an ultra-thin W film of 0.8 nm between two CoFeB films. The result shows a clear PMA behavior for the samples with CoFeB thickness up to 2.5 nm, and an in-plane magnetic anisotropy (IMA) when the CoFeB is thicker than 2.5 nm. Moreover, the thermal stability factor ∆ of the CoFeB stack with W insertion is about 132 for a 50 nm size STT-MRAM device, which is remarkably improved compared to 112 for a sample without W insertion. Our results represent an alternative way to realize the endurance at high annealing temperature, high-density and high ∆ in STT-MRAM device by ultra-thin W insertion. - Highlights: • The MgO/CoFeB/W multilayer can still maintain PMA in a CoFeB thickness of 1.9 nm. • The sample with 2.5 nm thickness of CoFeB by W insertion can still maintain PMA. • The sample with W insertion can still maintain PMA until the annealing temperature as high as 350 °C. • The thermal stability factor ∆ of sample with W insertion could be increase to about 132 for a 50 nm size STT-MRAM device.

  17. Chiral spiral induced by a strong magnetic field

    Directory of Open Access Journals (Sweden)

    Abuki Hiroaki

    2016-01-01

    Full Text Available We study the modification of the chiral phase structure of QCD due to an external magnetic field. We first demonstrate how the effect of magnetic field can systematically be incorporated into a generalized Ginzburg-Landau framework. We then analyze the phase structure in the vicinity of the chiral critical point. In the chiral limit, the effect is found to be so drastic that it brings a “continent” of chiral spiral in the phase diagram, by which the chiral tricritical point is totally washed out. This is the case no matter how small the intensity of magnetic field is. On the other hand, the current quark mass protects the chiral critical point from a weak magnetic field. However, the critical point will eventually be covered by the chiral spiral phase as the magnetic field grows.

  18. Ferromagnetic resonance investigation of physical origins of modification of the perpendicular magnetic anisotropy in Pd/Co layered films in the presence of hydrogen gas

    Science.gov (United States)

    Lueng, C.; Zighem, F.; Faurie, D.; Kostylev, M.

    2017-10-01

    In our work, we study the physical origins of the hydrogen gas induced reduction of the strength of perpendicular magnetic anisotropy (PMA) at the interface of cobalt and palladium layers. To this end, we grow these films on flexible substrates and carry out ferromagnetic resonance (FMR) measurements in the presence of two different stimuli—hydrogen gas and elastic strain. Exposing the samples to H2 results in a downshift of the FMR field. On the contrary, FMR measurements carried out in the presence of an externally applied predominantly tensile elastic stress show an up-shift in the resonance field consistent with negative values of the saturation magnetostriction coefficient for our samples. Qualitative analysis of these results demonstrates that the magneto-elastic contribution to the hydrogen-induced change in PMA is very small and is of the opposite sign to the electronic contribution related to the influence of hydrogen ions on the hybridisation of cobalt and palladium orbitals at the interface.

  19. Current induced domain wall motion and tilting in Pt/Co/Ta structures with perpendicular magnetic anisotropy in the presence of the Dyzaloshinskii–Moriya interaction

    Science.gov (United States)

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

    2018-04-01

    Current induced domain wall motion (CIDWM) was studied in Pt/Co/Ta structures with perpendicular magnetic anisotropy and the Dyzaloshinskii–Moriya interaction (DMI) by the spin-orbit torque (SOT). We measured the strength of DMI and SOT efficiency in Pt/Co/Ta with the variation of the thickness of Ta using a current induced hysteresis loop shift method. The results indicate that the DMI stabilizes a chiral Néel-type domain wall (DW), and the DW motion can be driven by the enhanced large SOT generated from Pt and Ta with opposite signs of spin Hall angle in Pt/Co/Ta stacks. The CIDWM velocity, which is 104 times larger than the field driven DW velocity, obeys a creep law, and reaches around tens of meters per second with current density of ~106 A cm‑2. We also found that the Joule heating accompanied with current also accelerates the DW motion. Meanwhile, a domain wall tilting was observed, which increases with current density increasing. These results can be explained by the spin Hall effect generated from both heavy metals Pt and Ta, inherent DMI, and the current accompanying Joule heating effect. Our results could provide some new designing prospects to move multiple DWs by SOT for achieving racetrack memories.

  20. Epitaxial Heusler superlattice Co2MnAl /Fe2MnAl with perpendicular magnetic anisotropy and termination-dependent half-metallicity

    Science.gov (United States)

    Brown-Heft, Tobias L.; Logan, John A.; McFadden, Anthony P.; Guillemard, Charles; Le Fèvre, Patrick; Bertran, François; Andrieu, Stéphane; Palmstrøm, Chris J.

    2018-03-01

    Single-crystal Heusler atomic-scale superlattices that have been predicted to exhibit perpendicular magnetic anisotropy and half-metallicity have been successfully grown by molecular beam epitaxy. Superlattices consisting of full-Heusler Co2MnAl and Fe2MnAl with one- to three-unit-cell periodicity were grown on GaAs (001), MgO (001), and Cr (001)/MgO (001). Electron-energy-loss spectroscopy maps confirmed clearly segregated epitaxial Heusler layers with high cobalt or high iron concentrations for samples grown near room temperature on GaAs (001). Superlattice structures grown with an excess of aluminum had significantly lower thin-film shape anisotropy and resulted in an out-of-plane spin reorientation transition at temperatures below 200 K for samples grown on GaAs (001). Synchrotron-based spin-resolved photoemission spectroscopy found that the superlattice structure improves the Fermi-level spin polarization near the X point in the bulk Brillouin zone. Stoichiometric Co2MnAl terminated superlattice grown on MgO (001) had a spin polarization of 95%, while a pure Co2MnAl film had a spin polarization of only 65%.

  1. The permanent magnet systems generating strong stray fields with large localization region

    International Nuclear Information System (INIS)

    Samofalov, V.N.; Belozorov, D.P.; Ravlik, A.G.

    2008-01-01

    Three systems of permanent magnets, which produce strong magnetic stray fields (SFs) with H>B r =4πM r were studied in this work. Remarkable feature of the developed systems is localization of the strong fields in large region with linear dimension Δr comparable to characteristic magnet dimension a. The first system composed of uniformly magnetized magnets generates sufficiently homogeneous strong SFs, which amounts up to 1.5 of magnets induction B r . The second system with nonuniform magnetization is represented by cylindrical and hemispheric magnets their magnetization vector directed at every point along the radius. Such distribution of magnetization is assumed to be the consequence of magnet radial crystal texture resulting in a high uniaxial anisotropy field H K . It is shown that maximal SFs can exist on the flat surface of cylindrical magnet at the distance r from its axis and their limiting value equals to 4πM r ln(2a/r). Here, the localization region of the fields is comparable to diameter of cylindrical magnet Δr∼2R. As for the hemisphere its SFs are less than corresponding SFs for the cylinder. The third so-called quasi-nonuniform system consists of uniformly magnetized cylindrical sectors their magnetization vector is directed along the sector bisectrix. The strong SFs and their localization region are calculated in details for this case. The passage to radial magnetized cylinder is considered

  2. Perpendicular STT_RAM cell in 8 nm technology node using Co1/Ni3(1 1 1)||Gr2||Co1/Ni3(1 1 1) structure as magnetic tunnel junction

    Science.gov (United States)

    Varghani, Ali; Peiravi, Ali; Moradi, Farshad

    2018-04-01

    The perpendicular anisotropy Spin-Transfer Torque Random Access Memory (P-STT-RAM) is considered to be a promising candidate for high-density memories. Many distinct advantages of Perpendicular Magnetic Tunnel Junction (P-MTJ) compared to the conventional in-plane MTJ (I-MTJ) such as lower switching current, circular cell shape that facilitates manufacturability in smaller technology nodes, large thermal stability, smaller cell size, and lower dipole field interaction between adjacent cells make it a promising candidate as a universal memory. However, for small MTJ cell sizes, the perpendicular technology requires new materials with high polarization and low damping factor as well as low resistance area product of a P-MTJ in order to avoid a high write voltage as technology is scaled down. A new graphene-based STT-RAM cell for 8 nm technology node that uses high perpendicular magnetic anisotropy cobalt/nickel (Co/Ni) multilayer as magnetic layers is proposed in this paper. The proposed junction benefits from enough Tunneling Magnetoresistance Ratio (TMR), low resistance area product, low write voltage, and low power consumption that make it suitable for 8 nm technology node.

  3. Magnetic dynamics of weakly and strongly interacting hematite nanoparticles

    DEFF Research Database (Denmark)

    Hansen, Mikkel Fougt; Bender Koch, Christian; Mørup, Steen

    2000-01-01

    The magnetic dynamics of two differently treated samples of hematite nanoparticles from the same batch with a particle size of about 20 nm have been studied by Mossbauer spectroscopy. The dynamics of the first sample, in which the particles are coated and dispersed in water, is in accordance.......3(-0.8)(+1.0) x 10(-10) s for a rotation of the sublattice magnetization directions in the rhombohedral (111) plane. The corresponding median superparamagnetic blocking temperature is about 150 K. The dynamics of the second, dry sample, in which the particles are uncoated and thus allowed to aggregate, is slowed...... down by interparticle interactions and a magnetically split spectrum is retained at room temperature. The temperature variation or the magnetic hyperfine field, corresponding to different quantiles in the hyperfine field distribution, can be consistently described by a mean field model...

  4. Quark matter and quark stars in strong magnetic fields at finite temperature within the confined-isospin-density-dependent mass model

    Science.gov (United States)

    Chu, Peng-Cheng; Li, Xiao-Hua; Ma, Hong-Yang; Wang, Bin; Dong, Yu-Min; Zhang, Xiao-Min

    2018-03-01

    We study the properties of strange quark matter (SQM) and quark stars (QSs) in strong magnetic fields within the extended confined isospin-density-dependent mass (CIDDM) model including the temperature dependence of the equivalent mass for quarks. The quark symmetry energy, quark symmetry free energy, and the equation of state (EOS) of SQM in constant magnetic fields at finite temperature are investigated, and it is found that including the temperature dependence in CIDDM model and considering strong magnetic fields can both significantly influence the properties of the SQM and the maximum mass of quark stars. Using the density-dependent magnetic field and assuming two extreme cases for the magnetic field orientation in QSs (the radial orientation in which the local magnetic fields are along the radial direction and the transverse orientation in which the local magnetic fields are randomly oriented but perpendicular to the radial orientation), we analyze the mass-radius relations for different stages of the protoquark stars (PQSs) along the star evolution. Our results indicate that the maximum mass of magnetized PQSs may depend on not only the strength distribution and the orientation of the magnetic fields inside the PQSs, but also the heating process and the cooling process in the star evolution.

  5. Neutron star in the presence of strong magnetic field

    Indian Academy of Sciences (India)

    Stars: neutron stars; magnetic fields; equation of state. PACS Nos 26.60.Kp; 52.35.Tc; 97.10.Cv. 1. Introduction. The central density of neutron stars (NS) exceeds the nuclear saturation density (n0 ∼. 0.15 fm. −3. ), thereby giving the idea that compact stars might contain deconfined and chirally restored quark matter in them.

  6. How strongly are the magnetic anisotropy and coordination numbers ...

    Indian Academy of Sciences (India)

    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 ...

  7. Cigar-shaped quarkonia under strong magnetic field

    Science.gov (United States)

    Suzuki, Kei; Yoshida, Tetsuya

    2016-03-01

    Heavy quarkonia in a homogeneous magnetic field are analyzed by using a potential model with constituent quarks. To obtain anisotropic wave functions and corresponding eigenvalues, the cylindrical Gaussian expansion method is applied, where the anisotropic wave functions are expanded by a Gaussian basis in the cylindrical coordinates. Deformation of the wave functions and the mass shifts of the S-wave heavy quarkonia (ηc, J /ψ , ηc(2 S ), ψ (2 S ) and bottomonia) are examined for the wide range of external magnetic field. The spatial structure of the wave functions changes drastically as adjacent energy levels cross each other. Possible observables in heavy-ion collision experiments and future lattice QCD simulations are also discussed.

  8. Strong magnetic field induces superconductivity in a Weyl semimetal

    Science.gov (United States)

    Rosenstein, Baruch; Shapiro, B. Ya.; Li, Dingping; Shapiro, I.

    2017-12-01

    Microscopic theory of the normal-to-superconductor coexistence line of a multiband Weyl superconductor subjected to magnetic field is constructed. It is shown that the Weyl semimetal that is nonsuperconducting or having a small critical temperature Tc at zero field might become a superconductor at higher temperatures when the magnetic field is tuned to a series of quantized values Hn. The pairing occurs on Landau levels. It is argued that the phenomenon is detectable much easier in Weyl semimetals than in parabolic band metals since the quantum limit already has been approached in several Weyl materials. The effect of Zeeman coupling leading to splitting of the reentrant superconducting regions on the magnetic phase diagram is considered. An experimental signature of the superconductivity on Landau levels is the reduction of magnetoresistivity. This has been observed already in Cd3As2 and several other compounds. The novel kind of quantum oscillations of magnetoresistance detected in ZrTe5 is discussed along these lines.

  9. H32+ molecular ion in a strong magnetic field: Triangular configuration

    International Nuclear Information System (INIS)

    Lopez Vieyra, J.C.; Turbiner, A.V.

    2002-01-01

    The existence of the molecular ion H 3 2+ in a magnetic field in a triangular configuration is revised. A variational method with an optimization of the form of the vector potential (gauge fixing) is used. It is shown that in the range of magnetic fields 10 8 11 G the system (pppe), with the protons forming an equilateral triangle perpendicular to the magnetic line, has a well-pronounced minimum in the total energy. This configuration is unstable under the decays (H atom)+p+p and H 2 + +p. The triangular configuration of H 3 2+ complements H 3 2+ in the linear configuration that exists for B > or approx. 10 10 G

  10. Sensitivity Analysis and Simulation of Theoretical Response of Ceramics to Strong Magnetic Fields

    Science.gov (United States)

    2016-09-01

    448. 23. Song Q, Zhang ZJ. Shape control and associated magnetic properties of spinel cobalt ferrite nanocrystals. Journal of the American Chemical...Strong Magnetic Fields by Carli A Moorehead, Michael M Kornecki, Victoria L Blair, Raymond E Brennan Approved for... Magnetic Fields by Carli A Moorehead Drexel University, Philadelphia, Pennsylvannia Michael M Kornecki, Victoria L Blair, and Raymond E Brennan

  11. A strong permanent magnet-assisted electromagnetic undulator

    Science.gov (United States)

    Halbach, K.

    1987-01-30

    This invention discloses an improved undulator comprising a plurality of electromagnet poles located along opposite sides of a particle beam axis with alternate north and south poles on each side of the beam to cause the beam to wiggle or undulate as it travels generally along the beam axis and permanent magnets spaced adjacent the electromagnetic poles on each side of the axis of said particle beam in an orientation sufficient to reduce the saturation of the electromagnet poles whereby the field strength of the electromagnet poles can be increased beyond the normal saturation levels of the electromagnetic poles. 4 figs.

  12. Sharp-front wave of strong magnetic field diffusion in solid metal

    Energy Technology Data Exchange (ETDEWEB)

    Xiao, Bo; Gu, Zhuo-wei; Kan, Ming-xian; Wang, Gang-hua; Zhao, Jian-heng [Institute of Fluid Physics, CAEP, P.O. Box 919-105, Mianyang 621900 (China)

    2016-08-15

    When a strong magnetic field diffuses into a solid metal, if the metal's resistance possesses an abrupt rise at some critical temperature and the magnetic field strength is above some critical value, the magnetic field will diffuse into the metal in the form of a sharp-front wave. Formulas for the critical conditions under which a sharp-front magnetic diffusion wave emerges and a formula for the wave-front velocity are derived in this work.

  13. One-loop QCD thermodynamics in a strong homogeneous and static magnetic field

    Science.gov (United States)

    Rath, Shubhalaxmi; Patra, Binoy Krishna

    2017-12-01

    We have studied how the equation of state of thermal QCD with two light flavors is modified in a strong magnetic field. We calculate the thermodynamic observables of hot QCD matter up to one-loop, where the magnetic field affects mainly the quark contribution and the gluon part is largely unaffected except for the softening of the screening mass. We have first calculated the pressure of a thermal QCD medium in a strong magnetic field, where the pressure at fixed temperature increases with the magnetic field faster than the increase with the temperature at constant magnetic field. This can be understood from the dominant scale of thermal medium in the strong magnetic field, being the magnetic field, in the same way that the temperature dominates in a thermal medium in the absence of magnetic field. Thus although the presence of a strong magnetic field makes the pressure of hot QCD medium larger, the dependence of pressure on the temperature becomes less steep. Consistent with the above observations, the entropy density is found to decrease with the temperature in the presence of a strong magnetic field which is again consistent with the fact that the strong magnetic field restricts the dynamics of quarks to two dimensions, hence the phase space becomes squeezed resulting in the reduction of number of microstates. Moreover the energy density is seen to decrease and the speed of sound of thermal QCD medium increases in the presence of a strong magnetic field. These findings could have phenomenological implications in heavy ion collisions because the expansion dynamics of the medium produced in non-central ultra-relativistic heavy ion collisions is effectively controlled by both the energy density and the speed of sound.

  14. Strongly Coupled Magnetic and Electronic Transitions in Multivalent Strontium Cobaltites

    OpenAIRE

    Lee, J. H.; Choi, Woo Seok; Jeen, H.; Lee, H.-J.; Seo, J. H.; Nam, J.; Yeom, M. S.; Lee, H. N.

    2017-01-01

    The topotactic phase transition in SrCoO x (x = 2.5–3.0) makes it possible to reversibly transit between the two distinct phases, i.e. the brownmillerite SrCoO2.5 that is a room-temperature antiferromagnetic insulator (AFM-I) and the perovskite SrCoO3 that is a ferromagnetic metal (FM-M), owing to their multiple valence states. For the intermediate x values, the two distinct phases are expected to strongly compete with each other. With oxidation of SrCoO2.5, however, it has been conjectured t...

  15. Pion Production from Proton Synchrotron Radiation under Strong Magnetic Field in a Relativistic Quantum Approach

    Directory of Open Access Journals (Sweden)

    Maruyama Tomoyuki

    2016-01-01

    Full Text Available We study pion production from proton synchrotron radiation in the presence of strong magnetic fields by using the exact proton propagator in a strong magnetic field and explicitly including the anomalous magnetic moment. Results in this exact quantum approach do not agree with those obtained in the semi-classical approach. Then, we find that the anomalous magnetic moment of the proton greatly enhances the production rate by about two orders magnitude, and that the decay width satisfies a robust scaling law.

  16. Pion Production from Proton Synchrotron Radiation under Strong Magnetic Field in Relativistic Quantum Approach

    Directory of Open Access Journals (Sweden)

    Maruyama Tomoyuki

    2016-01-01

    Full Text Available We study pion production from proton synchrotron radiation in the presence of strong magnetic fields by using the exact proton propagator in a strong magnetic field and explicitly including the anomalous magnetic moment. Results in this exact quantum-field approach do not agree with those obtained in the semi-classical approach. Furthermore, we also find that the anomalous magnetic moment of the proton greatly enhances the production rate about by two orders of magnitude, and that the polar angle of an emitted pion is the same as that of an initial proton.

  17. Giant Spin Hall Effect and Switching Induced by Spin-Transfer Torque in a W /Co40Fe40B20/MgO Structure with Perpendicular Magnetic Anisotropy

    Science.gov (United States)

    Hao, Qiang; Xiao, Gang

    2015-03-01

    We obtain robust perpendicular magnetic anisotropy in a β -W /Co40Fe40B20/MgO structure without the need of any insertion layer between W and Co40Fe40B20 . This is achieved within a broad range of W thicknesses (3.0-9.0 nm), using a simple fabrication technique. We determine the spin Hall angle (0.40) and spin-diffusion length for the bulk β form of tungsten with a large spin-orbit coupling. As a result of the giant spin Hall effect in β -W and careful magnetic annealing, we significantly reduce the critical current density for the spin-transfer-torque-induced magnetic switching in Co40Fe40B20 . The elemental β -W is a superior candidate for magnetic memory and spin-logic applications.

  18. Experimental demonstration of the equivalence of inductive and strongly coupled magnetic resonance wireless power transfer

    Science.gov (United States)

    Ricketts, David S.; Chabalko, Matthew J.; Hillenius, Andrew

    2013-02-01

    In this work, we show experimentally that wireless power transfer (WPT) using strongly coupled magnetic resonance (SCMR) and traditional induction are equivalent. We demonstrate that for a given coil separation, and to within 4%, strongly coupled magnetic resonance and traditional induction produce the same theoretical efficiency of wireless power transfer versus distance. Moreover, we show that the difference between traditional induction and strongly coupled magnetic resonance is in the implementation of the impedance matching network where strongly coupled magnetic resonance uses the mini-loop impedance match. The mini-loop impedance mach provides a low-loss, high-ratio impedance transformation that makes it desirable for longer distance wireless power transfer, where large impedance transformations are needed to maximize power transfer.

  19. Regularity and Chaos in the Hydrogen Atom Highly Excited with a Strong Magnetic Field

    Directory of Open Access Journals (Sweden)

    M. Amdouni

    2014-01-01

    Full Text Available The effects of the relativistic corrections on the energy spectra are analyzed. Effective simulations based on manipulations of operators in the Sturmian basis are developed. Discrete and continuous energy spectra of a hydrogen atom with realistic nucleus mass in a strong magnetic field are computed. The transition from regularity to chaos in diamagnetic problem with the effect of the nucleus recoil energy is explored. Anticrossing of energy levels is observed for strong magnetic field.

  20. Direct URCA-processes in neutron star quark core with strong magnetic field.

    Directory of Open Access Journals (Sweden)

    Belyaev Vasily

    2017-01-01

    In evaluations, the strength of magnetic field corresponds to the case, where the quarks of medium occupy a lot of Landau levels, while the electrons are in ground Landau level. The analytical dependence of neutrino emissivity on chemical potentials of quarks and electrons, temperature and magnetic field strength is obtained and briefly discussed. The result could be important in application to a massive strongly magnetized neutron star with quark core.

  1. Working with MRI: An investigation of occupational exposure to strong static magnetic fields and associated symptoms

    NARCIS (Netherlands)

    Schaap, K.

    2015-01-01

    Magnetic resonance imaging (MRI) makes use of electromagnetic fields in the non-ionizing radiation frequency ranges. One of them is a continuously present strong static magnetic field (SMF), which extends up to several meters around the scanner. Each time an MRI worker performs tasks near the

  2. Dependency of tunneling magnetoresistance ratio on Pt seed-layer thickness for double MgO perpendicular magnetic tunneling junction spin-valves with a top Co2Fe6B2 free layer ex-situ annealed at 400 °C.

    Science.gov (United States)

    Takemura, Yasutaka; Lee, Du-Yeong; Lee, Seung-Eun; Park, Jea-Gun

    2016-12-02

    For the double MgO based perpendicular magnetic tunneling junction (p-MTJ) spin-valves with a top Co 2 Fe 6 B 2 free layer ex situ annealed at 400 °C, the tunneling-magnetoresistance ratio (TMR) strongly depended on the platinum (Pt) seed layer thickness (t Pt ): it peaked (∼134%) at a specific t Pt (3.3 nm). The TMR ratio was initially and slightly increased from 113%-134% by the enhancement of the magnetic moment of the Co 2 Fe 6 B 2 pinned layer when t Pt increased from 2.0-3.3 nm, and then rapidly decreased from 134%-38.6% by the degrading face-centered-cubic crystallinity of the MgO tunneling barrier when t Pt increased from 3.3-14.3 nm.

  3. THE EXTRAORDINARY COMPLEX MAGNETIC FIELD OF THE HELIUM-STRONG STAR HD 37776

    International Nuclear Information System (INIS)

    Kochukhov, Oleg; Lundin, Andreas; Romanyuk, Iosif; Kudryavtsev, Dmitry

    2011-01-01

    The early-type chemically peculiar stars often show strong magnetic fields on their surfaces. These magnetic topologies are organized on large scales and are believed to be close to an oblique dipole for most of the stars. In a striking exception to this general trend, the helium-strong star HD 37776 shows an extraordinary double-wave rotational modulation of the longitudinal magnetic field measurements, indicating a topologically complex and, possibly, record-strong magnetic field. Here we present a new investigation of the magnetic field structure of HD 37776, using both simple geometrical interpretation of the longitudinal field curve and detailed modeling of the time-resolved circular polarization line profiles with the help of a magnetic Doppler imaging technique. We derive a model of the magnetic field structure of HD 37776, which reconciles for the first time all magnetic observations available for this star. We find that the local surface field strength does not exceed ∼30 kG, while the overall field topology of HD 37776 is dominated by a non-axisymmetric component and represents by far the most complex magnetic field configuration found among early-type stars.

  4. Buoyant convection during Czochralski silicon growth with a strong, non-uniform, axisymmetric magnetic field

    Science.gov (United States)

    Khine, Y. Y.; Walker, J. S.

    1995-02-01

    This paper treats the buoyant convection during the Czochralski growth of silicon crystals with a steady, strong, non-uniform, axisymmetric magnetic field. We consider a family of magnetic fields which includes a uniform axial magnetic field and a "cusp" field which is produced by identical solenoids placed symmetrically above and below the plane of the crystal-melt interface and free surface. We investigate the evolution of the buoyant convection as the magnetic field is changed continuously from a uniform axial field to a cusp field, with a constant value of the root-mean-squared magnetic flux density in the melt. We also investigate changes as the magnetic flux density is increased. While the cusp field appears very promising, perfect alignment between the local magnetic field vector and the crystal-melt interface or free surface is not possible, so the effects of a slight misalignment are also investigated.

  5. Rotational hysteresis measurements on alumite perpendicular media

    NARCIS (Netherlands)

    van Drent, W.P.; van Drent, W.P.; Sterringa, E.R.; Sterringa, E.R.; Lodder, J.C.; Bottoni, G.; Candolfo, D.; Cecchetti, A.; Masoli, F.

    1991-01-01

    Rotational hysteresis energy loss measurements have been performed to support the analysis of the magnetization processes of Fe- and Co-alumite perpendicular recording media. Two measurement techniques gave comparable results within error limits. The rotational hysteresis integral is severly lowered

  6. Abnormally big magnetic resistance in a strongly compensated silicon doped with manganese

    International Nuclear Information System (INIS)

    Sadullaev, A.B.

    2004-01-01

    The work is devoted to study of an influence of compensating impurities electro-active atoms concentration on galvanomagnetic properties of strongly compensated silicon doped with manganese. It was shown, the possibility for magnetic resistance control of the strongly compensated Si samples by manganese electro-active impurity atoms concentration regulation

  7. Light bending by nonlinear electrodynamics under strong electric and magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Jin Young; Lee, Taekoon, E-mail: jykim@kunsan.ac.kr, E-mail: tlee@kunsan.ac.kr [Department of Physics, Kunsan National University, Daihakro 558, Kunsan 573-701 (Korea, Republic of)

    2011-11-01

    We calculate the bending angles of light under the strong electric and magnetic fields by a charged black hole and a magnetized neutron star according to the nonlinear electrodynamics of Euler-Heisenberg interaction. The bending angle of light by the electric field of charged black hole is computed from geometric optics and a general formula is derived for light bending valid for any orientation of the magnetic dipole. The astronomical significance of the light bending by magnetic field of a neutron star is discussed.

  8. Investigating short-range magnetism in strongly correlated materials via magnetic pair distribution function analysis and ab initio theory

    Science.gov (United States)

    Frandsen, Benjamin; Page, Katharine; Brunelli, Michela; Staunton, Julie; Billinge, Simon

    Short-range magnetic correlations are known to exist in a variety of strongly correlated electron systems, but our understanding of the role they play is challenged by the difficulty of experimentally probing such correlations. Magnetic pair distribution function (mPDF) analysis is a newly developed neutron total scattering method that can reveal short-range magnetic correlations directly in real space, and may therefore help ameliorate this difficulty. We present temperature-dependent mPDF measurements of the short-range magnetic correlations in the paramagnetic phase of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. We observe significant correlations on a ~1 nm length scale that differ substantially from the low-temperature long-range-ordered spin arrangement. With no free parameters, ab initio calculations using the self-interaction-corrected local spin density approximation of density functional theory quantitatively reproduce the magnetic correlations to a high degree of accuracy. These results yield valuable insight into the magnetic exchange in MnO and showcase the utility of the mPDF technique for studying magnetic properties of strongly correlated electron systems.

  9. STRONG SOLAR WIND DYNAMIC PRESSURE PULSES: INTERPLANETARY SOURCES AND THEIR IMPACTS ON GEOSYNCHRONOUS MAGNETIC FIELDS

    International Nuclear Information System (INIS)

    Zuo, Pingbing; Feng, Xueshang; Wang, Yi; Xie, Yanqiong; Xu, Xiaojun

    2015-01-01

    In this investigation, we first present a statistical result of the interplanetary sources of very strong solar wind dynamic pressure pulses (DPPs) detected by WIND during solar cycle 23. It is found that the vast majority of strong DPPs reside within solar wind disturbances. Although the variabilities of geosynchronous magnetic fields (GMFs) due to the impact of positive DPPs have been well established, there appears to be no systematic investigations on the response of GMFs to negative DPPs. Here, we study both the decompression effects of very strong negative DPPs and the compression from strong positive DPPs on GMFs at different magnetic local time sectors. In response to the decompression of strong negative DPPs, GMFs on the dayside near dawn and near dusk on the nightside, are generally depressed. But near the midnight region, the responses of GMF are very diverse, being either positive or negative. For part of the events when GOES is located at the midnight sector, the GMF is found to abnormally increase as the result of magnetospheric decompression caused by negative DPPs. It is known that under certain conditions magnetic depression of nightside GMFs can be caused by the impact of positive DPPs. Here, we find that a stronger pressure enhancement may have a higher probability of producing the exceptional depression of GMF at the midnight region. Statistically, both the decompression effect of strong negative DPPs and the compression effect of strong positive DPPs depend on the magnetic local time, which are stronger at the noon sector

  10. The D sup - centre in a quantum well in the presence of parallel electric and strong magnetic fields

    CERN Document Server

    Monozon, B S

    2003-01-01

    An analytical approach to the problem of a negatively charged donor in an infinitely deep quantum well (QW) in the presence of parallel electric and strong magnetic external fields both directed perpendicular to the heteroplanes is developed. The double adiabatic approximation is employed. The dependences of the binding energy on the field strengths, the width of the well and the position of the impurity within the well are derived in explicit form. The effect of the inversion of the electric field is investigated. It is shown that the combined potential acting on the 'outer' electron resembles that of a double QW. When the levels associated with the two effective QWs anticross, a resonant structure arises. The explicit dependence of the resonant splitting on the width of the QW, the strength of the electric field and the position of the impurity are obtained. Using the parameters associated with the GaAs QW, estimates of the inversion shift of the binding energy and the frequency of the emitted resonant radi...

  11. Do strong, static magnetic fields act on living beings and chemical reactions

    International Nuclear Information System (INIS)

    Demmer, W.

    1986-01-01

    In general, magnetic fields are said to have no direct influence on living beings or simple chemical reactions. There is, however, evidence to confirm that changes in the earth's magnetic field or of artificially produced magnetic fields can alter the activity of different neuronal enzyme systems. An effect on the synthesis of β-galactosidase in the bacterium Escherichia coli by a feeble magnetic field (0.2 to 0.8 mT) and disturbances of the embryogenesis of frogs by a strong magnetic field (1.0 T) have been described. These and similar investigations with whole cells raise the question as to what the effect of magnetic fields on isolated and purified enzymes will be. (orig./SHA) [de

  12. Monte Carlo solutions of Schroedinger's equation for H2+ ion in strong magnetic fields

    International Nuclear Information System (INIS)

    Ozaki, Jiro; Tomishima, Yasuo

    1980-01-01

    The analytical expressions suitable for the Monte Carlo calculation to obtain the solution of Schroedinger's equation of hydrogen molecular ion in a strong magnetic field are derived. The wave functions, the energy values and the equilibrium internuclear distances of 1σsub(g) state of H 2 + are obtained numerically through the Monte Carlo simulation and compared with other results based on the variational method. The agreement between them is fairly good over a wide range of magnetic field. The calculation of the energy values of 1πsub(g) state of H 2 + for various internuclear distances taking a constant magnetic field as a parameter, shows that the antibonding 1πsub(g) state in the absence of the external magnetic field changes to a bonding state with an increasing magnetic field. The lowest energy values and the equilibrium internuclear distances of 1πsub(g) state are also calculated for various magnetic field. (author)

  13. In-medium covariant propagator of baryons under a strong magnetic field: Effect of the intrinsic magnetic moments

    Energy Technology Data Exchange (ETDEWEB)

    Aguirre, R.M.; Paoli, A.L. de [Universidad Nacional de La Plata, and IFLP, Departamento de Fisica, Facultad de Ciencias Exactas, La Plata (Argentina)

    2016-11-15

    We obtain the covariant propagator at finite temperature for interacting baryons immersed in a strong magnetic field. The effect of the intrinsic magnetic moments on the Green function are fully taken into account. We make an expansion in terms of eigenfunctions of a Dirac field, which leads us to a compact form of its propagator. We present some simple applications of these propagators, where the statistical averages of nuclear currents and energy density are evaluated. (orig.)

