Manganites in Perovskite Superlattices: Structural and Electronic Properties

KAUST Repository

Jiwuer, Jilili

2016-01-01

Perovskite manganites are widely investigated compounds due to the discovery of the colossal magnetoresistance effect in 1994. They have a broad range of structural, electronic, magnetic properties and potential device applications in sensors

NMR of Colossal Magnetoresistive Manganites and Expanded Lattice Intermetallics at High Pressure

International Nuclear Information System (INIS)

Kapusta, Cz.; Riedi, P. C.

2001-01-01

A survey is given of NMR studies of colossal magnetoresistive manganese perovskites (RE,Ca,Sr,Ba)MnO 3 (RE = rare earth) and the interstitially modified permanent magnet materials, RE 2 Fe 17 A x (A = N, C, H) at ambient pressure and at applied pressures of up to 10 kbar. The different pressure behavior of the Mn hyperfine field found in the metallic and in the insulating manganite compounds is discussed and related to the micro- and macroscopic properties of these magnetically inhomogeneous materials. In the RE 2 Fe 17 A x compounds a different pressure behavior of the hyperfine field at the RE sites with different number and type of interstitial atom neighbors is discussed in terms of local compressibility. The influence of the interstitial modification and the applied pressure on the RE hyperfine field and quadrupole splitting is analyzed and the impact of the 'chemical pressure' and covalent effects on these quantities is compared. A comparison of the behavior of the magnetic state of the 4f electron shell with pressure and with interstitial modification is made and the relation to the magnetocrystalline anisotropy is discussed

Colossal Magnetoresistance in La-Y-Ca-Mn-O Films

NARCIS (Netherlands)

Chen, L.H.; Tiefel, T.H.; Jin, S.; Palstra, T.T.M.; Ramesh, R.; Kwon, C.

1996-01-01

Magnetoresistance behavior of La0.60Y0.07CaMnOx, thin films epitaxially grown on LaAlO3 has been investigated. The films exhibit colossal magnetoresistance with the MR ratio in excess of 10^8% at ~60K, H = 7T, which is the highest ever reported for thin film manganites. The partial substitution of

Inhomogeneity in the spin channel of ferromagnetic CMR manganites

Energy Technology Data Exchange (ETDEWEB)

Heffner, R.H.; Sonier, J.E.; MacLaughlin, D.E.; Nieuwenhuys, G.J.; Mezei, F.; Ehlers, G.; Mitchell, J.F.; Cheong, S.-W

2003-02-01

Colossal magnetoresistance manganites are archetypes in which to study the strong coupling between spin, charge and lattice degrees of freedom in materials. We present muon spin-lattice relaxation data in ferromagnetic (FM) ground state materials from the manganite series La{sub 1-x}Ca{sub x}MnO{sub 3} and La{sub 1-x-y}Pr{sub y}Ca{sub x}MnO{sub 3}. These measurements reveal several characteristic relaxation modes arising from the strong spin-charge-lattice interactions. We also present results from neutron-spin-echo spectroscopy, which directly measures the spin-spin correlation function in a time domain comparable to {mu}SR. A qualitative model for the FM transition in the manganites involving microscopic phase separation is suggested by these data.

Piezoresistivity in films of nanocrystalline manganites.

Science.gov (United States)

Sarkar, Jayanta; Raychaudhuri, A K

2007-06-01

Rare earth manganites having perovskite structure are susceptible to lattice strain. So far most investigations have been done with hydrostatic pressure or biaxial strain. We have observed that hole doped rare-earth manganites, which are known to display colossal magnetoresistance (CMR) also show change in its resistance under the influence of uniaxial strain. We report the direct measurement of piezoresistive response of La0.67Ca0.33MnO3 (LCMO) and La0.67Sr0.33MnO3 (LSMO) of this manganite family. The measurements were carried out on nanostructured polycrystalline films of LCMO and LSMO grown on oxidized Si(100) substrates. The piezoresistance was measured by bending the Si cantilevers (on which the film is grown) in flexural mode both with compressive and tensile strain. At room temperature the gauge factor approximately 10-20 and it increases to a large value near metal-insulator transition temperature (Tp) where the resistivity shows a peak.

Surface characterization of colossal magnetoresistive manganites La1-xSr xMnO3 using photoelectron spectroscopy

International Nuclear Information System (INIS)

Mannella, N.; Rosenhahn, A.; Nambu, A.; Sell, B.C.; Mun, B.S.; Yang, S.-H.; Marchesini, S.; Watanabe, M.; Ibrahim, K.; Ritchey, S.B.; Tomioka, Y.; Fadley, C.S.

2006-01-01

We have studied the temperature and time dependence of Surface chemical composition and atomic structure of in situ fractured colossal magnetoresistive perovskites La 1-x Sr x MnO (x = 0.3, 0.4) using core-level photoelectron spectroscopy and diffraction, simultaneous with observing marked changes in both core and valence electronic structure on going above the Curie temperature [N. Mannella et al., Phys. Rev. Lett. 92 (2004) 166401]. Stoichiometric analyses via core-level intensity ratios show that the near-surface composition is very nearly the same as that of the nominal (bulk) stoichiometry and further show that, during duration of our experiments, the degree of surface stoichiometry alteration or contamination has been minimal. The effects of photoelectron diffraction on such analyses are also explored. We comment on the degree to which near-surface composition or atomic-structure alterations might influence spectroscopic investigations of these manganites, or other strongly correlated materials

Modulation of persistent magnetoresistance by piezo-strain effect in manganite-based heterostructures

Science.gov (United States)

Li, W.; Yan, H.; Chai, X. J.; Wang, S. H.; Dong, X. L.; Ren, L. X.; Chen, C. L.; Jin, K. X.

2017-05-01

Persistent magnetoresistance effects in the phase-separated Pr0.65(Ca0.25Sr0.75)0.35MnO3/SrTiO3 and Pr0.65(Ca0.25Sr0.75)0.35MnO3/0.7PbMg1/3Nb2/3O3-0.3PbTiO3 heterostructures under a low magnetic field are investigated. It is observed that the persistent magnetoresistance effects decrease with increasing temperatures and the values for the heterostructures on 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 and SrTiO3 substrates are about 86.6% and 33.2% at 40 K, respectively. More interestingly, the applied electric field on the 0.7PbMg1/3Nb2/3O3-0.3PbTiO3 substrate can suppress the persistent magnetoresistance effect, indicating that different energy landscapes can be dramatically modulated by the piezo-strain. These results are discussed in terms of the strain-induced competition in the ferromagnetic state and the charge-ordering phase by the energy scenario, which provide a promising approach for designing devices of electric-magnetic memories in all-oxide heterostructures.

Experimental investigation of temperature dependence of the magnetic susceptibility (T) of manganites La1-xAxMnO3

International Nuclear Information System (INIS)

Salakhitdinova, M.; Kuvandikov, O.; Shakarov, Kh.; Shodiev, Z.

2007-01-01

Full text: he interest to lanthanoid manganites is based that enormous magnetoresistance is found in them and this materials are capable to test diverse structural and magnetic phase transformations. The work is devoted to experimental investigation of temperature dependence of the magnetic susceptibility (T) of manganites La 1-x A x MnO 3 which doped with Ag, K, Sr metals in wide temperature interval 50-8500 C, as well as to determination of their magnetic characteristics from this dependence. The dependence (T) was measured by the Faraday method with high-temperature magnetic pendulum balance in the atmosphere of refined helium. Maximal relative error of the measurements did not exceed 3 %. The analysis of experimental (T) dependence of investigated manganites has shown that the rise of stoichiometric rate of doped metals the temperature dependence of magnetic susceptibility of manganites monotonously is decreased. (authors)

Intrinsic and extrinsic magnetic properties of the naturally layered manganites

International Nuclear Information System (INIS)

Berger, A.; Mitchell, J. F.; Miller, D. J.; Jiang, J. S.; Bader, S. D.

1999-01-01

Structural and magnetic properties of the two-layered Ruddlesden-Popper phase SrO(La 1-x Sr x MnO 3 ) 2 with x = 0.3--0.5 are highlighted. Intrinsic properties of these naturally layered manganites include a colossal magnetoresistance, a composition-dependent magnetic anisotropy, and almost no remanence. Above the Curie temperature there is a non-vanishing extrinsic magnetization attributed to intergrowths (stacking faults in the layered structure). These lattice imperfections consist of additional or missing manganite layers, as observed in transmission electron microscopy. Their role in influencing the properties of the host material is highlighted

Magnetoelectric effects in manganites

Science.gov (United States)

Jeen, Hyoung Jeen

Research on manganites has been conducted for more than half century. Recent discoveries of colossal responses to external fields such as colossal magnetoresistance effects and correlation among spin, orbital, and lattice in phase separated manganites and multiferroic manganites have motivated me to understand these materials. The main purpose of this dissertation is to understand magnetoelectric effects in phase separated (La1-yPr y)1-xCaxMnO3 (LPCMO) thin films and multiferroic BiMnO3 (BMO) thin films. First, high quality phase separated manganite thin films have been successfully grown. To grow the high quality manganite thin films, extensive effort was devoted to fine tuning of oxygen pressure, temperature, and laser fluence during film growth. As-grown films were characterized with various ex-situ techniques: magnetization measurements, transport measurements, x-ray diffraction, atomic force microscopy, and/or transmission electron microscopy to remove the effects of impurities and unwanted strains except substrate induced strain. Second, three major results were obtained in high quality phase separated LPCMO thin films. These results are based on the dynamic nature of phases in LPCMO. 1) LPCMO thin films showed single domain to multi-domain transition during cooling. This transition can be tuned by substrate stress induced in-plane magnetic anisotropy. 2) Evidence for the origin of colossal electroresistance (CER) effect has been observed. The CER is triggered by dielectrophoresis, or movements of ferromagnetic metallic (FMM) phase, which is manifested in anisotropic transport properties in microfabricated LPCMO cross structures. This fluidic nature of the FMM phase in LPCMO under high electric fields lead to exotic magnetoelectric effects. 3) Electric field effects on magnetotransport properties have been observed. This phenomena can also be tuned by the combined effect of substrate strain and current flow. This combined effect of electric and magnetic

Peculiar ferromagnetic insulator state in the low-hole-doped manganites

International Nuclear Information System (INIS)

Algarabel, P.A.; Teresa, J.M. de; Blasco, J.; Ibarra, M.R.; Kapusta, Cz.; Sikora, M.; Zajac, D.; Riedi, P.C.; Ritter, C.

2003-01-01

In this work we show the very different nature of the ferromagnetic state of the low-hole-doped manganites with respect to other manganites showing colossal magnetoresistance. High-field measurements definitively prove the coexistence of ferromagnetic-metallic and ferromagnetic-insulating regions even when the sample is magnetically saturated, with the ground state being inhomogeneous. We have investigated La 0.9 Ca 0.1 MnO 3 as a prototype compound. A wide characterization by means of magnetic and magnetotransport measurements, neutron diffraction, small-angle neutron scattering, and nuclear magnetic resonance has allowed us to establish that the ground state is based on the existence of disordered nanometric double-exchange metallic clusters that coexist with long-range superexchange-based ferromagnetic insulating regions. Under high magnetic field the system reaches magnetization saturation by aligning the magnetic clusters and the insulating matrix, but even if they grow in size, they do not reach the percolation limit

Spin-polarized transport in manganite-based magnetic nano structures

International Nuclear Information System (INIS)

Granada, Mara

2007-01-01

Giant magnetoresistance (G M R) and tunnel magnetoresistance are spin polarized transport phenomena which are observed in magnetic multilayers.They consist in a large variation of the electrical resistivity of the system depending on whether the magnetizations of the magnetic layers are aligned parallel or anti-parallel to each other. In order to be able to align the magnetic layers by means of an external magnetic field, they must not be strongly ferromagnetically coupled.The extrinsic magnetoresistance effects in magnetic multilayers, either G M R in the case of a metallic spacer, or T M R in the case of an insulating spacer, are observed at low magnetic fields, which makes these phenomena interesting for technological applications.We studied the possibility of using the ferromagnetic manganite La 0 ,75Sr 0 ,25MnO 3 (L S M O) in magneto resistive devices, with different materials as a spacer layer.As the main result of this work, we report G M R and T M R measurements in L S M O/LaNiO 3 /L S M O and L S M O/CaMnO 3 /L S M O tri layers, respectively, observed for the first time in these systems.This work included the deposition of films and multilayers by sputtering, the structural characterization of the samples and the study of their magnetic and electric transport properties.Our main interest was the study of G M R in L S M O/LaNiO 3 /L S M O tri layers.It was necessary to firstly characterize the magnetic coupling of L S M O layers through the L N O spacer. After that, we performed electric transport measurements with the current in the plane of the samples.We measured a G M R contribution of ∼ 0,55 % at T = 83 K.We designed a procedure for patterning the samples by e-beam lithography for electric transport measurements with the current perpendicular to the plane. We also performed the study of L S M O/CaMnO 3 /L S M O tri layers with an insulating spacer.We studied the magnetic coupling, as in the previous case.Then we fabricated a tunnel junction for

Experimental and theoretical studies of manganite and magnetite compounds

International Nuclear Information System (INIS)

Srinitiwarawong, Chatchai

2002-01-01

In the recent years interest in the transition oxide compounds has renewed among researchers in the field of condensed matter physics. This thesis presents the studies of the two families of the transition oxides, the manganite and magnetite compounds. Manganite has regained the interest since the discovery of the large magnetoresistance around its Curie temperature in 1990s. Magnetite on the other hand is the oldest magnetic material known to man however some of its physical properties are still controversial. The experimental works address some basic properties of these compounds when fabricated in the form of thin films. These include the resistivity measurements and magnetic measurements as well as the Hall effect. The various models of transport mechanism have been compared. The magnetic field and the temperature dependence of magnetoresistance have also been studied. Simple devices such as an artificial grain boundary and bilayers thin film have been investigated. The second part of this thesis concentrates on the theoretical aspects of the fundamental physics behind these two compounds. The problem of electrons tunnelling between the magnetite electrodes has been addressed taking into account the surface effect with distortion. The last chapter presents a theoretical study of the spinless-Hubbard model which is the simplest approximation of the conduction electrons in magnetite and manganite. The results are obtained from the Hartree-Fock and the Hubbard-I approximations as well as the exact diagonalisation method. (author)

Isotropic Kink and Quasiparticle Excitations in the Three-Dimensional Perovskite Manganite La_{0.6}Sr_{0.4}MnO_{3}.

Science.gov (United States)

Horiba, Koji; Kitamura, Miho; Yoshimatsu, Kohei; Minohara, Makoto; Sakai, Enju; Kobayashi, Masaki; Fujimori, Atsushi; Kumigashira, Hiroshi

2016-02-19

In order to reveal the many-body interactions in three-dimensional perovskite manganites that show colossal magnetoresistance, we performed an in situ angle-resolved photoemission spectroscopy on La_{0.6}Sr_{0.4}MnO_{3} and investigated the behavior of quasiparticles. We observed quasiparticle peaks near the Fermi momentum in both the electron and the hole bands, and clear kinks throughout the entire hole Fermi surface in the band dispersion. This isotropic behavior of quasiparticles and kinks suggests that polaronic quasiparticles produced by the coupling of electrons with Jahn-Teller phonons play an important role in the colossal magnetoresistance properties of the ferromagnetic metallic phase of three-dimensional manganites.

Spin-coupled charge dynamics in layered manganite crystals

CERN Document Server

Tokura, Y; Ishikawa, T

1998-01-01

Anisotropic charge dynamics has been investigated for single crystals of layered manganites, La sub 2 sub - sub 2 sub x Sr sub 1 sub + sub 2 sub x Mn sub 2 O sub 7 (0.3<=X<=0.5). Remarkable variations in the magnetic structure and in the charge-transport properties are observed by changing the doping level x . A crystal with x = 0.3 behaves like a 2-dimensional ferromagnetic metal in the temperature region between approx 90 K and approx 270 K and shows an interplane tunneling magnetoresistance at lower temperatures which is sensitive to the interplane magnetic coupling between the adjacent MnO sub 2 bilayers. Optical probing of these layered manganites has also clarified the highly anisotropic and incoherent charge dynamics.

Epitaxial stabilization of ultra thin films of electron doped manganites

Energy Technology Data Exchange (ETDEWEB)

Middey, S., E-mail: smiddey@uark.edu; Kareev, M.; Meyers, D.; Liu, X.; Cao, Y.; Tripathi, S.; Chakhalian, J. [Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701 (United States); Yazici, D.; Maple, M. B. [Department of Physics, University of California, San Diego, La Jolla, California 92093 (United States); Ryan, P. J.; Freeland, J. W. [Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

2014-05-19

Ultra-thin films of the electron doped manganite La{sub 0.8}Ce{sub 0.2}MnO{sub 3} were grown in a layer-by-layer growth mode on SrTiO{sub 3} (001) substrates by pulsed laser interval deposition. High structural quality and surface morphology were confirmed by a combination of synchrotron based x-ray diffraction and atomic force microscopy. Resonant X-ray absorption spectroscopy measurements confirm the presence of Ce{sup 4+} and Mn{sup 2+} ions. In addition, the electron doping signature was corroborated by Hall effect measurements. All grown films show a ferromagnetic ground state as revealed by both dc magnetization and x-ray magnetic circular dichroism measurements and remain insulating contrary to earlier reports of a metal-insulator transition. Our results hint at the possibility of electron-hole asymmetry in the colossal magnetoresistive manganite phase diagram akin to the high-T{sub c} cuprates.

A nanomagnetic study of phase transition in manganite thin films and ballistic magnetoresistance in magnetic nanocontacts

Science.gov (United States)

Chung, Seok-Hwan

This work focuses on two largely unexplored phenomena in micromagnetics: the temperature-driven paramagnetic insulator to ferromagnetic (FM) metallic phase transition in perovskite manganite and ballistic magnetoresistance in spin-polarized nanocontacts. To investigate the phase transition, an off-the-shelf commercial scanning force microscope was redesigned for operation at temperatures from 350 K to 100 K. This adaptation is elaborated in this thesis. Using this system, both ferromagnetic and charge-ordered domain structures of (La 1-xPrx)0.67Ca0.33MnO3 thin film were observed by magnetic force microscopy (MFM) and electric force microscopy (EFM) operated in the vicinity of the peak resistance temperature (Tp). Predominantly in-plane oriented FM domains of sub-micrometer size emerge below Tp and their local magnetic moment increased as the temperature is reduced. Charge-ordered insulating regions show a strong electrostatic interaction with an EFM tip at a few degrees above Tp and the interaction correlates well with the temperature dependence of resistivity of the film. Cross-correlation analysis between topography and magnetic structure on several substrates indicates FM domains form on the flat regions of the surface, while charge ordering occurs at surface protrusions. In the investigation of ballistic magnetoresistance, new results on half-metallic ferromagnets formed by atomic or nanometer contacts of CrO2-CrO 2 and CrO2-Ni are presented showing magnetoconductance as high as 400%. Analysis of the magnetoconductance versus conductance data for all materials known to exhibit so-called ballistic magnetoresistance strongly suggests that magnetoconductance of nanocontacts follows a universal mechanism. If the maximum magnetoconductance is normalized to unity and the conductance is scaled with the resistivity of the material, then all data points fall onto a universal curve independent of the contact material and the transport mechanism. The analysis has been

Mixed-phase description of colossal magnetoresistive manganites

Czech Academy of Sciences Publication Activity Database

Weiáe, A.; Loos, Jan; Fehske, H.

2003-01-01

Roč. 68, č. 2 (2003), s. 024402-1 - 021102-6 ISSN 0163-1829 Grant - others:DFG(DE) 436 TSE 113/33/0-2 Institutional research plan: CEZ:AV0Z1010914 Keywords : polarons * metal-insulator transitions * colossal magnetoresistance Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.962, year: 2003

Magnetoresistance effect in (La, Sr)MnO3 bicrystalline films.

Science.gov (United States)

Alejandro, G; Steren, L B; Pastoriza, H; Vega, D; Granada, M; Sánchez, J C Rojas; Sirena, M; Alascio, B

2010-09-01

The angular dependence of the magnetoresistance effect has been measured on bicrystalline La(0.75)Sr(0.25)MnO(3) films. The measurements have been performed on an electronically lithographed Wheatstone bridge. The study of the angular dependence of both the magnetoresistance and the resistance of single-crystalline and grain-boundary regions of the samples allowed us to isolate two contributions of low-field magnetoresistance in manganites. One of them is associated with the spin-orbit effect, i.e. the anisotropic magnetoresistance of ferromagnetic compounds, and the other one is related to spin-disorder regions at the grain boundary. Complementary x-ray diffraction, ferromagnetic resonance and low temperature magnetization experiments contribute to the characterization of the magnetic anisotropy of the samples and the general comprehension of the problem.

Magnetoresistance effect in (La, Sr)MnO3 bicrystalline films

International Nuclear Information System (INIS)

Alejandro, G; Pastoriza, H; Granada, M; Rojas Sanchez, J C; Sirena, M; Alascio, B; Steren, L B; Vega, D

2010-01-01

The angular dependence of the magnetoresistance effect has been measured on bicrystalline La 0.75 Sr 0.25 MnO 3 films. The measurements have been performed on an electronically lithographed Wheatstone bridge. The study of the angular dependence of both the magnetoresistance and the resistance of single-crystalline and grain-boundary regions of the samples allowed us to isolate two contributions of low-field magnetoresistance in manganites. One of them is associated with the spin-orbit effect, i.e. the anisotropic magnetoresistance of ferromagnetic compounds, and the other one is related to spin-disorder regions at the grain boundary. Complementary x-ray diffraction, ferromagnetic resonance and low temperature magnetization experiments contribute to the characterization of the magnetic anisotropy of the samples and the general comprehension of the problem.

Anisotropic imprint of amorphization and phase separation in manganite thin films via laser interference irradiation

KAUST Repository

Ding, Junfeng; Lin, Zhipeng; Wu, Jianchun; Dong, Zhili; Wu, Tao

2014-01-01

Materials with mesoscopic structural and electronic phase separation, either inherent from synthesis or created via external means, are known to exhibit functionalities absent in the homogeneous counterparts. One of the most notable examples is the colossal magnetoresistance discovered in mixed-valence manganites, where the coexistence of nano-to micrometer-sized phase-separated domains dictates the magnetotransport. However, it remains challenging to pattern and process such materials into predesigned structures and devices. In this work, a direct laser interference irradiation (LII) method is employed to produce periodic stripes in thin films of a prototypical phase-separated manganite Pr0.65(Ca0.75Sr0.25)0.35MnO3 (PCSMO). LII induces selective structural amorphization within the crystalline PCSMO matrix, forming arrays with dimensions commensurate with the laser wavelength. Furthermore, because the length scale of LII modification is compatible to that of phase separation in PCSMO, three orders of magnitude of increase in magnetoresistance and significant in-plane transport anisotropy are observed in treated PCSMO thin films. Our results show that LII is a rapid, cost-effective and contamination-free technique to tailor and improve the physical properties of manganite thin films, and it is promising to be generalized to other functional materials.

Anisotropic imprint of amorphization and phase separation in manganite thin films via laser interference irradiation

KAUST Repository

Ding, Junfeng

2014-09-16

Materials with mesoscopic structural and electronic phase separation, either inherent from synthesis or created via external means, are known to exhibit functionalities absent in the homogeneous counterparts. One of the most notable examples is the colossal magnetoresistance discovered in mixed-valence manganites, where the coexistence of nano-to micrometer-sized phase-separated domains dictates the magnetotransport. However, it remains challenging to pattern and process such materials into predesigned structures and devices. In this work, a direct laser interference irradiation (LII) method is employed to produce periodic stripes in thin films of a prototypical phase-separated manganite Pr0.65(Ca0.75Sr0.25)0.35MnO3 (PCSMO). LII induces selective structural amorphization within the crystalline PCSMO matrix, forming arrays with dimensions commensurate with the laser wavelength. Furthermore, because the length scale of LII modification is compatible to that of phase separation in PCSMO, three orders of magnitude of increase in magnetoresistance and significant in-plane transport anisotropy are observed in treated PCSMO thin films. Our results show that LII is a rapid, cost-effective and contamination-free technique to tailor and improve the physical properties of manganite thin films, and it is promising to be generalized to other functional materials.

Magnetoresistance effect in (La, Sr)MnO{sub 3} bicrystalline films

Energy Technology Data Exchange (ETDEWEB)

Alejandro, G; Pastoriza, H; Granada, M; Rojas Sanchez, J C; Sirena, M; Alascio, B [Centro Atomico Bariloche (CNEA), Av. Bustillo 9500, 8400 San Carlos de Bariloche, Pcia. de Rio Negro (Argentina); Steren, L B; Vega, D, E-mail: galejand@cab.cnea.gov.a [Centro Atomico Constituyentes (CNEA), 1650 San MartIn, Pcia. de Buenos Aires (Argentina)

2010-09-01

The angular dependence of the magnetoresistance effect has been measured on bicrystalline La{sub 0.75}Sr{sub 0.25}MnO{sub 3} films. The measurements have been performed on an electronically lithographed Wheatstone bridge. The study of the angular dependence of both the magnetoresistance and the resistance of single-crystalline and grain-boundary regions of the samples allowed us to isolate two contributions of low-field magnetoresistance in manganites. One of them is associated with the spin-orbit effect, i.e. the anisotropic magnetoresistance of ferromagnetic compounds, and the other one is related to spin-disorder regions at the grain boundary. Complementary x-ray diffraction, ferromagnetic resonance and low temperature magnetization experiments contribute to the characterization of the magnetic anisotropy of the samples and the general comprehension of the problem.

Twinning microstructure and charge ordering in the colossal magnetoresistive manganite Nd1/2Sr1/2MnO3

International Nuclear Information System (INIS)

Luo, Z.P.; Miller, D.J.; Mitchell, J.F.

2000-01-01

Charge ordering (C.O.) in the colossal magnetoresistive (CMR) manganites gives rise to an insulating, high-resistance state. This charge ordered state can be melted into a low-resistance metallic-like state by the application of magnetic field. Thus, the potential to attain high values of magnetoresistance with the application of small magnetic fields may be aided by a better understanding of the charge-ordering phenomenon. This study focused on microstructural characterization in Nd 1/2 Sr 1/2 MnO 3 . In Nd 1/2 Sr 1/2 MnO 3 , the nominal valence of Mn is 3.5+. On cooling, charge can localize and lead to a charge ordering between Mn 3+ and Mn 4+. The ordering of charge results in a superlattice structure and a reduction in symmetry. Thin foil specimens were prepared from bulk samples by conventional thinning and ion milling (at LiqN 2 temperature) methods. The room temperature TEM observation of Nd 1/2 Sr 1/2 MnO 3 reveals that it contains a highly twinned microstructure, together with a small number of stacking faults (SFS). A figure shows the same area of the specimen at different zone axes obtained by tilting around two perpendicular directions as indicated. Three grains A, B and C are labeled for each of the zone axes. The room temperature EDPs from the matrix and twins shows an approximate 90degree rotation suggesting a 90degree twin orientation. These results are further confirmed by C.O. at low temperatures. The twinning planes can be determined by tilting with large angles

Magnetoresistance at artificial interfaces in epitaxial ferromagnetic thin films

International Nuclear Information System (INIS)

Fontcuberta, J.; Bibes, M.; Martinez, B.; Trtik, V.; Ferrater, C.; Sanchez, F.; Varela, M.