  14. Strong magnetic enhancement in self-assembled multiferroic-ferrimagnetic nanostructures

    Science.gov (United States)

    Chen, Ying-Jiun; Hsieh, Ying-Hui; Liao, Sheng-Chieh; Hu, Zhiwei; Huang, Meng-Jie; Kuo, Wei-Cheng; Chin, Yi-Ying; Uen, Tzeng-Ming; Juang, Jenh-Yih; Lai, Chih-Huang; Lin, Hong-Ji; Chen, Chien-Te; Chu, Ying-Hao

    2013-05-01

    In the past decade, self-assembled vertical nano-heterostructures have drawn considerable attention because a high interface-to-volume ratio can be used to tailor or create functionalities. We have systematically investigated the magnetic properties of oxide heterostructures consisting of the CoFe2O4 nanopillars embedded in the BiFeO3 matrix using macroscopic magnetization measurements and element-selective soft X-ray absorption magnetic circular dichroism (XMCD) at the Co- and Fe-L2,3 edge. The magnetization and XMCD data show that the total ordered magnetic moment of Co2+ in CoFe2O4-BiFeO3 nano-heterostructures is strongly enhanced. This study clearly indicates that the high interface-to-volume ratio vertical nanostructure creates a strong ferromagnetic and antiferromagnetic magnetic coupling via an interface. Furthermore, the magnetic coupling can be tuned in the multiferroic-ferrimagnetic self-assembled heterostructures by controlling the spacing between nanopillars.In the past decade, self-assembled vertical nano-heterostructures have drawn considerable attention because a high interface-to-volume ratio can be used to tailor or create functionalities. We have systematically investigated the magnetic properties of oxide heterostructures consisting of the CoFe2O4 nanopillars embedded in the BiFeO3 matrix using macroscopic magnetization measurements and element-selective soft X-ray absorption magnetic circular dichroism (XMCD) at the Co- and Fe-L2,3 edge. The magnetization and XMCD data show that the total ordered magnetic moment of Co2+ in CoFe2O4-BiFeO3 nano-heterostructures is strongly enhanced. This study clearly indicates that the high interface-to-volume ratio vertical nanostructure creates a strong ferromagnetic and antiferromagnetic magnetic coupling via an interface. Furthermore, the magnetic coupling can be tuned in the multiferroic-ferrimagnetic self-assembled heterostructures by controlling the spacing between nanopillars. Electronic supplementary

  15. Heavy quark potential in a static and strong homogeneous magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Hasan, Mujeeb; Chatterjee, Bhaswar; Patra, Binoy Krishna [Indian Institute of Technology Roorkee, Department of Physics, Roorkee (India)

    2017-11-15

    We have investigated the properties of quarkonia in a thermal QCD medium in the background of strong magnetic field. For that purpose, we employ the Schwinger proper-time quark propagator in the lowest Landau level to calculate the one-loop gluon self-energy, which in the sequel gives the effective gluon propagator. As an artifact of strong magnetic field approximation (eB >> T{sup 2} and eB >> m{sup 2}), the Debye mass for massless flavors is found to depend only on the magnetic field which is the dominant scale in comparison to the scales prevalent in the thermal medium. However, for physical quark masses, it depends on both magnetic field and temperature in a low temperature and high magnetic field but the temperature dependence is very meager and becomes independent of the temperature beyond a certain temperature and magnetic field. With the above mentioned ingredients, the potential between heavy quark (Q) and anti-quark (anti Q) is obtained in a hot QCD medium in the presence of a strong magnetic field by correcting both short- and long-range components of the potential in the real-time formalism. It is found that the long-range part of the quarkonium potential is affected much more by magnetic field as compared to the short-range part. This observation facilitates us to estimate the magnetic field beyond which the potential will be too weak to bind Q anti Q together. For example, the J/ψ is dissociated at eB ∝ 10 m{sub π}{sup 2} and Υ is dissociated at eB ∝ 100 m{sub π}{sup 2} whereas its excited states, ψ{sup '} and Υ{sup '} are dissociated at smaller magnetic field eB = m{sub π}{sup 2}, 13 m{sub π}{sup 2}, respectively. (orig.)

  16. Effect of horizontal strong static magnetic field on swimming behaviour of Paramecium caudatum

    Science.gov (United States)

    Fujiwara, Yoshihisa; Tomishige, Masahiko; Itoh, Yasuhiro; Fujiwara, Masao; Shibata, Naho; Kosaka, Toshikazu; Hosoya, Hiroshi; Tanimoto, Yoshifumi

    2006-05-01

    Effect of horizontal strong static magnetic field on swimming behaviour of Paramecium caudatum was studied by using a superconducting magnet. Around a centre of a round vessel, random swimming at 0 T and aligned swimming parallel to the magnetic field (MF) of 8 T were observed. Near a wall of the vessel, however, swimming round and round along the wall at 0 T and aligned swimming of turning at right angles upon collision with the wall, which was remarkable around 1-4 T, were detected. It was experimentally revealed that the former MF-induced parallel swimming at the vessel centre was caused physicochemically by the parallel magnetic orientation of the cell itself. From magnetic field dependence of the extent of the orientation, the magnetic susceptibility anisotropy (χ ∥-χ ⊥) was first obtained to be 3.4× 10-23 emu cell-1 at 298 K for Paramecium caudatum. The orientation of the cell was considered to result from the magnetic orientation of the cell membrane. On the other hand, although mechanisms of the latter swimming near the vessel wall regardless of the absence and presence of the magnetic field are unclear at present, these experimental results indicate that whether the cell exists near the wall alters the magnetic field effect on the swimming in the horizontal magnetic field.

  17. One-electron atomic-molecular ions containing lithium in a strong magnetic field

    International Nuclear Information System (INIS)

    Olivares-Pilon, H; Turbiner, A V; Vieyra, J C Lopez; Baye, D

    2010-01-01

    The one-electron lithium-containing Coulomb systems of atomic type Li 2+ and molecular type Li 5+ 2 , LiHe 4+ and LiH 3+ are studied in the presence of a strong magnetic field B ≤ 10 7 au in a non-relativistic framework. They are considered at the Born-Oppenheimer approximation of zero order (infinitely massive centres) within the parallel configuration (molecular axis parallel to the magnetic field). The variational and Lagrange-mesh methods are employed, complementing each other. It is demonstrated that the molecular systems LiH 3+ , LiHe 4+ and Li 5+ 2 can exist for sufficiently strong magnetic fields B ∼> 10 4 au and that Li 5+ 2 can even be stable at magnetic fields typical of magnetars.

  18. The thermodynamic spin magnetization of strongly correlated 2d electrons in a silicon inversion layer

    OpenAIRE

    Prus, O.; Yaish, Y.; Reznikov, M.; Sivan, U.; Pudalov, V.

    2002-01-01

    A novel method invented to measure the minute thermodynamic spin magnetization of dilute two dimensional fermions is applied to electrons in a silicon inversion layer. Interplay between the ferromagnetic interaction and disorder enhances the low temperature susceptibility up to 7.5 folds compared with the Pauli susceptibility of non-interacting electrons. The magnetization peaks in the vicinity of the density where transition to strong localization takes place. At the same density, the suscep...

  19. Double MgO-based Perpendicular Magnetic-Tunnel-Junction Spin-valve Structure with a Top Co2Fe6B2Free Layer using a Single SyAF [Co/Pt]nLayer.

    Science.gov (United States)

    Choi, Jin-Young; Lee, Dong-Gi; Baek, Jong-Ung; Park, Jea-Gun

    2018-02-01

    A new perpendicular spin-transfer-torque magnetic-tunnel-junction (p-MTJ) spin-valve was developed to achieve a high tunneling magnetoresistance (TMR) ratio. It had a double MgO-based spin-valve structure with a top Co 2 Fe 6 B 2 free layer and incorporated a single SyAF [Co(0.4 nm)/Pt(0.3 nm)] 3 layer and a new buffer layer of Co(0.6)/Pt(0.3)/Co(0.4). It had a TMR ratio of 180% and anisotropy exchange field (H ex ) of 3.44 kOe after ex-situ annealing of 350 °C for 30 min under a vacuum below 10 -6 torr and a perpendicular magnetic field of 3 tesla, thereby ensuring a memory margin and avoiding read disturbance failures. Its high level of performance was due to the face-center-cubic crystallinity of the MgO tunneling barrier being significantly improved by decreasing its surface roughness (i.e., peak-to-valley length of 1.4 nm).

  20. Axion production from Landau quantization in the strong magnetic field of magnetars

    Science.gov (United States)

    Maruyama, Tomoyuki; Balantekin, A. Baha; Cheoun, Myung-Ki; Kajino, Toshitaka; Mathews, Grant J.

    2018-04-01

    We utilize an exact quantum calculation to explore axion emission from electrons and protons in the presence of the strong magnetic field of magnetars. The axion is emitted via transitions between the Landau levels generated by the strong magnetic field. The luminosity of axions emitted by protons is shown to be much larger than that of electrons and becomes stronger with increasing matter density. Cooling by axion emission is shown to be much larger than neutrino cooling by the Urca processes. Consequently, axion emission in the crust may significantly contribute to the cooling of magnetars. In the high-density core, however, it may cause heating of the magnetar.

  1. Chiral soliton lattice and charged pion condensation in strong magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Brauner, Tomáš [Faculty of Science and Technology, University of Stavanger,N-4036 Stavanger (Norway); Yamamoto, Naoki [Department of Physics, Keio University,Yokohama 223-8522 (Japan)

    2017-04-21

    The Chiral Soliton Lattice (CSL) is a state with a periodic array of topological solitons that spontaneously breaks parity and translational symmetries. Such a state is known to appear in chiral magnets. We show that CSL also appears as a ground state of quantum chromodynamics at nonzero chemical potential in a magnetic field. By analyzing the fluctuations of the CSL, we furthermore demonstrate that in strong but achievable magnetic fields, charged pions undergo Bose-Einstein condensation. Our results, based on a systematic low-energy effective theory, are model-independent and fully analytic.

  2. 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.)

  3. Study of Strong Magnetic Fields Using Parametric Instability in a Magnetised Plasma

    Science.gov (United States)

    Ivanov, V. V.; Maximov, A. V.; Anderson, A. A.; Bauer, B. S.; Yates, K.

    2014-10-01

    Generation of strong magnetic fields with a strength of 10--50 MG plays a key role in some recent conceptions for controlled fusion. We suggest a laser method for measuring the local magnetic field, B > 10 MG, based on the parametric decay of the laser radiation to ω/2 and 3/2 ω harmonics which are generated in the area with the electron density of a quarter of the critical plasma density. Spectral components of parametric harmonics carry a signature of both the plasma temperature and strong magnetic field. A two-plasmon decay of laser radiation was studied in a magnetized plasma at the 1 MA pulsed power Zebra facility at the University of Nevada, Reno. Dense magnetized plasma with a magnetic field of 1--3 MG was created by the 1MA current flowing in the metal rod 0.7--2 mm in diameter. Radiation from the narrowband laser with intensity >1014 W/cm2 was focused on the surface plasma. Spectrum of the backscattering 3/2 ω harmonic included ``red'' and ``blue'' shifted components. Large 2-3 nm shifts of spectral components was identified with laser heating of plasma. Components with a small 0.1 nm spectral shift of may be linked to the magnetic field. Work was supported by the DOE Grant DE-SC0008824 and DOE/NNSA UNR Grant DE-FC52-06NA27616.

  4. Nano-structure formation of Fe-Pt perpendicular magnetic recording media co-deposited with MgO, Al{sub 2}O{sub 3} and SiO{sub 2} additives

    Energy Technology Data Exchange (ETDEWEB)

    Safran, G. [Research Institute for Technical Physics and Materials Science, Hungarian Academy of Sciences 1121 Budapest, Konkoly-Thege ut 29-33 (Hungary)]. E-mail: safran@mfa.kfki.hu; Suzuki, T. [Akita Research Institute of Advanced Technology (AIT), 4-21 Sanuki, Araya, Akita 010-1623 (Japan); Ouchi, K. [Akita Research Institute of Advanced Technology (AIT), 4-21 Sanuki, Araya, Akita 010-1623 (Japan); Barna, P.B. [Research Institute for Technical Physics and Materials Science, Hungarian Academy of Sciences 1121 Budapest, Konkoly-Thege ut 29-33 (Hungary); Radnoczi, G. [Research Institute for Technical Physics and Materials Science, Hungarian Academy of Sciences 1121 Budapest, Konkoly-Thege ut 29-33 (Hungary)

    2006-02-21

    Perpendicular magnetic recording media samples were prepared by sputter deposition on sapphire with a layer sequence of MgO seed-layer/Cr under-layer/FeSi soft magnetic under-layer/MgO intermediate layer/FePt-oxide recording layer. The effects of MgO, Al{sub 2}O{sub 3} and SiO{sub 2} additives on the morphology and orientation of the FePt layer were investigated by transmission electron microscopy. The samples exhibited (001) orientation of the L1 FePt phase with the mutual orientations of sapphire substrate//MgO(100)[001]//Cr(100)[11-bar0]//FeSi(100)[11-bar0]//MgO(100) [001]//FePt(001)[100]. The morphology of the FePt films varied due to the co-deposited oxides: The FePt layers were continuous and segmented by stacking faults aligned at 54{sup o} to the surface. Films with SiO{sub 2} addition, beside the oriented columnar FePt grains, exhibited a fraction of misoriented crystallites due to random repeated nucleation. Al{sub 2}O{sub 3} addition resulted in a layered structure, i.e. an initial continuous epitaxial FePt layer covered by a secondary layer of FePt-Al{sub 2}O{sub 3} composite. Both components (FePt and MgO) of the MgO-added samples were grown epitaxially on the MgO intermediate layer, so that a nano-composite of intercalated (001) FePt and (001) MgO was formed. The revealed microstructures and formation mechanisms may facilitate the improvement of the structural and magnetic properties of the FePt-oxide composite perpendicular magnetic recording media.

  5. The determination of the rotation period and magnetic field geometry of the strongly magnetic roAp star HD 154708

    NARCIS (Netherlands)

    Hubrig, S.; Mathys, G.; Kurtz, D.W.; Schöller, M.; Elkin, V.G.; Henrichs, H.F.

    2009-01-01

    We obtained 13 spectropolarimetric observations of the strongly magnetic rapidly oscillating Ap star HD 154708 over 3 months with the multimode instrument FORS 1, installed at the 8-m Kueyen telescope of the Very Large Telescope. These observations have been used for the determination of the

  6. Description of the magnetic properties of strongly correlated disordered solid solutions in the coherent potential approximation

    Science.gov (United States)

    Korotin, M. A.; Skorikov, N. A.

    2015-06-01

    A method for electronic structure calculations of strongly correlated materials based on the coherent potential approximation is formulated and implemented. Method is applied for investigation of the electronic structure and local magnetic moments of the strongly correlated systems with d- and f-electrons: NiO-ZnO solid solution, nonstoichiometric perovskite LaMnO3-x, doped compound TiO2:Fe, and rare-earth transition-metal intermetallic compound GdNi2:Mn.

  7. Luminosity and cooling of highly magnetized white dwarfs: suppression of luminosity by strong magnetic fields

    Science.gov (United States)

    Bhattacharya, Mukul; Mukhopadhyay, Banibrata; Mukerjee, Subroto

    2018-03-01

    We investigate the luminosity and cooling of highly magnetized white dwarfs with electron-degenerate cores and non-degenerate surface layers where cooling occurs by diffusion of photons. We find the temperature and density profiles in the surface layers or envelope of white dwarfs by solving the magnetostatic equilibrium and photon diffusion equations in a Newtonian framework. We also obtain the properties of white dwarfs at the core-envelope interface, when the core is assumed to be practically isothermal. With the increase in magnetic field, the interface temperature increases whereas the interface radius decreases. For a given age of the white dwarf and for fixed interface radius or interface temperature, we find that the luminosity decreases significantly from about 10-6 L⊙ to 10-9 L⊙ as the magnetic field strength increases from about 109 G to 1012 G at the interface and hence the envelope. This is remarkable because it argues that magnetized white dwarfs are fainter and can be practically hidden in an observed H-R diagram. We also find the cooling rates corresponding to these luminosities. Interestingly, the decrease in temperature with time, for the fields under consideration, is not found to be appreciable.

  8. Critical point in the QCD phase diagram for extremely strong background magnetic fields

    International Nuclear Information System (INIS)

    Endrödi, Gergely

    2015-01-01

    Lattice simulations have demonstrated that a background (electro)magnetic field reduces the chiral/deconfinement transition temperature of quantum chromodynamics for eB<1 GeV 2 . On the level of observables, this reduction manifests itself in an enhancement of the Polyakov loop and in a suppression of the light quark condensates (inverse magnetic catalysis) in the transition region. In this paper, we report on lattice simulations of 1+1+1-flavor QCD at an unprecedentedly high value of the magnetic field eB=3.25 GeV 2 . Based on the behavior of various observables, it is shown that even at this extremely strong field, inverse magnetic catalysis prevails and the transition, albeit becoming sharper, remains an analytic crossover. In addition, we develop an algorithm to directly simulate the asymptotically strong magnetic field limit of QCD. We find strong evidence for a first-order deconfinement phase transition in this limiting theory, implying the presence of a critical point in the QCD phase diagram. Based on the available lattice data, we estimate the location of the critical point.

  9. Consequence of total lepton number violation in strongly magnetized iron white dwarfs

    Energy Technology Data Exchange (ETDEWEB)

    Belyaev, V.B. [Bogolyubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation); Ricci, P. [Istituto Nazionale di Fisica Nucleare, Sezione di Firenze, I-50019 Sesto Fiorentino (Firenze) (Italy); Šimkovic, F. [Department of Nuclear Physics and Biophysics, Comenius University, Mlynská dolina F1, SK-842 15, Bratislava (Slovakia); Bogolyubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation); Adam, J.; Tater, M. [Institute of Nuclear Physics ASCR, CZ-250 68 Řež (Czech Republic); Truhlík, E., E-mail: truhlik@ujf.cas.cz [Institute of Nuclear Physics ASCR, CZ-250 68 Řež (Czech Republic)

    2015-05-15

    The influence of a neutrinoless electron to positron conversion on a cooling of strongly magnetized iron white dwarfs is studied. It is shown that they can be good candidates for soft gamma-ray repeaters and anomalous X-ray pulsars.

  10. Numerical analysis of blood flow in realistic arteries subjected to strong non-uniform magnetic fields

    NARCIS (Netherlands)

    Kenjeres, S.

    2008-01-01

    The paper reports on a comprehensive mathematical model for simulations of blood flow under the presence of strong non-uniform magnetic fields. The model consists of a set of Navier–Stokes equations accounting for the Lorentz and magnetisation forces, and a simplified set of Maxwell’s equations

  11. Quantum magnetism in strongly interacting one-dimensional spinor Bose systems

    DEFF Research Database (Denmark)

    Salami Dehkharghani, Amin; Volosniev, A. G.; Lindgren, E. J.

    2015-01-01

    -range inter-species interactions much larger than their intra-species interactions and show that they have novel energetic and magnetic properties. In the strongly interacting regime, these systems have energies that are fractions of the basic harmonic oscillator trap quantum and have spatially separated...

  12. Study of rare earth local moment magnetism and strongly correlated phenomena in various crystal structures

    Energy Technology Data Exchange (ETDEWEB)

    Kong, Tai [Iowa State Univ., Ames, IA (United States)

    2016-12-17

    Benefiting from unique properties of 4f electrons, rare earth based compounds are known for offering a versatile playground for condensed matter physics research as well as industrial applications. This thesis focuses on three specific examples that further explore the rare earth local moment magnetism and strongly correlated phenomena in various crystal structures.

  13. Probing spin correlations with phonons in the strongly frustrated magnet ZnCr2O4.

    Science.gov (United States)

    Sushkov, A B; Tchernyshyov, O; Ratcliff, W; Cheong, S W; Drew, H D

    2005-04-08

    The spin-lattice coupling plays an important role in strongly frustrated magnets. In ZnCr2O4, an excellent realization of the Heisenberg antiferromagnet on the pyrochlore network, a lattice distortion relieves the geometrical frustration through a spin-Peierls-like phase transition at T(c)=12.5 K. Conversely, spin correlations strongly influence the elastic properties of a frustrated magnet. By using infrared spectroscopy and published data on magnetic specific heat, we demonstrate that the frequency of an optical phonon triplet in ZnCr2O4 tracks the nearest-neighbor spin correlations above T(c). The splitting of the phonon triplet below T(c) provides a way to measure the spin-Peierls order parameter.

  14. Spin polarization in high density quark matter under a strong external magnetic field

    DEFF Research Database (Denmark)

    Tsue, Yasuhiko; Da Providência, João; Providência, Constança

    2016-01-01

    In high density quark matter under a strong external magnetic field, possible phases are investigated by using the two-flavor Nambu-Jona-Lasinio (NJL) model with tensor-type four-point interaction between quarks, as well as the axial-vector-type four-point interaction. In the tensor-type interact......In high density quark matter under a strong external magnetic field, possible phases are investigated by using the two-flavor Nambu-Jona-Lasinio (NJL) model with tensor-type four-point interaction between quarks, as well as the axial-vector-type four-point interaction. In the tensor...... phase appears in the wide range of the quark chemical potential. In both the interactions, the quark mass in zero and small chemical potential regions increases which indicates that the chiral symmetry breaking is enhanced, namely the magnetic catalysis occurs....

  15. Optical investigation of the strong spin-orbit-coupled magnetic semimetal YbMnBi2

    Science.gov (United States)

    Chaudhuri, Dipanjan; Cheng, Bing; Yaresko, Alexander; Gibson, Quinn D.; Cava, R. J.; Armitage, N. P.

    2017-08-01

    Strong spin-orbit coupling (SOC) can result in ground states with nontrivial topological properties. The situation is even richer in magnetic systems where the magnetic ordering can potentially have strong influence over the electronic band structure. The class of A MnBi2 (A = Sr, Ca) compounds are important in this context as they are known to host massive Dirac fermions with strongly anisotropic dispersion, which is believed to be due to the interplay between strong SOC and magnetic degrees of freedom. We report the optical conductivity of YbMnBi2, a newly discovered member of this family and a proposed Weyl semimetal (WSM) candidate with broken time reversal symmetry. Together with density functional theory (DFT) band-structure calculations, we show that the complex conductivity can be interpreted as the sum of an intraband Drude response and interband transitions. We argue that the canting of the magnetic moments that has been proposed to be essential for the realization of the WSM in an otherwise antiferromagnetically ordered system is not necessary to explain the optical conductivity. We believe our data is explained qualitatively by the uncanted magnetic structure with a small offset of the chemical potential from strict stochiometry. We find no definitive evidence of a bulk Weyl nodes. Instead, we see signatures of a gapped Dirac dispersion, common in other members of A MnBi2 family or compounds with similar 2D network of Bi atoms. We speculate that the evidence for a WSM seen in ARPES arises through a surface magnetic phase. Such an assumption reconciles all known experimental data.

  16. First Detection of a Strong Magnetic Field on a Bursty Brown Dwarf: Puzzle Solved

    Science.gov (United States)

    Berdyugina, S. V.; Harrington, D. M.; Kuzmychov, O.; Kuhn, J. R.; Hallinan, G.; Kowalski, A. F.; Hawley, S. L.

    2017-09-01

    We report the first direct detection of a strong, 5 kG magnetic field on the surface of an active brown dwarf. LSR J1835+3259 is an M8.5 dwarf exhibiting transient radio and optical emission bursts modulated by fast rotation. We have detected the surface magnetic field as circularly polarized signatures in the 819 nm sodium lines when an active emission region faced the Earth. Modeling Stokes profiles of these lines reveals the effective temperature of 2800 K and log gravity acceleration of 4.5. These parameters place LSR J1835+3259 on evolutionary tracks as a young brown dwarf with the mass of 55+/- 4{M}{{J}} and age of 22 ± 4 Myr. Its magnetic field is at least 5.1 kG and covers at least 11% of the visible hemisphere. The active region topology recovered using line profile inversions comprises hot plasma loops with a vertical stratification of optical and radio emission sources. These loops rotate with the dwarf in and out of view causing periodic emission bursts. The magnetic field is detected at the base of the loops. This is the first time that we can quantitatively associate brown dwarf non-thermal bursts with a strong, 5 kG surface magnetic field and solve the puzzle of their driving mechanism. This is also the coolest known dwarf with such a strong surface magnetic field. The young age of LSR J1835+3259 implies that it may still maintain a disk, which may facilitate bursts via magnetospheric accretion, like in higher-mass T Tau-type stars. Our results pave a path toward magnetic studies of brown dwarfs and hot Jupiters.

  17. Centrifugal pumping during Czochralski silicon growth with a strong, non-uniform, axisymmetric magnetic field

    Science.gov (United States)

    Khine, Y. Y.; Walker, J. S.

    1996-08-01

    Centrifugal pumping flows are produced in the melt by the rotations of crystal and crucible during the Czochralski growth of silicon crystals. This paper treats the centrifugal pumping effects with a steady, strong, non-uniform axisymmetric magnetic field. We consider a family of magnetic fields ranging from a uniform axial field to a "cusp" field, which has a purely radial field at the crystal-melt interface and free surface. We present the numerical solutions for the centrifugal pumping flows as the magnetic field is changed continuously from a uniform axial field to a cusp one, and for arbitrary Hartmann number. Since the perfect alignment between the local magnetic field vector and the crystal-melt interface or free surface is not likely, we also investigate the effects of a slight misalignment.

  18. Sound absorption in a field of a strong electromagnetic wave in a quantizied magnetic field

    International Nuclear Information System (INIS)

    Chajkovskij, I.A.

    1974-01-01

    A coefficient of sound absorption GAMMA in a semiconductor and semi-metal in the quantized magnetic field is calculated for a system exposed to a field of strong electromagnetic radiation. The cases E parallel H and E orthogonal H are considered. Along with the already known strong oscillations of sound absorption in magnetic fields, the absorption spectrum GAMMAsub(par) and GAMMAsub(orth) shows new oscillations representing a manifestation of the quasi-energetic electron spectrum in the field of a strong electromagnetic wave. The oscillation height at E parallel H is modulated by the electromagnetic field. It is shown that the ratio GAMMAsub(par)/GAMMAsub(orth) allows the determination of the effective mass of the carriers

  19. ON MULTIPLE RECONNECTION X-LINES AND TRIPOLAR PERTURBATIONS OF STRONG GUIDE MAGNETIC FIELDS

    International Nuclear Information System (INIS)

    Eriksson, S.; Gosling, J. T.; Lapenta, G.; Newman, D. L.; Goldman, M. V.; Phan, T. D.; Lavraud, B.; Khotyaintsev, Yu. V.; Carr, C. M.; Markidis, S.

    2015-01-01

    We report new multi-spacecraft Cluster observations of tripolar guide magnetic field perturbations at a solar wind reconnection exhaust in the presence of a guide field B M   which is almost four times as strong as the reversing field B L . The novel tripolar field consists of two narrow regions of depressed B M , with an observed 7%–14% ΔB M magnitude relative to the external field, which are found adjacent to a wide region of enhanced B M within the exhaust. A stronger reversing field is associated with each B M depression. A kinetic reconnection simulation for realistic solar wind conditions and the observed strong guide field reveals that tripolar magnetic fields preferentially form across current sheets in the presence of multiple X-lines as magnetic islands approach one another and merge into fewer and larger islands. The simulated ΔB M /ΔX N over the normal width ΔX N between a B M minimum and the edge of the external region agree with the normalized values observed by Cluster. We propose that a tripolar guide field perturbation may be used to identify candidate regions containing multiple X-lines and interacting magnetic islands at individual solar wind current sheets with a strong guide field

  20. Bound-state β decay of a neutron in a strong magnetic field

    International Nuclear Information System (INIS)

    Kouzakov, Konstantin A.; Studenikin, Alexander I.

    2005-01-01

    The β decay of a neutron into a bound (pe - ) state and an antineutrino in the presence of a strong uniform magnetic field (B > or approx. 10 13 G) is considered. The β decay process is treated within the framework of the standard model of weak interactions. A Bethe-Salpeter formalism is employed for description of the bound (pe - ) system in a strong magnetic field. For the field strengths 10 13 18 G the estimate for the ratio of the bound-state decay rate w b and the usual (continuum-state) decay rate w c is derived. It is found that in such strong magnetic fields w b /w c ∼0.1-0.4. This is in contrast to the field-free case, where w b /w c ≅4.2x10 -6 [J. N. Bahcall, Phys. Rev. 124, 495 (1961); L. L. Nemenov, Sov. J. Nucl. Phys. 15, 582 (1972); X. Song, J. Phys. G: Nucl. Phys. 13, 1023 (1987)]. The dependence of the ratio w b /w c on the magnetic field strength B exhibits a logarithmiclike behavior. The obtained results can be important for applications in astrophysics and cosmology

  1. Experimental study of transport of relativistic electron beams in strong magnetic mirror field

    Science.gov (United States)

    Sakata, Shohei; Kondo, Kotaro; Bailly-Grandvaux, Mathiu; Bellei, Claudio; Santos, Joao; Firex Project Team

    2015-11-01

    Relativistic electron beams REB produced by ultra high intense laser pulses have generally a large divergence angle that results in degradation of energy coupling between the REB and a fuel core in the fast ignition scheme. Guiding and focusing of the REB by a strong external magnetic field was proposed to achieve high efficiency. We investigated REB transport through 50 μm or 250 μm thick plastic foils CuI doped under external magnetic fields, in magnetic mirror configurations of 1.2 or 4 mirror ratio. The experiment was carried out at the GEKKO XII and LFEX laser facility. Spatial pattern of the REB was measured by coherent transition radiation and/or Cu Ka x ray emission from the rear surface of the foil targets. Strong collimation of the REB by the external magnetic field was observed with 50 μm thick plastic targets, while the REB scattered in 250 μm thick targets. The experimental results are compared with computer simulations to understand the physical mechanisms of the REB transport in the external magnetic field. This work is supported by NIFS (Japan), MEXT/JSPS KAKENHI (Japan), JSPS Fellowship (Japan), ANR (France) and COST (Europe).

  2. Quantum Femtosecond Magnetism: Phase Transition in Step with Light in a Strongly Correlated Manganese Oxide

    Science.gov (United States)

    Wang, Jigang

    2014-03-01

    Research of non-equilibrium phase transitions of strongly correlated electrons is built around addressing an outstanding challenge: how to achieve ultrafast manipulation of competing magnetic/electronic phases and reveal thermodynamically hidden orders at highly non-thermal, femtosecond timescales? Recently we reveal a new paradigm called quantum femtosecond magnetism-photoinduced femtosecond magnetic phase transitions driven by quantum spin flip fluctuations correlated with laser-excited inter-atomic coherent bonding. We demonstrate an antiferromagnetic (AFM) to ferromagnetic (FM) switching during about 100 fs laser pulses in a colossal magneto-resistive manganese oxide. Our results show a huge photoinduced femtosecond spin generation, measured by magnetic circular dichroism, with photo-excitation threshold behavior absent in the picosecond dynamics. This reveals an initial quantum coherent regime of magnetism, while the optical polarization/coherence still interacts with the spins to initiate local FM correlations that compete with the surrounding AFM matrix. Our results thus provide a framework that explores quantum non-equilibrium kinetics to drive phase transitions between exotic ground states in strongly correlated elecrons, and raise fundamental questions regarding some accepted rules, such as free energy and adiabatic potential surface. This work is in collaboration with Tianqi Li, Aaron Patz, Leonidas Mouchliadis, Jiaqiang Yan, Thomas A. Lograsso, Ilias E. Perakis. This work was supported by the National Science Foundation (contract no. DMR-1055352). Material synthesis at the Ames Laboratory was supported by the US Department of Energy-Basic Energy Sciences (contract no. DE-AC02-7CH11358).