2000-01-01

Epitaxial La 2/3 Sr 1/3 MnO 3 and SrRuO 3 thin films have been grown by laser ablation on single-crystalline SrTiO 3 substrates. Prior to manganite or ruthenate deposition tracks have been patterned on the SrTiO 3 substrate by using an appropriately focused laser beam. In the experiments here reported linear tracks have been formed. The magnetotransport properties of the films, particularly the magnetoresistance, along paths parallel and perpendicular to the track have been extensively investigated and compared to similar data recorded on films grown on bicrystalline STO substrates. Whereas in LSMO a significant low-field tunnel magnetoresistance develops across the artificial interface, in SRO this tunnel contribution is absent. However, a significant high-field magnetoresistance is observed for both metallic and ferromagnetic systems. The results are analysed and discussed within the framework of the current understanding of double exchange and itinerant ferromagnets. Magnetoresistance data for various configurations of the track array are presented

Effect of pressure on the magnetoresistance of single crystal Nd0.5Sr0.36Pb0.14MnO3-δ

International Nuclear Information System (INIS)

Khazeni, K.; Jia, Y.X.; Lu, L.; Crespi, V.H.; Cohen, M.L.; Zettl, A.

1996-01-01

To investigate the observed huge variations in magnetoresistance between different samples of manganite perovskites we have performed the first high-pressure measurement of magnetoresistance in single crystal Nd 0.5 Sr 0.36 Pb 0.14 MnO 3-δ . Both resistivity and magnetoresistance are strongly suppressed upon application of pressure. The decrease in magnetoresistance with increasing pressure rules out substrate-induced compressive strain as a source of enhanced magnetoresistance. Instead, the magnetoresistance differences between samples are ascribed primarily to the more abrupt nature of the semiconductorlike to metallic phase transition at lower temperatures. copyright 1996 The American Physical Society

Theory of strain-controlled magnetotransport and stabilization of the ferromagnetic insulating phase in manganite thin films.

Science.gov (United States)

Mukherjee, Anamitra; Cole, William S; Woodward, Patrick; Randeria, Mohit; Trivedi, Nandini

2013-04-12

We show that applying strain on half-doped manganites makes it possible to tune the system to the proximity of a metal-insulator transition and thereby generate a colossal magnetoresistance (CMR) response. This phase competition not only allows control of CMR in ferromagnetic metallic manganites but can be used to generate CMR response in otherwise robust insulators at half-doping. Further, from our realistic microscopic model of strain and magnetotransport calculations within the Kubo formalism, we demonstrate a striking result of strain engineering that, under tensile strain, a ferromagnetic charge-ordered insulator, previously inaccessible to experiments, becomes stable.

Magnetoresistance and phase composition of La-Sn-Mn-O systems

DEFF Research Database (Denmark)

Li, Z.W.; Morrish, A.H.; Jiang, Jianzhong

1999-01-01

The transport properties of the manganites La1 - xSnxMnO3 + delta with x = 0.1-0.5 and of Fe-doped samples have been comprehensively studied using magnetoresistance measurements, Fe-57 and Sn-119 Mossbauer spectroscopy, and x-ray diffraction. At the Sn concentration x = 0.5, La0.5Sn0.5MnO3 + delta...

Phase separation in La-Ca manganites: Magnetic field effects

International Nuclear Information System (INIS)

Tovar, M.; Causa, M.T.; Ramos, C.A.; Laura-Ccahuana, D.

2008-01-01

The coexistence of magnetic phases seems to be a characteristic of the La-Ca family of in colossal magnetoresistant manganites. We have analyzed this phenomenon in terms of a free energy, F, where magnetic and electronic contributions of two coexistent phases are included. Three order parameters describe the behavior of the mixed material: the magnetization of each phase and the metallic fraction. Due to the coupling between order parameters there is a range: T**≤T≤T* where coexistence is possible. Values for the phenomenological parameters are obtained from the experiment. In this paper we analyze the effects of an applied magnetic field on the range of T where the phase coexistence takes place, based on results obtained from dc-magnetization and ESR measurements

Phase separation in La-Ca manganites: Magnetic field effects

Energy Technology Data Exchange (ETDEWEB)

Tovar, M; Causa, M T [Centro Atomico Bariloche and Instituto Balseiro, Comision Nacional de Energia Atomica and Universidad Nacional de Cuyo, 8400 San Carlos de Bariloche, Rio Negro (Argentina); Ramos, C.A. [Centro Atomico Bariloche and Instituto Balseiro, Comision Nacional de Energia Atomica and Universidad Nacional de Cuyo, 8400 San Carlos de Bariloche, Rio Negro (Argentina)], E-mail: cramos@cab.cnea.gov.ar; Laura-Ccahuana, D [Centro Atomico Bariloche and Instituto Balseiro, Comision Nacional de Energia Atomica and Universidad Nacional de Cuyo, 8400 San Carlos de Bariloche, Rio Negro (Argentina); Universidad Nacional de Ingenieria, Av. Tupac Amaru 210, Rimac/Lima 25 (Peru)

2008-02-15

The coexistence of magnetic phases seems to be a characteristic of the La-Ca family of in colossal magnetoresistant manganites. We have analyzed this phenomenon in terms of a free energy, F, where magnetic and electronic contributions of two coexistent phases are included. Three order parameters describe the behavior of the mixed material: the magnetization of each phase and the metallic fraction. Due to the coupling between order parameters there is a range: T**{<=}T{<=}T* where coexistence is possible. Values for the phenomenological parameters are obtained from the experiment. In this paper we analyze the effects of an applied magnetic field on the range of T where the phase coexistence takes place, based on results obtained from dc-magnetization and ESR measurements.

Colossal elastoresistance, electroresistance and magnetoresistance in Pr0.5Sr0.5MnO3 thin films

International Nuclear Information System (INIS)

Chen, Liping; Guo, Xuexiang; Gao, J.

2016-01-01

Pr 0.5 Sr 0.5 MnO 3 thin films on substrates of (001)-oriented LaAlO 3 were epitaxially grown by pulsed laser deposition. It was found that a substrate-induced strain of ~1.3% brings a great resistivity change of ~98% at 25 K. We studied the dependence of resistivity on the applied electric current and magnetic field. In the greatly strained films of 60 nm thickness the electroresistance ER=[ρ(I 1 μA )−ρ(I 1000 μA )]/ρ(I 1 μA ) reaches ~70% at T=25 K, much higher than ER~7% in the strain-relaxed films of 400 nm thickness, implying the strain effect on ER. Also the magnetoresistance of the film falls with strain-relaxation. Therefore the electric properties of the film could be efficiently modified by strain, electric current and magnetic field. All of them may be explained by the effect on the percolative phase separation and competition in the half-doped manganite material. The manganite films located at phase boundary are expected to be an ideal compound for providing practical colossal effects of elastoresistance, electroresistance and magnetoresistance due to the multiphase coexistence. - Highlights: • The electric current-induced electroresistance (ER) and magnetoresistance (MR)studies on PLD grown Pr 0.5 Sr 0.5 MnO 3 /(001) LaAlO 3 films were found to be greatly sensitive to the film thickness arising from the strain. • It is shown that, 60 nm film exhibit compressive in-plane strain which leads to phase separation and hence colossal MR and ER. • Our results suggest that the manganites located at phase boundary may be an ideal compound for providing practical colossal effects of elastoresistance, electroresistance and magnetoresistance.

Manganite perovskite ceramics, their precursors and methods for forming

Science.gov (United States)

Payne, David Alan; Clothier, Brent Allen

2015-03-10

Disclosed are a variety of ceramics having the formula Ln.sub.1-xM.sub.xMnO.sub.3, where 0.Itoreq.x.Itoreq.1 and where Ln is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or Y; M is Ca, Sr, Ba, Cd, or Pb; manganite precursors for preparing the ceramics; a method for preparing the precursors; and a method for transforming the precursors into uniform, defect-free ceramics having magnetoresistance properties. The manganite precursors contain a sol and are derived from the metal alkoxides: Ln(OR).sub.3, M(OR).sub.2 and Mn(OR).sub.2, where R is C.sub.2 to C.sub.6 alkyl or C.sub.3 to C.sub.9 alkoxyalkyl, or C.sub.6 to C.sub.9 aryl. The preferred ceramics are films prepared by a spin coating method and are particularly suited for incorporation into a device such as an integrated circuit device.

Electronically soft phases in manganites.

Science.gov (United States)

Milward, G C; Calderón, M J; Littlewood, P B

2005-02-10

The phenomenon of colossal magnetoresistance in manganites is generally agreed to be a result of competition between crystal phases with different electronic, magnetic and structural order; a competition which can be strong enough to cause phase separation between metallic ferromagnetic and insulating charge-modulated states. Nevertheless, closer inspection of phase diagrams in many manganites reveals complex phases where the two order parameters of magnetism and charge modulation unexpectedly coexist. Here we show that such experiments can be naturally explained within a phenomenological Ginzburg-Landau theory. In contrast to models where phase separation originates from disorder or as a strain-induced kinetic phenomenon, we argue that magnetic and charge modulation coexist in new thermodynamic phases. This leads to a rich diagram of equilibrium phases, qualitatively similar to those seen experimentally. The success of this model argues for a fundamental reinterpretation of the nature of charge modulation in these materials, from a localized to a more extended 'charge-density wave' picture. The same symmetry considerations that favour textured coexistence of charge and magnetic order may apply to many electronic systems with competing phases. The resulting 'electronically soft' phases of matter with incommensurate, inhomogeneous and mixed order may be general phenomena in correlated systems.

Evolution and sign control of square-wave-like anisotropic magneto-resistance in spatially confined La{sub 0.3}Pr{sub 0.4}Ca{sub 0.3}MnO{sub 3}/LaAlO{sub 3}(001) manganite thin films

Energy Technology Data Exchange (ETDEWEB)

Alagoz, H. S., E-mail: alagoz@ualberta.ca; Jeon, J.; Keating, S.; Chow, K. H., E-mail: khchow@ualberta.ca; Jung, J., E-mail: jjung@ualberta.ca [Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1 (Canada)

2016-04-14

We investigated magneto-transport properties of a compressively strained spatially confined La{sub 0.3}Pr{sub 0.4}Ca{sub 0.3}MnO{sub 3} (LPCMO) thin film micro-bridge deposited on LaAlO{sub 3}. Angular dependence of the magneto-resistance R(θ) of this bridge, where θ is the angle between the magnetic field and the current directions in the film plane, exhibits sharp positive and negative percolation jumps near T{sub MIT}. The sign and the magnitude of these jumps can be tuned using the magnetic field. Such behavior has not been observed in LPCMO micro-bridges subjected to tensile strain, indicating a correlation between the type of the lattice strain, the distribution of electronic domains, and the anisotropic magneto-resistance in spatially confined manganite systems.

Strain-induced metal-insulator phase coexistence in perovskite manganites.

Science.gov (United States)

Ahn, K H; Lookman, T; Bishop, A R

2004-03-25

The coexistence of distinct metallic and insulating electronic phases within the same sample of a perovskite manganite, such as La(1-x-y)Pr(y)Ca(x)MnO3, presents researchers with a tool for tuning the electronic properties in materials. In particular, colossal magnetoresistance in these materials--the dramatic reduction of resistivity in a magnetic field--is closely related to the observed texture owing to nanometre- and micrometre-scale inhomogeneities. Despite accumulated data from various high-resolution probes, a theoretical understanding for the existence of such inhomogeneities has been lacking. Mechanisms invoked so far, usually based on electronic mechanisms and chemical disorder, have been inadequate to describe the multiscale, multiphase coexistence within a unified picture. Moreover, lattice distortions and long-range strains are known to be important in the manganites. Here we show that the texturing can be due to the intrinsic complexity of a system with strong coupling between the electronic and elastic degrees of freedom. This leads to local energetically favourable configurations and provides a natural mechanism for the self-organized inhomogeneities over both nanometre and micrometre scales. The framework provides a physical understanding of various experimental results and a basis for engineering nanoscale patterns of metallic and insulating phases.

Crossover of angular dependent magnetoresistance with the metal-insulator transition in colossal magnetoresistive manganite films

DEFF Research Database (Denmark)

Chen, Yunzhong; Sun, J.R.; Zhao, T.Y.

2009-01-01

The temperature and magnetic field dependence of angular dependent magnetoresistance (AMR) along two orthogonal directions ([100] and [01]) was investigated in a charge-orbital-ordered Sm0.5Ca0.5MnO3 (SCMO) film grown on (011)-oriented SrTiO3 substrates. A dramatic decrease of AMR magnitude in bo...

Local probe studies on lattice distortions and electronic correlations in manganites

CERN Document Server

lopes, Armandina; Correia, João Guilherme

This thesis presents an experimental study on lattice distortions and electronic correlations in colossal magnetoresistive magnetic oxides. The Perturbed Angular Correlation local probe technique is used to study selected manganite systems in order to obtain relevant insight into microscopic phenomena responsible for their macroscopic pr operties. Complementary structural, magnetic and electric characterization was performed. The work is focused on the following aspects: \\\\Lattice distortions and polaron clusters in LaMnO$_{3+ \\Delta}$ system. A study of the electric field gradi ent and magnetic hyperfine field was performed in representative samples of the LaMnO$_{3+ \\Delta}$ system, and correlated with macroscopic information obtained in the same samples. Particular attention was given to the LaMnO$_{3.12}$ sample since this compound is a prototype of a ferromagnetic-insulat or manganite, presenting a rhombohedric- orthorhombic structural phase transition near room temperature. We found that random distribu...

Percolative nature of A-site disordered La0.75Ca0.25-xSrxMnO3 manganites

DEFF Research Database (Denmark)

Venkatesh, R.; Yadam, Sankararao; Venkateshwarlu, D.

2015-01-01

Magnetic, resistive, and magnetoresistance measurements were used to investigate the percolative nature of A-site disordered La0.75Ca0.25-xSrxMnO3(x = 0, 0.10) manganites. La0.75Ca0.15Sr0.10MnO3 has an orthorhombic structure and second order magnetic phase transition indicates the presence of two...

Colossal elastoresistance, electroresistance and magnetoresistance in Pr{sub 0.5}Sr{sub 0.5}MnO{sub 3} thin films

Energy Technology Data Exchange (ETDEWEB)

Chen, Liping, E-mail: chenliping0003@163.com [Department of Physics, Zhejiang Normal University, Jinhua 321004 (China); Department of Physics, Hong Kong University, Hong Kong (China); Guo, Xuexiang [Department of Physics, Zhejiang Normal University, Jinhua 321004 (China); Gao, J. [Department of Physics, Hong Kong University, Hong Kong (China)

2016-05-01

Pr{sub 0.5}Sr{sub 0.5}MnO{sub 3} thin films on substrates of (001)-oriented LaAlO{sub 3} were epitaxially grown by pulsed laser deposition. It was found that a substrate-induced strain of ~1.3% brings a great resistivity change of ~98% at 25 K. We studied the dependence of resistivity on the applied electric current and magnetic field. In the greatly strained films of 60 nm thickness the electroresistance ER=[ρ(I{sub 1} {sub μA})−ρ(I{sub 1000} {sub μA})]/ρ(I{sub 1} {sub μA}) reaches ~70% at T=25 K, much higher than ER~7% in the strain-relaxed films of 400 nm thickness, implying the strain effect on ER. Also the magnetoresistance of the film falls with strain-relaxation. Therefore the electric properties of the film could be efficiently modified by strain, electric current and magnetic field. All of them may be explained by the effect on the percolative phase separation and competition in the half-doped manganite material. The manganite films located at phase boundary are expected to be an ideal compound for providing practical colossal effects of elastoresistance, electroresistance and magnetoresistance due to the multiphase coexistence. - Highlights: • The electric current-induced electroresistance (ER) and magnetoresistance (MR)studies on PLD grown Pr{sub 0.5}Sr{sub 0.5}MnO{sub 3}/(001) LaAlO{sub 3} films were found to be greatly sensitive to the film thickness arising from the strain. • It is shown that, 60 nm film exhibit compressive in-plane strain which leads to phase separation and hence colossal MR and ER. • Our results suggest that the manganites located at phase boundary may be an ideal compound for providing practical colossal effects of elastoresistance, electroresistance and magnetoresistance.

Microstructure, interparticle interactions and magnetotransport of manganite-polyaniline nanocomposites

Energy Technology Data Exchange (ETDEWEB)

Romero, Mariano; Faccio, Ricardo; Pardo, Helena [Centro NanoMat/Cryssmat Lab, DETEMA, Facultad de Química, Universidad de la República (Uruguay); Centro Interdisciplinario de Nanotecnología, Química y Física de Materiales, Espacio Interdisciplinario, Universidad de la República (Uruguay); Tumelero, Milton A. [Laboratorio de filmes finos e superficies, Departamento de Física, Universidad Federal de Santa Catarina, Florianópolis (Brazil); Campos Plá Cid, Cristiani [Laboratorio Central de Microscopia Electronica, Universidad Federal de Santa Catarina, Florianópolis (Brazil); Pasa, André A. [Laboratorio de filmes finos e superficies, Departamento de Física, Universidad Federal de Santa Catarina, Florianópolis (Brazil); Laboratorio Central de Microscopia Electronica, Universidad Federal de Santa Catarina, Florianópolis (Brazil); Mombrú, Álvaro W., E-mail: amombru@fq.edu.uy [Centro NanoMat/Cryssmat Lab, DETEMA, Facultad de Química, Universidad de la República (Uruguay); Centro Interdisciplinario de Nanotecnología, Química y Física de Materiales, Espacio Interdisciplinario, Universidad de la República (Uruguay)

2016-03-01

In this report, we present the study on the microstructure and interparticle interactions of manganite-polyaniline nanocomposites using grazing incidence small angle X-ray scattering (SAXS). In order to determine the nanoparticles mean diameter and correlation distances, data analysis was performed using the Guinier and Beaucage fits, in good agreement with transmission electron microscopy and X-ray diffraction analysis. The analysis of the interference functions revealed the existence of attractive interactions between nanoparticles. The nanocomposites with higher manganite concentration showed best fitting using the sticky hard sphere approximation. A weakening in the attractive interaction with increasing the dilution of nanoparticles in the polymer matrix was observed until a critical volume fraction (ϕ{sub c} ∼ 0.4) is reached, upon which the hard sphere approximation showed best fitting. The interaction potentials were estimated at room temperature revealing a decrease in the depth and width of the square well with increasing nanoparticle dilution. Coercive field and remanent magnetization showed a decrease with increasing polymer addition suggesting the declining of dipole–dipole interactions, in agreement with SAXS analysis. Magnetoresistance also showed an enhancement that could be probably associated to the decrease in the dipole–dipole interactions between ferromagnetic La{sub 2/3}Sr{sub 1/3}MnO{sub 3} (LSMO) nanoparticles at a critical separation distance in these nanocomposites. - Highlights: • A SAXS study on the microstructure of manganite-polyaniline nanocomposites is reported. • We report the presence of attractive interactions for the composites with higher concentration in manganite. • Interparticle dipole–dipole interactions were estimated by means of the SAXS interference function. • Coercive field and remanent magnetization studies showed agreement with SAXS analysis. • Magnetotransport showed an enhancement in relation to

Control of the colossal magnetoresistance by strain effect in Nd.sub.0.5./sub.Ca.sub.0.5./sub.MnO.sub.3./sub. thin films

Czech Academy of Sciences Publication Activity Database

Buzin, R. E.; Prellier, W.; Simon, Ch.; Mercone, S.; Mercey, B.; Raveau, B.; Šebek, Josef; Hejtmánek, Jiří

2001-01-01

Roč. 79, č. 5 (2001), s. 647-649 ISSN 0003-6951 Institutional research plan: CEZ:AV0Z1010914 Keywords : manganite thin films * colossal magnetoresistance Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.849, year: 2001

Temperature dependent evolution of the electronic and local atomic structure in the cubic colossal magnetoresistive manganite La1-xSrxMnO3

International Nuclear Information System (INIS)

Arenholz, Elke; Mannella, N.; Booth, C.H.; Rosenhahn, A.; Sell, B.C.; Nambu, A.; Marchesini, S.; Mun, B. S.; Yang, S.-H.; Watanabe, M.; Ibrahim, K.; Arenholz, E.; Young, A.; Guo, J.; Tomioka, Y.; Fadley, C.S.

2007-01-01

We have studied the temperature-dependent evolution of the electronic and local atomic structure in the cubic colossal magnetoresistive manganite La 1-x Sr x MnO 3 (x= 0.3-0.4) with core and valence level photoemission (PE), x-ray absorption spectroscopy (XAS), x-ray emission spectroscopy (XES), resonant inelastic x-ray scattering (RIXS), extended x-ray absorption fine structure (EXAFS) spectroscopy and magnetometry. As the temperature is varied across the Curie temperature T c , our PE experiments reveal a dramatic change of the electronic structure involving an increase in the Mn spin moment from ∼ 3 (micro)B to ∼ 4 (micro)B, and a modification of the local chemical environment of the other constituent atoms indicative of electron localization on the Mn atom. These effects are reversible and exhibit a slow-timescale ∼200 K-wide hysteresis centered at T c . Based upon the probing depths accessed in our PE measurements, these effects seem to survive for at least 35-50 (angstrom) inward from the surface, while other consistent signatures for this modification of the electronic structure are revealed by more bulk sensitive spectroscopies like XAS and XES/RIXS. We interpret these effects as spectroscopic fingerprints for polaron formation, consistent with the presence of local Jahn-Teller distortions of the MnO 6 octahedra around the Mn atom, as revealed by the EXAFS data. Magnetic susceptibility measurements in addition show typical signatures of ferro-magnetic clusters formation well above the Curie temperature

Tuning the metal-insulator transition in manganite films through surface exchange coupling with magnetic nanodots.

Science.gov (United States)

Ward, T Z; Gai, Z; Xu, X Y; Guo, H W; Yin, L F; Shen, J

2011-04-15

In strongly correlated electronic systems, the global transport behavior depends sensitively on spin ordering. We show that spin ordering in manganites can be controlled by depositing isolated ferromagnetic nanodots at the surface. The exchange field at the interface is tunable with nanodot density and makes it possible to overcome dimensionality and strain effects in frustrated systems to greatly increasing the metal-insulator transition and magnetoresistance. These findings indicate that electronic phase separation can be controlled by the presence of magnetic nanodots.

Colossal elastoresistance, electroresistance and magnetoresistance in Pr0.5Sr0.5MnO3 thin films

Science.gov (United States)

Chen, Liping; Guo, Xuexiang; Gao, J.

2016-05-01

Pr0.5Sr0.5MnO3 thin films on substrates of (001)-oriented LaAlO3 were epitaxially grown by pulsed laser deposition. It was found that a substrate-induced strain of 1.3% brings a great resistivity change of 98% at 25 K. We studied the dependence of resistivity on the applied electric current and magnetic field. In the greatly strained films of 60 nm thickness the electroresistance ER=[ρ(I1 μA)-ρ(I1000 μA)]/ρ(I1 μA) reaches 70% at T=25 K, much higher than ER 7% in the strain-relaxed films of 400 nm thickness, implying the strain effect on ER. Also the magnetoresistance of the film falls with strain-relaxation. Therefore the electric properties of the film could be efficiently modified by strain, electric current and magnetic field. All of them may be explained by the effect on the percolative phase separation and competition in the half-doped manganite material. The manganite films located at phase boundary are expected to be an ideal compound for providing practical colossal effects of elastoresistance, electroresistance and magnetoresistance due to the multiphase coexistence.

Observation of large low field magnetoresistance in ramp-edge tunneling junctions based on doped manganite ferromagnetic electrodes and a SrTiO{sub 3} insulator

Energy Technology Data Exchange (ETDEWEB)

Kwon, C.; Jia, Q.X.; Fan, Y.; Hundley, M.F.; Reagor, D.W.; Hawley, M.E.; Peterson, D.E.

1998-07-01

The authors report the fabrication of ferromagnet-insulator-ferromagnet junction devices using a ramp-edge geometry based on (La{sub 0.7}Sr{sub 0.3})MnO{sub 3} ferromagnetic electrodes and a SrTiO{sub 3} insulator. The multilayer thin films were deposited using pulsed laser deposition and the devices were patterned using photolithography and ion milling. As expected from the spin-dependent tunneling, the junction magnetoresistance depends on the relative orientation of the magnetization in the electrodes. The maximum junction magnetoresistance (JMR) of 30% is observed below 300 Oe at low temperatures (T < 100 K).

The influence of magnetic and electronic inhomogeneities on magnetotransmission and magnetoresistance of La0.67Sr0.33MnO3 films

International Nuclear Information System (INIS)

Sukhorukov, Yu.P.; Nosov, A.P.; Loshkareva, N.N.; Mostovshchikova, E.V.; Telegin, A.V.; Favre-Nicolin, E.; Ranno, L.

2005-01-01

The optical (absorption of light and magnetotransmission of IR radiation), magnetic, and transport properties of the epitaxial La 0.67 Sr 0.33 MnO 3 films of different thickness grown by laser ablation on the (100) SrTiO 3 and LaAlO 3 substrates were investigated. The effect of magnetotransmission reaches 6% at the temperature of 350 K while magnetoresistance reaches 7.6% at 354 K in a magnetic field of 8 kOe. The factors, which influence the values of magnetotransmission and magnetoresistance of manganite films, are discussed

Resonant x-ray scattering in manganites: study of the orbital degree of freedom

International Nuclear Information System (INIS)

Ishihara, Sumio; Maekawa, Sadamichi

2002-01-01

The orbital degree of freedom of electrons and its interplay with spin, charge and lattice degrees of freedom are some of the central issues in colossal magnetoresistive manganites. The orbital degree of freedom has until recently remained hidden, since it does not couple directly to most experimental probes. Development of synchrotron light sources has changed the situation; by the resonant x-ray scattering (RXS) technique the orbital ordering has successfully been observed. In this article, we review progress in the recent studies of RXS in manganites. We start with a detailed review of the RXS experiments applied to the orbital-ordered manganites and other correlated electron systems. We derive the scattering cross section of RXS, where the tensor character of the atomic scattering factor (ASF) with respect to the x-ray polarization is stressed. Microscopic mechanisms of the anisotropic tensor character of the ASF are introduced and numerical results of the ASF and the scattering intensity are presented. The azimuthal angle scan is a unique experimental method to identify RXS from the orbital degree of freedom. A theory of the azimuthal angle and polarization dependence of the RXS intensity is presented. The theoretical results show good agreement with the experiments in manganites. Apart from the microscopic description of the ASF, a theoretical framework of RXS to relate directly to the 3d orbital is presented. The scattering cross section is represented by the correlation function of the pseudo-spin operator for the orbital degree of freedom. A theory is extended to the resonant inelastic x-ray scattering and methods to observe excitations of the orbital degree of freedom are proposed. (author)

Rectifying characteristics and magnetoresistance in La0.9Sr0.1MnO3/Nb-doped SrTiO3 heterojunctions

International Nuclear Information System (INIS)

Luo, Z.; Gao, J.