  3. Linear theory of a cold relativistic beam in a strongly magnetized finite-geometry plasma

    International Nuclear Information System (INIS)

    Gagne, R.R.J.; Shoucri, M.M.

    1976-01-01

    The linear theory of a finite-geometry cold relativistic beam propagating in a cold homogeneous finite-geometry plasma, is investigated in the case of a strongly magnetized plasma. The beam is assumed to propagate parallel to the external magnetic field. It is shown that the instability which takes place at the Cherenkov resonance ωapprox. =k/subz/v/subb/ is of the convective type. The effect of the finite geometry on the instability growth rate is studied and is shown to decrease the growth rate, with respect to the infinite geometry, by a factor depending on the ratio of the beam-to-plasma radius

  4. Transport coefficients of InSb in a strong magnetic field

    International Nuclear Information System (INIS)

    Nakamura, Hiroaki; Ikeda, Kazuaki; Yamaguchi, Satarou

    1998-02-01

    Improvement of a superconducting magnet system makes induction of a strong magnetic field easier. This fact gives us a possibility of energy conversion by the Nernst effect. As the first step to study the Nernst element, we measured the conductivity, the Hall coefficient, the thermoelectric power and the Nernst coefficient of the InSb, which is one of candidates of the Nernst elements. From this experiment, it is concluded that the Nernst coefficient is smaller than the theoretical values. On the other hand, the conductivity, the Hall coefficient and the thermoelectric power has the values expected by the theory. (author)

  5. Magnetic and resonant X-ray scattering investigations of strongly correlated electron systems

    International Nuclear Information System (INIS)

    Paolasini, L.; Bergevin, F. de

    2008-01-01

    Resonant X-ray scattering is a method which combines high-Q resolution X-ray elastic diffraction and atomic core-hole spectroscopy for investigating electronic and magnetic long-range ordered structures in condensed matter. During recent years the development of theoretical models to describe resonant X-ray scattering amplitudes and the evolution of experimental techniques, which include the control and analysis of linear photon polarization and the introduction of extreme environment conditions such as low temperatures, high magnetic field and high pressures, have opened a new field of investigation in the domain of strongly correlated electron systems. (authors)

  6. A general assignment method for oriented sample (OS) solid-state NMR of proteins based on the correlation of resonances through heteronuclear dipolar couplings in samples aligned parallel and perpendicular to the magnetic field.

    Science.gov (United States)

    Lu, George J; Son, Woo Sung; Opella, Stanley J

    2011-04-01

    A general method for assigning oriented sample (OS) solid-state NMR spectra of proteins is demonstrated. In principle, this method requires only a single sample of a uniformly ¹⁵N-labeled membrane protein in magnetically aligned bilayers, and a previously assigned isotropic chemical shift spectrum obtained either from solution NMR on micelle or isotropic bicelle samples or from magic angle spinning (MAS) solid-state NMR on unoriented proteoliposomes. The sequential isotropic resonance assignments are transferred to the OS solid-state NMR spectra of aligned samples by correlating signals from the same residue observed in protein-containing bilayers aligned with their normals parallel and perpendicular to the magnetic field. The underlying principle is that the resonances from the same residue have heteronuclear dipolar couplings that differ by exactly a factor of two between parallel and perpendicular alignments. The method is demonstrated on the membrane-bound form of Pf1 coat protein in phospholipid bilayers, whose assignments have been previously made using an earlier generation of methods that relied on the preparation of many selectively labeled (by residue type) samples. The new method provides the correct resonance assignments using only a single uniformly ¹⁵N-labeled sample, two solid-state NMR spectra, and a previously assigned isotropic spectrum. Significantly, this approach is equally applicable to residues in alpha helices, beta sheets, loops, and any other elements of tertiary structure. Moreover, the strategy bridges between OS solid-state NMR of aligned samples and solution NMR or MAS solid-state NMR of unoriented samples. In combination with the development of complementary experimental methods, it provides a step towards unifying these apparently different NMR approaches. Copyright © 2011 Elsevier Inc. All rights reserved.

  7. Drag force in strongly coupled { N }=4 supersymmetric Yang–Mills plasma in a magnetic field

    Science.gov (United States)

    Zhang, Zi-qiang; Ma, Ke; Hou, De-fu

    2018-02-01

    Applying AdS/CFT correspondence, we study the effect of a constant magnetic field { B } on the drag force associated with a heavy quark moving through a strongly-coupled { N }=4 supersymmetric Yang–Mills plasma. The quark is considered moving transverse and parallel to { B }. It is shown that for transverse case, the drag force is linearly dependent on { B } in all regions, while for parallel case, the drag force increases monotonously with increasing { B } and also reveals a linear behavior in the regions of strong { B }. In addition, we find that { B } has a more important effect in the transverse case than for the parallel.

  8. Thermal conductivity of magnetic insulators with strong spin-orbit coupling

    Science.gov (United States)

    Stamokostas, Georgios; Lapas, Panteleimon; Fiete, Gregory A.

    We study the influence of spin-orbit coupling on the thermal conductivity of various types of magnetic insulators. In the absence of spin-orbit coupling and orbital-degeneracy, the strong-coupling limit of Hubbard interactions at half filling can often be adequately described in terms of a pure spin Hamiltonian of the Heisenberg form. However, in the presence of spin-orbit coupling the resulting exchange interaction can become highly anisotropic. The effect of the atomic spin-orbit coupling, taken into account through the effect of magnon-phonon interactions and the magnetic order and excitations, on the lattice thermal conductivity of various insulating magnetic systems is studied. We focus on the regime of low temperatures where the dominant source of scattering is two-magnon scattering to one-phonon processes. The thermal current is calculated within the Boltzmann transport theory. We are grateful for financial support from NSF Grant DMR-0955778.

  9. AC magnetization loss characteristics of HTS coated-conductors with magnetic substrates

    International Nuclear Information System (INIS)

    Tsukamoto, O.; Liu, M.; Odaka, S.; Miyagi, D.; Ohmatsu, K.

    2007-01-01

    AC magnetization loss characteristics of an HTS coated tape conductor with magnetic substrate subjected to an external AC magnetic field were investigated. The external magnetic field was perpendicular or parallel to the wide face of the tape conductor. Magnetization losses in the conductor and in the magnetic substrate itself without the superconductor layer, were measured by electric and calorimetric methods. The influence of the magnetic property of the substrate was strongly dependent on the direction of the external magnetic field. When the external magnetic field was perpendicular, magnetic property of the substrate did not affect the magnetization loss characteristics. This result suggests that the magnetization losses can be reduced by subdivisions of the superconducting layers even in the case of magnetic substrate conductors. When the external magnetic field was parallel, the magnetization losses were dominated by the losses in the magnetic substrate. Therefore, to reduce the magnetization losses in this case, reduction of magnetization losses in the substrate is necessary

  10. MFM study of magnetic interaction between recording and soft magnetic layers

    International Nuclear Information System (INIS)

    Honda, Yukio; Tanahashi, Kiwamu; Hirayama, Yoshiyuki; Kikukawa, Atsushi; Futamoto, Masaaki

    2001-01-01

    Magnetic force microscopy was used to study the magnetic interaction between the recording and the soft magnetic layers in double-layer perpendicular media by observing the magnetization structure from the soft magnetic layer side. There was a strong magnetic interaction between the recording and the soft magnetic layers. Introducing a thin nonmagnetic intermediate layer between the two layers greatly reduced the magnetic interaction and drastically reduced the medium noise

  11. Ideal magnetohydrodynamic simulations of unmagnetized dense plasma jet injection into a hot strongly magnetized plasma

    OpenAIRE

    Liu, Wei; Hsu, Scott C.

    2010-01-01

    We present results from three-dimensional ideal magnetohydrodynamic simulations of unmagnetized dense plasma jet injection into a uniform hot strongly magnetized plasma, with the aim of providing insight into core fueling of a tokamak with parameters relevant for ITER and NSTX (National Spherical Torus Experiment). Unmagnetized dense plasma jet injection is similar to compact toroid injection but with much higher plasma density and total mass, and consequently lower required injection velocit...

  12. Limiting and Fedosov's Currents of a Strongly Magnetized Electron Beam in Asymmetric Transportation Channels

    Science.gov (United States)

    Goikhman, M. B.; Gromov, A. V.; Kovalev, N. F.; V. Palitsin, A.

    2016-12-01

    We consider the properties of thin-walled, strongly magnetized electron beams in closed evacuated transportation channels with arbitrary cross sections of the channel and the electron beam. Explicit precise formulas are obtained for the limiting and Fedosov's currents of such electron beams. The found relationships allow one to explain many observed phenomena and can serve as a basis for verification of the results of more complicated calculations.

  13. Nanosized helical magnetic domains in strongly frustrated Fe3PO4O3

    Science.gov (United States)

    Ross, K. A.; Bordelon, M. M.; Terho, G.; Neilson, J. R.

    2015-10-01

    Fe3PO4O3 forms a noncentrosymmetric lattice structure (space group R 3 m ) comprising triangular motifs of Fe3 + coupled by strong antiferromagnetic interactions (| ΘC W|>900 K). Neutron diffraction from polycrystalline samples shows that strong frustration eventually gives way to an ordered helical incommensurate structure below TN = 163 K, with the helical axis in the hexagonal a b plane and a modulation length to ˜86 Å. The magnetic structure consists of an unusual needlelike correlation volume that extends past 900 Å along the hexagonal c axis but is limited to ˜70 Å in the a b plane, despite the three-dimensional nature of the magnetic sublattice topology. The small in-plane correlation length, which persists to at least T =TN/40 , indicates a robust blocking of long-range order of the helical magnetic structure, and therefore stable domain walls, or other defect spin textures, must be abundant in Fe3PO4O3 . Temperature-dependent neutron powder diffraction reveals small negative thermal expansion below TN. No change in lattice symmetry is observed on cooling through TN, as revealed by high-resolution synchrotron x-ray diffraction. The previously reported reduced moment of the Fe3 + ions (S =5 /2 ), μ ˜4.2 μB , is confirmed here through magnetization studies of a magnetically diluted solid solution series of compounds, Fe(3 -x )GaxPO4O3 , and is consistent with the refined magnetic moment from neutron diffraction 4.14(2) μB. We attribute the reduced moment to a modified spin density distribution arising from ligand charge transfer in this insulating oxide.

  14. Unexpected strong magnetism of Cu doped single-layer MoS₂ and its origin.

    Science.gov (United States)

    Yun, Won Seok; Lee, J D

    2014-05-21

    The magnetism of the 3d transition-metal (TM) doped single-layer (1L) MoS2, where the Mo atom is partially replaced by the 3d TM atom, is investigated using the first-principles density functional calculations. In a series of 3d TM doped 1L-MoS2's, the induced spin polarizations are negligible for Sc, Ti, and Cr dopings, while the induced spin polarizations are confirmed for V, Mn, Fe, Co, Ni, Cu, and Zn dopings and the systems become magnetic. Especially, the Cu doped system shows unexpectedly strong magnetism although Cu is nonmagnetic in its bulk state. The driving force is found to be a strong hybridization between Cu 3d states and 3p states of neighboring S, which results in an extreme unbalanced spin-population in the spin-split impurity bands near the Fermi level. Finally, we also discuss further issues of the Cu induced magnetism of 1L-MoS2 such as investigation of additional charge states, the Cu doping at the S site instead of the Mo site, and the Cu adatom on the layer (i.e., 1L-MoS2).

  15. Numerical analysis of blood flow in realistic arteries subjected to strong non-uniform magnetic fields

    International Nuclear Information System (INIS)

    Kenjeres, Sasa

    2008-01-01

    The paper reports on a comprehensive mathematical model for simulations of blood flow under the presence of strong non-uniform magnetic fields. The model consists of a set of Navier-Stokes equations accounting for the Lorentz and magnetisation forces, and a simplified set of Maxwell's equations (Biot-Savart/Ampere's law) for treating the imposed magnetic fields. The relevant hydrodynamic and electromagnetic properties of human blood were taken from the literature. The model is then validated for different test cases ranging from a simple cylindrical geometry to real-life right-coronary arteries in humans. The time-dependency of the wall-shear-stress for different stenosis growth rates and the effects of the imposed strong non-uniform magnetic fields on the blood flow pattern are presented and analysed. It is concluded that an imposed non-uniform magnetic field can create significant changes in the secondary flow patterns, thus making it possible to use this technique for optimisations of targeted drug delivery

  16. Anomaly disturbances of the magnetic fields before the strong earthquake in Japan on March 11, 2011

    Directory of Open Access Journals (Sweden)

    Masashi Hayakawa

    2012-04-01

    Full Text Available

    One of the strongest earthquakes, with magnitude M 8.9, occurred at the sea bottom near to the east coast of Japan on March 11, 2011. This study is devoted to the investigation of anomaly disturbances in the main magnetic field of the Earth and in ultra-low frequency magnetic variations (F <10 Hz observed before this earthquake. Secular variations of the main geomagnetic field were investigated using three-component 1-h data from three magnetic observatories over the 11-year period of January 1, 2000, to January 31, 2011. The Esashi and Mizusawa magnetic stations are situated northwest of the earthquake epicenter, at distances of around 170 km to 200 km, and the Kakioka observatory is situated southwest of the earthquake epicenter, at a distance of about 300 km. During this period, there were four local anomalies in the secular variations. The last anomaly was the biggest, which began around 3 years prior to the earthquake moment. All of the anomalies can be most distinctly recognized, in the form of differences in the corresponding magnetic components at these remote magnetic stations. For investigations of the ultra-low frequency magnetic field disturbances, three-component 1-s data at two magnetic stations (Kakioka and Uchiura were used. The Uchiura station is situated 119 km south of Kakioka, at a distance of about 420 km from the earthquake epicenter. Data from the time interval of February 18, 2011 to March 10, 2011 (only at night-time: 01:00 to 04:00 local time were investigated in a wide frequency range. In the frequency range of 0.033 Hz to 0.01 Hz, there was the clearest anomaly, seen as a decrease in the correlation coefficients of the corresponding magnetic components at these two stations, from February 22, 2011. Differences in the Z components showed an increase, and became positive after this date. This might suggest that the ultra-low frequency lithospheric source appeared north of the Kakioka station. Outside this specified

  17. Two regimes in conductivity and the Hall coefficient of underdoped cuprates in strong magnetic fields.

    Science.gov (United States)

    Gor'kov, L P; Teitel'baum, G B

    2014-01-29

    We address recent experiments shedding light on the energy spectrum of under and optimally doped cuprates at temperatures above the superconducting transition. Angle resolved photoemission reveals coherent excitation only near nodal points on parts of the 'bare' Fermi surface known as the Fermi arcs. The question debated in the literature is whether the small normal pocket, seen via quantum oscillations, exists at higher temperatures or forms below a charge order transition in strong magnetic fields. Assuming the former case as a possibility, expressions are derived for the resistivity and the Hall coefficient (in weak and strong magnetic fields) with both types of carriers participating in the transport. There are two regimes. At higher temperatures (at a fixed field) electrons are dragged by the Fermi arcs' holes. The pocket being small, its contribution to conductivity and the Hall coefficient is negligible. At lower temperatures electrons decouple from holes behaving as a Fermi gas in the magnetic field. As the mobility of holes on the arcs decreases in strong fields with a decrease of temperature, below a crossover point the pocket electrons prevail, changing the sign of the Hall coefficient in the low temperature limit. Such behavior finds its confirmation in recent high-field experiments.

  18. Pd Layer Thickness Dependence of Tunnel Magnetoresistance Properties in CoFeB/MgO-Based Magnetic Tunnel Junctions with Perpendicular Anisotropy CoFe/Pd Multilayers

    Science.gov (United States)

    Mizunuma, Kotaro; Yamanouchi, Michihiko; Ikeda, Shoji; Sato, Hideo; Yamamoto, Hiroyuki; Gan, Hua-Dong; Miura, Katsuya; Hayakawa, Jun; Matsukura, Fumihiro; Ohno, Hideo

    2011-02-01

    The authors investigated tunnel magnetoresistance (TMR) properties in [CoFe/Pd]-multilayer/CoFeB/MgO/CoFeB/[Pd/CoFe]-multilayer magnetic tunnel junctions (MTJs) having two different Pd layer thicknesses. By reducing the Pd layer thickness from 1.2 to 0.2 nm, the TMR ratio was enhanced from 7 to 101% at the annealing temperature (Ta) of 300 °C. The thin Pd layers resulted in high residual B concentration in the CoFeB layer after high-Ta annealing and in the suppression of crystallization of the CoFeB layer from the fcc(111)-Pd layer side.

  19. A strong magnetic field around the supermassive black hole at the centre of the Galaxy.

    Science.gov (United States)

    Eatough, R P; Falcke, H; Karuppusamy, R; Lee, K J; Champion, D J; Keane, E F; Desvignes, G; Schnitzeler, D H F M; Spitler, L G; Kramer, M; Klein, B; Bassa, C; Bower, G C; Brunthaler, A; Cognard, I; Deller, A T; Demorest, P B; Freire, P C C; Kraus, A; Lyne, A G; Noutsos, A; Stappers, B; Wex, N

    2013-09-19

    Earth's nearest candidate supermassive black hole lies at the centre of the Milky Way. Its electromagnetic emission is thought to be powered by radiatively inefficient accretion of gas from its environment, which is a standard mode of energy supply for most galactic nuclei. X-ray measurements have already resolved a tenuous hot gas component from which the black hole can be fed. The magnetization of the gas, however, which is a crucial parameter determining the structure of the accretion flow, remains unknown. Strong magnetic fields can influence the dynamics of accretion, remove angular momentum from the infalling gas, expel matter through relativistic jets and lead to synchrotron emission such as that previously observed. Here we report multi-frequency radio measurements of a newly discovered pulsar close to the Galactic Centre and show that the pulsar's unusually large Faraday rotation (the rotation of the plane of polarization of the emission in the presence of an external magnetic field) indicates that there is a dynamically important magnetic field near the black hole. If this field is accreted down to the event horizon it provides enough magnetic flux to explain the observed emission--from radio to X-ray wavelengths--from the black hole.

  20. Two-photon annihilation of thermal pairs in strong magnetic fields

    Science.gov (United States)

    Baring, Matthew G.; Harding, Alice K.

    1992-01-01

    The annihilation spectrum of pairs with 1-D thermal distributions in the presence of a strong magnetic field is calculated. Numerical analysis of the spectrum are performed for mildly relativistic temperatures and for different angles of emission with respect to field lines. Teragauss magnetic fields are assumed so that conditions are typical of gamma ray burst and pulsar environments. The spectra at each viewing angle reveal asymmetric line profiles that are signatures of the magnetic broadening and red shifting of the line: these asymmetries are more prominent for small viewing angles. Thermal Doppler broadening tends to dominate in the right wing of the line and obscures the magnetic broadening more at high temperatures and smaller viewing angles. This angular dependence of the line asymmetry may prove a valuable diagnostic tool. For low temperatures and magnetic field strengths, useful analytic expressions are presented for the line width, and also for the annihilation spectrum at zero viewing angle. The results presented find application in gamma ray burst and pulsar models, and may prove very helpful in deducing field strengths and temperatures of the emission regions of these objects from line observations made by Compton GRO and future missions.

  1. Strong post-midnight Equatorial Ionospheric Anomaly and Equatorial spread F Observations during magnetically quiet period

    Science.gov (United States)

    Moldwin, M. B.; Yizengaw, E.; Sahai, Y.

    2008-12-01

    Post sunset equatorial ionospheric irregularities, especially during magnetically active periods, have been a subject of many studies. The most prominent irregularities often observed right after sunset are the resurgence of the equatorial ionospheric anomaly (EIA) and equatorial spread F (ESF). It is well understood and documented that pre-reversal enhancement, due to the ionospheric conductivity gradient at the dusk, is one of the prime triggering mechanisms for the post-sunset irregularities in the equatorial region. However, less attention has been given to the equatorial irregularities (EIA and ESF) that often occur in post-midnight, especially during magnetically quiet periods. It has been suggested that the primary process responsible for the dramatic post-midnight ESF during magnetically active periods is the change in magnitude and direction of the usual equatorial electric field. Earlier studies speculated that during magnetically active post-midnight periods the change in electric field direction from westward to eastward for a short intervals cause an upward E × B drift, resulting in increased h'F and decreased electron densities at the magnetic equator. Individual scans of Jicamarca vertical drift also often observe significant upward drift during post-midnight periods. We present a case of post-midnight strong equatorial ionospheric anomaly during a magnetically quiet (Kp < 3) period using TOPEX altimeter TEC data. Simultaneously, the ionosonde station at S.J. Campos (23.2°S, 45.9°W; dip lat. 17.6°S) observed strong ESF and unusual h'F height rise during post-midnight period, where TOPEX detected strong EIA. At the same time ROCSAT-1 and DMSP satellites also clearly show existence of EIA during post-midnight period at their orbiting altitude. The former satellite also detected post-midnight in situ density irregularities (such as bubbles) at the same time as strong EIA and ESF. The questions here are what triggers these post-midnight equatorial

  2. Study of Fluid Flow Control in Protein Crystallization using Strong Magnetic Fields

    Science.gov (United States)

    Ramachandran, Narayanan; Leslie, Fred; Ciszak, Ewa

    2002-01-01

    An important component in biotechnology, particularly in the area of protein engineering and rational drug design is the knowledge of the precise three-dimensional molecular structure of proteins. The quality of structural information obtained from X-ray diffraction methods is directly dependent on the degree of perfection of the protein crystals. As a consequence, the growth of high quality macromolecular crystals for diffraction analyses has been the central focus for biochemists, biologists, and bioengineers. Macromolecular crystals are obtained from solutions that contain the crystallizing species in equilibrium with higher aggregates, ions, precipitants, other possible phases of the protein, foreign particles, the walls of the container, and a likely host of other impurities. By changing transport modes in general, i.e., reduction of convection and sedimentation, as is achieved in "microgravity", researchers have been able to dramatically affect the movement and distribution of macromolecules in the fluid, and thus their transport, formation of crystal nuclei, and adsorption to the crystal surface. While a limited number of high quality crystals from space flights have been obtained, as the recent National Research Council (NRC) review of the NASA microgravity crystallization program pointed out, the scientific approach and research in crystallization of proteins has been mainly empirical yielding inconclusive results. We postulate that we can reduce convection in ground-based experiments and we can understand the different aspects of convection control through the use of strong magnetic fields and field gradients. Whether this limited convection in a magnetic field will provide the environment for the growth of high quality crystals is still a matter of conjecture that our research will address. The approach exploits the variation of fluid magnetic susceptibility with concentration for this purpose and the convective damping is realized by appropriately

  3. Femtosecond switching of magnetism via strongly correlated spin-charge quantum excitations.

    Science.gov (United States)

    Li, Tianqi; Patz, Aaron; Mouchliadis, Leonidas; Yan, Jiaqiang; Lograsso, Thomas A; Perakis, Ilias E; Wang, Jigang

    2013-04-04

    The technological demand to push the gigahertz (10(9) hertz) switching speed limit of today's magnetic memory and logic devices into the terahertz (10(12) hertz) regime underlies the entire field of spin-electronics and integrated multi-functional devices. This challenge is met by all-optical magnetic switching based on coherent spin manipulation. By analogy to femtosecond chemistry and photosynthetic dynamics--in which photoproducts of chemical and biochemical reactions can be influenced by creating suitable superpositions of molecular states--femtosecond-laser-excited coherence between electronic states can switch magnetic order by 'suddenly' breaking the delicate balance between competing phases of correlated materials: for example, manganites exhibiting colossal magneto-resistance suitable for applications. Here we show femtosecond (10(-15) seconds) photo-induced switching from antiferromagnetic to ferromagnetic ordering in Pr0.7Ca0.3MnO3, by observing the establishment (within about 120 femtoseconds) of a huge temperature-dependent magnetization with photo-excitation threshold behaviour absent in the optical reflectivity. The development of ferromagnetic correlations during the femtosecond laser pulse reveals an initial quantum coherent regime of magnetism, distinguished from the picosecond (10(-12) seconds) lattice-heating regime characterized by phase separation without threshold behaviour. Our simulations reproduce the nonlinear femtosecond spin generation and underpin fast quantum spin-flip fluctuations correlated with coherent superpositions of electronic states to initiate local ferromagnetic correlations. These results merge two fields, femtosecond magnetism in metals and band insulators, and non-equilibrium phase transitions of strongly correlated electrons, in which local interactions exceeding the kinetic energy produce a complex balance of competing orders.

  4. He2+ molecular ion and the He- atomic ion in strong magnetic fields

    Science.gov (United States)

    Vieyra, J. C. Lopez; Turbiner, A. V.

    2017-08-01

    We study the question of existence, i.e., stability with respect to dissociation of the spin-quartet permutation- and reflection-symmetric 4(-3) +g (Sz=-3 /2 ,M =-3 ) state of the (α α e e e ) Coulomb system: the He2 + molecular ion, placed in a magnetic field 0 ≤B ≤10 000 a.u. We assume that the α particles are infinitely massive (Born-Oppenheimer approximation of zero order) and adopt the parallel configuration, when the molecular axis and the magnetic field direction coincide, as the optimal configuration. The study of the stability is performed variationally with a physically adequate trial function. To achieve this goal, we explore several helium-containing compounds in strong magnetic fields, in particular; we study the spin-quartet ground state of the He- ion and the ground (spin-triplet) state of the helium atom, both for a magnetic field in 100 ≤B ≤10 000 a.u. The main result is that the He2 + molecular ion in the state 4(-3) +g is stable towards all possible decay modes for magnetic fields B ≳120 a .u . and with the magnetic field increase the ion becomes more tightly bound and compact with a cigar-type form of electronic cloud. At B =1000 a .u . , the dissociation energy of He2 + into He-+α is ˜702 eV and the dissociation energy for the decay channel to He +α +e is ˜729 eV , and both energies are in the energy window for one of the observed absorption features of the isolated neutron star 1E1207.4-5209.

  5. Active galaxies. A strong magnetic field in the jet base of a supermassive black hole.

    Science.gov (United States)

    Martí-Vidal, Ivan; Muller, Sébastien; Vlemmings, Wouter; Horellou, Cathy; Aalto, Susanne

    2015-04-17

    Active galactic nuclei (AGN) host some of the most energetic phenomena in the universe. AGN are thought to be powered by accretion of matter onto a rotating disk that surrounds a supermassive black hole. Jet streams can be boosted in energy near the event horizon of the black hole and then flow outward along the rotation axis of the disk. The mechanism that forms such a jet and guides it over scales from a few light-days up to millions of light-years remains uncertain, but magnetic fields are thought to play a critical role. Using the Atacama Large Millimeter/submillimeter Array (ALMA), we have detected a polarization signal (Faraday rotation) related to the strong magnetic field at the jet base of a distant AGN, PKS 1830-211. The amount of Faraday rotation (rotation measure) is proportional to the integral of the magnetic field strength along the line of sight times the density of electrons. The high rotation measures derived suggest magnetic fields of at least tens of Gauss (and possibly considerably higher) on scales of the order of light-days (0.01 parsec) from the black hole. Copyright © 2015, American Association for the Advancement of Science.

  6. Dynamics of liquid metal droplets and jets influenced by a strong axial magnetic field

    Science.gov (United States)

    Hernández, D.; Karcher, Ch

    2017-07-01

    Non-contact electromagnetic control and shaping of liquid metal free surfaces is crucial in a number of high-temperature metallurgical processes like levitation melting and electromagnetic sealing, among others. Other examples are the electromagnetic bending or stabilization of liquid metal jets that frequently occur in casting or fusion applications. Within this context, we experimentally study the influence of strong axial magnetic fields on the dynamics of falling metal droplets and liquid metal jets. GaInSn in eutectic composition is used as test melt being liquid at room temperature. In the experiments, we use a cryogen-free superconducting magnet (CFM) providing steady homogeneous fields of up to 5 T and allowing a tilt angle between the falling melt and the magnet axis. We vary the magnetic flux density, the tilt angle, the liquid metal flow rate, and the diameter and material of the nozzle (electrically conducting/insulating). Hence, the experiments cover a parameter range of Hartmann numbers Ha, Reynolds numbers Re, and Weber numbers We within 0 rotation ceases and the droplets are stretched in the field direction. Moreover, we observe that the jet breakup into droplets (spheroidization) is suppressed, and in the case of electrically conducting nozzles and tilt, the jets are bent towards the field axis.

  7. The mass limit of white dwarfs with strong magnetic fields in general relativity

    International Nuclear Information System (INIS)

    Wen De-Hua; Liu He-Lei; Zhang Xiang-Dong

    2014-01-01

    Recently, U. Das and B. Mukhopadhyay proposed that the Chandrasekhar limit of a white dwarf could reach a new high level (2.58M⊙) if a superstrong magnetic field were considered (Das U and Mukhopadhyay B 2013 Phys. Rev. Lett. 110 071102), where the structure of the strongly magnetized white dwarf (SMWD) is calculated in the framework of Newtonian theory (NT). As the SMWD has a far smaller size, in contrast with the usual expectation, we found that there is an obvious general relativistic effect (GRE) in the SMWD. For example, for the SMWD with a one Landau level system, the super-Chandrasekhar mass limit in general relativity (GR) is approximately 16.5% lower than that in NT. More interestingly, the maximal mass of the white dwarf will be first increased when the magnetic field strength keeps on increasing and reaches the maximal value M = 2.48M⊙ with B D = 391.5. Then if we further increase the magnetic fields, surprisingly, the maximal mass of the white dwarf will decrease when one takes the GRE into account. (geophysics, astronomy, and astrophysics)

  8. Photogeneration of neutrino and axions under stimulating effect of strong magnetic field

    CERN Document Server

    Skobelev, V V

    2001-01-01

    The processes of the neutrino and axions photoproduction on the gamma(Ze) -> gamma(nu nu-bar), gamma alpha nuclei, as well as the photon inelastic scattering on the gamma gamma -> gamma(nu nu-bar), gamma alpha photon are considered within the frames of the developed two-dimensional co-variant theory for calculating the matrix of the Feynman diagrams in the strong magnetic field. The contribution of the neutrino radiative photoproduction on the nuclei to the luminosity of the magnetic neutron stars on the early stages of their evolution may compete with the URCA-processes, because the matrix elements in the four-pole diagram depend linearly on the induction of B magnetic field by the B values approx 10 sup 3 -10 sup 4 B sub 0 (B sub 0 = m sub e sup 2 /|e| = 4.41 x 10 sup 1 sup 3 Gs). The evaluation of the axion mass upper boundary, compatible with other independent results, is obtained from the condition of the neutrino luminosity prevailing over the axion one at supposed temperature and magnetic field inducti...

  9. Process γγ → νν-bar in a strong magnetic field

    International Nuclear Information System (INIS)

    Kuznetsov, A.V.; Mikheev, N.V.; Rumyantsev, D.A.

    2003-01-01

    The three-vertex loop amplitude in a strong magnetic field are analyzed in a general form by using the asymptotic behavior of the electron propagator in an external field. The process γγ → νν-bar is studied in terms of the scalar-vector-vector (SVV), pseudoscalar-vector-vector (PVV), vector-vector-vector (VVV), and axial-vector-vector-vector (AVV) combinations of couplings. It is shown that only in the case of the SVV combination does the amplitude grow linearly with increasing magnetic-field strength, the amplitudes evaluated with the other combinations of couplings (PVV, VVV, and AVV) featuring no linearly increasing terms. The process γγ → νν-bar is also studied within the left-right model, which is an extension of the Standard Model of electroweak interactions and which may involve an effective scalar ννee coupling. Possible astrophysical manifestations of this process are discussed

  10. Classical Spin Liquid Instability Driven By Off-Diagonal Exchange in Strong Spin-Orbit Magnets

    Science.gov (United States)

    Rousochatzakis, Ioannis; Perkins, Natalia B.

    2017-04-01

    We show that the off-diagonal exchange anisotropy drives Mott insulators with strong spin-orbit coupling to a classical spin liquid regime, characterized by an infinite number of ground states and Ising variables living on closed or open strings. Depending on the sign of the anisotropy, quantum fluctuations either fail to lift the degeneracy down to very low temperatures, or select noncoplanar magnetic states with unconventional spin correlations. The results apply to all 2D and 3D tricoordinated materials with bond-directional anisotropy and provide a consistent interpretation of the suppression of the x-ray magnetic circular dichroism signal reported recently for β -Li2IrO3 under pressure.