2007-01-01

Manganite-based heterojunctions have attracted lots of attention as one of the most promising practical applications of colossal magnetoresistance materials. In this work, heterojunctions were fabricated by depositing La 0.9 Sr 0.1 MnO 3 (LSMO) films on substrates of 0.7 wt.% Nb-doped SrTiO 3 using pulsed laser deposition technique. X-ray diffraction spectra confirmed that the grown films are of single phase and have an orientation with the c-axis perpendicular to the substrate surface. As temperature decreases, the resistivity of LSMO films first increases gradually and then increases abruptly at temperature lower than 150 K. These junctions showed clear rectifying characteristics and strong temperature dependent current-voltage relation. Diffusion voltage decreases as temperature increases. Under forward bias, current is proportion to exp(eV/nkT). Ideal factor increases quickly and tunneling current plays more and more important role as temperature decreases. At 50 K, tunneling current becomes nearly dominant. Large magnetoresistance was observed. The sign and value of such magnetoresistance depends on the direction and value of current

Room temperature electrically tunable rectification magnetoresistance in Ge-based Schottky devices.

Science.gov (United States)

Huang, Qi-Kun; Yan, Yi; Zhang, Kun; Li, Huan-Huan; Kang, Shishou; Tian, Yu-Feng

2016-11-23

Electrical control of magnetotransport properties is crucial for device applications in the field of spintronics. In this work, as an extension of our previous observation of rectification magnetoresistance, an innovative technique for electrical control of rectification magnetoresistance has been developed by applying direct current and alternating current simultaneously to the Ge-based Schottky devices, where the rectification magnetoresistance could be remarkably tuned in a wide range. Moreover, the interface and bulk contribution to the magnetotransport properties has been effectively separated based on the rectification magnetoresistance effect. The state-of-the-art electrical manipulation technique could be adapt to other similar heterojunctions, where fascinating rectification magnetoresistance is worthy of expectation.

Investigation of magnetic transitions through ultrasonic measurements in double-layered CMR manganite La1.2Sr1.8Mn2O7

Science.gov (United States)

Reddy, Y. S.; Vishnuvardhan Reddy, C.

2014-03-01

A polycrystalline, double-layered, colossal magnetoresistive manganite La1.2Sr1.8Mn2O7 is synthesized by sol-gel process and its magnetic and ultrasonic properties were investigated in the temperature range 80-300 K. The sample has Curie temperature at 124 K, where the sample exhibits a transition from paramagnetic insulator to ferromagnetic metallic state. The longitudinal sound velocity measurements show a significant hardening of sound velocity below TC, which may be attributed to the coupling between ferromagnetic spins and longitudinal acoustic phonons. The magnetization and ultrasonic studies reveal the presence of secondary transition at ≈ 260 K in this sample. The present sound velocity measurement results confirm the reliability of ultrasonic investigations as an independent tool to probe magnetic transitions in manganites.

Mesoscopic Percolating Resistance Network in a Strained Manganite Thin Film

KAUST Repository

Lai, K.; Nakamura, M.; Kundhikanjana, W.; Kawasaki, M.; Tokura, Y.; Kelly, M. A.; Shen, Z.-X.

2010-01-01

Many unusual behaviors in complex oxides are deeply associated with the spontaneous emergence of microscopic phase separation. Depending on the underlying mechanism, the competing phases can form ordered or random patterns at vastly different length scales. By using a microwave impedance microscope, we observed an orientation-ordered percolating network in strained Nd 1/2Sr1/2MnO3 thin films with a large period of 100 nanometers. The filamentary metallic domains align preferentially along certain crystal axes of the substrate, suggesting the anisotropic elastic strain as the key interaction in this system. The local impedance maps provide microscopic electrical information of the hysteretic behavior in strained thin film manganites, suggesting close connection between the glassy order and the colossal magnetoresistance effects at low temperatures.

Mesoscopic Percolating Resistance Network in a Strained Manganite Thin Film

KAUST Repository

Lai, K.

2010-07-08

Many unusual behaviors in complex oxides are deeply associated with the spontaneous emergence of microscopic phase separation. Depending on the underlying mechanism, the competing phases can form ordered or random patterns at vastly different length scales. By using a microwave impedance microscope, we observed an orientation-ordered percolating network in strained Nd 1/2Sr1/2MnO3 thin films with a large period of 100 nanometers. The filamentary metallic domains align preferentially along certain crystal axes of the substrate, suggesting the anisotropic elastic strain as the key interaction in this system. The local impedance maps provide microscopic electrical information of the hysteretic behavior in strained thin film manganites, suggesting close connection between the glassy order and the colossal magnetoresistance effects at low temperatures.

Mesoscopic percolating resistance network in a strained manganite thin film.

Science.gov (United States)

Lai, Keji; Nakamura, Masao; Kundhikanjana, Worasom; Kawasaki, Masashi; Tokura, Yoshinori; Kelly, Michael A; Shen, Zhi-Xun

2010-07-09

Many unusual behaviors in complex oxides are deeply associated with the spontaneous emergence of microscopic phase separation. Depending on the underlying mechanism, the competing phases can form ordered or random patterns at vastly different length scales. By using a microwave impedance microscope, we observed an orientation-ordered percolating network in strained Nd(1/2)Sr(1/2)MnO3 thin films with a large period of 100 nanometers. The filamentary metallic domains align preferentially along certain crystal axes of the substrate, suggesting the anisotropic elastic strain as the key interaction in this system. The local impedance maps provide microscopic electrical information of the hysteretic behavior in strained thin film manganites, suggesting close connection between the glassy order and the colossal magnetoresistance effects at low temperatures.

A tight binding model study of tunneling conductance spectra of spin and orbitally ordered CMR manganites

Science.gov (United States)

Panda, Saswati; Sahoo, D. D.; Rout, G. C.

2018-04-01

We report here a tight binding model for colossal magnetoresistive (CMR) manganites to study the pseudo gap (PG) behavior near Fermi level. In the Kubo-Ohata type DE model, we consider first and second nearest neighbor interactions for transverse spin fluctuations in core band and hopping integrals in conduction band, in the presence of static band Jahn-Teller distortion. The model Hamiltonian is solved using Zubarev's Green's function technique. The electron density of states (DOS) is found out from the Green's functions. We observe clear PG near Fermi level in the electron DOS.

Electroresistance and magnetoresistance in La0.9Ba0.1MnO3 thin films

International Nuclear Information System (INIS)

Hu, F.X.; Gao, J.; Wang, Z.H.

2006-01-01

The electroresistance and magnetoresistance effects have been investigated in La 0.9 Ba 0.1 MnO 3 epitaxial thin films. Tensile strain caused by substrate mismatch makes the Curie temperature T C of the film at ∼300 K. The influence of an applied dc-current on the resistance in the absence of a magnetic field was studied. Significant change of the peak resistance at different currents was found. The reduction of the peak resistance reaches ∼27% with an electric current density up to 1.3 x 10 5 A cm -2 . We also studied colossal magnetoresistance (CMR) effect in the films. Applying a magnetic field of 2 T could lead to a magnetoresistance as large as 42%. The reduction of resistance caused by a current density ∼1.3 x 10 5 A cm -2 was found to be equivalent to the CMR effect caused by 1.5 T near T C . The phenomenon that the resistance in CMR manganites could be easily controlled by the electric current should be of high interest for both fundamental research and practical applications

Pressure effect on magnetic and magnetotransport properties of intermetallic and colossal magnetoresistance oxide compounds

International Nuclear Information System (INIS)

Arnold, Z; Ibarra, M R; Algarabel, P A; Marquina, C; Teresa, Jose MarIa de; Morellon, L; Blasco, J; Magen, C; Prokhnenko, O; Kamarad, J; Ritter, C

2005-01-01

The joint power of neutron diffraction and pressure techniques allows us to characterize under unique conditions the nature and different role of basic interactions in solids. We have covered a broad phenomenology in archetypical compounds: intermetallics and magnetic oxides. We have selected compounds in which the effect of moderate pressure is able to modify the electronic structure and bond angles that in turn are in the bases of magnetic and structural transitions. Complex magnetic and structural phase diagrams are reported for compounds with magnetic (Tb 1-X Y X Mn 2 ) and structural (RE 5 Si 4-X Ge X ) instabilities. Pressure-induced change of the magnetic structure in (R 2 Fe 17 ) intermetallics and the effect on the colossal magnetoresistance manganites are described

Colossal magnetoresistance and phase separation in manganite thin films

Science.gov (United States)

Srivastava, M. K.; Agarwal, V.; Kaur, A.; Singh, H. K.

2017-05-01

In the present work, polycrystalline Sm0.55Sr0.45MnO3 thin films were prepared on LSAT (001) single crystal substrates by ultrasonic nebulized spray pyrolysis technique. The X-ray diffraction θ-2θ scan reveals that these films (i) have very good crystallinity, (ii) are oriented along out-of-plane c-direction, and (iii) are under small tensile strain. The impact of oxygen vacancy results into (i) higher value of paramagnetic insulator (PMI) to ferromagnetic metal (FMM) transition temperature, i.e., TC/TIM, (ii) sharper PMI-FMM transition, (iii) higher value of magnetization and magnetic saturation moment, and (iv) higher value of magnetoresistance (˜99%). We suggest here that oxygen vacancy favors FMM phase while oxygen vacancy annihilation leads to antiferromagnetic-charge ordered insulator (AFM-COI) phase. The observed results have been explained in context of phase separation (PS) caused by different fractions of the competing FMM and AFM-COI phases.

Electrical Transport and Magnetoresistance Properties of Tensile-Strained CaMnO3 Thin Films

Science.gov (United States)

Ullery, Dustin; Lawson, Bridget; Zimmerman, William; Neubauer, Samuel; Chaudhry, Adeel; Hart, Cacie; Yong, Grace; Smolyaninova, Vera; Kolagani, Rajeswari

We will present our studies of the electrical transport and magnetoresistance properties of tensile strained CaMnO3 thin films. We observe that the resistivity decreases significantly as the film thickness decreases which is opposite to what is observed in thin films of hole doped manganites. The decrease in resistivity is more pronounced in the films on (100) SrTiO3, with resistivity of the thinnest films being about 3 orders of magnitude lower than that of bulk CaMnO3. Structural changes accompanying resistivity changes cannot be fully explained as due to tensile strain, and indicate the presence of oxygen vacancies. These results also suggest a coupling between tensile strain and oxygen deficiency, consistent with predictions from models based on density functional theory calculations. We observe a change in resistance under the application of moderate magnetic field. Experiments are underway to understand the origin of the magnetoresistance and its possible relation to the tensile strain effects. We acknowledge support from: Towson Office of University Undergraduate Research, Fisher Endowment Grant and Undergraduate Research Grants from the Fisher College of Science and Mathematics, and Seed Funding Grant from the School of Emerging technologies.

Wet chemical deposition of single crystalline epitaxial manganite thin films with atomically flat surface

International Nuclear Information System (INIS)

Mishra, Amita; Dutta, Anirban; Samaddar, Sayanti; Gupta, Anjan K.

2013-01-01

We report the wet chemical deposition of single crystalline epitaxial thin films of the colossal magneto-resistive manganite La 0.67 Sr 0.33 MnO 3 on the lattice-matched (001)-face of a La 0.3 Sr 0.7 Al 0.65 Ta 0.35 O 3 substrate. Topographic images of these films taken with a scanning tunneling microscope show atomically flat terraces separated by steps of monatomic height. The resistivity of these films shows an insulator-metal transition at 310 K, nearly coincident with the Curie temperature of 340 K, found from magnetization measurements. The films show a magnetoresistance of 7% at 300 K and 1.2 T. Their saturation magnetization value at low temperatures is consistent with that of the bulk. - Highlights: ► Wet chemical deposition of La 0.67 Sr 0.33 MnO 3 (LSMO) on a lattice-matched substrate. ► Single crystalline epitaxial LSMO films obtained. ► Flat terraces separated by monatomic steps observed by scanning tunneling microscope

Effect of CDW and magnetic interactions on the eg electrons of the manganite systems

International Nuclear Information System (INIS)

Rout, G.C.; Panda, S.; Behera, S.N.

2009-01-01

We address a model study which includes the co-existence of the charge density wave (CDW) and ferromagnetic interactions in order to explain the colossal magnetoresistance (CMR) in manganites. The Hamiltonian consists of the ferromagnetic Hund's rule exchange interaction between e g and t 2g spins, Heisenberg core spin interactions and the CDW interaction present in the e g band electrons. The core electron magnetization, induced e g electron magnetization and the CDW gap are calculated using Zubarev's Green's function technique and determined self-consistently. The effect of core electron magnetization and the CDW interaction on the induced magnetization as well as on the occupation number in the different spin states of the e g band electrons are investigated by varying the model parameters of the system like the CDW coupling, the exchange coupling, the Heisenberg coupling and the external field. It is observed that the induced magnetization exhibits re-entrant behaviour and exists within a narrow temperature range just below the Curie temperature. This unusual behaviour of the e g band electrons will throw some new insights on the physical properties of the manganite systems.