  11. Metal-insulator crossover in superconducting cuprates in strong magnetic fields

    International Nuclear Information System (INIS)

    Marchetti, P.A.; Su Zhaobin; Yu Lu

    2001-02-01

    The metal-insulator crossover of the in-plane resistivity upon temperature decrease, recently observed in several classes of cuprate superconductors, when a strong magnetic field suppresses the superconductivity, is explained using the U(1)xSU(2) Chern-Simons gauge field theory. The origin of this crossover is the same as that for a similar phenomenon observed in heavily underdoped cuprates without magnetic field. It is due to the interplay between the diffusive motion of the charge carriers and the 'peculiar' localization effect due to short-range antiferromagnetic order. We also calculate the in-plane transverse magnetoresistance which is in a fairly good agreement with available experimental data. (author)

  12. Resonance enhancement of two photon absorption by magnetically trapped atoms in strong rf-fields

    Science.gov (United States)

    Chakraborty, A.; Mishra, S. R.

    2018-01-01

    Applying a many mode Floquet formalism for magnetically trapped atoms interacting with a polychromatic rf-field, we predict a large two photon transition probability in the atomic system of cold 87Rb atoms. The physical origin of this enormous increase in the two photon transition probability is due to the formation of avoided crossings between eigen-energy levels originating from different Floquet sub-manifolds and redistribution of population in the resonant intermediate levels to give rise to the resonance enhancement effect. Other exquisite features of the studied atom-field composite system include the splitting of the generated avoided crossings at the strong field strength limit and a periodic variation of the single and two photon transition probabilities with the mode separation frequency of the polychromatic rf-field. This work can find applications to characterize properties of cold atom clouds in the magnetic traps using rf-spectroscopy techniques.

  13. The process γγ → νν-bar in a strong magnetic field

    International Nuclear Information System (INIS)

    Kuznetsov, A.V.; Mikheev, N.V.; Rumyantsev, D.A.

    2003-01-01

    A general analysis of the three-vertex loop amplitude in a strong magnetic field, based on the asymptotic form of the electron propagator in the field, is performed. In order to investigate the photon-neutrino process γγ → νν-bar, the vertex combinations of the scalar-vector-vector (SVV), pseudoscalar- vector-vector (PVV), 3-vector (VVV), and axial-vector-vector (AVV) types are considered. It is shown that only the SVV amplitude grows linearly with the magnetic-field strength, while in the other amplitudes, PVV, VVV, and AVV, the linearly growing terms are cancelled. The process γγ → νν-bar is investigated in the left-right-symmetric extension of the standard model of electroweak interaction, where the effective scalar ννee coupling could exist. Possible astrophysical manifestations of the considered process are discussed [ru

  14. Strong Coupling of Microwave Photons to Antiferromagnetic Fluctuations in an Organic Magnet

    Science.gov (United States)

    Mergenthaler, Matthias; Liu, Junjie; Le Roy, Jennifer J.; Ares, Natalia; Thompson, Amber L.; Bogani, Lapo; Luis, Fernando; Blundell, Stephen J.; Lancaster, Tom; Ardavan, Arzhang; Briggs, G. Andrew D.; Leek, Peter J.; Laird, Edward A.

    2017-10-01

    Coupling between a crystal of di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium radicals and a superconducting microwave resonator is investigated in a circuit quantum electrodynamics (circuit QED) architecture. The crystal exhibits paramagnetic behavior above 4 K, with antiferromagnetic correlations appearing below this temperature, and we demonstrate strong coupling at base temperature. The magnetic resonance acquires a field angle dependence as the crystal is cooled down, indicating anisotropy of the exchange interactions. These results show that multispin modes in organic crystals are suitable for circuit QED, offering a platform for their coherent manipulation. They also utilize the circuit QED architecture as a way to probe spin correlations at low temperature.

  15. An analytical method for the investigation of instability of a collisionless plasma in strong magnetic fields

    International Nuclear Information System (INIS)

    Zakharov, V.U.

    1993-01-01

    An analytical method for the investigation of special types of dispersion relations is presented. In particular, analysis of the propagation of small-amplitude hydromagnetic waves in a collisionless plasma in a strong magnetic field leads to such dispersion relations. The fifth-degree dispersion relation corresponding to a particular case is considered. The necessary stability condition for a steady state and conditions for the degeneration of small-amplitude waves are derived. A comparison with other methods for the analysis of similar dispersion relations is also presented. (author)

  16. Integrated electronic transport and thermometry at milliKelvin temperatures and in strong magnetic fields.

    Science.gov (United States)

    Samkharadze, N; Kumar, A; Manfra, M J; Pfeiffer, L N; West, K W; Csáthy, G A

    2011-05-01

    We fabricated a He-3 immersion cell for transport measurements of semiconductor nanostructures at ultra low temperatures and in strong magnetic fields. We have a new scheme of field-independent thermometry based on quartz tuning fork Helium-3 viscometry which monitors the local temperature of the sample's environment in real time. The operation and measurement circuitry of the quartz viscometer is described in detail. We provide evidence that the temperature of two-dimensional electron gas confined to a GaAs quantum well follows the temperature of the quartz viscometer down to 4 mK.

  17. Laser-driven platform for generation and characterization of strong quasi-static magnetic fields

    Czech Academy of Sciences Publication Activity Database

    Santos, J.J.; Bailly-Grandvaux, M.; Giuffrida, Lorenzo; Forestier-Colleoni, P.; Fujioka, H.; Zhang, Z.; Korneev, P.; Bouillaud, R.; Dorard, S.; Batani, D.; Chevrot, M.; Cross, J. E.; Crowston, R.; Dubois, J.L.; Gazave, J.; Gregori, G.; d'Humieres, E.; Hulin, S.; Ishihara, K.; Kojima, S.; Loyez, E.; Marqués, J.-R.; Morace, A.; Nicolaï, P.; Peyrusse, O.; Poyé, A.; Raffestin, D.; Ribolzi, J.; Roth, M.; Schaumann, G.; Serres, F.; Tikhonchuk, V.T.; Vacar, P.; Woolsey, N.

    2015-01-01

    Roč. 17, Aug (2015), s. 1-10, č. článku 083051. ISSN 1367-2630 R&D Projects: GA MŠk ED1.1.00/02.0061 Grant - others:ELI Beamlines(XE) CZ.1.05/1.1.00/02.0061 Institutional support: RVO:68378271 Keywords : strong magnetic field * laser-driven coil targets * laser-plasma interaction Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 3.570, year: 2015

  18. Study of Fluid Flow Control in Protein Crystallization using Strong Magnetic Fields

    Science.gov (United States)

    Ramachandran, Narayanan; Leslie, Fred; Ciszak, Ewa

    2002-11-01

    An important component in biotechnology, particularly in the area of protein engineering and rational drug design is the knowledge of the precise three-dimensional molecular structure of proteins. The quality of structural information obtained from X-ray diffraction methods is directly dependent on the degree of perfection of the protein crystals. As a consequence, the growth of high quality macromolecular crystals for diffraction analyses has been the central focus for biochemists, biologists, and bioengineers. Macromolecular crystals are obtained from solutions that contain the crystallizing species in equilibrium with higher aggregates, ions, precipitants, other possible phases of the protein, foreign particles, the walls of the container, and a likely host of other impurities. By changing transport modes in general, i.e., reduction of convection and sedimentation, as is achieved in "microgravity", researchers have been able to dramatically affect the movement and distribution of macromolecules in the fluid, and thus their transport, formation of crystal nuclei, and adsorption to the crystal surface. While a limited number of high quality crystals from space flights have been obtained, as the recent National Research Council (NRC) review of the NASA microgravity crystallization program pointed out, the scientific approach and research in crystallization of proteins has been mainly empirical yielding inconclusive results. We postulate that we can reduce convection in ground-based experiments and we can understand the different aspects of convection control through the use of strong magnetic fields and field gradients. Whether this limited convection in a magnetic field will provide the environment for the growth of high quality crystals is still a matter of conjecture that our research will address. The approach exploits the variation of fluid magnetic susceptibility with concentration for this purpose and the convective damping is realized by appropriately

  19. Charge transfer of He2 + with H in a strong magnetic field

    Science.gov (United States)

    Liu, Chun-Lei; Zou, Shi-Yang; He, Bin; Wang, Jian-Guo

    2015-09-01

    By solving a time-dependent Schrödinger equation (TDSE), we studied the electron capture process in the He2 + +H collision system under a strong magnetic field in a wide projectile energy range. The strong enhancement of the total charge transfer cross section is observed for the projectile energy below 2.0 keV/u. With the projectile energy increasing, the cross sections will reduce a little and then increase again, compared with those in the field-free case. The cross sections to the states with different magnetic quantum numbers are presented and analyzed where the influence due to Zeeman splitting is obviously found, especially in the low projectile energy region. The comparison with other models is made and the tendency of the cross section varying with the projectile energy is found closer to that from other close coupling models. Project supported by the National Natural Science Foundation of China (Grants Nos. 11104017, 11025417, 11275029, and 11474032), the National Basic Research Programm of China (Grant No. 2013CB922200), and the Foundation for the Development of Science and Technology of the Chinese Academy of Engineering Physics (Grant Nos. 2014B09036 and 2013A0102005).

  20. Breakdown of the Chiral Anomaly in Weyl Semimetals in a Strong Magnetic Field

    Science.gov (United States)

    Kim, Pilkwang; Ryoo, Ji Hoon; Park, Cheol-Hwan

    2017-12-01

    The low-energy quasiparticles of Weyl semimetals are a condensed-matter realization of the Weyl fermions introduced in relativistic field theory. Chiral anomaly, the nonconservation of the chiral charge under parallel electric and magnetic fields, is arguably the most important phenomenon of Weyl semimetals and has been explained as an imbalance between the occupancies of the gapless, zeroth Landau levels with opposite chiralities. This widely accepted picture has served as the basis for subsequent studies. Here we report the breakdown of the chiral anomaly in Weyl semimetals in a strong magnetic field based on ab initio calculations. A sizable energy gap that depends sensitively on the direction of the magnetic field may open up due to the mixing of the zeroth Landau levels associated with the opposite-chirality Weyl points that are away from each other in the Brillouin zone. Our study provides a theoretical framework for understanding a wide range of phenomena closely related to the chiral anomaly in topological semimetals, such as magnetotransport, thermoelectric responses, and plasmons, to name a few.

  1. Strong Static Magnetic Fields Increase the Gel Signal in Partially Hydrated DPPC/DMPC Membranes

    Directory of Open Access Journals (Sweden)

    Jennifer Tang

    2015-09-01

    Full Text Available NIt was recently reported that static magnetic fields increase lipid order in the hydrophobic membrane core of dehydrated native plant plasma membranes [Poinapen, Soft Matter 9:6804-6813, 2013]. As plasma membranes are multicomponent, highly complex structures, in order to elucidate the origin of this effect, we prepared model membranes consisting of a lipid species with low and high melting temperature. By controlling the temperature, bilayers coexisting of small gel and fluid domains were prepared as a basic model for the plasma membrane core. We studied molecular order in mixed lipid membranes made of dimyristoyl-sn-glycero-3-phosphocholine (DMPC and dipalmitoyl-sn-glycero-3-phosphocholine (DPPC using neutron diffraction in the presence of strong static magnetic fields up to 3.5 T. The contribution of the hydrophobic membrane core was highlighted through deuterium labeling the lipid acyl chains. There was no observable effect on lipid organization in fluid or gel domains at high hydration of the membranes. However, lipid order was found to be enhanced at a reduced relative humidity of 43%: a magnetic field of 3.5 T led to an increase of the gel signal in the diffraction patterns of 5%. While all biological materials have weak diamagnetic properties, the corresponding energy is too small to compete against thermal disorder or viscous effects in the case of lipid molecules. We tentatively propose that the interaction between the fatty acid chains’ electric moment and the external magnetic field is driving the lipid tails in the hydrophobic membrane core into a better ordered state.

  2. Strong Static Magnetic Fields Increase the Gel Signal in Partially Hydrated DPPC/DMPC Membranes.

    Science.gov (United States)

    Tang, Jennifer; Alsop, Richard J; Schmalzl, Karin; Epand, Richard M; Rheinstädter, Maikel C

    2015-09-29

    NIt was recently reported that static magnetic fields increase lipid order in the hydrophobic membrane core of dehydrated native plant plasma membranes [Poinapen, Soft Matter 9:6804-6813, 2013]. As plasma membranes are multicomponent, highly complex structures, in order to elucidate the origin of this effect, we prepared model membranes consisting of a lipid species with low and high melting temperature. By controlling the temperature, bilayers coexisting of small gel and fluid domains were prepared as a basic model for the plasma membrane core. We studied molecular order in mixed lipid membranes made of dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) using neutron diffraction in the presence of strong static magnetic fields up to 3.5 T. The contribution of the hydrophobic membrane core was highlighted through deuterium labeling the lipid acyl chains. There was no observable effect on lipid organization in fluid or gel domains at high hydration of the membranes. However, lipid order was found to be enhanced at a reduced relative humidity of 43%: a magnetic field of 3.5 T led to an increase of the gel signal in the diffraction patterns of 5%. While all biological materials have weak diamagnetic properties, the corresponding energy is too small to compete against thermal disorder or viscous effects in the case of lipid molecules. We tentatively propose that the interaction between the fatty acid chains' electric moment and the external magnetic field is driving the lipid tails in the hydrophobic membrane core into a better ordered state.

  3. Role of top and bottom interfaces of a Pt/Co/AlOx system in Dzyaloshinskii-Moriya interaction, interface perpendicular magnetic anisotropy, and magneto-optical Kerr effect

    Directory of Open Access Journals (Sweden)

    Nam-Hui Kim

    2017-03-01

    Full Text Available We investigate the role of top and bottom interfaces in inversion symmetry-breaking Pt/Co/AlOx systems by inserting ultra-thin Cu layers. Wedge-type ultrathin Cu layers (0-0.5 nm are introduced between Pt/Co or Co/AlOx interfaces. Interface sensitive physical quantities such as the interfacial Dzyaloshinskii-Moriya interaction (iDMI energy density, the interfacial perpendicular magnetic anisotropy (iPMA, and the magneto-optical Kerr effects (MOKE are systematically measured as a function of Cu-insertion layer thickness. We find that the Cu-insertion layer in the bottom interface (Pt/Co plays a more important role in iDMI, PMA, and MOKE. In contrast, the top interface (Co/AlOx noticeably contributes to only PMA, while its contributions to iDMI and MOKE enhancement are less significant. Although the PMA mainly comes from the bottom interface (Pt/Co, the Cu-insertion layers of all interfaces (Pt/Co, Co/AlOx influence PMA. For iDMI, only the Cu-insertion layer in the bottom interface exerts SOC suppression which leads iDMI energy to decrease rapidly.

  4. Tunneling-Magnetoresistance Ratio Comparison of MgO-Based Perpendicular-Magnetic-Tunneling-Junction Spin Valve Between Top and Bottom Co2Fe6B2 Free Layer Structure.

    Science.gov (United States)

    Lee, Du-Yeong; Lee, Seung-Eun; Shim, Tae-Hun; Park, Jea-Gun

    2016-12-01

    For the perpendicular-magnetic-tunneling-junction (p-MTJ) spin valve with a nanoscale-thick bottom Co2Fe6B2 free layer ex situ annealed at 400 °C, which has been used as a common p-MTJ structure, the Pt atoms of the Pt buffer layer diffused into the MgO tunneling barrier. This transformed the MgO tunneling barrier from a body-centered cubic (b.c.c) crystallized layer into a mixture of b.c.c, face-centered cubic, and amorphous layers and rapidly decreased the tunneling-magnetoresistance (TMR) ratio. The p-MTJ spin valve with a nanoscale-thick top Co2Fe6B2 free layer could prevent the Pt atoms diffusing into the MgO tunneling barrier during ex situ annealing at 400 °C because of non-necessity of a Pt buffer layer, demonstrating the TMR ratio of ~143 %.

  5. Tiny Stars, Strong Fields: Exploring the Origin of Intense Magnetism in M Stars

    Science.gov (United States)

    Toomre, Juri

    . We bring to this our prior experience with studying dynamo processes in the outer convective envelopes of G- (the Sun) and Ftype stars, briefly of M dwarfs, and in full convective cores within more massive A- and B-type stars. Our previous work suggests that M dwarfs could display a broad range of dynamo behavior, from cyclic reversals to more chaotic variations, and further to both weak and strong dynamo states. We will focus on the latter, exploring how superequipartition magnetic fields could be achieved by dynamo action in M dwarfs, as are likely needed to energize super-flares and huge active regions, and what limits the peak field strengths. M-type stars are distinctive in becoming fully convective with decreasing mass at about M3.5 in spectral type (or about 0.35 solar masses). At this transition, a steep rise in the fraction of magnetically active stars is observed that is accompanied by an increasing rotational velocity. Clearly how mass-loss and spin-down can lead to this is of interest in itself. However, here we propose to study the manner in which dynamos operating in fully convective M dwarf interiors beyond the transition may be able to achieve very strong magnetic fields, and how field strengths and apparent magnetic activity increases with rotation rate as suggested by observations. We believe that global connectivity of flows and fields across the core center will admit new classes of strong behavior, as revealed by our B star core dynamos, not realized when a convective envelope is bounded below by a tachocline. These ideas need to be tested in a self-consistent manner with global ASH simulations to gain theoretical insights into what is the origin of the fierce magnetic activity in some of M dwarfs that may be potential hosts to Earth-like planets. Such 3-D MHD simulations, though challenging, are now feasible and would complement the intensive observational searches under way.

  6. Strong impact of lattice vibrations on electronic and magnetic properties of paramagnetic Fe revealed by disordered local moments molecular dynamics

    NARCIS (Netherlands)

    Alling, B.; Kormann, F.H.W.; Grabowski, B; Glensk, A; Abrikosov, I.A.

    2016-01-01

    We study the impact of lattice vibrations on magnetic and electronic properties of paramagnetic bcc and fcc iron at finite temperature, employing the disordered local moments molecular dynamics (DLM-MD) method. Vibrations strongly affect the distribution of local magnetic moments at finite

  7. Asymptotic behaviour of the equilibrium nuclear separation for the H{sup +}{sub 2} molecule in a strong magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Benguria, Rafael [Pontificia Universidad Catolica de Chile, Departamento de Fisica, Casilla 306, Santiago 22, Chile (Chile); Brummelhuis, Raymond [School of Economics, Mathematics and Statistics, 7-15 Gresse Street, University of London (United Kingdom); Duclos, Pierre [Centre de Physique Theorique UMR 6207-Unite Mixte de Recherche du CNRS et des Universites Aix-Marseille I, Aix-Marseille II et de l' Universite du Sud Toulon-Var-Laboratoire affilie a la FRUMAM, Luminy Case 907, F-13288 Marseille Cedex 9 (France); Perez-Oyarzun, Santiago [Instituto de Ciencias Basicas, Facultad de Ingenieria, Universidad Diego Portales, Av. Ejercito 441, Casilla 298-v, Santiago (Chile); Vytras, Petr [Katedra Matematiky, FJFI, CVUT, Trojanova 13, CZ-Prague 12000 (Czech Republic)

    2006-06-30

    We consider the hydrogen molecular ion H{sup +}{sub 2} in the fixed nuclear approximation, in the presence of a strong homogeneous magnetic field. We determine the leading asymptotic behaviour for the equilibrium distance between the nuclei of this molecule in the limit when the strength of the magnetic field goes to infinity.

  8. Semiclassical quantization of integrable systems of few interacting anyons in a strong magnetic field

    International Nuclear Information System (INIS)

    Sivan, N.; Levit, S.

    1992-01-01

    We present a semiclassical theory of charged interacting anyons in a strong magnetic field. We derive the appropriate generalization of the WKB quantization conditions and determine the corresponding wave functions for non separable integrable anyonic systems. This theory is applies to a system of two interacting anyons, two interacting anyons in the presence of an impurity and three interacting anyons. We calculate the dependence of the semiclassical energy levels on the statistical parameter and find regions in which dependence follows very different patterns. The semiclassical treatment allows to find the correlation between these patterns and the change in the character of the classical motion of the system. We also test the accuracy of the mean field approximation for low and high energy states of the three anyons. (author)

  9. Influence of strong magnetic fields on laser pulse propagation in underdense plasma

    Science.gov (United States)

    Wilson, T. C.; Li, F. Y.; Weikum, M.; Sheng, Z. M.

    2017-06-01

    We examine the interaction between intense laser pulses and strongly magnetised plasmas in the weakly relativistic regime. An expression for the electron Lorentz factor coupling both relativistic and cyclotron motion nonlinearities is derived for static magnetic fields along the laser propagation axis. This is applied to predict modifications to the refractive index, critical density, group velocity dispersion and power threshold for relativistic self-focusing. It is found that electron quiver response is enhanced under right circularly-polarised light, decreasing the power threshold for various instabilities, while a dampening effect occurs under left circularly-polarised light, increasing the power thresholds. Derived theoretical predictions are tested by one- and three-dimensional particle-in-cell simulations.

  10. Hot electromagnetic outflows. III. Displaced fireball in a strong magnetic field

    International Nuclear Information System (INIS)

    Thompson, Christopher; Gill, Ramandeep

    2014-01-01

    The evolution of a dilute electron-positron fireball is calculated in the regime of strong magnetization and high compactness (ℓ ∼ 10 3 -10 8 ). Heating is applied at a low effective temperature (<25 keV), appropriate to breakout from a confining medium, so that relaxation to a blackbody is inhibited by pair annihilation. The diffusion equation for Compton scattering by thermal pairs is coupled to a trans-relativistic cyclo-synchrotron source. We find that the photon spectrum develops a quasi-thermal peak at energy ∼0.1 m e c 2 in the comoving frame, with a power-law slope below it that is characteristic of gamma-ray bursts (GRBs; F ω ∼ const). The formation of a thermal high-energy spectrum is checked using the full kinetic equations. Calculations for a baryon-dominated photosphere reveal a lower spectral peak energy, and a harder low-energy spectrum, unless ion rest mass carries ≲ 10 –5 of the energy flux. We infer that (1) the GRB spectrum is inconsistent with the neutron-rich wind emitted by a young magnetar or neutron torus, and points to an event horizon in the engine; (2) neutrons play a negligible role in prompt gamma-ray emission; (3) the relation between observed peak frequency and burst energy is bounded below by the observed Amati relation if the Lorentz factor ∼(opening angle) –1 at breakout, and the jet is surrounded by a broader sheath that interacts with a collapsing stellar core; (4) X-ray flashes are consistent with magnetized jets with ion-dominated photospheres; (5) high-frequency Alfvén waves may become charge starved in the dilute pair gas; (6) limitations on magnetic reconnection from plasma collisionality have been overestimated.

  11. Global Pc5 pulsations during strong magnetic storms: excitation mechanisms and equatorward expansion

    Science.gov (United States)

    Marin, J. A.; Pilipenko, V.; Vega, P.; Zesta, E.; Stepanova, M. V.; Uozumi, T.

    2012-12-01

    The spatial structure of Pc5 waves during the recovery phases of strong magnetic storms is important not only for the identification of possible physical mechanisms of its excitation, but as an important parameter of the ULF driver of relativistic electrons. The dynamics of global Pc5 waves during the magnetic storms on October 29-31, 2003 and May 15, 2005 is studied, using the data from the trans-American network of magnetometers comprising SAMBA, MAGDAS, CARISMA, and MACCS arrays. We study the behavior of Pc5 wave properties and spectral characteristics with respect to latitude. One of the accepted sources of Pc5 wave activity is Kelvin-Helmholtz instability in the flanks of the magnetosphere. In our study we examine whether the KH instability is sufficient as an excitation mechanism for the observed waves? More specifically, we attempt to determine, what is the Pc5 wave generation type: self-excitation, resonant response, trigger? While the KH instability generation takes place at the outer flanks of the magnetosphere, Pc5 waves are observed at all latitudes. We determine how deep into the magnetosphere these Pc5 waves activity can extend and what is the wave energy transmission mechanism: surface mode, cavity mode, Alfven field-line resonance, magnetospheric MHD waveguide?

  12. Disorder effects on helical edge transport in graphene under a strong tilted magnetic field

    Science.gov (United States)

    Huang, Chunli; Cazalilla, Miguel A.

    2015-10-01

    In a recent experiment, Young et al. [Nature (London) 505, 528 (2014), 10.1038/nature12800] observed a metal to insulator transition as well as transport through helical edge states in monolayer graphene under a strong, tilted magnetic field. Under such conditions, the bulk is a magnetic insulator which can exhibit metallic conduction through helical edges. It was found that the two-terminal conductance of the helical channels deviates from the expected quantized value (=e2/h per edge, at zero temperature). Motivated by this observation, we study the effect of disorder on the conduction through the edge channels. We show that, unlike for helical edges of topological insulators in semiconducting quantum wells, a disorder Rashba spin-orbit coupling does not lead to backscattering, at least to leading order. Instead, we find that the lack of perfect antialignment of the electron spins in the helical channels to be the most likely cause for backscattering arising from scalar (i.e., spin-independent) impurities. The intrinsic spin-orbit coupling and other time-reversal symmetry-breaking and/or sublattice parity-breaking potentials also lead to (subleading) corrections to the channel conductance.

  13. The Design of a Device for the Generation of a Strong Magnetic Field in an Air Gap Using Permanent Magnets

    Czech Academy of Sciences Publication Activity Database

    Žežulka, Václav; Straka, Pavel

    2017-01-01

    Roč. 22, č. 2 (2017), s. 250-256 ISSN 1226-1750 Institutional support: RVO:67985891 Keywords : magnet ic field * permanent magnet s * NdFeB magnet s * Halbach arrays Subject RIV: BM - Solid Matter Physics ; Magnet ism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 0.713, year: 2016

  14. The First in situ Observation of Kelvin-Helmholtz Waves at High-Latitude Magnetopause during Strongly Dawnward Interplanetary Magnetic Field Conditions

    Science.gov (United States)

    Hwang, K.-J.; Goldstein, M. L.; Kuznetsova, M. M.; Wang, Y.; Vinas, A. F.; Sibeck, D. G.

    2012-01-01

    We report the first in situ observation of high-latitude magnetopause (near the northern duskward cusp) Kelvin-Helmholtz waves (KHW) by Cluster on January 12, 2003, under strongly dawnward interplanetary magnetic field (IMF) conditions. The fluctuations unstable to Kelvin-Helmholtz instability (KHI) are found to propagate mostly tailward, i.e., along the direction almost 90 deg. to both the magnetosheath and geomagnetic fields, which lowers the threshold of the KHI. The magnetic configuration across the boundary layer near the northern duskward cusp region during dawnward IMF is similar to that in the low-latitude boundary layer under northward IMF, in that (1) both magnetosheath and magnetospheric fields across the local boundary layer constitute the lowest magnetic shear and (2) the tailward propagation of the KHW is perpendicular to both fields. Approximately 3-hour-long periods of the KHW during dawnward IMF are followed by the rapid expansion of the dayside magnetosphere associated with the passage of an IMF discontinuity that characterizes an abrupt change in IMF cone angle, Phi = acos (B(sub x) / absolute value of Beta), from approx. 90 to approx. 10. Cluster, which was on its outbound trajectory, continued observing the boundary waves at the northern evening-side magnetopause during sunward IMF conditions following the passage of the IMF discontinuity. By comparing the signatures of boundary fluctuations before and after the IMF discontinuity, we report that the frequencies of the most unstable KH modes increased after the discontinuity passed. This result demonstrates that differences in IMF orientations (especially in f) are associated with the properties of KHW at the high-latitude magnetopause due to variations in thickness of the boundary layer, and/or width of the KH-unstable band on the surface of the dayside magnetopause.

  15. The mean energy loss by neutrino with magnetic moment in strong magnetic field with consideration of positronium contribution to photon dispersion

    Science.gov (United States)

    Mosichkin, A. F.

    2017-11-01

    The process of radiative decay of the neutrino with a magnetic moment in a strong magnetic field with consideration of positronium influence on photon dispersion has been studied. Positronium contribution to the photon polarization operator induces significant modifications of the photon dispersion law and neutrino radiative decay amplitude. It has been shown that the mean energy loss of a neutrino with magnetic a moment significantly increases, when the positronium contribution to photon dispersion is taken into account.

  16. Behavior of Particle Depots in Molten Silicon During Float-Zone Growth in Strong Magnetic Fields

    Science.gov (United States)

    Jauss, T.; Croell, A.; SorgenFrei, T.; Azizi, M.; Reimann, C.; Friedrich, J.; Volz, M. P.

    2014-01-01

    Solar cells made from directionally solidified silicon cover 57% of the photovoltaic industry's market [1]. One major issue during directional solidification of silicon is the precipitation of foreign phase particles. These particles, mainly SiC and Si3N4, are precipitated from the dissolved crucible coating, which is made of silicon nitride, and the dissolution of carbon monoxide from the furnace atmosphere. Due to their hardness and size of several hundred micrometers, those particles can lead to severe problems during the wire sawing process for wafering the ingots. Additionally, SiC particles can act as a shunt, short circuiting the solar cell. Even if the particles are too small to disturb the wafering process, they can lead to a grit structure of silicon micro grains and serve as sources for dislocations. All of this lowers the yield of solar cells and reduces the performance of cells and modules. We studied the behaviour of SiC particle depots during float-zone growth under an oxide skin, and strong static magnetic fields. For high field strengths of 3T and above and an oxide layer on the sample surface, convection is sufficiently suppressed to create a diffusive like regime, with strongly dampened convection [2, 3]. To investigate the difference between atomically rough phase boundaries and facetted growth, samples with [100] and [111] orientation were processed.

  17. COMPRESSIBLE RELATIVISTIC MAGNETOHYDRODYNAMIC TURBULENCE IN MAGNETICALLY DOMINATED PLASMAS AND IMPLICATIONS FOR A STRONG-COUPLING REGIME

    Energy Technology Data Exchange (ETDEWEB)

    Takamoto, Makoto [Department of Earth and Planetary Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-0033 (Japan); Lazarian, Alexandre, E-mail: mtakamoto@eps.s.u-tokyo.ac.jp, E-mail: alazarian@facstaff.wisc.edu [Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, WI 53706 (United States)

    2016-11-10

    In this Letter, we report compressible mode effects on relativistic magnetohydrodynamic (RMHD) turbulence in Poynting-dominated plasmas using three-dimensional numerical simulations. We decomposed fluctuations in the turbulence into 3 MHD modes (fast, slow, and Alfvén) following the procedure of mode decomposition in Cho and Lazarian, and analyzed their energy spectra and structure functions separately. We also analyzed the ratio of compressible mode to Alfvén mode energy with respect to its Mach number. We found the ratio of compressible mode increases not only with the Alfvén Mach number, but also with the background magnetization, which indicates a strong coupling between the fast and Alfvén modes. It also signifies the appearance of a new regime of RMHD turbulence in Poynting-dominated plasmas where the fast and Alfvén modes are strongly coupled and, unlike the non-relativistic MHD regime, cannot be treated separately. This finding will affect particle acceleration efficiency obtained by assuming Alfvénic critical-balance turbulence and can change the resulting photon spectra emitted by non-thermal electrons.

  18. Local Magnetism in Strongly Correlated Electron Systems with Orbital Degrees of Freedom

    Science.gov (United States)

    Ducatman, Samuel Charles

    The central aim of my research is to explain the connection between the macroscopic behavior and the microscopic physics of strongly correlated electron systems with orbital degrees of freedom through the use of effective models. My dissertation focuses on the sub-class of these materials where electrons appear to be localized by interactions, and magnetic ions have well measured magnetic moments. This suggests that we can capture the low-energy physics of the material by employing a minimal model featuring localized spins which interact with each other through exchange couplings. I describe Fe1+y Te and beta-Li2IrO3 with effective models primarily focusing on the spins of the magnetic ions, in this case Fe and Ir, respectively. The goal with both materials is to gain insight and make predictions for experimentalists. In chapter 2, I focus on Fe1+yTe. I describe why we believe the magnetic ground state of this material, with an observed Bragg peak at Q +/- pi/2, pi/2), can be described by a Heisenberg model with 1st, 2nd, and 3rd neighbor interactions. I present two possible ground states of this model in the small J1 limit, the bicollinear and plaquette states. In order to predict which ground state the model prefers, I calculate the spin wave spectrum with 1/S corrections, and I find the model naturally selects the "plaquette state." I give a brief description of the ways this result could be tested using experimental techniques such as polarized neutron scattering. In chapter 3, I extend the model used in chapter 2. This is necessary because the Heisenberg model we employed cannot explain why Fe1+yTe undergoes a phase transition as y is increased. We add an additional elements to our calculation; we assume that electrons in some of the Fe 3D orbitals have selectively localized while others remain itinerant. We write a new Hamiltonian, where localized moments acquire a new long-range RKKY-like interaction from interactions with the itinerant electrons. We are

  19. The contribution of Diamond Light Source to the study of strongly correlated electron systems and complex magnetic structures.