Role of structure imperfection in the formation of the magnetotransport properties of rare-earth manganites with a perovskite structure

Energy Technology Data Exchange (ETDEWEB)

Pashchenko, A. V., E-mail: alpash@mail.ru; Pashchenko, V. P.; Prokopenko, V. K. [National Academy of Sciences of Ukraine, Galkin Donetsk Institute for Physics and Engineering (Ukraine); Turchenko, V. A. [Joint Institute for Nuclear Research (Russian Federation); Revenko, Yu. F.; Mazur, A. S.; Sycheva, V. Ya.; Liedienov, N. A. [National Academy of Sciences of Ukraine, Galkin Donetsk Institute for Physics and Engineering (Ukraine); Pitsyuga, V. G. [Donetsk National University (Ukraine); Levchenko, G. G. [National Academy of Sciences of Ukraine, Galkin Donetsk Institute for Physics and Engineering (Ukraine)

2017-01-15

The structure, the structure imperfection, and the magnetoresistance, magnetotransport, and microstructure properties of rare-earth perovskite La{sub 0.3}Ln{sub 0.3}Sr{sub 0.3}Mn{sub 1.1}O{sub 3–δ} manganites are studied by X-ray diffraction, thermogravimetry, electrical resistivity measurement, magnetic, {sup 55}Mn NMR, magnetoresistance measurement, and scanning electron microscopy. It is found that the structure imperfection increases, and the symmetry of a rhombohedrally distorted R3̅c perovskite structure changes into its pseudocubic type during isovalent substitution for Ln = La{sup 3+}, Pr{sup 3+}, Nd{sup 3+}, Sm{sup 3+}, or Eu{sup 3+} when the ionic radius of an A cation decreases. Defect molar formulas are determined for a real perovskite structure, which contains anion and cation vacancies. The decrease in the temperatures of the metal–semiconductor (T{sub ms}) and ferromagnet–paramagnet (T{sub C}) phase transitions and the increase in electrical resistivity ρ and activation energy E{sub a} with increasing serial number of Ln are caused by an increase in the concentration of vacancy point defects, which weaken the double exchange 3d{sup 4}(Mn{sup 3+})–2p{sup 6}(O{sup 2–})–3d{sup 3}(Mn{sup 4+})–V{sup (a)}–3d{sup 4}(Mn{sup 3+}). The crystal structure of the compositions with Ln = La contains nanostructured planar clusters, which induce an anomalous magnetic hysteresis at T = 77 K. Broad and asymmetric {sup 55}Mn NMR spectra support the high-frequency electronic double exchange Mn{sup 3+}(3d{sup 4}) ↔ O{sup 2–}(2p{sup 6}) ↔ Mn{sup 4+}(3d{sup 3}) and indicate a heterogeneous surrounding of manganese by other ions and vacancies. A correlation is revealed between the tunneling magnetoresistance effect and the crystallite size. A composition–structure imperfection–property experimental phase diagram is plotted. This diagram supports the conclusion about a strong influence of structure imperfection on the formation of the magnetic

Anisotropic strains and magnetoresistance of La0.7Ca0.3MnO3

International Nuclear Information System (INIS)

Koo, T.Y.; Park, S.H.; Lee, K.; Jeong, Y.H.

1997-01-01

Thin films of perovskite manganite La 0.7 Ca 0.3 MnO 3 were grown epitaxially on SrTiO 3 (100), MgO(100) and LaAlO 3 (100) substrates by the pulsed laser deposition method. Microscopic structures of these thin film samples as well as a bulk sample were fully determined by x-ray diffraction measurements. The unit cells of the three films have different shapes, i.e., contracted tetragonal, cubic, and elongated tetragonal for SrTiO 3 , MgO, and LaAlO 3 , respectively, while the unit cell of the bulk is cubic. It is found that the samples with a cubic unit cell show smaller peak magnetoresistance at low fields (approx-lt 1T) than the noncubic ones do. The present result demonstrates that the magnetoresistance of La 0.7 Ca 0.3 MnO 3 at low fields can be controlled by lattice distortion via externally imposed strains. copyright 1997 American Institute of Physics

Coulomb blockade and magnetoresistance in granular La{sub 1.32}Sr{sub 1.68}Mn{sub 2}O{sub 7} under hydrostatic pressure

Energy Technology Data Exchange (ETDEWEB)

Narjis, A., E-mail: narjis78@gmail.com [Research Group ESNPS, Physics Department, University Ibn Zohr, Faculty of Sciences, B.P 8106, Hay Dakhla, 80000 Agadir (Morocco); El Kaaouachi, A.; Limouny, L.; Dlimi, S.; Errai, M.; Sybous, A. [Research Group ESNPS, Physics Department, University Ibn Zohr, Faculty of Sciences, B.P 8106, Hay Dakhla, 80000 Agadir (Morocco); Kumaresavanji, M. [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rua Dr. Xavier Sigaud, 150 Urca, Rio de Janeiro (Brazil)

2013-04-15

The transport properties in the La{sub 1.32}Sr{sub 1.68}Mn{sub 2}O{sub 7} layered manganite system have been studied in the presence of magnetic field up to 5 T. An analysis of the low temperature (T<45 K) dependence of the resistivity under hydrostatic pressure up to 25 kbars shows the spin-dependent Coulomb Blockade phenomenon. The surface phase and the link condition in grain boundaries are suggested to be responsible for the magnetoresistance data while influencing the charge transfer probability between grains. - Highlights: ►Magnetotransport in a colossal magnetoresistive material La{sub 1.32}Sr{sub 1.68}Mn{sub 2}O{sub 7}. ► The effect of the forming pressure on the magnetoresistance (MR). ► The grain size effect and charge transfer probability between grains. ► A simple model to explain the negative MR.

Dependence on film thickness of grain boundary low-field magnetoresistance in thin films of La0.7Ca0.3MnO3

International Nuclear Information System (INIS)

Todd, N. K.; Mathur, N. D.; Blamire, M. G.

2001-01-01

The magnetoresistance of grain boundaries in the perovskite manganites is being studied, both in polycrystalline materials, and thin films grown on bicrystal substrates, because of interest in low-field applications. In this article we show that epitaxial films grown on SrTiO 3 bicrystal substrates of 45 degree misorientation show magnetoresistance behavior which is strongly dependent on the thickness of the film. Thin films, e.g., 40 nm, can show a large low-field magnetoresistance at low temperatures, with very sharp switching between distinct high and low resistance states for fields applied in plane and parallel to the boundary. Thicker films show a more complex behavior of resistance as a function of field, and the dependence on the angle between the applied field and the grain boundary is altered. These changes in magnetoresistance behavior are linked to the variation in morphology of the films. Thin films are coherently strained, due to the mismatch with the substrate, and very smooth. Thicker films relax, with the formation of defects, and hence different micromagnetic behavior. [copyright] 2001 American Institute of Physics

Magnetoresistive logic and biochip

International Nuclear Information System (INIS)

Brueckl, Hubert; Brzeska, Monika; Brinkmann, Dirk; Schotter, J.Joerg; Reiss, Guenter; Schepper, Willi; Kamp, P.-B.; Becker, Anke

2004-01-01

While some magnetoresistive devices based on giant magnetoresistance or spin-dependent tunneling are already commercialized, a new branch of development is evolving towards magnetoresistive logic with magnetic tunnel junctions. Furthermore, the new magnetoelectronic effects show promising properties in magnetoresistive biochips, which are capable of detecting even single molecules (e.g. DNA) by functionalized magnetic markers. The unclear limits of this approach are discussed with two model systems

Manganites in Perovskite Superlattices: Structural and Electronic Properties

KAUST Repository

Jilili, Jiwuer

2016-07-13

Perovskite oxides have the general chemical formula ABO3, where A is a rare-earth or alkali-metal cation and B is a transition metal cation. Perovskite oxides can be formed with a variety of constituent elements and exhibit a wide range of properties ranging from insulators, metals to even superconductors. With the development of growth and characterization techniques, more information on their physical and chemical properties has been revealed, which diversified their technological applications. Perovskite manganites are widely investigated compounds due to the discovery of the colossal magnetoresistance effect in 1994. They have a broad range of structural, electronic, magnetic properties and potential device applications in sensors and spintronics. There is not only the technological importance but also the need to understand the fundamental mechanisms of the unusual magnetic and transport properties that drive enormous attention. Manganites combined with other perovskite oxides are gaining interest due to novel properties especially at the interface, such as interfacial ferromagnetism, exchange bias, interfacial conductivity. Doped manganites exhibit diverse electrical properties as compared to the parent compounds. For instance, hole doped La0.7Sr0.3MnO3 is a ferromagnetic metal, whereas LaMnO3 is an antiferromagnetic insulator. Since manganites are strongly correlated systems, heterojunctions composed of manganites and other perovskite oxides are sunject to complex coupling of the spin, orbit, charge, and lattice degrees of freedom and exhibit unique electronic, magnetic, and transport properties. Electronic reconstructions, O defects, doping, intersite disorder, magnetic proximity, magnetic exchange, and polar catastrophe are some effects to explain these interfacial phenomena. In our work we use first-principles calculations to study the structural, electronic, and magnetic properties of manganite based superlattices. Firstly, we investigate the electronic

Colossal magnetoresistance

International Nuclear Information System (INIS)

Fontcuberta, J.

1999-01-01

In 1986 Alex Mueller and Georg Bednorz of IBM Zurich discovered high-temperature superconductivity in copper-based oxides. This finding, which was rewarded with the Nobel Prize for Physics in the following year, triggered intense research into the properties of the transition metal oxides. Since then scientists have questioned the very nature of the metallic state in these materials. A few years after the initial discovery, in 1993, more excitement greeted reports that certain manganese oxides showed a huge change in electrical resistivity when a magnetic field was applied. This effect is generally known as magnetoresistance, but the resistivity change observed in these oxides was so large that it could not be compared with any other forms of magnetoresistance. The effect observed in these materials the manganese perovskites was therefore dubbed ''colossal'' magnetoresistance to distinguish it from the giant magnetoresistance observed in magnetic multilayers. In this article the author explains why magnetoresistance is an expanding field of physics research. (UK)

Synthesis and characterisation of La1-xNaxMnO3+δ thin films manganites

International Nuclear Information System (INIS)

Alessandri, I.; Malavasi, L.; Bontempi, E.; Mozzati, M.C.; Azzoni, C.B.; Flor, G.; Depero, L.E.

2004-01-01

Optimally sodium doped lanthanum manganite (LNMO) thin films have been grown onto differently oriented NdGaO 3 single crystals substrates by means of radio-frequency (RF)-magnetron sputtering technique, in order to investigate the role of the strain imposed by lattice mismatch on the magnetotransport properties. Films deposited onto NdGaO 3 (1 1 0) experiment a slight in-plane compressive strain that can be tuned by the thickness and allows to achieve colossal magnetoresistive effects. On the contrary, the change of the substrate orientation induces an in-plane tensile strain, making the film insulating. Above observations are explained by considering the effect of distortions of the Mn-O coordination polyhedra

Theoretical study of the Raman active CDW gap mode in manganites

International Nuclear Information System (INIS)

Rout, G C; Panda, Saswati; Behera, S N

2010-01-01

We report here the microscopic theory of the Raman spectra of the colossal magnetoresistive (CMR) manganite systems. The system is described by a model Hamiltonian consisting of the double exchange interaction in addition to the charge ordering interaction in the e g band and spin-spin interaction among the t 2g core electrons. Further the phonon coupling to the conduction electron density is incorporated in the model for phonons in the harmonic approximation. The spectral density function for the Raman spectra is calculated from the imaginary part of the phonon Green's function. The calculated spectra display the Raman active bare phonon peak along with the charge ordering peak. The magnetic field and temperature dependence of the charge ordering peak agrees with the 480 cm -1 JT mode observed in the experiments. The evolution of this mode is investigated in the report.

Effect of CDW and magnetic interactions on the e{sub g} electrons of the manganite systems

Energy Technology Data Exchange (ETDEWEB)

Rout, G.C., E-mail: gcr@iopb.res.i [Condensed Matter Physics Group, P. G. Department of Applied Physics and Ballistics, F. M. University, Balasore 756 019 (India); Panda, S. [Trident Academy of Technology, F2/A, Chandaka Industrial Estate, Bhubaneswar 751 024 (India); Behera, S.N. [Institute of Materials Science, Planetarium Building, Bhubaneswar 751 013 (India)

2009-11-15

We address a model study which includes the co-existence of the charge density wave (CDW) and ferromagnetic interactions in order to explain the colossal magnetoresistance (CMR) in manganites. The Hamiltonian consists of the ferromagnetic Hund's rule exchange interaction between e{sub g} and t{sub 2g} spins, Heisenberg core spin interactions and the CDW interaction present in the e{sub g} band electrons. The core electron magnetization, induced e{sub g} electron magnetization and the CDW gap are calculated using Zubarev's Green's function technique and determined self-consistently. The effect of core electron magnetization and the CDW interaction on the induced magnetization as well as on the occupation number in the different spin states of the e{sub g} band electrons are investigated by varying the model parameters of the system like the CDW coupling, the exchange coupling, the Heisenberg coupling and the external field. It is observed that the induced magnetization exhibits re-entrant behaviour and exists within a narrow temperature range just below the Curie temperature. This unusual behaviour of the e{sub g} band electrons will throw some new insights on the physical properties of the manganite systems.

Strained superlattices and magnetic tunnel junctions based on doped manganites

International Nuclear Information System (INIS)

Yafeng Lu

2001-01-01

In the first part of this work the effect of biaxial strain on the structure and transport properties of doped manganites has been studied to explore the relevance of Jahn-Teller electron-lattice interaction for the CMR phenomenon in these materials. A series of high quality, coherently strained La 2/3 (Ca or Ba) 1/3 MnO 3 /SrTiO 3 superlattices with different modulation periods have been fabricated on (001) SrTiO 3 and NdGaO 3 substrates by laser molecular beam epitaxy. A detailed structural characterization was performed by high-angle X-ray diffraction (HAXRD) and low-angle X-ray reflectivity (LAXRR). The fabricated superlattices are very flat, show excellent structural coherence and very small mosaic spread (0.2 ∝0.03 ). The in-plane coherency strain could be varied by changing the thickness ratio of the constituent layers allowing for a systematic variation of the resulting lattice distortion of La 2/3 (Ca or Ba) 1/3 MnO 3 . By the in-plane coherency strain the out-of-plane lattice constant could be continuously adjusted by varying the relative thickness of the SrTiO 3 and La 2/3 (Ca or Ba) 1/3 MnO 3 layers: the c-axis lattice constant of La 2/3 Ba 1/3 MnO 3 was found to vary from 3.910 A to 3.975 A due to a compressive in-plane strain, whereas the c-axis constant of La 2/3 Ca 1/3 MnO 3 was found to change from 3.87 A to 3.79A due to tensile in-plane strain. The strain results in a biaxial distortion ε bi of La 2/3 (Ca or Ba) 1/3 MnO 3 that strongly affects the electrical transport properties and the magnetoresistance. Our measurements show that there is a clear correlation between ε bi and the temperature T p corresponding to the maximum in the resistivity versus temperature curves as well as the measured magnetoresistance in the two systems. In the second part of this work we have investigated the spin-dependent tunneling in trilayer structures of La 2/3 Ba 1/3 MnO 3 /SrTiO 3 /La 2/3 Ba 1/3 MnO 3 . (orig.)

Giant magnetoelectric effect in pure manganite-manganite heterostructures

Energy Technology Data Exchange (ETDEWEB)

Paul, Sanjukta; Pankaj, Ravindra; Yarlagadda, Sudhakar; Majumdar, Pinaki; Littlewood, Peter B.

2017-11-01

Obtaining strong magnetoelectric couplings in bulk materials and heterostructures is an ongoing challenge. We demonstrate that manganite heterostructures of the form (Insulator) /(LaMnO3)(n)/Interface/(CaMnO3)(n)/(Insulator) show strong multiferroicity in magnetic manganites where ferroelectric polarization is realized by charges leaking from LaMnO3 to CaMnO3 due to repulsion. Here, an effective nearest-neighbor electron-electron (electron-hole) repulsion (attraction) is generated by cooperative electron-phonon interaction. Double exchange, when a particle virtually hops to its unoccupied neighboring site and back, produces magnetic polarons that polarize antiferromagnetic regions. Thus a striking giant magnetoelectric effect ensues when an external electrical field enhances the electron leakage across the interface.

Tunneling Negative Magnetoresistance via δ Doping in a Graphene-Based Magnetic Tunnel Junction

International Nuclear Information System (INIS)

Yuan Jian-Hui; Chen Ni; Mo Hua; Zhang Yan; Zhang Zhi-Hai

2016-01-01

We investigate the tunneling magnetoresistance via δ doping in a graphene-based magnetic tunnel junction in detail. It is found that the transmission probability and the conductance oscillates with the position and the aptitude of the δ doping. Also, both the transmission probability and the conductance at the parallel configuration are suppressed by the magnetic field more obviously than that at the antiparallel configuration, which implies a large negative magnetoresistance for this device. The results show that the negative magnetoresistance of over 300% at B = 1.0 T is observed by choosing suitable doped parameters, and the temperature plays an important role in the magnetoresistance. Thus it is possible to open a way to effectively manipulate the magnetoresistance devices, and to make a type of magnetoresistance device by controlling the structural parameter of the δ doping. (paper)

Graphic User Interface for Monte Carlo Simulation of Ferromagnetic/Antiferromagnetic Manganite Bilayers

Directory of Open Access Journals (Sweden)

Hector Barco-Ríos

2011-06-01

Full Text Available The manganites have been widely studied because of their important properties as colossal magnetoresistance and exchange bias that are important phenomena used in many technological applications. For this reason, in this work, a study of the exchange bias effect present in La2/3Ca1/3MnO3/La1/3Ca2/3MnO3. This study was carried out by using the Monte Carlo method and the Metropolis Algorithm. In order to make easy this study, a graphic user interface was built alloying a friendly interaction. The interface permits to control the thickness of Ferromagnetic and Antiferromagnetic layer, temperatures the magnetic field, the number of Monte Carlo steps and the exchange parameters. Results obtained reflected the influence of all of these parameters on the exchange bias and coercive fields.

Reversibility of magnetic field driven transition from electronic phase separation state to single-phase state in manganites: A microscopic view

Science.gov (United States)

Liu, Hao; Lin, Lingfang; Yu, Yang; Lin, Hanxuan; Zhu, Yinyan; Miao, Tian; Bai, Yu; Shi, Qian; Cai, Peng; Kou, Yunfang; Lan, Fanli; Wang, Wenbin; Zhou, Xiaodong; Dong, Shuai; Yin, Lifeng; Shen, Jian

2017-11-01

Electronic phase separation (EPS) is a common phenomenon in strongly correlated oxides. For colossal magnetoresistive (CMR) manganites, the EPS is so pronounced that not only does it govern the CMR behavior, but also raises a question whether EPS exists as a ground state for systems or a metastable state. While it has been well known that a magnetic field can drive the transition of the EPS state into a single-phase state in manganites, the reversibility of this transition is not well studied. In this work we use magnetic force microscopy (MFM) to directly visualize the reversibility of the field driven transition between the EPS state and the single-phase state at different temperatures. The MFM images correspond well with the global magnetic and transport property measurements, uncovering the underlying mechanism of the field driven transition between the EPS state and the single-phase state. We argue that EPS state is a consequence of system quenching whose response to an external magnetic field is governed by a local energy landscape.

Correlation between vacancies and magnetoresistance changes in FM manganites using the Monte Carlo method

Energy Technology Data Exchange (ETDEWEB)

Agudelo-Giraldo, J.D. [PCM Computational Applications, Universidad Nacional de Colombia-Sede Manizales, Km. 9 vía al aeropuerto, Manizales (Colombia); Restrepo-Parra, E., E-mail: erestrepopa@unal.edu.co [PCM Computational Applications, Universidad Nacional de Colombia-Sede Manizales, Km. 9 vía al aeropuerto, Manizales (Colombia); Restrepo, J. [Grupo de Magnetismo y Simulación, Instituto de Física, Universidad de Antioquia, A.A. 1226, Medellín (Colombia)

2015-10-01

The Metropolis algorithm and the classical Heisenberg approximation were implemented by the Monte Carlo method to design a computational approach to the magnetization and resistivity of La{sub 2/3}Ca{sub 1/3}MnO{sub 3}, which depends on the Mn ion vacancies as the external magnetic field increases. This compound is ferromagnetic, and it exhibits the colossal magnetoresistance (CMR) effect. The monolayer was built with L×L×d dimensions, and it had L=30 umc (units of magnetic cells) for its dimension in the x–y plane and was d=12 umc in thickness. The Hamiltonian that was used contains interactions between first neighbors, the magnetocrystalline anisotropy effect and the external applied magnetic field response. The system that was considered contains mixed-valence bonds: Mn{sup 3+eg’}–O–Mn{sup 3+eg}, Mn{sup 3+eg}–O–Mn{sup 4+d3} and Mn{sup 3+eg’}–O–Mn{sup 4+d3}. The vacancies were placed randomly in the sample, replacing any type of Mn ion. The main result shows that without vacancies, the transitions T{sub C} (Curie temperature) and T{sub MI} (metal–insulator temperature) are similar, whereas with the increase in the vacancy percentage, T{sub MI} presented lower values than T{sub C}. This situation is caused by the competition between the external magnetic field, the vacancy percentage and the magnetocrystalline anisotropy, which favors the magnetoresistive effect at temperatures below T{sub MI}. Resistivity loops were also observed, which shows a direct correlation with the hysteresis loops of magnetization at temperatures below T{sub C}. - Highlights: • Changes in the resistivity of FM materials as a function of the temperature and external magnetic field can be obtained by the Monte Carlo method, Metropolis algorithm, classical Heisenberg and Kronig–Penney approximation for magnetic clusters. • Increases in the magnetoresistive effect were observed at temperatures below T{sub MI} by the vacancies effect. • The resistive hysteresis

Phase shift of oscillatory magnetoresistance in a double-cross thin film structure of La0.3Pr0.4Ca0.3MnO3 via strain-engineered elongation of electronic domains

Science.gov (United States)

Alagoz, H. S.; Prasad, B.; Jeon, J.; Blamire, M. G.; Chow, K. H.; Jung, J.

2018-02-01

The subtle balance between the competing electronic phases in manganites due to complex interplay between spin, charge, and orbital degrees of freedom could allow one to modify the properties of electronically phase separated systems. In this paper, we show that the phase shift in the oscillatory magnetoresistance ρ (θ ) can be modified by engineering strain driven elongation of electronic domains in La0.3Pr0.4Ca0.3MnO3 (LPCMO) thin films. Strain-driven elongation of magnetic domains can produce different percolation paths and hence different anisotropic magnetoresistance responses. This tunability provides a unique control that is unattainable in conventional 3 d ferromagnetic metals and alloys.

A model study of tunneling conductance spectra of ferromagnetically ordered manganites

Science.gov (United States)

Panda, Saswati; Kar, J. K.; Rout, G. C.

2018-02-01

We report here the interplay of ferromagnetism (FM) and charge density wave (CDW) in manganese oxide systems through the study of tunneling conductance spectra. The model Hamiltonian consists of strong Heisenberg coupling in core t2g band electrons within mean-field approximation giving rise to ferromagnetism. Ferromagnetism is induced in the itinerant eg electrons due to Kubo-Ohata type double exchange (DE) interaction among the t2g and eg electrons. The charge ordering (CO) present in the eg band giving rise to CDW interaction is considered as the extra-mechanism to explain the colossal magnetoresistance (CMR) property of manganites. The magnetic and CDW order parameters are calculated using Zubarev's Green's function technique and solved self-consistently and numerically. The eg electron density of states (DOS) calculated from the imaginary part of the Green's function explains the experimentally observed tunneling conductance spectra. The DOS graph exhibits a parabolic gap near the Fermi energy as observed in tunneling conductance spectra experiments.

Intrinsic colossal magnetoresistance effect in thin-film Pr0.5Sr0.5MnO3 through dimensionality switching.

Science.gov (United States)

Uozu, Y; Wakabayashi, Y; Ogimoto, Y; Takubo, N; Tamaru, H; Nagaosa, N; Miyano, K

2006-07-21

A homogeneous colossal magnetoresistance (CMR) effect at low temperatures has been found in a thin-film perovskite manganite Pr0.5Sr0.5MnO3. The transition is driven not by the spin alignment as in usual CMR in bulk samples but by the localization-delocalization transition switched by the change in the effective dimensionality. Two-dimensional (x2-y2)-orbital ordering enhanced by the substrate strain is essential for the stabilization of the insulating localized state, which is on the verge of the first-order transition to the three-dimensional metallic ferromangetic state.

Percolative Theory of Organic Magnetoresistance and Fringe-Field Magnetoresistance

Science.gov (United States)

Flatté, Michael E.

2013-03-01

A recently-introduced percolation theory for spin transport and magnetoresistance in organic semiconductors describes the effects of spin dynamics on hopping transport by considering changes in the effective density of hopping sites, a key quantity determining the properties of percolative transport. Increases in the spin-flip rate open up ``spin-blocked'' pathways to become viable conduction channels and hence, as the spin-flip rate changes with magnetic field, produce magnetoresistance. Features of this percolative magnetoresistance can be found analytically in several regimes, and agree with measurements of the shape and saturation of measured magnetoresistance curves. We find that the threshold hopping distance is analogous to the branching parameter of a phenomenological two-site model, and that the distinction between slow and fast hopping is contingent on the threshold hopping distance. Regimes of slow and fast hopping magnetoresistance are uniquely characterized by their line shapes. Studies of magnetoresistance in known systems with controllable positional disorder would provide an additional stringent test of this theory. Extensions to this theory also describe fringe-field magnetoresistance, which is the influence of fringe magnetic fields from a nearby unsaturated magnetic electrode on the conductance of an organic film. This theory agrees with several key features of the experimental fringe-field magnetoresistance, including the applied fields where the magnetoresistance reaches extrema, the applied field range of large magnetoresistance effects from the fringe fields, and the sign of the effect. All work done in collaboration with N. J. Harmon, and fringe-field magnetoresistance work in collaboration also with F. Macià, F. Wang, M. Wohlgenannt and A. D. Kent. This work was supported by an ARO MURI.

Negative magnetoresistance of pitch-based carbon fibers Temperature and pressure dependence

Science.gov (United States)

Hambourger, P. D.

1986-01-01

The negative transverse magnetoresistance of high-modulus pitch-based carbon fibers has been measured over the temperature range 1.3-4.2 K at ambient pressure and at 4.2 K under hydrostatic pressure up to 16 kbar. At low fields (less than 0.5 torr) the magnitude of the magnetoresistance increases markedly as the temperature is lowered from 4.2 K to 1.3 K, in disagreement with Bright's theoretical model, and decreases with pressure at the rate -0.6 percent/kbar.