    Science.gov (United States)

    Radaelli, P G; Dhesi, S S

    2015-03-06

    We review some of the significant contributions to the field of strongly correlated materials and complex magnets, arising from experiments performed at the Diamond Light Source (Harwell Science and Innovation Campus, Didcot, UK) during the first few years of operation (2007-2014). We provide a comprehensive overview of Diamond research on topological insulators, multiferroics, complex oxides and magnetic nanostructures. Several experiments on ultrafast dynamics, magnetic imaging, photoemission electron microscopy, soft X-ray holography and resonant magnetic hard and soft X-ray scattering are described. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

  20. Numerical simulations of a cylinder wake under a strong axial magnetic field

    Science.gov (United States)

    Dousset, Vincent; Pothérat, Alban

    2008-01-01

    We study the flow of a liquid metal in a square duct past a circular cylinder in a strong externally imposed magnetic field. In these conditions, the flow is quasi-two-dimensional, which allows us to model it using a two-dimensional (2D) model. We perform a parametric study by varying the two control parameters Re and Ha (Ha2 is the ratio of Lorentz to viscous forces) in the ranges [0…6000] and [0…2160], respectively. The flow is found to exhibit a sequence of four regimes. The first three regimes are similar to those of the non-magnetohydrodynamic (non-MHD) 2D circular wake, with transitions controlled by the friction parameter Re /Ha. The fourth one is characterized by vortices raising from boundary layer separations at the duct side walls, which strongly disturbs the Kármán vortex street. This provides the first explanation for the breakup of the 2D Kármán vortex street first observed experimentally by Frank, Barleon, and Müller [Phys. Fluids 13, 2287 (2001)]. We also show that, for high values of Ha (Ha⩾1120), the transition to the fourth regime occurs for Re ∝0.56Ha, and that it is accompanied by a sudden drop in the Strouhal number. In the first three regimes, we show that the drag coefficient and the length of the steady recirculation regions located behind the cylinder are controlled by the parameter Re /Ha4/5. Also, the free shear layer that separates the recirculation region from the free stream is similar to a free MHD parallel layer, with a thickness of the order of Ha-1/2 that is quite different to that of the non-MHD case, and therefore strongly influences the dynamics of this region. We also present one case at Re =3×104 and Ha =1120, where this layer undergoes an instability of the Kelvin-Helmholtz-type.

  1. Magnetic structure of RPdSn (R=Tb, Ho) single crystal compounds under strong magnetic field

    International Nuclear Information System (INIS)

    Andoh, Y.; Kurisu, M.; Nakamoto, G.; Tsutaoka, T.; Kawano, S.

    2003-01-01

    Rare earth compounds RTX, where R stands for rare earth elements, T for Ni, Pd or Rh, and X for Sn or Ge, crystallize to a rhombic ε-TiNiSi structure. Only rare earth elements R contribute to magnetic properties since T and X atoms are nonmagnetic. The competition between RKKY indirect interaction and large magnetic anisotropy generates many complicated magnetic phases. At a low temperature phase, complicated magnetisms such as meta-magnetism were observed in magnetization curves with many steps. In previous experiments dealing with RPdSn where R means Tb or Ho, some characteristics of magnetic properties of these compounds were deduced from magnetization measurements and neutron diffraction without external magnetic field. In this report, the change of magnetic scattering of neutron diffraction was studied under external magnetic fields in order to reveal the mechanism of the phase transformations of the compounds. The difference between TbPdSn and HoPdSn compounds was observed in magnetic field dependence of the wave vectors of the magnetic scattering. Two independent wave vectors in magnetic scattering existed in HoPdSn compound. (Y. Kazumata)

  2. Accurate and balanced anisotropic Gaussian type orbital basis sets for atoms in strong magnetic fields

    Science.gov (United States)

    Zhu, Wuming; Trickey, S. B.

    2017-12-01

    In high magnetic field calculations, anisotropic Gaussian type orbital (AGTO) basis functions are capable of reconciling the competing demands of the spherically symmetric Coulombic interaction and cylindrical magnetic (B field) confinement. However, the best available a priori procedure for composing highly accurate AGTO sets for atoms in a strong B field [W. Zhu et al., Phys. Rev. A 90, 022504 (2014)] yields very large basis sets. Their size is problematical for use in any calculation with unfavorable computational cost scaling. Here we provide an alternative constructive procedure. It is based upon analysis of the underlying physics of atoms in B fields that allow identification of several principles for the construction of AGTO basis sets. Aided by numerical optimization and parameter fitting, followed by fine tuning of fitting parameters, we devise formulae for generating accurate AGTO basis sets in an arbitrary B field. For the hydrogen iso-electronic sequence, a set depends on B field strength, nuclear charge, and orbital quantum numbers. For multi-electron systems, the basis set formulae also include adjustment to account for orbital occupations. Tests of the new basis sets for atoms H through C (1 ≤ Z ≤ 6) and ions Li+, Be+, and B+, in a wide B field range (0 ≤ B ≤ 2000 a.u.), show an accuracy better than a few μhartree for single-electron systems and a few hundredths to a few mHs for multi-electron atoms. The relative errors are similar for different atoms and ions in a large B field range, from a few to a couple of tens of millionths, thereby confirming rather uniform accuracy across the nuclear charge Z and B field strength values. Residual basis set errors are two to three orders of magnitude smaller than the electronic correlation energies in multi-electron atoms, a signal of the usefulness of the new AGTO basis sets in correlated wavefunction or density functional calculations for atomic and molecular systems in an external strong B field.

  3. Accurate and balanced anisotropic Gaussian type orbital basis sets for atoms in strong magnetic fields.

    Science.gov (United States)

    Zhu, Wuming; Trickey, S B

    2017-12-28

    In high magnetic field calculations, anisotropic Gaussian type orbital (AGTO) basis functions are capable of reconciling the competing demands of the spherically symmetric Coulombic interaction and cylindrical magnetic (B field) confinement. However, the best available a priori procedure for composing highly accurate AGTO sets for atoms in a strong B field [W. Zhu et al., Phys. Rev. A 90, 022504 (2014)] yields very large basis sets. Their size is problematical for use in any calculation with unfavorable computational cost scaling. Here we provide an alternative constructive procedure. It is based upon analysis of the underlying physics of atoms in B fields that allow identification of several principles for the construction of AGTO basis sets. Aided by numerical optimization and parameter fitting, followed by fine tuning of fitting parameters, we devise formulae for generating accurate AGTO basis sets in an arbitrary B field. For the hydrogen iso-electronic sequence, a set depends on B field strength, nuclear charge, and orbital quantum numbers. For multi-electron systems, the basis set formulae also include adjustment to account for orbital occupations. Tests of the new basis sets for atoms H through C (1 ≤ Z ≤ 6) and ions Li + , Be + , and B + , in a wide B field range (0 ≤ B ≤ 2000 a.u.), show an accuracy better than a few μhartree for single-electron systems and a few hundredths to a few mHs for multi-electron atoms. The relative errors are similar for different atoms and ions in a large B field range, from a few to a couple of tens of millionths, thereby confirming rather uniform accuracy across the nuclear charge Z and B field strength values. Residual basis set errors are two to three orders of magnitude smaller than the electronic correlation energies in multi-electron atoms, a signal of the usefulness of the new AGTO basis sets in correlated wavefunction or density functional calculations for atomic and molecular systems in an external strong B

  4. Induced moment due to perpendicular field cycling in trained ...

    Indian Academy of Sciences (India)

    Depth-sensitive polarized neutron scattering in specular and off-specular mode has recently revealed that perpendicular field cycling brings about a modification in the interfacial magnetization of a trained exchange coupled interface. We show here by various model fits to our neutron reflectivity data that a restoration of the ...

  5. SU-E-T-227: Could the Alpha/Beta Ratio Change in a Strong Magnetic Field?

    Energy Technology Data Exchange (ETDEWEB)

    Pang, G [Odette Cancer Centre, 2075 Bayview Avenue, Toronto M4N 3M5, Canada and Sunnybrook Research Institute and Departments of Radiation Oncology and Medical Biophysics, University of Toronto, Toronto (Canada)

    2015-06-15

    Purpose: Magnetic resonance imaging (MRI) is being integrated into radiotherapy delivery for MRI-guided radiotherapy. The presence of a strong magnetic field from a MRI machine during radiotherapy delivery presents a new challenge since the trajectories of electrons liberated by ionizing radiation in patients are strongly dependent on the applied magnetic field. The purpose of this work is to explore the potential effect of a strong magnetic field on the α/β ratio, an important radiobiological parameter in radiotherapy. Methods: Based on the theory of dual radiation action, the α/β ratio can be expressed by an integral of the product of two microdosimetry quantities γ(x) and t(x), where γ(x) is the probability that two energy transfers, a distance x apart, results in a lesion, and t(x) is the proximity function, which is the energy-weighted point-pair distribution of distances between energy transfer points in a track. The quantity t(x) depends on the applied magnetic field. An analytical approach has been used to derive a formula that can be used to calculate the α/β ratio in an extremely strong magnetic field. Results: The α/β ratio has been evaluated in the special case when the applied magnetic field approaches infinity, which gives the upper limit of the potential change of the α/β ratio due to the presence of a strong magnetic field. For V79 Chinese hamster cells it has been shown that the α/β ratio could be increased by 2.90 times for Pd-103, 2.97 times for I-125 and about 2.3 times for Co-60 sources when the applied magnetic field approaches infinity. Conclusion: It has been shown theoretically that the α/β ratio can change in a strong magnetic field, and there could be up to a nearly three-fold increase in the α/β ratio, depending on the strength of the applied magnetic field, the cell type and the radiation used.

  6. Biological effects of electromagnetic fields and recently updated safety guidelines for strong static magnetic fields

    International Nuclear Information System (INIS)

    Yamaguchi-Sekino, Sachiko; Sekino, Masaki; Ueno, Shoogo

    2011-01-01

    Humans are exposed daily to artificial and naturally occurring magnetic fields that originate from many different sources. We review recent studies that examine the biological effects of and medical applications involving electromagnetic fields, review the properties of static and pulsed electromagnetic fields that affect biological systems, describe the use of a pulsed electromagnetic field in combination with an anticancer agent as an example of a medical application that incorporates an electromagnetic field, and discuss the recently updated safety guidelines for static electromagnetic fields. The most notable modifications to the 2009 International Commission on Non-Ionizing Radiation Protection guidelines are the increased exposure limits, especially for those who work with or near electromagnetic fields (occupational exposure limits). The recommended increases in exposure were determined using recent scientific evidence obtained from animal and human studies. Several studies since the 1994 publication of the guidelines have examined the effects on humans after exposure to high static electromagnetic fields (up to 9.4 tesla), but additional research is needed to ascertain further the safety of strong electromagnetic fields. (author)

  7. Biological effects of electromagnetic fields and recently updated safety guidelines for strong static magnetic fields.

    Science.gov (United States)

    Yamaguchi-Sekino, Sachiko; Sekino, Masaki; Ueno, Shoogo

    2011-01-01

    Humans are exposed daily to artificial and naturally occurring magnetic fields that originate from many different sources. We review recent studies that examine the biological effects of and medical applications involving electromagnetic fields, review the properties of static and pulsed electromagnetic fields that affect biological systems, describe the use of a pulsed electromagnetic field in combination with an anticancer agent as an example of a medical application that incorporates an electromagnetic field, and discuss the recently updated safety guidelines for static electromagnetic fields. The most notable modifications to the 2009 International Commission on Non-Ionizing Radiation Protection guidelines are the increased exposure limits, especially for those who work with or near electromagnetic fields (occupational exposure limits). The recommended increases in exposure were determined using recent scientific evidence obtained from animal and human studies. Several studies since the 1994 publication of the guidelines have examined the effects on humans after exposure to high static electromagnetic fields (up to 9.4 tesla), but additional research is needed to ascertain further the safety of strong electromagnetic fields.

  8. Concepts relating magnetic interactions, intertwined electronic orders, and strongly correlated superconductivity

    Science.gov (United States)

    Davis, J. C. Séamus; Lee, Dung-Hai

    2013-01-01

    Unconventional superconductivity (SC) is said to occur when Cooper pair formation is dominated by repulsive electron–electron interactions, so that the symmetry of the pair wave function is other than an isotropic s-wave. The strong, on-site, repulsive electron–electron interactions that are the proximate cause of such SC are more typically drivers of commensurate magnetism. Indeed, it is the suppression of commensurate antiferromagnetism (AF) that usually allows this type of unconventional superconductivity to emerge. Importantly, however, intervening between these AF and SC phases, intertwined electronic ordered phases (IP) of an unexpected nature are frequently discovered. For this reason, it has been extremely difficult to distinguish the microscopic essence of the correlated superconductivity from the often spectacular phenomenology of the IPs. Here we introduce a model conceptual framework within which to understand the relationship between AF electron–electron interactions, IPs, and correlated SC. We demonstrate its effectiveness in simultaneously explaining the consequences of AF interactions for the copper-based, iron-based, and heavy-fermion superconductors, as well as for their quite distinct IPs. PMID:24114268

  9. MULTI-WAVELENGTH STUDY OF A DELTA-SPOT. I. A REGION OF VERY STRONG, HORIZONTAL MAGNETIC FIELD

    International Nuclear Information System (INIS)

    Jaeggli, S. A.

    2016-01-01

    Active region NOAA 11035 appeared in 2009 December, early in the new solar activity cycle. This region achieved a delta sunspot (δ spot) configuration when parasitic flux emerged near the rotationally leading magnetic polarity and traveled through the penumbra of the largest sunspot in the group. Both visible and infrared imaging spectropolarimetry of the magnetically sensitive Fe i line pairs at 6302 and 15650 Å show large Zeeman splitting in the penumbra between the parasitic umbra and the main sunspot umbra. The polarized Stokes spectra in the strongest field region display anomalous profiles, and strong blueshifts are seen in an adjacent region. Analysis of the profiles is carried out using a Milne–Eddington inversion code capable of fitting either a single magnetic component with stray light or two independent magnetic components to verify the field strength. The inversion results show that the anomalous profiles cannot be produced by the combination of two profiles with moderate magnetic fields. The largest field strengths are 3500–3800 G in close proximity to blueshifts as strong as 3.8 km s −1 . The strong, nearly horizontal magnetic field seen near the polarity inversion line in this region is difficult to understand in the context of a standard model of sunspot magnetohydrostatic equilibrium

  10. MULTI-WAVELENGTH STUDY OF A DELTA-SPOT. I. A REGION OF VERY STRONG, HORIZONTAL MAGNETIC FIELD

    Energy Technology Data Exchange (ETDEWEB)

    Jaeggli, S. A., E-mail: sarah.jaeggli@nasa.gov [NASA Goddard Space Flight Center, Solar Physics Laboratory, Code 671, Greenbelt, MD 20771 (United States)

    2016-02-10

    Active region NOAA 11035 appeared in 2009 December, early in the new solar activity cycle. This region achieved a delta sunspot (δ spot) configuration when parasitic flux emerged near the rotationally leading magnetic polarity and traveled through the penumbra of the largest sunspot in the group. Both visible and infrared imaging spectropolarimetry of the magnetically sensitive Fe i line pairs at 6302 and 15650 Å show large Zeeman splitting in the penumbra between the parasitic umbra and the main sunspot umbra. The polarized Stokes spectra in the strongest field region display anomalous profiles, and strong blueshifts are seen in an adjacent region. Analysis of the profiles is carried out using a Milne–Eddington inversion code capable of fitting either a single magnetic component with stray light or two independent magnetic components to verify the field strength. The inversion results show that the anomalous profiles cannot be produced by the combination of two profiles with moderate magnetic fields. The largest field strengths are 3500–3800 G in close proximity to blueshifts as strong as 3.8 km s{sup −1}. The strong, nearly horizontal magnetic field seen near the polarity inversion line in this region is difficult to understand in the context of a standard model of sunspot magnetohydrostatic equilibrium.

  11. Magnetic properties of the strongly correlated chain antiferromagnet KTb(WO4)2

    International Nuclear Information System (INIS)

    Khatsko, E.; Loginov, A.; Cherny, A.; Rykova, A.

    2006-01-01

    The susceptibility and magnetization of a single crystal of KTb(WO 4 ) 2 has been measured in the temperature range 0.5-80 K in magnetic fields up to 6 T. It is shown that KTb(WO 4 ) 2 is an Ising magnet with only one component of the magnetic moment. The three-dimensional phase transition to the antiferromagnetically ordered state has been found below 0.7 K. This transition can be described in the molecular field two-level approximation. The principal exchange constant has been estimated. By using experimental data the magnetic structure of KTb(WO 4 ) 2 is proposed

  12. Perpendicularity misjudgments caused by contextual stimulus elements.

    Science.gov (United States)

    Bulatov, Aleksandr; Bulatova, Natalija; Surkys, Tadas

    2012-10-15

    It has been demonstrated in previous studies that the illusions of extent of the Brentano type can be explained by the perceptual positional shifts of the stimulus terminators in direction of the centers-of-masses (centroids) of adjacent contextual flanks [Bulatov, A. et al. (2011). Contextual flanks' tilting and magnitude of illusion of extent. Vision Research, 51(1), 58-64]. In the present study, the applicability of the centroid approach to explain the right-angle misjudgments was tested psychophysically using stimuli composed of three small disks (dots) forming an imaginary rectangular triangle. Stimuli comprised the Müller-Lyer wings or line segments (bars) as the contextual distracters rotated around the vertices of the triangle, and changes in the magnitude of the illusion of perpendicularity were measured in a set of experiments. A good resemblance between the experimental data and theoretical predictions obtained strongly supports the suggestion regarding the common "centroid" origin of the illusions of extent of the Brentano type and misperception of the perpendicularity investigated. 2012 Elsevier Ltd. All rights reserved

  13. Strongly magnetic soil developed on a non-magnetic rock basement: A case study from NW Bulgaria

    Czech Academy of Sciences Publication Activity Database

    Grison, Hana; Petrovský, Eduard; Jordanova, N.; Kapička, Aleš

    2011-01-01

    Roč. 55, č. 4 (2011), s. 697-716 ISSN 0039-3169 R&D Projects: GA AV ČR(CZ) KJB300120604 Institutional research plan: CEZ:AV0Z30120515 Keywords : magnetic susceptibility * magnetite * soil * pollution * climate * limestone Subject RIV: DE - Earth Magnetism, Geodesy, Geography Impact factor: 0.700, year: 2011

  14. Light-induced changes of cubic and uniaxial magnetic aniosotropy in a magnet doped by strongly anisotropic ions

    Czech Academy of Sciences Publication Activity Database

    Zaytseva, I.; Stupakiewicz, A.; Maziewski, A.; Zablotskyy, Vitaliy A.

    254-255, - (2003), s. 118-120 ISSN 0304-8853. [Soft Magnetic Material Conference ( SMM 15). Bilbao, 05.09.2001-07.09.2001] Institutional research plan: CEZ:AV0Z1010914 Keywords : photomagnetic effects * light-induced anisotropy * garnets Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.910, year: 2003

  15. Magnetics Research Facility

    Data.gov (United States)

    Federal Laboratory Consortium — The Magnetics Research Facility houses three Helmholtz coils that generate magnetic fields in three perpendicular directions to balance the earth's magnetic field....

  16. Molecular quantum magnetism with strong spin-orbit coupling in inorganic solid Ba3Yb2Zn5O11

    Science.gov (United States)

    Park, Sang-Youn; Ji, Sungdae; Park, Jae-Hoon; Do, Seunghwan; Choi, Kwang-Yong; Jang, Dongjin; Schmidt, Burkhard; Brando, Manuel; Butch, Nicholas

    The molecular magnet, assembly of finite number of spins which are isolated from environment, is a model system to study the quantum information process such as the qubit or spintronic devices. In past decades, the molecular magnet has been mostly realized in organic material, however, it has difficulty synthesizing materials or controlling their properties, meanwhile tremendous endeavors to search inorganic molecular magnet are continuing. Here, we propose Ba3Yb2Zn5O11 as a candidate of inorganic molecular magnet. This material consists of an alternating 3D-array of small and large tetrahedron containing antiferromagnetically coupled four pseudospin-1/2 Yb ions, and magnetic properties are described by an isolated tetrahedron without long-range magnetic ordering. Inelastic neutron scattering measurement with external magnetic field reveals that extraordinarily huge Dzyaloshinsky-Moriya (DM) interaction originating from strong spin-orbit coupling in Yb isospin is the key to explain energy level of tetrahedron in addition to Heisenberg exchange interaction and Zeeman effect. Magnetization measurement shows the Landau-Zener transition between avoided crossing levels caused by DM interaction.

  17. Method for Transformation of Weakly Magnetic Minerals (Hematite, Goethite into Strongly Magnetic Mineral (Magnetite to Improve the Efficiency of Technologies for Oxidized Iron Ores Benefication

    Directory of Open Access Journals (Sweden)

    Ponomarenko, O.

    2015-03-01

    Full Text Available A new method for relatively simple transformation of weakly magnetic minerals (goethite (α-FeOOH and hematite (α-Fe2O3 into strongly magnetic mineral (magnetite (Fe3O4 was developed. It was shown, that transformation of structure and magnetic characteristics of go ethite and hematite are realized in the presence of starch at relatively low temperatures (in the range of 300—600 °С. Obtained results open up new possibilities for development of effective technologies for oxidized iron ore beneficiation.

  18. The sharp-front magnetic diffusion wave of a strong magnetic field diffusing into a solid metal

    Science.gov (United States)

    Xiao, Bo; Gu, Zhuo-Wei; Kan, Ming-Xian; Wang, Gang-Hua; Zhao, Jian-Heng; Computational Physics Team

    2016-10-01

    When a mega-gauss magnetic field diffuses into a solid metal, the Joule heat would rise rapidly the temperature of the metal, and the rise of temperature leads to an increase of the metal's resistance, which in turn accelerates the magnetic field diffusion. Those positive feedbacks acting iteratively would lead to an interesting sharp-front magnetic diffusion wave. By assuming that the metal's resistance has an abrupt change from a small value ηS to larger value ηL at some critical temperature Tc, the sharp-front magnetic diffusion wave can be solved analytically. The conditions for the emerging of the sharp-front magnetic diffusion wave are B0 >Bc , ηL /ηS >> 1 , and ηL/ηSB0/-Bc Bc >> 1 , where Bc =√{ 2μ0Jc } , B0 is the vacuum magnetic field strength, and Jc is the critical Joule heat density. The wave-front velocity of the diffusion wave is Vc =ηL/μ0B0/-Bc Bc1/xc , where xc is the depth the wave have propagated in the metal. In this presentation we would like to discuss the derivation of the formulas and its impact to magnetically driven experiments. The work is supported by the Foundation of China Academy of Engineering Physics (No. 2015B0201023).

  19. Magnetization reversal in ultrashort magnetic field pulses

    International Nuclear Information System (INIS)

    Bauer, M.; Lopusnik, R.; Fassbender, J.; Hillebrands, B.

    2000-01-01

    We report the switching properties of a thin magnetic film subject to an ultrashort, laterally localized magnetic field pulse, obtained by numerical investigations. The magnetization distribution in the film is calculated on a grid assuming Stoner-like coherent rotation within the grid square size. Perpendicularly and in-plane magnetized films exhibit a magnetization reversal due to a 4 ps magnetic field pulse. Outside the central region the pulse duration is short compared to the precession period. In this area the evolution of the magnetization during the field pulse does not depend strongly on magnetic damping and/or pulse shape. However, the final magnetization distribution is affected by the magnetic damping. Although the pulse duration is short compared to the precession period, the time needed for the relaxation of the magnetization to the equilibrium state is rather large. The influence of the different magnetic anisotropy contributions and the magnetic damping parameter enters into the magnetization reversal process. Comparing the case of perpendicular anisotropy with different kinds of in-plane anisotropies, a principal difference is found due to the symmetry of the shape anisotropy with respect to the anisotropy in question

  20. Vlasov simulations of self generated strong magnetic fields in plasmas and laser-plasma interaction

    Directory of Open Access Journals (Sweden)

    Inglebert A.

    2013-11-01

    Full Text Available A new formulation based on Hamiltonian reduction technique using the invariance of generalized canonical momentum is introduced for the study of relativistic Weibel-type instability. An example of application is given for the current filamentation instability resulting from the propagation of two counter-streaming electron beams in the relativistic regime of the instability. This model presents a double advantage. From an analytical point of view, the method is exact and standard fluid dispersion relations for Weibel or filamentation instabilies can be recovered. From a numerical point of view, the method allows a drastic reduction of the computational time. A 1D multi-stream Vlasov-Maxwell code is developed using such dynamical invariants in the perpendicular momentum space. Numerical comparison with a full Vlasov-Maxwell system has also been carried out to show the efficiency of this reduction technique.

  1. STRONG MAGNETIC-X-RAY DICHROISM IN 2P ABSORPTION-SPECTRA OF 3D TRANSITION-METAL IONS

    NARCIS (Netherlands)

    VANDERLAAN, G; THOLE, BT

    1991-01-01

    From atomic calculations in crystal-field symmetry we find a very strong circular and linear dichroism in the 2p x-ray absorption edges of magnetically ordered 3d transition-metal ions. The spectral shape changes drastically with the character of the ground state, which is determined by the presence

  2. Study of muon triggers and momentum reconstruction in a strong magnetic field for a muon detector at LHC

    CERN Document Server

    Della Negra, Michel; Eggert, Karsten; Hervé, A; Wittgenstein, F; Karimäki, V; Kinnunen, Ritva; Pimiä, M; Tuominiemi, Jorma; Dau, D; Ferrando, A; Torrente-Lujan, E; Bettini, A; Centro, Sandro; Martinelli, R; Meneguzzo, Anna Teresa; Zotto, P L; Bacci, Cesare; Ceradini, F; Ciapetti, G; Lacava, F; Nisati, A; Petrolo, E; Pontecorvo, L; Veneziano, Stefano; Zanello, L; Cardarelli, R; Di Ciaccio, Anna; Santonico, R; Cline, D; Lazic, S; Mohammadi, M; Park, J; Szoncsó, F; Walzel, G; Wulz, Claudia Elisabeth; CERN. Geneva. Detector Research and Development Committee

    1990-01-01

    We propose to construct a small fraction of a muon detector in a strong magnetic field, for possible use in an LHC experiment, and to test it in a beam containing hadrons and muons. Properties of muons from hadron decays and of hadron punch-through, i.e. angle, momentum and timing distributions of the outgoing particles, will be measured for various absorber thicknesses, including the effect of strong magnetization of the absorber. The efficiency of different muon triggers and the rejection against hadron punch-through and decay muons will be studied. Reconstruction of muons and their momentum measurement in magnetized iron will be investigated, including the effect of catastrophic energy losses of high momentum muons. The performance of resistive plate chambers (RPC) as fast trigger hodoscopes will be studied.

  3. Aversive responses of captive sandbar sharks Carcharhinus plumbeus to strong magnetic fields

    NARCIS (Netherlands)

    Siegenthaler, A.; Niemantsverdriet, P.R.W.; Laterveer, M.; Heitkönig, I.M.A.

    2016-01-01

    This experimental study focused on the possible deterrent effect of permanent magnets on adult sandbar sharks Carcharhinus plumbeus. Results showed that the presence of a magnetic field significantly reduced the number of approaches of conditioned C. plumbeus towards a target indicating that

  4. Effect of angular momentum alignment and strong magnetic fields on the formation of protostellar discs

    Science.gov (United States)

    Gray, William J.; McKee, Christopher F.; Klein, Richard I.

    2018-01-01

    Star-forming molecular clouds are observed to be both highly magnetized and turbulent. Consequently, the formation of protostellar discs is largely dependent on the complex interaction between gravity, magnetic fields, and turbulence. Studies of non-turbulent protostellar disc formation with realistic magnetic fields have shown that these fields are efficient in removing angular momentum from the forming discs, preventing their formation. However, once turbulence is included, discs can form in even highly magnetized clouds, although the precise mechanism remains uncertain. Here, we present several high-resolution simulations of turbulent, realistically magnetized, high-mass molecular clouds with both aligned and random turbulence to study the role that turbulence, misalignment, and magnetic fields have on the formation of protostellar discs. We find that when the turbulence is artificially aligned so that the angular momentum is parallel to the initial uniform field, no rotationally supported discs are formed, regardless of the initial turbulent energy. We conclude that turbulence and the associated misalignment between the angular momentum and the magnetic field are crucial in the formation of protostellar discs in the presence of realistic magnetic fields.

  5. Two-dimensional superconducting state of monolayer Pb films grown on GaAs(110) in a strong parallel magnetic field.

    Science.gov (United States)

    Sekihara, Takayuki; Masutomi, Ryuichi; Okamoto, Tohru

    2013-08-02

    Two-dimensional (2D) superconductivity was studied by magnetotransport measurements on single-atomic-layer Pb films on a cleaved GaAs(110) surface. The superconducting transition temperature shows only a weak dependence on the parallel magnetic field up to 14T, which is higher than the Pauli paramagnetic limit. Furthermore, the perpendicular-magnetic-field dependence of the sheet resistance is almost independent of the presence of the parallel field component. These results are explained in terms of an inhomogeneous superconducting state predicted for 2D metals with a large Rashba spin splitting.

  6. A Solar Eruption from a Weak Magnetic Field Region with Relatively Strong Geo-Effectiveness

    Science.gov (United States)

    Wang, R.

    2017-12-01

    A moderate flare eruption giving rise to a series of geo-effectiveness on 2015 November 4 caught our attentions, which originated from a relatively weak magnetic field region. The associated characteristics near the Earth are presented, which indicates that the southward magnetic field in the sheath and the ICME induced a geomagnetic storm sequence with a Dst global minimum of 90 nT. The ICME is indicated to have a small inclination angle by using a Grad-Shafranov technique, and corresponds to the flux rope (FR) structure horizontally lying on the solar surface. A small-scale magnetic cancelling feature was detected which is beneath the FR and is co-aligned with the Atmospheric Imaging Assembly (AIA) EUV brightening prior to the eruption. Various magnetic features for space-weather forecasting are computed by using a data product from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) called Space-weather HMI Active Region Patches (SHARPs), which help us identify the changes of the photospheric magnetic fields during the magnetic cancellation process and prove that the magnetic reconnection associated with the flux cancellation is driven by the magnetic shearing motion on the photosphere. An analysis on the distributions at different heights of decay index is carried out. Combining with a filament height estimation method, the configurations of the FR is identified and a decay index critical value n = 1 is considered to be more appropriate for such a weak magnetic field region. Through a comprehensive analysis to the trigger mechanisms and conditions of the eruption, a clearer scenario of a CME from a relatively weak region is presented.

  7. Spin excitations in systems with hopping electron transport and strong position disorder in a large magnetic field

    Science.gov (United States)

    Shumilin, A. V.

    2016-10-01

    We discuss the spin excitations in systems with hopping electron conduction and strong position disorder. We focus on the problem in a strong magnetic field when the spin Hamiltonian can be reduced to the effective single-particle Hamiltonian and treated with conventional numerical technics. It is shown that in a 3D system with Heisenberg exchange interaction the spin excitations have a delocalized part of the spectrum even in the limit of strong disorder, thus leading to the possibility of the coherent spin transport. The spin transport provided by the delocalized excitations can be described by a diffusion coefficient. Non-homogenous magnetic fields lead to the Anderson localization of spin excitations while anisotropy of the exchange interaction results in the Lifshitz localization of excitations. We discuss the possible effect of the additional exchange-driven spin diffusion on the organic spin-valve devices.

  8. Strong compression of a magnetic field with a laser-accelerated foil.

    Science.gov (United States)

    Yoneda, Hitoki; Namiki, Tomonori; Nishida, Akinori; Kodama, Ryosuke; Sakawa, Youichi; Kuramitsu, Yasuhiro; Morita, Taichi; Nishio, Kento; Ide, Takao

    2012-09-21

    We demonstrate the generation of high magnetic fields for condensed matter research using a high-power laser system. A cavity in which a seed magnetic field is applied is compressed by a kJ ns laser pulse. The time history of the compressed magnetic field is monitored by observing the Faraday effect rotation of polarization of a probe pulse in a glass fiber. To maintain a low-temperature condition in the final high-field region, we put a high-resistance foil around the final compression area. If we assume the length of the compression region is equal to the laser spot size, a magnetic field of more than 800 T is observed by Faraday rotation. Because of the large mass of the compression foil, this high magnetic field is sustained during almost 2 ns. During compression, a rarefaction wave from the backside of the accelerated foil and expanding material from the inner protection foil affect the magnetic field compression history, but the final compressed magnetic field strength agrees with the ratio between the initial sample area and the compressed cavity area.

  9. Magnetic-field dependence of strongly anisotropic spin reorientation transition in NdFeO3: a terahertz study.

    Science.gov (United States)

    Jiang, Junjie; Song, Gaibei; Wang, Dongyang; Jin, Zuanming; Tian, Zhen; Lin, Xian; Han, Jiaguang; Ma, Guohong; Cao, Shixun; Cheng, Zhenxiang

    2016-03-23

    One of the biggest challenges in spintronics is finding how to switch the magnetization of a material. One way of the spin switching is the spin reorientation transition (SRT), a switching of macroscopic magnetization rotated by 90°. The macroscopic magnetization in a NdFeO3 single crystal rotates from Γ4 to Γ2 via Γ24 as the temperature is decreased from 170 to 100 K, while it can be switched back to Γ4 again by increasing the temperature. However, the precise roles of the magnetic-field induced SRT are still unclear. By using terahertz time-domain spectroscopy (THz-TDS), here, we show that the magnetic-field induced SRT between Γ4 and Γ2 is strongly anisotropic, depending on the direction of the applied magnetic field. Our experimental results are well interpreted by the anisotropy of rare-earth Nd(3+) ion. Furthermore, we find that the critical magnetic-field required for SRT can be modified by changing the temperature. Our study suggests that the anisotropic SRT in NdFeO3 single crystal provides a platform to facilitate the potential applications in robust spin memory devices.

  10. Electronic bond structure of the H2+ ion in a strong magnetic field: A study of the parallel configuration

    International Nuclear Information System (INIS)

    Kappes, U.; Schmelcher, P.

    1995-01-01

    A large number of magnetically dressed states of the hydrogen molecular ion for parallel internuclear and magnetic field axes are investigated. The numerical calculations of the molecular states and potential-energy curves in the fixed-nuclei approximation are based on a recently established and optimized atomic orbital basis set. We study electronic states within the range 0≤|m|≤10 of magnetic quantum numbers and for several field strengths. In particular, we also investigate many excited states within a subspace for fixed magnetic quantum number and parity. In order to understand the influence of the magnetic field on theof excited molecular states, we perform a detailed comparison of the electronic probability distributions and potential-energy curves in the field-free space with those in the presence of a magnetic field. As a major result we observe the existence of two different classes of strongly bound, i.e., stable, magnetically dressed states whose corresponding counterparts in the field-free space exhibit purely repulsive potential-energy curves, i.e., are unstable. Corrections which are going beyond the fixed-nuclei approach, i.e., the coupling of the center of mass to the electronic motion, as well as the mass corrections are investigated in order to ensure the physical validity of our results

  11. Influence of calculation error of total field anomaly in strongly magnetic environments

    Science.gov (United States)

    Yuan, Xiaoyu; Yao, Changli; Zheng, Yuanman; Li, Zelin

    2016-04-01

    An assumption made in many magnetic interpretation techniques is that ΔTact (total field anomaly - the measurement given by total field magnetometers, after we remove the main geomagnetic field, T0) can be approximated mathematically by ΔTpro (the projection of anomalous field vector in the direction of the earth's normal field). In order to meet the demand for high-precision processing of magnetic prospecting, the approximate error E between ΔTact and ΔTpro is studied in this research. Generally speaking, the error E is extremely small when anomalies not greater than about 0.2T0. However, the errorE may be large in highly magnetic environments. This leads to significant effects on subsequent quantitative inference. Therefore, we investigate the error E through numerical experiments of high-susceptibility bodies. A systematic error analysis was made by using a 2-D elliptic cylinder model. Error analysis show that the magnitude of ΔTact is usually larger than that of ΔTpro. This imply that a theoretical anomaly computed without accounting for the error E overestimate the anomaly associated with the body. It is demonstrated through numerical experiments that the error E is obvious and should not be ignored. It is also shown that the curves of ΔTpro and the error E had a certain symmetry when the directions of magnetization and geomagnetic field changed. To be more specific, the Emax (the maximum of the error E) appeared above the center of the magnetic body when the magnetic parameters are determined. Some other characteristics about the error Eare discovered. For instance, the curve of Emax with respect to the latitude was symmetrical on both sides of magnetic equator, and the extremum of the Emax can always be found in the mid-latitudes, and so on. It is also demonstrated that the error Ehas great influence on magnetic processing transformation and inversion results. It is conclude that when the bodies have highly magnetic susceptibilities, the error E can

  12. Shannon entropy as an indicator of atomic avoided crossings in strong parallel magnetic and electric fields.

    Science.gov (United States)

    González-Férez, R; Dehesa, J S

    2003-09-12

    Avoided crossings are the most distinctive atomic spectroscopic features in the presence of magnetic and electric fields. We point out the role of Shannon's information entropy as an indicator or predictor of these phenomena by studying the dynamics of some excited states of hydrogen in the presence of parallel magnetic and electric fields. Moreover, in addition to the well-known energy level repulsion, it is found that Shannon's entropy manifests the informational exchange of the involved states as the magnetic field strength is varied across the narrow region where an avoided crossing occurs.

  13. Chemical spots on the surface of the strongly magnetic Herbig Ae star HD 101412

    DEFF Research Database (Denmark)

    Järvinen, S. P.; Hubrig, S.; Schöller, M.

    2016-01-01

    of HD 101412 were recently obtained on seven different epochs. Our study of the spectral variability over the part of the rotation cycle covered by HARPS observations reveals that the line profiles of the elements Mg, Si, Ca, Ti, Cr, Mn, Fe, and Sr are clearly variable while He exhibits variability...... that is opposite to the behaviour of the other elements studied. Since classical Ap stars usually show a relationship between the magnetic field geometry and the distribution of element spots, we used in our magnetic field measurements different line samples belonging to the three elements with the most numerous...... values determined in previous low-resolution FORS 2 measurements, where hydrogen Balmer lines are the main contributors to the magnetic field measurements, indicating the presence of concentration of the studied iron-peak elements in the region of the magnetic equator. Further, we discuss the potential...

  14. High-latitude ionospheric convection during strong interplanetary magnetic field B-y

    DEFF Research Database (Denmark)

    Huang, C.S.; Sofko, G.J.; Murr, D.

    1999-01-01

    . The interplanetary magnetic field (IMF) conditions corresponding to the occurrence of the ionospheric convection were B-x approximate to 1 nT, B-y approximate to 10 nT, and B-z ...An unusual high-latitude ionospheric pattern was observed on March 23, 1995. ionospheric convection appeared as clockwise merging convection cell focused at 84 degrees magnetic latitude around 1200 MLT. No signature of the viscous convection cell in the afternoon sector was observed...

  15. H2+ molecule in strong magnetic fields, studied by the method of linear combinations of orbitals

    International Nuclear Information System (INIS)

    de Melo, L.C.; Das, T.K.; Ferreira, R.C.; Miranda, L.C.M.; Brandi, H.S.

    1978-01-01

    We have studied the ground state of the H 2 + molecular ion in the presence of a homogeneous magnetic field, basing this study on a linear combination of atomic orbitals obtained from the hydrogen atom in a magnetic field. The calculations have shown that this scheme is adequate to describe the binding energy of the molecule at field strengths up to approximately 10 10 G

  16. Strong geomagnetic activity forecast by neural networks under dominant southern orientation of the interplanetary magnetic field

    Czech Academy of Sciences Publication Activity Database

    Valach, F.; Bochníček, Josef; Hejda, Pavel; Revallo, M.

    2014-01-01

    Roč. 53, č. 4 (2014), s. 589-598 ISSN 0273-1177 R&D Projects: GA AV ČR(CZ) IAA300120608; GA MŠk OC09070 Institutional support: RVO:67985530 Keywords : geomagnetic activity * interplanetary magnetic field * artificial neural network * ejection of coronal mass * X-ray flares Subject RIV: DE - Earth Magnetism, Geodesy, Geography Impact factor: 1.358, year: 2014

  17. Investigation of thin manganite films at strong pulsed electric and magnetic fields

    OpenAIRE

    Cimmperman, Piotras

    2006-01-01

    The main aim of this work was to investigate electrical conductivity of La-Ca(Sr)-MnO thin films at high pulsed electric and magnetic fields and to clear up the possibilities to use these materials for high pulsed magnetic field sensor and fault current limiter applications. The dissertation consists of the preface, six chapters, summary and main conclusions, references, list of publications and abstract (in Lithuanian). The main objectives of the work, scientific novelty, goals, valida...

  18. The Creation of a Strong Magnetic Field by Means of Large Magnetic Blocks from NdFeB Magnets in Opposing Linear Halbach Arrays

    Czech Academy of Sciences Publication Activity Database

    Žežulka, Václav; Straka, Pavel

    2016-01-01

    Roč. 21, č. 3 (2016), 364-373 ISSN 1226-1750 Institutional support: RVO:67985891 Keywords : magnetic field * permanent magnets * NdFeB magnets * Halbach Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.713, year: 2016 http://komag.org/journal/

  19. Strong 3D and 1D magnetism in hexagonal Fe-chalcogenides FeS and FeSe vs. weak magnetism in hexagonal FeTe

    Energy Technology Data Exchange (ETDEWEB)

    Parker, David S. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2017-06-13

    We present a comparative theoretical study of the hexagonal forms of the Fe-chalcogenides FeS, FeSe and FeTe with their better known tetragonal forms. While the tetragonal forms exhibit only an incipient antiferromagnetism and experimentally show superconductivity when doped, the hexagonal forms of FeS and FeSe display a robust magnetism. We show that this strong magnetism arises from a van Hove singularity associated with the direct Fe-Fe c-axis chains in the generally more three-dimensional NiAs structure. We also find that hexagonal FeTe is much less magnetic than the other two hexagonal materials, so that unconventional magnetically-mediated superconductivity is possible, although a large Tc value is unlikely.

  20. Strong 3D and 1D magnetism in hexagonal Fe-chalcogenides FeS and FeSe vs. weak magnetism in hexagonal FeTe.

    Science.gov (United States)

    Parker, David S

    2017-06-13

    We present a comparative theoretical study of the hexagonal forms of the Fe-chalcogenides FeS, FeSe and FeTe with their better known tetragonal forms. While the tetragonal forms exhibit only an incipient antiferromagnetism and experimentally show superconductivity when doped, the hexagonal forms of FeS and FeSe display a robust magnetism. We show that this strong magnetism arises from a van Hove singularity associated with the direct Fe-Fe c-axis chains in the generally more three-dimensional NiAs structure. We also find that hexagonal FeTe is much less magnetic than the other two hexagonal materials, so that unconventional magnetically-mediated superconductivity is possible, although a large T c value is unlikely.

  1. Signatures of pairing in the magnetic excitation spectrum of strongly correlated two-leg ladders

    Science.gov (United States)

    Nocera, A.; Patel, N. D.; Dagotto, E.; Alvarez, G.

    2017-11-01

    Magnetic interactions are widely believed to play a crucial role in the microscopic mechanism leading to high critical temperature superconductivity. It is therefore important to study the signatures of pairing in the magnetic excitation spectrum of simple models known to show unconventional superconducting tendencies. Using the density matrix renormalization group technique, we calculate the dynamical spin structure factor S (k ,ω ) of a generalized t -U -J Hubbard model away from half filling in a two-leg ladder geometry. The addition of J enhances pairing tendencies. We analyze quantitatively the signatures of pairing in the magnetic excitation spectra. We found that the superconducting pair-correlation strength, that can be estimated independently from ground state properties, is closely correlated with the integrated low-energy magnetic spectral weight in the vicinity of (π ,π ) . In this wave-vector region, robust spin incommensurate features develop with increasing doping. The branch of the spectrum with rung direction wave vector krung=0 does not change substantially with doping where pairing dominates and thus plays a minor role. We discuss the implications of our results for neutron scattering experiments, where the spin excitation dynamics of hole-doped quasi-one-dimensional magnetic materials can be measured and also address implications for recent resonant inelastic x-ray scattering experiments.

  2. Layered Black Phosphorus: Strongly Anisotropic Magnetic, Electronic, and Electron-Transfer Properties.

    Science.gov (United States)

    Sofer, Zdeněk; Sedmidubský, David; Huber, Štěpán; Luxa, Jan; Bouša, Daniel; Boothroyd, Chris; Pumera, Martin

    2016-03-01

    Layered elemental materials, such as black phosphorus, exhibit unique properties originating from their highly anisotropic layered structure. The results presented herein demonstrate an anomalous anisotropy for the electrical, magnetic, and electrochemical properties of black phosphorus. It is shown that heterogeneous electron transfer from black phosphorus to outer- and inner-sphere molecular probes is highly anisotropic. The electron-transfer rates differ at the basal and edge planes. These unusual properties were interpreted by means of calculations, manifesting the metallic character of the edge planes as compared to the semiconducting properties of the basal plane. This indicates that black phosphorus belongs to a group of materials known as topological insulators. Consequently, these effects render the magnetic properties highly anisotropic, as both diamagnetic and paramagnetic behavior can be observed depending on the orientation in the magnetic field. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. H2+ molecular ion in a strong magnetic field: Ground state

    International Nuclear Information System (INIS)

    Turbiner, A. V.; Lopez Vieyra, J. C.

    2003-01-01

    A detailed quantitative analysis of the system of two protons and one electron (ppe) placed in magnetic field ranging from 10 9 -4.414x10 13 G is presented. The present study is focused on the question of the existence of the molecular ion H 2 + in a magnetic field. A variational method with an optimization of the form of the vector potential (optimal gauge fixing) is used as a tool. It is shown that in the domain of applicability of the nonrelativistic approximation the (ppe) system in the Born-Oppenheimer approximation has a well-pronounced minimum in the total energy at a finite interproton distance for B(less-or-similar sign)10 11 G, thus manifesting the existence of H 2 + . For B(greater-or-similar sign)10 11 G and large inclinations (of the molecular axis with respect to the magnetic line) the minimum disappears and hence the molecular ion H 2 + does not exist. It is shown that the most stable configuration of H 2 + always corresponds to protons situated along the magnetic line. With magnetic field growth the H 2 + ion becomes more and more tightly bound and compact, and the electronic distribution evolves from a two-peak to a one-peak pattern. The domain of inclinations where the H 2 + ion exists reduces with magnetic field increase and finally becomes 0 degree sign -25 degree sign at B=4.414x10 13 G. Phase-transition-type behavior of variational parameters for some interproton distances related to the beginning of the chemical reaction H 2 + ↔H+p is found

  4. Electromagnetic processes in pulsars under strong electric and magnetic field conditions

    International Nuclear Information System (INIS)

    Ayasli, S.; Hacinliyan, A.; Oegelman, H.B.; Daugherty, I.K.

    1977-01-01

    It is believed that pulsars possess huge electric and magnetic fields. However, the electric field is commonly neglected in calculations of the rate of pair production, a process which is thought to be greatly important in the radiation mechanisms of pulsars. To see the effect of the electric field, the pair production is calculated for arbitrary electric and magnetic field configurations. The formulae thus obtained are then applied to pulsars. It is shown that the correction to the ''polar gap'' height calculated in the Ruderman and Sutherland model is negligible, although it might be important for the spectrum of emerging photons. (author)

  5. Exchange interaction of strongly anisotropic tripodal erbium single-ion magnets with metallic surfaces

    DEFF Research Database (Denmark)

    Dreiser, Jan; Wäckerlin, Christian; Ali, Md. Ehesan

    2014-01-01

    We present a comprehensive study of Er(trensal) single-ion magnets deposited in ultrahigh vacuum onto metallic surfaces. X-ray photoelectron spectroscopy reveals that the molecular structure is preserved after sublimation, and that the molecules are physisorbed on Au(111) while they are chemisorbed....... Furthermore XMCD indicates a weak antiferromagnetic exchange coupling between the single-ion magnets and the ferromagnetic Ni/Cu(100) substrate. For the latter case, spin-Hamiltonian fits to the XMCD M(H) suggest a significant structural distortion of the molecules. Scanning tunneling microscopy reveals...

  6. Nonlinear dispersion of resonance extraordinary wave in a plasma with strong magnetic field

    International Nuclear Information System (INIS)

    Krasovitskiy, V. B.; Turikov, V. A.; Sotnikov, V. I.

    2007-01-01

    In this paper, the efficiency of electron acceleration by a short, powerful laser pulse propagating across an external magnetic field is investigated. Conditions for the decay of a laser pulse with frequency close to the upper hybrid resonance frequency are analyzed. It is also shown that a laser pulse propagating as an extraordinary wave in cold, magnetized, low-density plasma takes the form of a nonlinear wave with the modulated amplitude (envelope soliton). Finally, simulation results on the interaction of an electromagnetic pulse with a semi-infinite plasma, obtained with the help of an electromagnetic relativistic PIC code, are discussed and a comparison with the obtained theoretical results is presented

  7. Path-integral calculation of the density of states in heavily doped strongly compensated semiconductors in a magnetic field

    International Nuclear Information System (INIS)

    Koinov, Z.G.; Yanchev, I.Y.

    1981-09-01

    The density of states in heavily doped strongly compansated semiconductors in a strong magnetic field is calculated by using the path-integral method. The case is considered when correlation exists in the impurity positions owing to the Coulomb interactions between the charged donors and acceptors during the high-temperature preparation of the samples. The semiclassical formula is rederived and corrections to it due to the long-range character of the potential and its short-range fluctuations are obtained. The density of states in the tail is studied and analytical results are given in the classical and quantum cases. (author)

  8. Onset of magnetic order in strongly-correlated systems from ab initio electronic structure calculations: application to transition metal oxides

    Science.gov (United States)

    Hughes, I. D.; Däne, M.; Ernst, A.; Hergert, W.; Lüders, M.; Staunton, J. B.; Szotek, Z.; Temmerman, W. M.

    2008-06-01

    We describe an ab initio theory of finite temperature magnetism in strongly-correlated electron systems. The formalism is based on spin density functional theory, with a self-interaction corrected local spin density approximation (SIC-LSDA). The self-interaction correction is implemented locally, within the Kohn-Korringa-Rostoker (KKR) multiple-scattering method. Thermally induced magnetic fluctuations are treated using a mean-field 'disordered local moment' (DLM) approach and at no stage is there a fitting to an effective Heisenberg model. We apply the theory to the 3d transition metal oxides, where our calculations reproduce the experimental ordering tendencies, as well as the qualitative trend in ordering temperatures. We find a large insulating gap in the paramagnetic state which hardly changes with the onset of magnetic order.

  9. 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.

  10. Imposed, ordered dust structures and other plasma features in a strongly magnetized plasma

    Science.gov (United States)

    Thomas, Edward; Leblanc, Spencer; Lynch, Brian; Konopka, Uwe; Merlino, Robert; Rosenberg, Marlene

    2015-11-01

    The Magnetized Dusty Plasma Experiment (MDPX) device has been in operation for just over one year. In that time, the MDPX device has been operating using a uniform magnetic field configuration up to 3.0 Tesla and has successfully produced plasmas and dusty plasmas at high magnetic fields. In these experimental studies, we have made observations of a new type of imposed, ordered structure in a dusty plasma at magnetic fields above 1 T. These dusty plasma structures are shown to scale inversely with neutral pressure and are shown to reflect the spatial structure of a wire mesh placed in the plasma. Additionally, recent measurements have been made that give insights into the effective potential that establishes the ordered structures in the plasma. In this presentation, we report on details of the imposed, ordered dusty plasma structure as well as filamentary features that also appear in the plasma and modify the confinement of the dusty plasma. This work is supported with funding from the NSF and Department of Energy.

  11. Parallel-beam correlation technique for measuring density fluctuations in plasmas with strong magnetic shear

    International Nuclear Information System (INIS)

    Jacobson, A.R.

    1981-04-01

    A laser diagnostic scheme is described which facilitates localization of density fluctuations along the line of sight. The method exploits both the generally observed anisotropy of density fluctuations in low-beta plasmas, as well as the twisting of the magnetic field which occurs across the minor diameter of reversed-field pinches, spheromaks, etc. Both interferometric and schlieren variations are discussed

  12. High-latitude ionospheric convection during strong interplanetary magnetic field B-y

    DEFF Research Database (Denmark)

    Huang, C.S.; Sofko, G.J.; Murr, D.

    1999-01-01

    . The interplanetary magnetic field (IMF) conditions corresponding to the occurrence of the ionospheric convection were B-x approximate to 1 nT, B-y approximate to 10 nT, and B-z y). We have compared our observations with statistical patterns and MHD numerical models for similar IMF...

  13. The Vlasov equation with strong magnetic field and oscillating electric field as a model for isotop resonant separation

    Directory of Open Access Journals (Sweden)

    Emmanuel Frenod

    2002-01-01

    Full Text Available We study the qualitative behavior of solutions to the Vlasov equation with strong external magnetic field and oscillating electric field. This model is relevant to the understanding of isotop resonant separation. We show that the effective equation is a kinetic equation with a memory term. This memory term involves a pseudo-differential operator whose kernel is characterized by an integral equation involving Bessel functions. The kernel is explicitly given in some particular cases.

  14. Tunable photonic crystal for THz radiation in layered superconductors: Strong magnetic-field dependence of the transmission coefficient

    International Nuclear Information System (INIS)

    Savel'ev, Sergey; Rakhmanov, A.L.; Nori, Franco

    2006-01-01

    Josephson plasma waves are scattered by the Josephson vortex lattice. This scattering results in a strong dependence, on the in-plane magnetic-field H ab , of the reflection and transmission of THz radiation propagating in layered superconductors. In particular, a tunable band-gap structure (THz photonic crystal) occurs in such a medium. These effects can be used, by varying H ab , for the selective frequency-filtering of THz radiation

  15. Current-density functional theory study of the H2 molecule evolving under a strong ultrashort magnetic field

    Science.gov (United States)

    Vikas, Hash(0xb7f6e60)

    2012-01-01

    Hydrogen molecule in a strong ultrashort magnetic field is investigated through a current-density functional theory (CDFT) and quantum fluid dynamics (QFD) based approach employing current-density dependent vector exchange-correlation potential and energy density functional derived with a vorticity variable. The numerical computations through the CDFT based approach are performed for the H2 molecule, starting initially from its field-free ground state, in a parallel internuclear axis and magnetic field-axis configuration with the internuclear separation R ranging from 0.1 a.u. to 14.0 a.u., and the strength of the time-dependent (TD) magnetic field varying between 0-1011 G over a few femtoseconds. The numerical results are compared with that obtained using an approach based on the current-density independent approximation under similar computational constraints but employing only scalar exchange-correlation potential dependent on the electronic charge-density alone. The current-density based approach yields exchange- and correlation energy as well as electronic charge-density of the H2 molecule drastically different from that obtained using current-independent approach, in particular, at TD magnetic field-strengths >109 G during a typical time-period of the field when the magnetic-field had attained maximum applied field-strength and is switched to a decreasing ramp function. This nonadiabatic behavior of the TD electronic charge-density is traced to the TD vorticity-dependent vector exchange-correlation potential of the CDFT based approach. The interesting electron dynamics of the H2 molecule in strong TD magnetic field is further elucidated by treating electronic charge-density as an `electron-fluid'. The present work also reveals interesting real-time dynamics on the attosecond time-scale in the electronic charge-density distribution of the hydrogen molecule.

  16. Hall effect in a strong magnetic field: Direct comparisons of compressible magnetohydrodynamics and the reduced Hall magnetohydrodynamic equations

    International Nuclear Information System (INIS)

    Martin, L. N.; Dmitruk, P.; Gomez, D. O.

    2010-01-01

    In this work we numerically test a model of Hall magnetohydrodynamics in the presence of a strong mean magnetic field: the reduced Hall magnetohydrodynamic model (RHMHD) derived by [Gomez et al., Phys. Plasmas 15, 102303 (2008)] with the addition of weak compressible effects. The main advantage of this model lies in the reduction of computational cost. Nevertheless, up until now the degree of agreement with the original Hall MHD system and the range of validity in a regime of turbulence were not established. In this work direct numerical simulations of three-dimensional Hall MHD turbulence in the presence of a strong mean magnetic field are compared with simulations of the weak compressible RHMHD model. The results show that the degree of agreement is very high (when the different assumptions of RHMHD, such as spectral anisotropy, are satisfied). Nevertheless, when the initial conditions are isotropic but the mean magnetic field is maintained strong, the results differ at the beginning but asymptotically reach a good agreement at relatively short times. We also found evidence that the compressibility still plays a role in the dynamics of these systems, and the weak compressible RHMHD model is able to capture these effects. In conclusion the weak compressible RHMHD model is a valid approximation of the Hall MHD turbulence in the relevant physical context.

  17. Flow of a two-dimensional liquid metal jet in a strong magnetic field

    International Nuclear Information System (INIS)

    Reed, C.B.; Molokov, S.

    2002-01-01

    Two-dimensional, steady flow of a liquid metal slender jet pouring from a nozzle in the presence of a transverse, nonuniform magnetic field is studied. The surface tension has been neglected, while gravity is shown to be not important. The main aim of the study is to evaluate the importance of the inertial effects. It has been shown that for gradually varying fields characteristic for the divertor region of a tokamak, inertial effects are negligible for N > 10, where N is the interaction parameter. Thus the inertialess flow model is expected to give good results even for relatively low magnetic fields and high jet velocity. Simple relations for the jet thickness and velocity have been derived. The results show that the jet becomes thicker if the field increases along the flow and thinner if it decreases

  18. Variational Monte Carlo calculations of lithium atom in strong magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Doma, S. B., E-mail: sbdoma@alexu.edu.eg [Alexandria University, Mathematics Department, Faculty of Science (Egypt); Shaker, M. O.; Farag, A. M. [Tanta University, Mathematics Department, Faculty of Science (Egypt); El-Gammal, F. N., E-mail: famta-elzahraa4@yahoo.com [Menofia University, Mathematics Department, Faculty of Science (Egypt)

    2017-01-15

    The variational Monte Carlo method is applied to investigate the ground state and some excited states of the lithium atom and its ions up to Z = 10 in the presence of an external magnetic field regime with γ = 0–100 arb. units. The effect of increasing field strength on the ground state energy is studied and precise values for the crossover field strengths were obtained. Our calculations are based on using accurate forms of trial wave functions, which were put forward in calculating energies in the absence of magnetic field. Furthermore, the value of Y at which ground-state energy of the lithium atom approaches to zero was calculated. The obtained results are in good agreement with the most recent values and also with the exact values.

  19. Magnetic field induced strong valley polarization in the three-dimensional topological semimetal LaBi

    Science.gov (United States)

    Kumar, Nitesh; Shekhar, Chandra; Klotz, J.; Wosnitza, J.; Felser, Claudia

    2017-10-01

    LaBi is a three-dimensional rocksalt-type material with a surprisingly quasi-two-dimensional electronic structure. It exhibits excellent electronic properties such as the existence of nontrivial Dirac cones, extremely large magnetoresistance, and high charge-carrier mobility. The cigar-shaped electron valleys make the charge transport highly anisotropic when the magnetic field is varied from one crystallographic axis to another. We show that the electrons can be polarized effectively in these electron valleys under a rotating magnetic field. We achieved a polarization of 60% at 2 K despite the coexistence of three-dimensional hole pockets. The valley polarization in LaBi is compared to the sister compound LaSb where it is found to be smaller. The performance of LaBi is comparable to the highly efficient bismuth.

  20. Magnetic susceptibility as a method of investigation of short-range order in strongly nonstoichiometric carbides

    International Nuclear Information System (INIS)

    Nazarova, S.Z.; Gusev, A.I.

    2001-01-01

    Magnetic susceptibility in disordered and ordered carbides of transition metals (M = Ti, Zr, Hf, Nb, Ta) was studied, the results are generalized. It was ascertained that the change in carbide susceptibility induced by deviation from stoichiometry stems from specific features of electronic spectra of the compounds. The use of magnetic susceptibility for determining structural disorder-order transitions is discussed. It is shown that change in the contribution made by orbital paramagnetism, resulting from short-range order formation, is the reason of decrease in susceptibility of nonstoichiometric carbides during the ordering. Experimentally obtained data on susceptibility permitted evaluating short- and far-range order parameters in NbC y , TaC y , TiC y and HfC y carbides [ru

  1. A kinetic model of retarding field analyser measurements in strongly magnetized, flowing, collisional plasmas

    Czech Academy of Sciences Publication Activity Database

    Gunn, J. P.; Fuchs, Vladimír; Kočan, M.

    2013-01-01

    Roč. 55, č. 4 (2013), 045012-045012 ISSN 0741-3335 R&D Projects: GA MŠk 7G10072 Institutional support: RVO:61389021 Keywords : plasma * collisions * magnetic field * retarding field analyzer Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.386, year: 2013 http://iopscience.iop.org/0741-3335/55/4/045012/pdf/0741-3335_55_4_045012.pdf

  2. The LACARA Vacuum Laser Accelerator Experiment: Beam Positioning and Alignment in a Strong Magnetic Field

    International Nuclear Information System (INIS)

    Shchelkunov, Sergey V.; Marshall, T. C.; Hirshfield, J. L.; Wang, Changbiao; LaPointe, M. A.

    2006-01-01

    LACARA (laser cyclotron auto-resonance accelerator) is a vacuum laser accelerator of electrons that is under construction at the Accelerator Test Facility (ATF), Brookhaven National Laboratory. It is expected that the experiment will be assembled by September 2006; this paper presents progress towards this goal. According to numerical studies, as an electron bunch moves along the LACARA solenoidal magnetic field (∼5.2 T, length ∼1 m), it will be accelerated from 50 to ∼75 MeV by interacting with a 0.8 TW Gaussian-mode circularly polarized optical pulse provided by the ATF CO2 10.6μm laser system. The LACARA laser transport optics must handle 10 J and be capable of forming a Gaussian beam inside the solenoid with a 1.4 mm waist and a Rayleigh range of 60 cm. The electron optics must transport a bunch having input emittance of 0.015 mm-mrad and 100 μm waist through the magnet. Precision alignment between the electron beam and the solenoid magnetic axis is required, and a method to achieve this is described in detail. Emittance- filtering may be necessary to yield an accelerated bunch having a narrow (∼1%) energy-spread

  3. Structural analysis of mixed alkali borosilicate glasses containing Cs+ and Na+ using strong magnetic field magic angle spinning nuclear magnetic resonance

    Directory of Open Access Journals (Sweden)

    S. Kaneko

    2017-03-01

    Full Text Available We have investigated the local structure of alkali atoms in mixed alkali silicate, borate, and borosilicate glasses, which contain Cs+ and Na+, using strong magnetic field magic angle spinning nuclear magnetic resonance (MAS NMR spectroscopy of 133Cs and 23Na. The spectral peaks of 133Cs in borosilicate (Si:B = 1:1 and Si-rich borosilicate (Si:B = 2:1 glasses shifted to upfield with increasing Cs+/(Na+ + Cs+ ratio, which implies that the coordination number of Cs+ decreased as in the case of silicate and borate glasses. However, this trend was not observed in the 23Na spectra of either borosilicate glass. This might be because the chemical shift of 23Na in borosilicate glass is strongly affected by nearby species such as Si or B, and not by the coordination number of Na+.

  4. Magnetic study of a few antiferromagnets in very-strong pulsed fields (450 kOE)

    International Nuclear Information System (INIS)

    Krebs, J.

    1968-01-01

    In this thesis we describe a pulsed field device with which we obtain magnetization curves up to 450 kOE at all temperatures between 1. 6 and 300. We have studied the 'spin-flopping'(and therefore the anisotropy) in MnF 2 versus temperature, below the Neel point. We have also studied the antiferromagnets MnSO 4 . and MnSO 4 .H 2 O which have revealed saturation fields respectively of 250 kOE and 320 kOE. (author) [fr

  5. Accretion disc dynamo activity in local simulations spanning weak-to-strong net vertical magnetic flux regimes

    Science.gov (United States)

    Salvesen, Greg; Simon, Jacob B.; Armitage, Philip J.; Begelman, Mitchell C.

    2016-03-01

    Strongly magnetized accretion discs around black holes have attractive features that may explain enigmatic aspects of X-ray binary behaviour. The structure and evolution of these discs are governed by a dynamo-like mechanism, which channels part of the accretion power liberated by the magnetorotational instability (MRI) into an ordered toroidal magnetic field. To study dynamo activity, we performed three-dimensional, stratified, isothermal, ideal magnetohydrodynamic shearing box simulations. The strength of the self-sustained toroidal magnetic field depends on the net vertical magnetic flux, which we vary across almost the entire range over which the MRI is linearly unstable. We quantify disc structure and dynamo properties as a function of the initial ratio of mid-plane gas pressure to vertical magnetic field pressure, β _0^mid = p_gas / p_B. For 10^5 ≥ β _0^mid ≥ 10 the effective α-viscosity parameter scales as a power law. Dynamo activity persists up to and including β _0^mid = 10^2, at which point the entire vertical column of the disc is magnetic pressure dominated. Still stronger fields result in a highly inhomogeneous disc structure, with large density fluctuations. We show that the turbulent steady state βmid in our simulations is well matched by the analytic model of Begelman et al. describing the creation and buoyant escape of toroidal field, while the vertical structure of the disc can be broadly reproduced using this model. Finally, we discuss the implications of our results for observed properties of X-ray binaries.

  6. Density-matrix-functional calculations for matter in strong magnetic fields: Ground states of heavy atoms

    DEFF Research Database (Denmark)

    Johnsen, Kristinn; Yngvason, Jakob

    1996-01-01

    We report on a numerical study of the density matrix functional introduced by Lieb, Solovej, and Yngvason for the investigation of heavy atoms in high magnetic fields. This functional describes exactly the quantum mechanical ground state of atoms and ions in the limit when the nuclear charge Z...... and the electron number N tend to infinity with N/Z fixed, and the magnetic field B tends to infinity in such a way that B/Z4/3→∞. We have calculated electronic density profiles and ground-state energies for values of the parameters that prevail on neutron star surfaces and compared them with results obtained...... by other methods. For iron at B=1012 G the ground-state energy differs by less than 2% from the Hartree-Fock value. We have also studied the maximal negative ionization of heavy atoms in this model at various field strengths. In contrast to Thomas-Fermi type theories atoms can bind excess negative charge...

  7. A strong, highly-tilted interstellar magnetic field near the Solar System.

    Science.gov (United States)

    Opher, M; Bibi, F Alouani; Toth, G; Richardson, J D; Izmodenov, V V; Gombosi, T I

    2009-12-24

    Magnetic fields play an important (sometimes dominant) role in the evolution of gas clouds in the Galaxy, but the strength and orientation of the field in the interstellar medium near the heliosphere has been poorly constrained. Previous estimates of the field strength range from 1.8-2.5 microG and the field was thought to be parallel to the Galactic plane or inclined by 38-60 degrees (ref. 2) or 60-90 degrees (ref. 3) to this plane. These estimates relied either on indirect observational inferences or modelling in which the interstellar neutral hydrogen was not taken into account. Here we report measurements of the deflection of the solar wind plasma flows in the heliosheath to determine the magnetic field strength and orientation in the interstellar medium. We find that the field strength in the local interstellar medium is 3.7-5.5 microG. The field is tilted approximately 20-30 degrees from the interstellar medium flow direction (resulting from the peculiar motion of the Sun in the Galaxy) and is at an angle of about 30 degrees from the Galactic plane. We conclude that the interstellar medium field is turbulent or has a distortion in the solar vicinity.

  8. Strong coupling operation of a free-electron-laser amplifier with an axial magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Rullier, J.L.; Devin, A.; Gardelle, J.; Labrouche, J.; Le Taillandier, P. [Commissariat a lEnergie Atomique, Boite Postale 2, 33114 Le Barp (France); Donohue, J.T. [Centre dEtudes Nucleaires de Bordeaux-Gradignan, Boite Postale 120, 33175 Gradignan (France)

    1996-03-01

    We present the results of a free-electron-laser (FEL) experiment at 35 GHz, using a strongly relativistic electron beam ({ital T}=1.75 MeV). The electron pulse length is 30 ns full width at half maximum with a peak current of 400 A. The FEL is designed to operate in the high-gain Compton regime, with a negative coupling parameter ({Phi}{lt}0) leading to a strong growth rate. More than 50 MW of rf power in the TE{sub 1}{sub 1} mode (43 dB gain) has been obtained with good reproducibility. The experimental results are in good agreement with predictions made using the three-dimensional stationary simulation code solitude. {copyright} {ital 1996 The American Physical Society.}

  9. The dynamics of magnetic Rossby waves in spherical dynamo simulations: A signature of strong-field dynamos?

    Science.gov (United States)

    Hori, K.; Teed, R. J.; Jones, C. A.

    2018-03-01

    We investigate slow magnetic Rossby waves in convection-driven dynamos in rotating spherical shells. Quasi-geostrophic waves riding on a mean zonal flow may account for some of the geomagnetic westward drifts and have the potential to allow the toroidal field strength within the planetary fluid core to be estimated. We extend the work of Hori et al. (2015) to include a wider range of models, and perform a detailed analysis of the results. We find that a predicted dispersion relation matches well with the longitudinal drifts observed in our strong-field dynamos. We discuss the validity of our linear theory, since we also find that the nonlinear Lorentz terms influence the observed waveforms. These wave motions are excited by convective instability, which determines the preferred azimuthal wavenumbers. Studies of linear rotating magnetoconvection have suggested that slow magnetic Rossby modes emerge in the magnetostrophic regime, in which the Lorentz and Coriolis forces are in balance in the vorticity equation. We confirm this to be predominant balance for the slow waves we have detected in nonlinear dynamo systems. We also show that a completely different wave regime emerges if the magnetic field is not present. Finally we report the corresponding radial magnetic field variations observed at the surface of the shell in our simulations and discuss the detectability of these waves in the geomagnetic secular variation.

  10. On the thermoelectric power in degenerate narrow gap semiconductors in the presence of a strong magnetic field

    International Nuclear Information System (INIS)

    Ghatak, K.P.; De, B.

    1991-01-01

    In this paper the authors have studied the thermoelectric power under strong magnetic field in degenerate semiconductors on the basis of fourth order in affective mass theory and taking into account the interactions of the conduction electrons, heavy-holes, light-holes and split-off holes respectively. The results obtained are then compared to those derived on the basis of the well-known three-band Kane model. It is found, taking n-Hg 1-x Cd x Te as an example, that the magneto-thermo power increases with decreasing electron concentration and increasing magnetic field respectively for both the models in an oscillatory way. The oscillations are due to SdH effects and the theoretical analysis in accordance with fourth order in effective mass theory i in agreement with the experimental observation as reported elsewhere. In addition, the corresponding results for parabolic energy bands have also been obtained as special cases of our generalized formulations

  11. Preparation of cold ions in strong magnetic field and its application to gas-phase NMR spectroscopy

    International Nuclear Information System (INIS)

    Fuke, K.; Ohshima, Y.; Tona, M.

    2015-01-01

    Nuclear Magnetic Resonance (NMR) technique is widely used as a powerful tool to study the physical and chemical properties of materials. However, this technique is limited to the materials in condensed phases. To extend this technique to the gas-phase molecular ions, we are developing a gas-phase NMR apparatus. In this note, we describe the basic principle of the NMR detection for molecular ions in the gas phase based on a Stern-Gerlach type experiment in a Penning trap and outline the apparatus under development. We also present the experimental procedures and the results on the formation and the manipulation of cold ions under a strong magnetic field, which are the key techniques to detect the NMR by the present method

  12. Analytical GIAO and hybrid-basis integral derivatives: application to geometry optimization of molecules in strong magnetic fields.

    Science.gov (United States)

    Tellgren, Erik I; Reine, Simen S; Helgaker, Trygve

    2012-07-14

    Analytical integral evaluation is a central task of modern quantum chemistry. Here we present a general method for evaluating differentiated integrals over standard Gaussian and mixed Gaussian/plane-wave hybrid orbitals. The main idea is to have a representation of basis sets that is flexible enough to enable differentiated integrals to be reinterpreted as standard integrals over modified basis functions. As an illustration of the method, we report a very simple implementation of Hartree-Fock level geometrical derivatives in finite magnetic fields for gauge-origin independent atomic orbitals, within the London program. As a quantum-chemical application, we optimize the structure of helium clusters and some well-known covalently bound molecules (water, ammonia and benzene) subject to strong magnetic fields.

  13. Magnetic properties of Hf177 and Hf180 in the strong-coupling deformed model

    Science.gov (United States)

    Muto, S.; Stone, N. J.; Bingham, C. R.; Stone, J. R.; Walker, P. M.; Audi, G.; Gaulard, C.; Köster, U.; Nikolov, J.; Nishimura, K.; Ohtsubo, T.; Podolyak, Z.; Risegari, L.; Simpson, G. S.; Veskovic, M.; Walters, W. B.

    2014-04-01

    This paper reports NMR measurements of the magnetic dipole moments of two high-K isomers, the 37/2-, 51.4 m, 2740 keV state in Hf177 and the 8-, 5.5 h, 1142 keV state in Hf180 by the method of on-line nuclear orientation. Also included are results on the angular distributions of γ transitions in the decay of the Hf177 isotope. These yield high precision E2/M1 multipole mixing ratios for transitions in bands built on the 23/2+, 1.1 s, isomer at 1315 keV and on the 9/2+, 0.663 ns, isomer at 321 keV. The new results are discussed in the light of the recently reported finding of systematic dependence of the behavior of the gR parameter upon the quasiproton and quasineutron make up of high-K isomeric states in this region.

  14. Dst Index in the 2008 GEM Modeling Challenge - Model Performance for Moderate and Strong Magnetic Storms

    Science.gov (United States)

    Rastaetter, Lutz; Kuznetsova, Maria; Hesse, Michael; Chulaki, Anna; Pulkkinen, Antti; Ridley, Aaron J.; Gombosi, Tamas; Vapirev, Alexander; Raeder, Joachim; Wiltberger, Michael James; hide

    2010-01-01

    The GEM 2008 modeling challenge efforts are expanding beyond comparing in-situ measurements in the magnetosphere and ionosphere to include the computation of indices to be compared. The Dst index measures the largest deviations of the horizontal magnetic field at 4 equatorial magnetometers from the quiet-time background field and is commonly used to track the strength of the magnetic disturbance of the magnetosphere during storms. Models can calculate a proxy Dst index in various ways, including using the Dessler-Parker Sckopke relation and the energy of the ring current and Biot-Savart integration of electric currents in the magnetosphere. The GEM modeling challenge investigates 4 space weather events and we compare models available at CCMC against each other and the observed values of Ost. Models used include SWMF/BATSRUS, OpenGGCM, LFM, GUMICS (3D magnetosphere MHD models), Fok-RC, CRCM, RAM-SCB (kinetic drift models of the ring current), WINDMI (magnetosphere-ionosphere electric circuit model), and predictions based on an impulse response function (IRF) model and analytic coupling functions with inputs of solar wind data. In addition to the analysis of model-observation comparisons we look at the way Dst is computed in global magnetosphere models. The default value of Dst computed by the SWMF model is for Bz the Earth's center. In addition to this, we present results obtained at different locations on the Earth's surface. We choose equatorial locations at local noon, dusk (18:00 hours), midnight and dawn (6:00 hours). The different virtual observatory locations reveal the variation around the earth-centered Dst value resulting from the distribution of electric currents in the magnetosphere during different phases of a storm.

  15. Effect of a dc magnetic field on the magnetization relaxation of uniaxial single-domain ferromagnetic particles driven by a strong ac magnetic field

    International Nuclear Information System (INIS)

    Dejardin, Pierre-Michel; Kalmykov, Yuri P.

    2010-01-01

    The nonlinear ac stationary response of the magnetization of noninteracting uniaxial single-domain ferromagnetic particles acted on by superimposed dc and ac magnetic fields applied along the anisotropy axis is evaluated from the Fokker-Planck equation, expressed as an infinite hierarchy of recurrence equations for Fourier components of the relaxation functions governing longitudinal relaxation of the magnetization. The exact solution of this hierarchy comprises a matrix continued fraction, allowing one to evaluate the ac nonlinear response and reversal time of the magnetization. For weak ac fields, the results agree with perturbation theory. It is shown that the dc bias field changes substantially the magnetization dynamics leading to new nonlinear effects. In particular, it is demonstrated that for a nonzero bias field as the magnitude of the ac field increases the reversal time first increases and having attained its maximum at some critical value of the ac field, decreases exponentially.

  16. Photometric variability in a warm, strongly magnetic DQ white dwarf, SDSS J103655.39+652252.2

    International Nuclear Information System (INIS)

    Williams, Kurtis A.; Winget, D. E.; Montgomery, M. H.; Hermes, J. J.; Falcon, Ross E.; Winget, K. I.; Dufour, Patrick; Kepler, S. O.; Bolte, Michael; Rubin, Kate H. R.; Liebert, James

    2013-01-01

    We present the discovery of photometric variability in the DQ white dwarf SDSS J103655.39+652252.2 (SDSS J1036+6522). Time-series photometry reveals a coherent monoperiodic modulation at a period of 1115.64751(67) s with an amplitude 0.442% ± 0.024%; no other periodic modulations are observed with amplitudes ≳ 0.13%. The period, amplitude, and phase of this modulation are constant within errors over 16 months. The spectrum of SDSS J1036+6522 shows magnetic splitting of carbon lines, and we use Paschen-Back formalism to develop a grid of model atmospheres for mixed carbon and helium atmospheres. Our models, while reliant on several simplistic assumptions, nevertheless match the major spectral and photometric properties of the star with a self-consistent set of parameters: T eff ≈ 15, 500 K, log g ≈ 9, log (C/He) = –1.0, and a mean magnetic field strength of 3.0 ± 0.2 MG. The temperature and abundances strongly suggest that SDSS J1036+6522 is a transition object between the hot, carbon-dominated DQs and the cool, helium-dominated DQs. The variability of SDSS J1036+6522 has characteristics similar to those of the variable hot carbon-atmosphere white dwarfs (DQVs), however, its temperature is significantly cooler. The pulse profile of SDSS J1036+6522 is nearly sinusoidal, in contrast with the significantly asymmetric pulse shapes of the known magnetic DQVs. If the variability in SDSS J1036+6522 is due to the same mechanism as other DQVs, then the pulse shape is not a definitive diagnostic on the absence of a strong magnetic field in DQVs. It remains unclear whether the root cause of the variability in SDSS J1036+6522 and the other hot DQVs is the same.

  17. On the theory of stationary charged particle ensembles in strongly non-homogeneous azimuthally symmetric magnetic fields

    International Nuclear Information System (INIS)

    Auluck, S.K.H.

    1982-01-01

    A method of treating problems involving strongly nonadiabatic particle orbits in a magnetic field is described for the case when the system is long-lived on the collisional time scale. A canonical distribution P=Z -1 exp-β(H+Ωpsub(theta)) results from maximization of entropy subject to conservation of the Hamiltonian H and canonical angular momentum psub(theta) for an azimuthally symmetric system. By taking the MIGMA problem as an example, the method of determining the constants β,Ω,Z from the average energy, average angular momentum and the total number of particles is illustrated. Associated physical effects are discussed. (author)

  18. Global well-posedness and decay estimates of strong solutions to a two-phase model with magnetic field

    Science.gov (United States)

    Wen, Huanyao; Zhu, Limei

    2018-02-01

    In this paper, we consider the Cauchy problem for a two-phase model with magnetic field in three dimensions. The global existence and uniqueness of strong solution as well as the time decay estimates in H2 (R3) are obtained by introducing a new linearized system with respect to (nγ -n˜γ , n - n ˜ , P - P ˜ , u , H) for constants n ˜ ≥ 0 and P ˜ > 0, and doing some new a priori estimates in Sobolev Spaces to get the uniform upper bound of (n - n ˜ ,nγ -n˜γ) in H2 (R3) norm.

  19. Magnetic pinning in superconductor-ferromagnet multilayers

    International Nuclear Information System (INIS)

    Bulaevskii, L. N.; Chudnovsky, E. M.; Maley, M. P.

    2000-01-01

    We argue that superconductor/ferromagnet multilayers of nanoscale period should exhibit strong pinning of vortices by the magnetic domain structure in magnetic fields below the coercive field when ferromagnetic layers exhibit strong perpendicular magnetic anisotropy. The estimated maximum magnetic pinning energy for single vortex in such a system is about 100 times larger than the pinning energy by columnar defects. This pinning energy may provide critical currents as high as 10 6 -10 7 A/cm 2 at high temperatures (but not very close to T c ) at least in magnetic fields below 0.1 T. (c) 2000 American Institute of Physics

  20. Magnetic pinning in superconductor-ferromagnet multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Bulaevskii, L. N. [Department of Physics and Astronomy, CUNY Lehman College 250 Bedford Park Boulevard West, Bronx, New York 10468-1589 (United States); Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Chudnovsky, E. M. [Department of Physics and Astronomy, CUNY Lehman College, 250 Bedford Park Boulevard West, Bronx, New York 10468-1589 (United States); Maley, M. P. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

    2000-05-01

    We argue that superconductor/ferromagnet multilayers of nanoscale period should exhibit strong pinning of vortices by the magnetic domain structure in magnetic fields below the coercive field when ferromagnetic layers exhibit strong perpendicular magnetic anisotropy. The estimated maximum magnetic pinning energy for single vortex in such a system is about 100 times larger than the pinning energy by columnar defects. This pinning energy may provide critical currents as high as 10{sup 6}-10{sup 7} A/cm{sup 2} at high temperatures (but not very close to T{sub c}) at least in magnetic fields below 0.1 T. (c) 2000 American Institute of Physics.

  1. Strong Transverse Photosphere Magnetic Fields and Twist in Light Bridge Dividing Delta Sunspot of Active Region 12673

    Science.gov (United States)

    Wang, Haimin; Yurchyshyn, Vasyl; Liu, Chang; Ahn, Kwangsu; Toriumi, Shin; Cao, Wenda

    2018-01-01

    Solar Active Region (AR) 12673 is the most flare productive AR in the solar cycle 24. It produced four X-class flares including the X9.3 flare on 06 September 2017 and the X8.2 limb event on 10 September. Sun and Norton (2017) reported that this region had an unusual high rate of flux emergence, while Huang et al. (2018) reported that the X9.3 flare had extremely strong white-light flare emissions. Yang at al. (2017) described the detailed morphological evolution of this AR. In this report, we focus on usual behaviors of the light bridge (LB) dividing the delta configuration of this AR, namely the strong magnetic fields (above 5500 G) in the LB and apparent photospheric twist as shown in observations with a 0.1 arcsec spatial resolution obtained by the 1.6m telescope at Big Bear Solar Observatory.

  2. Faraday effect in rare-earth ferrite garnets located in strong magnetic fields

    International Nuclear Information System (INIS)

    Valiev, U.V.; Zvezdin, A.K.; Krinchik, G.S.; Levitin, R.Z.; Mukimov, K.M.; Popov, A.I.

    1983-01-01

    The Faraday effect is investigated experimentally in single crystal specimens of rare earth iron garnets (REIG) R 3 Fe 5 O 12 (R=Y, Gd, Tb, Dy, Er, Tm, Yb, Eu, Sm and Ho) and also in mixed iron garnets Rsub(x)Ysub(3-x)Fesub(5)Osub(12) (R=Tb, Dy). The m.easurements are carried out in pulsed magnetic fields of intensity up to 200 kOe, in a temperature range from 4.2 to 300 K and at a wavelength of the light lambda=1.15 μm. The field dependence of the Faraday effect observed in the REIG cannot be explained if only the usually considered ''paramagnetic'' contribution to the Faraday effect is taken into account. A theory is developed which, besides the paramagnetic mechanism, takes into account a diamagnetic mechanism and also the mixing of the wave functions of the ground and excited multiplets. The contributions of each of these three mechanisms to the angle of rotation of the plane of polarization by the rare earth sublattice of the iron garnet are estimated theoretically. It is concluded that the mixing mechanism contributes significantly to the field and temperature dependences of the Faraday effect in REIG

  3. Magnetism and local symmetry breaking in a Mott insulator with strong spin orbit interactions.

    Science.gov (United States)

    Lu, L; Song, M; Liu, W; Reyes, A P; Kuhns, P; Lee, H O; Fisher, I R; Mitrović, V F

    2017-02-09

    Study of the combined effects of strong electronic correlations with spin-orbit coupling (SOC) represents a central issue in quantum materials research. Predicting emergent properties represents a huge theoretical problem since the presence of SOC implies that the spin is not a good quantum number. Existing theories propose the emergence of a multitude of exotic quantum phases, distinguishable by either local point symmetry breaking or local spin expectation values, even in materials with simple cubic crystal structure such as Ba 2 NaOsO 6 . Experimental tests of these theories by local probes are highly sought for. Our local measurements designed to concurrently probe spin and orbital/lattice degrees of freedom of Ba 2 NaOsO 6 provide such tests. Here we show that a canted ferromagnetic phase which is preceded by local point symmetry breaking is stabilized at low temperatures, as predicted by quantum theories involving multipolar spin interactions.

  4. Giant current-perpendicular-to-plane magnetoresistance in multilayer graphene as grown on nickel.

    Science.gov (United States)

    Bodepudi, S C; Singh, A P; Pramanik, S

    2014-05-14

    Strong magnetoresistance effects are often observed in ferromagnet-nonmagnet multilayers, which are exploited in state-of-the-art magnetic field sensing and data storage technologies. In this work we report a novel current-perpendicular-to-plane magnetoresistance effect in multilayer graphene as grown on a catalytic nickel surface by chemical vapor deposition. A negative magnetoresistance effect of ∼10(4)% has been observed, which persists even at room temperature. This effect is correlated with the shape of the 2D peak as well as with the occurrence of D peak in the Raman spectrum of the as-grown multilayer graphene. The observed magnetoresistance is extremely high as compared to other known materials systems for similar temperature and field range and can be qualitatively explained within the framework of "interlayer magnetoresistance" (ILMR).

  5. Comparative studies of density-functional approximations for light atoms in strong magnetic fields

    Science.gov (United States)

    Zhu, Wuming; Zhang, Liang; Trickey, S. B.

    2014-08-01

    For a wide range of magnetic fields, 0≤B≤2000 a.u., we present a systematic comparative study of the performance of different types of density-functional approximations in light atoms (2≤Z≤6). Local, generalized-gradient approximation (GGA; semilocal), and meta-GGA ground-state exchange-correlation (xc) functionals are compared on an equal footing with exact-exchange, Hartree-Fock (HF), and current-density-functional-theory (CDFT) approximations. Comparison also is made with published quantum Monte Carlo data. Though all approximations give qualitatively reasonable results, the exchange energies from local and GGA functionals are too negative for large B. Results from the Perdew-Burke-Ernzerhof ground-state GGA and Tao-Perdew-Staroverov-Scuseria (TPSS) ground-state meta-GGA functionals are very close. Because of confinement, self-interaction error in such functionals is more severe at large B than at B =0, hence self-interaction correction is crucial. Exact exchange combined with the TPSS correlation functional results in a self-interaction-free (xc) functional, from which we obtain atomic energies of comparable accuracy to those from correlated wave-function methods. Specifically for the B and C atoms, we provide beyond-HF energies in a wide range of B fields. Fully self-consistent CDFT calculations were done with the Vignale-Rasolt-Geldart (VRG) functional in conjunction with the PW92 xc functional. Current effects turn out to be small, and the vorticity variable in the VRG functional diverges in some low-density regions. This part of the study suggests that nonlocal, self-interaction-free functionals may be better than local approximations as a starting point for CDFT functional construction and that some basic variable other than the vorticity could be helpful in making CDFT calculations practical.

  6. A device to measure the effects of strong magnetic fields on the image resolution of PET scanners

    CERN Document Server

    Burdette, D; Chesi, E; Clinthorne, N H; Cochran, E; Honscheid, K; Huh, S S; Kagan, H; Knopp, M; Lacasta, C; Mikuz, M; Schmalbrock, P; Studen, A; Weilhammer, P

    2009-01-01

    Very high resolution images can be achieved in small animal PET systems utilizing solid state silicon pad detectors. As these systems approach sub-millimeter resolutions, the range of the positron is becoming the dominant contribution to image blur. The size of the positron range effect depends on the initial positron energy and hence the radioactive tracer used. For higher energy positron emitters, such as and , which are gaining importance in small animal studies, the width of the annihilation point distribution dominates the spatial resolution. This positron range effect can be reduced by embedding the field of view of the PET scanner in a strong magnetic field. In order to confirm this effect experimentally, we developed a high resolution PET instrument based on silicon pad detectors that can operate in a 7 T magnetic field. In this paper, we describe the instrument and present initial results of a study of the effects of magnetic fields up to 7 T on PET image resolution for and point sources.

  7. Performance and analysis of wireless power charging system from room temperature to HTS magnet via strong resonance coupling method

    Energy Technology Data Exchange (ETDEWEB)

    Chung, Y. D.; Lee, S. Y.; Lee, T. W.; Kim, J. S. [Suwon Science College, Suwon (Korea, Republic of); Lee, C. Y. [Korea Railroad Institute, Uiwang (Korea, Republic of)

    2016-03-15

    The technology of supplying the electric power by wireless power transfer (WPT) is expected for the next generation power feeding system since it can supply the power to portable devices without any connectors through large air gap. As such a technology based on strongly coupled electromagnetic resonators is possible to deliver the large power and recharge them seamlessly; it has been considered as a noble option to wireless power charging system in the various power applications. Recently, various HTS wires have now been manufactured for demonstrations of transmission cables, motors, MAGLEV, and other electrical power components. However, since the HTS magnets have a lower index n value intrinsically, they are required to be charged from external power system through leads or internal power system. The portable area is limited as well as the cryogen system is bulkier. Thus, we proposed a novel design of wireless power charging system for superconducting HTS magnet (WPC4SM) based on resonance coupling method. As the novel system makes possible a wireless power charging using copper resonance coupled coils, it enables to portable charging conveniently in the superconducting applications. This paper presented the conceptual design and operating characteristics of WPC4SM using different shapes' copper resonance coil. The proposed system consists of four components; RF generator of 370 kHz, copper resonance coupling coils, impedance matching (IM) subsystem and HTS magnet including rectifier system.

  8. Test of Horizontal Magnetic Field Measurements in the Presence of a Strong Vertical Field

    CERN Document Server

    Vasserman, Isaac

    2004-01-01

    Trajectory straightness is an important parameter defining the performance of free-electron laser (FEL) devices. The first test of horizontal field measurements using Hall probes was done in 1998 as a preparation to the tuning of undulators for the FEL project at the Advanced Photon Source. This work continues the 1998 work, now associated with Linac Coherent Light Source (LCLS) project. Tolerances for the LCLS FEL undulator specify 2 um trajectory excursion in both (horizontal and vertical) planes for a particle energy of 14.1 GeV, which means that measurements of a small horizontal field in presence of strong (up to 1.5 T) vertical field are required. Hall probe measurements under such conditions are complicated due to a planar Hall probe effect. Previous tests done in 1998 showed that a 2- axis Sentron probe is a possible choice. The high sensitivity of horizontal field integrals to the vertical position of the sensor was observed. It was shown that this probe could be used for fast measurements and tuning...

  9. Effects of a strong magnetic field on internal gravity waves: trapping, phase mixing, reflection and dynamical chaos

    Science.gov (United States)

    Loi, Shyeh Tjing; Papaloizou, John C. B.

    2018-04-01

    The spectrum of oscillation modes of a star provides information not only about its material properties (e.g. mean density), but also its symmetries. Spherical symmetry can be broken by rotation and/or magnetic fields. It has been postulated that strong magnetic fields in the cores of some red giants are responsible for their anomalously weak dipole mode amplitudes (the "dipole dichotomy" problem), but a detailed understanding of how gravity waves interact with strong fields is thus far lacking. In this work, we attack the problem through a variety of analytical and numerical techniques, applied to a localised region centred on a null line of a confined axisymmetric magnetic field which is approximated as being cylindrically symmetric. We uncover a rich variety of phenomena that manifest when the field strength exceeds a critical value, beyond which the symmetry is drastically broken by the Lorentz force. When this threshold is reached, the spatial structure of the g-modes becomes heavily altered. The dynamics of wave packet propagation transitions from regular to chaotic, which is expected to fundamentally change the organisation of the mode spectrum. In addition, depending on their frequency and the orientation of field lines with respect to the stratification, waves impinging on different parts of the magnetised region are found to undergo either reflection or trapping. Trapping regions provide an avenue for energy loss through Alfvén wave phase mixing. Our results may find application in various astrophysical contexts, including the dipole dichotomy problem, the solar interior, and compact star oscillations.

  10. Temperature dependence of the interfacial magnetic anisotropy in W/CoFeB/MgO

    OpenAIRE

    Kyoung-Min Lee; Jun Woo Choi; Junghyun Sok; Byoung-Chul Min

    2017-01-01

    The interfacial perpendicular magnetic anisotropy in W/CoFeB (1.2 ∼ 3 nm)/MgO thin film structures is strongly dependent on temperature, and is significantly reduced at high temperature. The interfacial magnetic anisotropy is generally proportional to the third power of magnetization, but an additional factor due to thermal expansion is required to explain the temperature dependence of the magnetic anisotropy of ultrathin CoFeB films. The reduction of the magnetic anisotropy is more prominent...

  11. Anomalously strong relaxation of the polarization of muons in the magnetically ordered and paramagnetic states of the TbMnO3 multiferroic

    Science.gov (United States)

    Andrievskii, D. S.; Vorob'ev, S. I.; Getalov, A. L.; Golovenchits, E. I.; Komarov, E. N.; Kotov, S. A.; Sanina, V. A.; Shcherbakov, G. V.

    2017-09-01

    An anomalously strong relaxation of the muon polarization in a magnetically ordered state in the TbMnO3 multiferroic has been revealed by the method below the μ SR Néel temperature (42 K). Such a relaxation is due to the muon channel of relaxation of the polarization and the interaction of the magnetic moment of the muon with inhomogeneities of the internal magnetic field of an ordered state in the form of a cycloid. Above the Néel temperature, beginning with temperatures depending on the applied magnetic field, a two-phase state has been revealed where one phase has an anomalously strong relaxation of the muon polarization for a paramagnetic state. These features of the paramagnetic state are due to short-range magnetic order domains that appear in strongly frustrated TbMnO3. A true paramagnetic state has been observed only at T ≥ 150 K.

  12. High-latitude dayside electric fields and currents during strong northward interplanetary magnetic field: Observations and model simulation

    International Nuclear Information System (INIS)

    Clauer, C.R.; Friis-Christensen, E.

    1988-01-01

    On July 23, 1983, the Interplanetary Magnetic Field turned strongly northward, becoming about 22 nT for several hours. Using a combined data set of ionospheric convection measurements made by the Sondre Stromfjord incoherent scatter radar and convection inferred from Greenland magnetometer measurements, we observe the onset of the reconfiguration of the high-latitude ionospheric currents to occur about 3 min following the northward IMF encountering the magnetopause. The large-scale reconfiguration of currents, however, appears to evolve over a period of about 22 min. Using a computer model in which the distribution of field-aligned current in the polar cleft is directly determined by the strength and orientation of the interplanetary electric field, we are able to simulate the time-varying pattern of ionospheric convection, including the onset of high-latitude ''reversed convection'' cells observed to form during the interval of strong northward IMF. These observations and the simulation results indicate that the dayside polar cap electric field observed during strong northward IMF is produced by a direct electrical current coupling with the solar wind. copyright American Geophysical Union 1988

  13. Current perpendicular to plane giant magnetoresistance in laminated nanostructures

    International Nuclear Information System (INIS)

    Vedyayev, A.; Zhukov, I.; Dieny, B.

    2005-01-01

    We theoretically studied spin-dependent electron transport perpendicular-to-plain (CPP) in magnetic laminated multilayered structures by using Kubo formalism. We took into account not only bulk scattering, but the interface resistance due to both specular and diffuse reflection and also spin conserving and spin-flip processes. It was shown that spin-flip scattering at interfaces substantially reduces the value of giant magnetoresistance (GMR). This can explain the experimental observations that the CPP GMR ratio for laminated structures only slightly increases as compared to non-laminated ones even though lamination induces a significant increase in CPP resistance

  14. Multiprobe perpendicular giant magnetoresistance measurements on isolated multilayered nanowires

    International Nuclear Information System (INIS)

    Elhoussine, F.; Vila, L.; Piraux, L.; Faini, G.

    2005-01-01

    By combining electrochemical deposition into nanopores with electron-beam lithography, we developed an experiment setup to probe the giant magnetoresistance effects with current perpendicular to the plane (CPP-GMR) on isolated nanowires. Here we present four-probe magnetotransport measurements on multilayered Co (55 nm)/Cu (5 nm) nanowires of 100 nm diameter. The multiprobe technique allowed us to measure high GMR ratio on wire segments as short as 500 nm, without any additional contact resistance. We present different magnetic behaviors and GMR ratios depending on the measured segment and the applied field orientation. Results are discussed in terms of the CPP-GMR theory

  15. Phase manipulation of Goos–Hänchen shifts in a single-layer of graphene nanostructure under strong magnetic field

    Science.gov (United States)

    Solookinejad, Gh; Jabbari, M.; Panahi, M.; Ahmadi Sangachin, E.

    2017-11-01

    In this paper, we discuss the phase management of Goos–Hänchen (GH) shifts of a probe light through a cavity with a single-layer graphene nanostructure under a strong magnetic field. By using the quantum mechanical density matrix formalism we study the GH shifts of reflected and transmitted light beams. It is realized that negative or positive GH shifts can be achieved simultaneously by tuning some controllable parameters such as relative phase and the Rabi frequency of the applied fields. Moreover, the thickness effect of the cavity structure is considered as an effective parameter for adjusting the GH shifts of reflected and transmitted light beams. We find that by choosing suitable parameters, a maximum negative shift of 4.5 mm and positive shift of 5.4 mm are possible for GH shifts in reflected and transmitted light. Our proposed model may be useful for developing all-optical devices in the infrared region.

  16. Fibrous polymer grafted magnetic chitosan beads with strong poly(cation-exchange) groups for single step purification of lysozyme.

    Science.gov (United States)

    Bayramoglu, Gulay; Tekinay, Turgay; Ozalp, V Cengiz; Arica, M Yakup

    2015-05-15

    Lysozyme is an important polypetide used in medical and food applications. We report a novel magnetic strong cation exchange beads for efficient purification of lysozyme from chicken egg white. Magnetic chitosan (MCHT) beads were synthesized via phase inversion method, and then grafted with poly(glycidyl methacrylate) (p(GMA)) via the surface-initiated atom transfer radical polymerization (SI-ATRP). Epoxy groups of the grafted polymer, were modified into strong cation-exchange groups (i.e., sulfonate groups) in the presence of sodium sulfite. The MCTH and MCTH-g-p(GMA)-SO3H beads were characterized by ATR-FTIR, SEM, and VSM. The sulphonate groups content of the modified MCTH-g-p(GMA)-4 beads was found to be 0.53mmolg(-1) of beads by the potentiometric titration method. The MCTH-g-p(GMA)-SO3H beads were first used as an ion-exchange support for adsorption of lysozyme from aqueous solution. The influence of different experimental parameters such as pH, contact time, and temperature on the adsorption process was evaluated. The maximum adsorption capacity was found to be 208.7mgg(-1) beads. Adsorption of lysozyme on the MCTH-g-p(GMA)-SO3H beads fitted to Langmuir isotherm model and followed the pseudo second-order kinetic. More than 93% of the adsorbed lysozyme was desorbed using Na2CO3 solution (pH 11.0). The purity of the lysozyme was checked by HPLC and SDS gel electrophoresis. In addition, the MCTH-g-p(GMA)-SO3H beads prepared in this work showed promising potential for separation of various anionic molecules. Copyright © 2015 Elsevier B.V. All rights reserved.

  17. He 2++ molecular ion in a strong time-dependent magnetic field: a current-density functional study.

    Science.gov (United States)

    Vikas

    2011-08-01

    The He 2++ molecular ion exposed to a strong ultrashort time-dependent (TD) magnetic field of the order of 10(9) G is investigated through a quantum fluid dynamics (QFD) and current-density functional theory (CDFT) based approach using vector exchange-correlation (XC) potential and energy density functional that depend not only on the electronic charge-density but also on the current density. The TD-QFD-CDFT computations are performed in a parallel internuclear-axis and magnetic field-axis configuration at the field-free equilibrium internuclear separation R = 1.3 au with the field-strength varying between 0 and 10(11) G. The TD behavior of the exchange- and correlation energy of the He 2++ is analyzed and compared with that obtained using a [B-TD-QFD-density functional theory (DFT)] approach based on the conventional TD-DFT under similar computational constraints but using only scalar XC potential and energy density functional dependent on the electronic charge-density alone. The CDFT based approach yields TD exchange- and correlation energy and TD electronic charge-density significantly different from that obtained using the conventional TD-DFT based approach, particularly, at typical magnetic field strengths and during a typical time period of the TD field. This peculiar behavior of the CDFT-based approach is traced to the TD current-density dependent vector XC potential, which can induce nonadiabatic effects causing retardation of the oscillating electronic charge density. Such dissipative electron dynamics of the He 2++ molecular ion is elucidated by treating electronic charge density as an electron-"fluid" in the terminology of QFD. Copyright © 2011 Wiley Periodicals, Inc.

  18. Quasilongitudinal soliton in a two-dimensional strongly coupled complex dusty plasma in the presence of an external magnetic field.

    Science.gov (United States)

    Ghosh, Samiran

    2014-09-01

    The propagation of a nonlinear low-frequency mode in two-dimensional (2D) monolayer hexagonal dusty plasma crystal in presence of external magnetic field and dust-neutral collision is investigated. The standard perturbative approach leads to a 2D Korteweg-de Vries (KdV) soliton for the well-known dust-lattice mode. However, the Coriolis force due to crystal rotation and Lorentz force due to magnetic field on dust particles introduce a linear forcing term, whereas dust-neutral drag introduce the usual damping term in the 2D KdV equation. This new nonlinear equation is solved both analytically and numerically to show the competition between the linear forcing and damping in the formation of quasilongitudinal soliton in a 2D strongly coupled complex (dusty) plasma. Numerical simulation on the basis of the typical experimental plasma parameters and the analytical solution reveal that the neutral drag force is responsible for the usual exponential decay of the soliton, whereas Coriolis and/or Lorentz force is responsible for the algebraic decay as well as the oscillating tail formation of the soliton. The results are discussed in the context of the plasma crystal experiment.

  19. X-Ray Magnetic Dichroism of Antiferromagnet Fe2O3 : The Orientation of Magnetic Moments Observed by Fe 2p X-Ray Absorption Spectroscopy

    NARCIS (Netherlands)

    Kuiper, Pieter; Searle, Barry G.; Rudolf, Petra; Tjeng, L.H.; Chen, C.T.

    1993-01-01

    We report strong magnetic linear dichroism at the Fe L2,3 edge of the antiferromagnet Fe2O3 (hematite). The relative difference in absorption for light polarized parallel and perpendicular to the magnetic moment is as high as 40% at the Fe L2 edge. The spectra are in excellent agreement with

  20. Thermal fluctuations in perpendicular recording media: New methodology for estimation of activation moment

    International Nuclear Information System (INIS)

    Mamiya, H; Oba, Y; Ohnuma, M; Hagiya, H; Oku, T; Suzuki, J; Yokoyama, M; Nishihara, Y; Katayama, T; Awano, H; Koda, T

    2011-01-01

    In nanoparticulate films with perpendicular magnetic anisotropy, a large demagnetizing field almost compensates for the experimentally designed change in the magnetic field applied parallel to the film normal. We propose a new method based on field-cycling to eliminate the uncertainty in the demagnetizing response from the analysis of the activation volume of the reversal or magnetic activation moment in such films. In this method, the applied field induced variation in the magnetic relaxation rate is measured before the effect of the demagnetizing field becomes dominant. We also discuss an analogical thermal-cycling method to clarify the temperature dependence of the barrier height for magnetization reversal in a magnetic field. We apply these methods to a Co 74 Pt 16 Cr 10 -SiO 2 nanoparticulate film as an example. The results demonstrate that these methods are useful for studying thermal fluctuations in perpendicular recording media.

  1. Strong temperature dependence of extraordinary magnetoresistance correlated to mobility in a two-contact device

    KAUST Repository

    Sun, Jian

    2012-02-21

    A two-contact extraordinary magnetoresistance (EMR) device has been fabricated and characterized at various temperatures under magnetic fields applied in different directions. Large performance variations across the temperature range have been found, which are due to the strong dependence of the EMR effect on the mobility. The device shows the highest sensitivity of 562ω/T at 75 K with the field applied perpendicularly. Due to the overlap between the semiconductor and the metal shunt, the device is also sensitive to planar fields but with a lower sensitivity of about 20 to 25% of the one to perpendicular fields. © 2012 The Japan Society of Applied Physics.

  2. Validation of numerical solvers for liquid metal flow in a complex geometry in the presence of a strong magnetic field

    Science.gov (United States)

    Patel, Anita; Pulugundla, Gautam; Smolentsev, Sergey; Abdou, Mohamed; Bhattacharyay, Rajendraprasad

    2018-04-01

    Following the magnetohydrodynamic (MHD) code validation and verification proposal by Smolentsev et al. (Fusion Eng Des 100:65-72, 2015), we perform code to code and code to experiment comparisons between two computational solvers, FLUIDYN and HIMAG, which are presently considered as two of the prospective CFD tools for fusion blanket applications. In such applications, an electrically conducting breeder/coolant circulates in the blanket ducts in the presence of a strong plasma-confining magnetic field at high Hartmann numbers, it{Ha} (it{Ha}^2 is the ratio between electromagnetic and viscous forces) and high interaction parameters, it{N} (it{N} is the ratio of electromagnetic to inertial forces). The main objective of this paper is to provide the scientific and engineering community with common references to assist fusion researchers in the selection of adequate computational means to be used for blanket design and analysis. As an initial validation case, the two codes are applied to the classic problem of a laminar fully developed MHD flows in a rectangular duct. Both codes demonstrate a very good agreement with the analytical solution for it{Ha} up to 15, 000. To address the capabilities of the two codes to properly resolve complex geometry flows, we consider a case of three-dimensional developing MHD flow in a geometry comprising of a series of interconnected electrically conducting rectangular ducts. The computed electric potential distributions for two flows (Case A) it{Ha}=515, it{N}=3.2 and (Case B) it{Ha}=2059, it{N}=63.8 are in very good agreement with the experimental data, while the comparisons for the MHD pressure drop are still unsatisfactory. To better interpret the observed differences, the obtained numerical data are analyzed against earlier theoretical and experimental studies for flows that involve changes in the relative orientation between the flow and the magnetic field.

  3. Two-stream instabilities from the lower-hybrid frequency to the electron cyclotron frequency: application to the front of quasi-perpendicular shocks

    Science.gov (United States)

    Muschietti, Laurent; Lembège, Bertrand

    2017-09-01

    Quasi-perpendicular supercritical shocks are characterized by the presence of a magnetic foot due to the accumulation of a fraction of the incoming ions that is reflected by the shock front. There, three different plasma populations coexist (incoming ion core, reflected ion beam, electrons) and can excite various two-stream instabilities (TSIs) owing to their relative drifts. These instabilities represent local sources of turbulence with a wide frequency range extending from the lower hybrid to the electron cyclotron. Their linear features are analyzed by means of both a dispersion study and numerical PIC simulations. Three main types of TSI and correspondingly excited waves are identified: i. Oblique whistlers due to the (so-called fast) relative drift between reflected ions/electrons; the waves propagate toward upstream away from the shock front at a strongly oblique angle (θ ˜ 50°) to the ambient magnetic field Bo, have frequencies a few times the lower hybrid, and have wavelengths a fraction of the ion inertia length c/ωpi. ii. Quasi-perpendicular whistlers due to the (so-called slow) relative drift between incoming ions/electrons; the waves propagate toward the shock ramp at an angle θ a few degrees off 90°, have frequencies around the lower hybrid, and have wavelengths several times the electron inertia length c/ωpe. iii. Extended Bernstein waves which also propagate in the quasi-perpendicular domain, yet are due to the (so-called fast) relative drift between reflected ions/electrons; the instability is an extension of the electron cyclotron drift instability (normally strictly perpendicular and electrostatic) and produces waves with a magnetic component which have frequencies close to the electron cyclotron as well as wavelengths close to the electron gyroradius and which propagate toward upstream. Present results are compared with previous works in order to stress some features not previously analyzed and to define a more synthetic view of these TSIs.

  4. Behavior of Particle Depots in Molten Silicon During Float-Zone Growth in Strong Static Magnetic Fields

    Science.gov (United States)

    Jauss, T.; SorgenFrei, T.; Croell, A.; Azizi, M.; Reimann, C.; Friedrich, J.; Volz, M. P.

    2014-01-01

    In the photovoltaics industry, the largest market share is represented by solar cells made from multicrystalline silicon, which is grown by directional solidification. During the growth process, the silicon melt is in contact with the silicon nitride coated crucible walls and the furnace atmosphere which contains carbon monoxide. The dissolution of the crucible coating, the carbon bearing gas, and the carbon already present in the feedstock, lead to the precipitation of silicon carbide, and silicon nitride, at later stages of the growth process. The precipitation of Si3N4 and SiC particles of up to several hundred micrometers in diameter leads to severe problems during the wire sawing process for wafering the ingots. Furthermore the growth of the silicon grains can be negatively influenced by the presence of particles, which act as nucleation sources and lead to a grit structure of small grains and are sources for dislocations. If doped with Nitrogen from the dissolved crucible coating, SiC is a semi conductive material, and can act as a shunt, short circuiting parts of the solar cell. For these reasons, the incorporation of such particles needs to be avoided. In this contribution we performed model experiments in which the transport of intentionally added SiC particles and their interaction with the solid-liquid interface during float zone growth of silicon in strong steady magnetic fields was investigated. SiC particles of 7µm and 60µm size are placed in single crystal silicon [100] and [111] rods of 8mm diameter. This is achieved by drilling a hole of 2mm diameter, filling in the particles and closing the hole by melting the surface of the rod until a film of silicon covers the hole. The samples are processed under a vacuum of 1x10(exp -5) mbar or better, to prevent gas inclusions. An oxide layer to suppress Marangoni convection is applied by wet oxidation. Experiments without and with static magnetic field are carried out to investigate the influence of melt

  5. Driving Perpendicular Decay by the Parametric Instabilities of Parallel Propagating Alfven Waves

    Science.gov (United States)

    Comisel, H.; Nariyuki, Y.; Narita, Y.; Motschmann, U. M.

    2017-12-01

    The decay of monochromatic Alfven waves is studied by means of 2-D and 3-D hybrid simulations. The goal of the work is to follow up the long-time nonlinear development of theparametric decays after the saturation process in a multi-spatial dimension for coherent Alfven waves with three different polarizations: left-handed circularly polarized -, right-handed circularly polarized - and linearly polarized - Alfven pump waves. The analyzing is restricted for the parallel propagation with respect to the direction of the mean magnetic field in low beta plasmas. Numerical results suggest that the parametric instabilities can lead to broadband decays along the perpendicular direction, in which the magnetic field spectrum is extended towards the perpendicular direction.Perpendicular propagating daughter waves are observed atfinite perpendicular wave numbers as well as direct incompressible energy cascades driven by plasma turbulence.The density power spectrum shows inverse compressible cascades at smallerperpendicular wave numbers and direct cascades at larger wave numbers. The one-dimensional reduced spectra of the magnetic field and densities show correlations for a significant large range of perpendicular wave numbers beforedissipation. The time evolution of the anisotropy index is also determined for all the three analyzed setups.

  6. Strong magnetism observed in carbon nanoparticles produced by the laser vaporization of a carbon pellet in hydrogen-containing Ar balance gas.

    Science.gov (United States)

    Asano, Hirohito; Muraki, Susumu; Endo, Hiroki; Bandow, Shunji; Iijima, Sumio

    2010-08-25

    Nanometer-scale carbon particles driven by the pulsed-laser vaporization of pelletized pure carbon powder at 1000 °C in a hydrogen-containing environment show anomalous magnetism like a superparamagnet, while the sample prepared in 100% of Ar does not show such magnetism. The observed magnetism was unchanged over months in the ambient. The structure of this nanomaterial resembles the foam of a laundry detergent and transmission electron microscopy indicates a clear corrugated line contrast. On the other hand, a sample without strong magnetism does not give such an image contrast. The x-ray diffraction pattern coincides with that of graphite and no other peak is detected. Thermogravimetry indicates that all samples completely burn out up to approx. 820 °C and no material remains after combustion, indicating that the sample does not contain impurity metals. Magnetization is easily saturated by ∼10,000 G at 280 K with no hysteresis, but the hysteresis appears at 4.2 K. This phenomenon is explained by introducing a crystalline anisotropy which restricts the motion of the magnetic moment and stabilizes the remnant magnetization at zero magnetic field. Magnitudes of the saturation magnetization are in the range of 1-5 emu G g(-1) at 4.2 K, which correspond to 0.002-0.01 Bohr magneton per carbon atom. This concentration may be increased by ten times or more, because only about 4-10% of particles have a magnetic domain in the present samples.

  7. Strong magnetism observed in carbon nanoparticles produced by the laser vaporization of a carbon pellet in hydrogen-containing Ar balance gas

    Energy Technology Data Exchange (ETDEWEB)

    Asano, Hirohito; Muraki, Susumu; Endo, Hiroki; Bandow, Shunji; Iijima, Sumio, E-mail: bandow@meijo-u.ac.j [Department of Materials Science and Engineering, Meijo University, 1-501 Shiogamaguchi, Tenpaku, Nagoya 468-8502 (Japan)

    2010-08-25

    Nanometer-scale carbon particles driven by the pulsed-laser vaporization of pelletized pure carbon powder at 1000 {sup 0}C in a hydrogen-containing environment show anomalous magnetism like a superparamagnet, while the sample prepared in 100% of Ar does not show such magnetism. The observed magnetism was unchanged over months in the ambient. The structure of this nanomaterial resembles the foam of a laundry detergent and transmission electron microscopy indicates a clear corrugated line contrast. On the other hand, a sample without strong magnetism does not give such an image contrast. The x-ray diffraction pattern coincides with that of graphite and no other peak is detected. Thermogravimetry indicates that all samples completely burn out up to approx. 820 {sup 0}C and no material remains after combustion, indicating that the sample does not contain impurity metals. Magnetization is easily saturated by {approx} 10 000 G at 280 K with no hysteresis, but the hysteresis appears at 4.2 K. This phenomenon is explained by introducing a crystalline anisotropy which restricts the motion of the magnetic moment and stabilizes the remnant magnetization at zero magnetic field. Magnitudes of the saturation magnetization are in the range of 1-5 emu G g{sup -1} at 4.2 K, which correspond to 0.002-0.01 Bohr magneton per carbon atom. This concentration may be increased by ten times or more, because only about 4-10% of particles have a magnetic domain in the present samples.

  8. CeCo5 thin films with perpendicular anisotropy grown by molecular beam epitaxy

    Science.gov (United States)

    Sharma, S.; Hildebrandt, E.; Major, M.; Komissinskiy, P.; Radulov, I.; Alff, L.

    2018-04-01

    Buffer-free, highly textured (0 0 1) oriented CeCo5 thin films showing perpendicular magnetic anisotropy were synthesized on (0 0 1) Al2O3 substrates by molecular beam epitaxy. Ce exists in a mixture of Ce3+ and Ce4+ valence states as shown by X-ray photoelectron spectroscopy. The first anisotropy constant, K1, as measured by torque magnetometry was 0.82 MJ/m3 (8.2 ×106erg /cm3) . A maximum coercivity of 5.16 kOe with a negative temperature coefficient of -0.304%K-1 and a magnetization of 527.30 emu/cm3 was measured perpendicular to the film plane at 5 K. In addition, a large anisotropy of the magnetic moment of 15.5% was observed. These magnetic parameters make CeCo5 a potential candidate material for spintronic and magnetic recording applications.

  9. Progress on The GEMS (Gravity Electro-Magnetism-Strong) Theory of Field Unification and Its Application to Space Problems

    International Nuclear Information System (INIS)

    Brandenburg, J. E.

    2008-01-01

    Progress on the GEMS (Gravity Electro-Magnetism-Strong), theory is presented as well as its application to space problems. The GEMS theory is now validated through the Standard Model of physics. Derivation of the value of the Gravitation constant based on the observed variation of α with energy: results in the formula G congruent with (ℎ/2π)c/M ηc 2 exp(-1/(1.61α)), where α is the fine structure constant,(ℎ/2π), is Planck's constant, c, is the speed of light, and M ηc is the mass of the η cc Charmonium meson that is shown to be identical to that derived from the GEM postulates. Covariant formulation of the GEM theory is now possible through definition of the spacetime metric tensor as a portion of the EM stress tensor normalized by its own trace: g ab = 4(F c a F cb )/(F ab F ab ), it is found that this results in a massless ground state vacuum and a Newtonian gravitation potential φ = 1/2 E 2 /B 2 . It is also found that a Lorentz or flat-space metric is recovered in the limit of a full spectrum ZPF

  10. Parametric dependence of the perpendicular velocity shear layer formation in TJ-II plasmas

    International Nuclear Information System (INIS)

    Guimarais, Luis; Estrada, Teresa; Ascasibar, Enrique

    2008-01-01

    In TJ-II plasmas, the perpendicular rotation velocity of the turbulence changes from positive to negative (from ion to electron diamagnetic direction) inside the Last Closed Magnetic Surface (LCMS) when the line-averaged plasma density exceeds some critical value, this change being dominated by the inversion in the radial electric field. In this work we study the parameters that control the inversion in the perpendicular rotation. A parametric dependence of the critical density has been obtained studying plasmas confined in different magnetic configurations (different rotational transform and/or plasma volume) and heated with different ECH power levels. The studied data set shows a positive exponential dependence on heating power and a negative one on plasma radius, while the dependence on rotational transform has low statistical meaning. Besides, analysis of local plasma parameters points to plasma collisionally as the parameter that controls the inversion of the perpendicular rotation velocity of the turbulence. (author)

  11. Time-Dependence effect in alumite recording media with perpendicular anisotropy

    NARCIS (Netherlands)

    Phan le kim, P.L.K.; Lodder, J.C.

    1999-01-01

    In this paper, we will present a study of the time-dependence effect in alumite perpendicular media at different thicknesses. Important parameters of the time-dependence effect such as magnetic viscosity and activation volume are investigated. Viscosity as a function of applied field (viscosity

  12. A new method for intrinsic viscosity measurements on perpendicular recording media

    NARCIS (Netherlands)

    Phan le kim, P.L.K.; Lodder, J.C.

    2002-01-01

    Summary form only given. In the case of perpendicular media, it is hard to measure the magnetic viscosity S (from the relaxation curve) because the internal field (H/sub 1/) is continuously changing with time due to the change in the demagnetizing field. Correction for this effect using an

  13. Three-dimensional visualization of magnetic domain structure with strong uniaxial anisotropy via scanning hard X-ray microtomography

    Science.gov (United States)

    Suzuki, Motohiro; Kim, Kab-Jin; Kim, Sanghoon; Yoshikawa, Hiroki; Tono, Takayuki; Yamada, Kihiro T.; Taniguchi, Takuya; Mizuno, Hayato; Oda, Kent; Ishibashi, Mio; Hirata, Yuushou; Li, Tian; Tsukamoto, Arata; Chiba, Daichi; Ono, Teruo

    2018-03-01

    An X-ray tomographic technique was developed to investigate the internal magnetic domain structure in a micrometer-sized ferromagnetic sample. The technique is based on a scanning hard X-ray nanoprobe using X-ray magnetic circular dichroism (XMCD). From transmission XMCD images at the Gd L3 edge as a function of the sample rotation angle, the three-dimensional (3D) distribution of a single component of the magnetic vector in a GdFeCo microdisc was reconstructed with a spatial resolution of 360 nm, using a modified algebraic reconstruction algorithm. The method is applicable to practical magnetic materials and can be extended to 3D visualization of the magnetic domain formation process under external magnetic fields.

  14. EBSD Study on the Effect of a Strong Axial Magnetic Field on the Microstructure and Crystallography of Al-Ni Alloys During Solidification

    Science.gov (United States)

    Li, Xi; Fautrelle, Yves; Gagnoud, Annie; Moreau, Rene; Du, Dafan; Ren, Zhongming; Lu, Xionggang

    2016-03-01

    The effect of a strong magnetic field on the microstructure and crystallography of the primary and eutectic Al3Ni phases in Al-Ni alloys was investigated by using EBSD. The results show that the magnetic field significantly affected the microstructures and crystallography during both volume and directional solidification. As a result, the Al3Ni primary phases were aligned with the crystal direction along the magnetic field and formed a layer-like structure. The magnetic field intensity, solidification temperature, growth speed, and alloy composition played important roles during the alignment process of the Al3Ni primary phase. Indeed, the alignment degree increased with the magnetic field and the solidification temperature during normal solidification. Moreover, the effect of the magnetic field on the crystallography of the Al-Al3Ni eutectic in the Al-Ni alloys was also studied. The applied magnetic field modified the orientation of the preferred growth direction of the Al3Ni eutectic fiber and the crystallographic orientation relationship of the Al-Al3Ni eutectic. The orientation of the preferred growth direction of the Al3Ni eutectic fiber depended mainly on the solidification direction and the alignment of the Al3Ni primary phase. Furthermore, a method for controlling the crystallization process by adjusting the angle between the solidification direction and the magnetic field was proposed.

  15. Electron spin resonance and nuclear magnetic resonance of sodium macrostructures in strongly irradiated NaCl-K crystals: Manifestation of quasi-one-dimensional behavior of electrons

    NARCIS (Netherlands)

    Cherkasov, FG; Mustafin, RG; L'vov, SG; Denisenko, GA; den Hartog, HW; Vainshtein, D. I.

    1998-01-01

    Data from an investigation of electron spin resonance and nuclear magnetic resonance of NaCl-K (similar to 1 mole%) crystals strongly irradiated with electrons imply the observation of a metal-insulator transition with decreasing temperature and the manifestation of quasi-one-dimensional electron

  16. Rotationally modulated variability and pulsations of the He-rich star CPD -62°2124 with an extraordinarily strong magnetic field

    Science.gov (United States)

    Hubrig, S.; Mikulášek, Z.; Kholtygin, A. F.; Ilyin, I.; Schöller, M.; Järvinen, S. P.; Scholz, R.-D.; Zejda, M.

    2017-11-01

    A longitudinal magnetic field with a strength of 5.2 kG was recently detected in CPD -62°2124, which has a fractional main-sequence lifetime of about 60 per cent. Strongly magnetic early-B type chemically peculiar stars in an advanced evolutionary state are of special interest to understand the evolution of the angular momentum and spin-down time-scales in the presence of a global magnetic field. We made use of 17 FORS 2 low-resolution spectropolarimetric observations and 844 ASAS3 photometric measurements for the determination of the rotation period, pulsationsand the magnetic field geometry of the star. We calculated periodograms and applied phenomenological models of photometric, spectral and spectropolarimetric variability. We found that all quantities studied, specifically equivalent widths, the mean longitudinal magnetic field 〈Bz〉 and the flux in the V filter, vary with the same period P = 2.628 d, which was identified as the rotation period. The observed variations can be fully explained by a rigidly rotating main-sequence star with an uneven distribution of chemical elements, photometric spots and a stable, nearly dipolar magnetic field with a polar field strength of about 21 kG, frozen into the body of the star. The magnetic field of CPD -62°2124 is tilted to the rotation axis by β = 28° ± 7°, while the inclination of the rotation axis towards the line of sight is only i = 20° ± 5°. In the acquired FORS 2 spectra, we detect short-term line profile variations indicating the presence of β Cephei type pulsations. As of today, no other pulsating star of this type is known to possess such a strong magnetic field.

  17. From Positive to Negative Zero-Field Splitting in a Series of Strongly Magnetically Anisotropic Mononuclear Metal Complexes.

    Science.gov (United States)

    Novitchi, Ghénadie; Jiang, Shangda; Shova, Sergiu; Rida, Fatima; Hlavička, Ivo; Orlita, Milan; Wernsdorfer, Wolfgang; Hamze, Rana; Martins, Cyril; Suaud, Nicolas; Guihéry, Nathalie; Barra, Anne-Laure; Train, Cyrille

    2017-12-18

    A series of mononuclear [M(hfa) 2 (pic) 2 ] (Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione; pic = 4-methylpyridine; M = Fe II , Co II , Ni II , Zn II ) compounds were obtained and characterized. The structures of the complexes have been resolved by single-crystal X-ray diffraction, indicating that, apart from the zinc derivative, the complexes are in a trans configuration. Moreover, a dramatic lenghthening of the Fe-N distances was observed, whereas the nickel(II) complex is almost perfectly octahedral. The magnetic anisotropy of these complexes was thoroughly studied by direct-current (dc) magnetic measurements, high-field electron paramagnetic resonance, and infrared (IR) magnetospectroscopy: the iron(II) derivative exhibits an out-of-plane anisotropy (D Fe = -7.28 cm -1 ) with a high rhombicity, whereas the cobalt(II) and nickel(II) complexes show in-plane anisotropy (D Co ∼ 92-95 cm -1 ; D Ni = 4.920 cm -1 ). Ab initio calculations were performed to rationalize the evolution of the structure and identify the excited states governing the magnetic anisotropy along the series. For the iron(II) complex, an out-of-phase alternating-current (ac) magnetic susceptibility signal was observed using a 0.1 T dc field. For the cobalt(II) derivative, the ac magnetic susceptibility shows the presence of two field-dependent relaxation phenomena: at low field (500 Oe), the relaxation process is beyond single-ion behavior, whereas at high field (2000 Oe), the relaxation of magnetization implies several mechanisms including an Orbach process with U eff = 25 K and quantum tunneling of magnetization. The observation by μ-SQUID magnetization measurements of hysteresis loops of up to 1 K confirmed the single-ion-magnet behavior of the cobalt(II) derivative.

  18. Commensurability oscillations in a quasi-two-dimensional electron gas subject to strong in-plane magnetic field

    Czech Academy of Sciences Publication Activity Database

    Smrčka, Ludvík

    2016-01-01

    Roč. 77, Mar (2016), s. 108-113 ISSN 1386-9477 Institutional support: RVO:68378271 Keywords : lateral superlattices * commensurability oscillations * in-plane magnetic field Subject RIV: BE - Theoretical Physics Impact factor: 2.221, year: 2016

  19. Electron Pre-acceleration at Nonrelativistic High-Mach-number Perpendicular Shocks

    Science.gov (United States)

    Bohdan, Artem; Niemiec, Jacek; Kobzar, Oleh; Pohl, Martin

    2017-09-01

    We perform particle-in-cell simulations of perpendicular nonrelativistic collisionless shocks to study electron heating and pre-acceleration for parameters that permit the extrapolation to the conditions at young supernova remnants. Our high-resolution large-scale numerical experiments sample a representative portion of the shock surface and demonstrate that the efficiency of electron injection is strongly modulated with the phase of the shock reformation. For plasmas with low and moderate temperature (plasma beta {β }{{p}}=5\\cdot {10}-4 and {β }{{p}}=0.5), we explore the nonlinear shock structure and electron pre-acceleration for various orientations of the large-scale magnetic field with respect to the simulation plane, while keeping it at 90° to the shock normal. Ion reflection off of the shock leads to the formation of magnetic filaments in the shock ramp, resulting from Weibel-type instabilities, and electrostatic Buneman modes in the shock foot. In all of the cases under study, the latter provides first-stage electron energization through the shock-surfing acceleration mechanism. The subsequent energization strongly depends on the field orientation and proceeds through adiabatic or second-order Fermi acceleration processes for configurations with the out-of-plane and in-plane field components, respectively. For strictly out-of-plane field, the fraction of suprathermal electrons is much higher than for other configurations, because only in this case are the Buneman modes fully captured by the 2D simulation grid. Shocks in plasma with moderate {β }{{p}} provide more efficient pre-acceleration. The relevance of our results to the physics of fully 3D systems is discussed.

  20. Ce3 - xMgxCo9 : Transformation of a Pauli Paramagnet into a Strong Permanent Magnet

    Science.gov (United States)

    Lamichhane, Tej N.; Taufour, Valentin; Palasyuk, Andriy; Lin, Qisheng; Bud'ko, Sergey L.; Canfield, Paul C.

    2018-02-01

    We report on the synthesis of single-crystal and polycrystalline samples of Ce3 -xMgxCo9 solid solution (0 ≤x ≲1.4 ) and characterization of their structural and magnetic properties. The crystal structure remains rhombohedral in the whole composition range and Mg partially replaces Ce in the 6 c site of the CeCo3 structure. Ferromagnetism is induced by Mg substitutions starting as low as x =0.18 and reaching a Curie temperature as high as 450 K for x =1.35 . Measurements on single crystals with x =1.34 and TC=440 K indicate an axial magnetic anisotropy with an anisotropy field of 6 T and a magnetization of 6 μB/f .u . at 300 K. Coercicity is observed in the polycrystalline samples consistent with the observed axial magnetic anisotropy. Our discovery of ferromagnetism with large axial magnetic anisotropy induced by substituting a rare-earth element by Mg is a very promising result in the search of inexpensive permanent-magnet materials and suggests that other nonmagnetic phases, similar to CeCo3 , may also conceal nearby ferromagnetic phases.