Significant enhancement of magnetoresistance with the reduction of particle size in nanometer scale

Science.gov (United States)

Das, Kalipada; Dasgupta, P.; Poddar, A.; Das, I.

2016-01-01

The Physics of materials with large magnetoresistance (MR), defined as the percentage change of electrical resistance with the application of external magnetic field, has been an active field of research for quite some times. In addition to the fundamental interest, large MR has widespread application that includes the field of magnetic field sensor technology. New materials with large MR is interesting. However it is more appealing to vast scientific community if a method describe to achieve many fold enhancement of MR of already known materials. Our study on several manganite samples [La1−xCaxMnO3 (x = 0.52, 0.54, 0.55)] illustrates the method of significant enhancement of MR with the reduction of the particle size in nanometer scale. Our experimentally observed results are explained by considering model consisted of a charge ordered antiferromagnetic core and a shell having short range ferromagnetic correlation between the uncompensated surface spins in nanoscale regime. The ferromagnetic fractions obtained theoretically in the nanoparticles has been shown to be in the good agreement with the experimental results. The method of several orders of magnitude improvement of the magnetoresistive property will have enormous potential for magnetic field sensor technology. PMID:26837285

Anomalous magnetoresistance in Fibonacci multilayers.

Energy Technology Data Exchange (ETDEWEB)

Machado, L. D.; Bezerra, C. G.; Correa, M. A.; Chesman, C.; Pearson, J. E.; Hoffmann, A. (Materials Science Division); (Universidade Federal do Rio Grande do Norte)

2012-01-01

We theoretically investigated magnetoresistance curves in quasiperiodic magnetic multilayers for two different growth directions, namely, [110] and [100]. We considered identical ferromagnetic layers separated by nonmagnetic layers with two different thicknesses chosen based on the Fibonacci sequence. Using parameters for Fe/Cr multilayers, four terms were included in our description of the magnetic energy: Zeeman, cubic anisotropy, bilinear coupling, and biquadratic coupling. The minimum energy was determined by the gradient method and the equilibrium magnetization directions found were used to calculate magnetoresistance curves. By choosing spacers with a thickness such that biquadratic coupling is stronger than bilinear coupling, unusual behaviors for the magnetoresistance were observed: (i) for the [110] case, there is a different behavior for structures based on even and odd Fibonacci generations, and, more interesting, (ii) for the [100] case, we found magnetic field ranges for which the magnetoresistance increases with magnetic field.

Roll Attitude Determination of Spin Projectile Based on GPS and Magnetoresistive Sensor

Directory of Open Access Journals (Sweden)

Dandan Yuan

2017-01-01

Full Text Available Improvement in attack accuracy of the spin projectiles is a very significant objective, which increases the overall combat efficiency of projectiles. The accurate determination of the projectile roll attitude is the recent objective of the efficient guidance and control. The roll measurement system for the spin projectile is commonly based on the magnetoresistive sensor. It is well known that the magnetoresistive sensor produces a sinusoidally oscillating signal whose frequency slowly decays with time, besides the possibility of blind spot. On the other hand, absolute sensors such as GPS have fixed errors even though the update rates are generally low. To earn the benefit while eliminating weaknesses from both types of sensors, a mathematical model using filtering technique can be designed to integrate the magnetoresistive sensor and GPS measurements. In this paper, a mathematical model is developed to integrate the magnetoresistive sensor and GPS measurements in order to get an accurate prediction of projectile roll attitude in a real flight time. The proposed model is verified using numerical simulations, which illustrated that the accuracy of the roll attitude measurement is improved.

Large magnetoresistance effect in nitrogen-doped silicon

Directory of Open Access Journals (Sweden)

Tao Wang

2017-05-01

Full Text Available In this work, we reported a large magnetoresistance effect in silicon by ion implantation of nitrogen atoms. At room temperature, the magnetoresistance of silicon reaches 125 % under magnetic field 1.7 T and voltage bias -80 V. By applying an alternating magnetic field with a frequency (f of 0.008 Hz, we find that the magnetoresistance of silicon is divided into f and 2f two signal components, which represent the linear and quadratic magnetoresistance effects, respectively. The analysis based on tuning the magnetic field and the voltage bias reveals that electric-field-induced space-charge effect plays an important role to enhance both the linear and quadratic magnetoresistance effects. Observation as well as a comprehensive explanation of large MR in silicon, especially based on semiconductor CMOS implantation technology, will be an important progress towards magnetoelectronic applications.

Seed layer technique for high quality epitaxial manganite films

Directory of Open Access Journals (Sweden)

P. Graziosi

2016-08-01

Full Text Available We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived.

Microstructural, magnetic and transport properties of La{sub 0.5}Pr{sub 0.2}Pb{sub 0.3-x}Sr{sub x}MnO{sub 3} manganites

Energy Technology Data Exchange (ETDEWEB)

Craus, M.-L., E-mail: kraus@nf.jinr.ru [Joint Institute for Nuclear Research, Dubna (Russian Federation); National Institute of Research and Development for Technical Physics, Iasi (Romania); Islamov, A.Kh., E-mail: islamov@nf.jinr.ru [Joint Institute for Nuclear Research, Dubna (Russian Federation); Laboratory of Advanced Research of Membrane Proteins, Moscow Institute of Physics and Technology, Dolgoprudniy (Russian Federation); Anitas, E.M., E-mail: anitas@theor.jinr.ru [Joint Institute for Nuclear Research, Dubna (Russian Federation); Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele (Romania); Cornei, N., E-mail: ncornei@uaic.ro [“Al. I. Cuza” University, Chemistry Department, Iasi (Romania); Luca, D., E-mail: dluca@tuiasi.ro [“Gh. Asachi” Technical University, Faculty of Materials Science and Engineering, Iasi (Romania)

2014-04-01

manganites with x=0.05 and x=0.15 have large intrinsic resistance maxima, generating an important magnetoresistance effect.

Giant magnetoresistance and extraordinary magnetoresistance in inhomogeneous semiconducting DyNiBi

OpenAIRE

Casper, Frederick; Felser, Claudia

2007-01-01

The semiconducting half-Heulser compound DyNiBi shows a negative giant magnetoresistance (GMR) below 200 K. Except for a weak deviation, this magnetoresistance scales roughly with the square of the magnetization in the paramagnetic state, and is related to the metal-insulator transition. At low temperature, a positive magnetoresistance is found, which can be suppressed by high fields. The magnitude of the positive magnetoresistance changes slightly with the amount of impurity phase.

Large rectification magnetoresistance in nonmagnetic Al/Ge/Al heterojunctions.

Science.gov (United States)

Zhang, Kun; Li, Huan-Huan; Grünberg, Peter; Li, Qiang; Ye, Sheng-Tao; Tian, Yu-Feng; Yan, Shi-Shen; Lin, Zhao-Jun; Kang, Shi-Shou; Chen, Yan-Xue; Liu, Guo-Lei; Mei, Liang-Mo

2015-09-21

Magnetoresistance and rectification are two fundamental physical properties of heterojunctions and respectively have wide applications in spintronics devices. Being different from the well known various magnetoresistance effects, here we report a brand new large magnetoresistance that can be regarded as rectification magnetoresistance: the application of a pure small sinusoidal alternating-current to the nonmagnetic Al/Ge Schottky heterojunctions can generate a significant direct-current voltage, and this rectification voltage strongly varies with the external magnetic field. We find that the rectification magnetoresistance in Al/Ge Schottky heterojunctions is as large as 250% at room temperature, which is greatly enhanced as compared with the conventional magnetoresistance of 70%. The findings of rectification magnetoresistance open the way to the new nonmagnetic Ge-based spintronics devices of large rectification magnetoresistance at ambient temperature under the alternating-current due to the simultaneous implementation of the rectification and magnetoresistance in the same devices.

Tunable two-phase coexistence in half-doped manganites

Indian Academy of Sciences (India)

Our recent work on half-doped manganites builds on those ideas to explain our data showing continuously tunable phase coexistence of FM and AFM states. Macroscopic hysteresis across transitions is often used to assert their first-order nature, and this has also been done in the case of half-doped manganites [6]. Kuwa-.

Large, non-saturating magnetoresistance in WTe2.

Science.gov (United States)

Ali, Mazhar N; Xiong, Jun; Flynn, Steven; Tao, Jing; Gibson, Quinn D; Schoop, Leslie M; Liang, Tian; Haldolaarachchige, Neel; Hirschberger, Max; Ong, N P; Cava, R J

2014-10-09

Magnetoresistance is the change in a material's electrical resistance in response to an applied magnetic field. Materials with large magnetoresistance have found use as magnetic sensors, in magnetic memory, and in hard drives at room temperature, and their rarity has motivated many fundamental studies in materials physics at low temperatures. Here we report the observation of an extremely large positive magnetoresistance at low temperatures in the non-magnetic layered transition-metal dichalcogenide WTe2: 452,700 per cent at 4.5 kelvins in a magnetic field of 14.7 teslas, and 13 million per cent at 0.53 kelvins in a magnetic field of 60 teslas. In contrast with other materials, there is no saturation of the magnetoresistance value even at very high applied fields. Determination of the origin and consequences of this effect, and the fabrication of thin films, nanostructures and devices based on the extremely large positive magnetoresistance of WTe2, will represent a significant new direction in the study of magnetoresistivity.

Large anisotropy in colossal magnetoresistance of charge orbital ordered epitaxial Sm(0.5)Ca(0.5)MnO(3) films.

Science.gov (United States)

Chen, Y Z; Sun, J R; Zhao, J L; Wang, J; Shen, B G; Pryds, N

2009-11-04

We investigated the structure and magnetotransport properties of Sm(0.5)Ca(0.5)MnO(3) (SCMO) films epitaxially grown on (011)-oriented SrTiO(3) substrates, which exhibited clear charge/orbital ordering transition. A significant anisotropy of ∼1000 in the colossal magnetoresistance (CMR) effect was observed in the films with a thickness between 50 and 80 nm, which was distinctly different from the basically isotropic CMR effect in bulk SCMO. The large anisotropy in the CMR can be ascribed to the intrinsic asymmetric strain in the film, which plays an important role in tuning the spin-orbit coupling in manganite films. The origin of the peculiar CMR effect is discussed.

Giant superconductivity-induced modulation of the ferromagnetic magnetization in a cuprate-manganite superlattice.

Science.gov (United States)

Hoppler, J; Stahn, J; Niedermayer, Ch; Malik, V K; Bouyanfif, H; Drew, A J; Rössle, M; Buzdin, A; Cristiani, G; Habermeier, H-U; Keimer, B; Bernhard, C

2009-04-01

Artificial multilayers offer unique opportunities for combining materials with antagonistic orders such as superconductivity and ferromagnetism and thus to realize novel quantum states. In particular, oxide multilayers enable the utilization of the high superconducting transition temperature of the cuprates and the versatile magnetic properties of the colossal-magnetoresistance manganites. However, apart from exploratory work, the in-depth investigation of their unusual properties has only just begun. Here we present neutron reflectometry measurements of a [Y(0.6)Pr(0.4)Ba(2)Cu(3)O(7) (10 nm)/La(2/3)Ca(1/3)MnO(3) (10 nm)](10) superlattice, which reveal a surprisingly large superconductivity-induced modulation of the vertical ferromagnetic magnetization profile. Most surprisingly, this modulation seems to involve the density rather than the orientation of the magnetization and is highly susceptible to the strain, which is transmitted from the SrTiO(3) substrate. We outline a possible explanation of this unusual superconductivity-induced phenomenon in terms of a phase separation between ferromagnetic and non-ferromagnetic nanodomains in the La(2/3)Ca(1/3)MnO(3) layers.

A device model framework for magnetoresistive sensors based on the Stoner–Wohlfarth model

International Nuclear Information System (INIS)

Bruckner, Florian; Bergmair, Bernhard; Brueckl, Hubert; Palmesi, Pietro; Buder, Anton; Satz, Armin; Suess, Dieter

2015-01-01

The Stoner–Wohlfarth (SW) model provides an efficient analytical model to describe the behavior of magnetic layers within magnetoresistive sensors. Combined with a proper description of magneto-resistivity an efficient device model can be derived, which is necessary for an optimal electric circuit design. Parameters of the model are determined by global optimization of an application specific cost function which contains measured resistances for different applied fields. Several application cases are examined and used for validation of the device model. - Highlights: • An efficient device model framework for various types of magnetoresistive sensors is presented. • The model is based on the analytical solution of the Stoner–Wohlfarth model. • Numerical optimization methods provide optimal model parameters for a different application cases. • The model is applied to several application cases and is able to reproduce measured hysteresis and swiching behavior

Large magnetoresistance tunnelling through a magnetically modulated nanostructure

International Nuclear Information System (INIS)

Lu Maowang; Zhang Lide

2003-01-01

Based on a combination of an inhomogeneous magnetic field and a two-dimensional electron gas, we have constructed a giant magnetoresistance nanostructure, which can be realized experimentally by the deposition of two parallel ferromagnetic strips on top of a semiconductor heterostructure. We have theoretically studied the magnetoresistance for electrons tunnelling through this nanostructure. It is shown that there exists a significant transmission difference between the parallel and antiparallel magnetization configurations, which leads to a large magnetoresistance. It is also shown that the magnetoresistance ratio strongly depends not only on incident electronic energy but also on the ferromagnetic strips, and thus a much larger magnetoresistance ratio can be obtained by properly fabricating the ferromagnetic strips in the system

Magnetoimpedance effect in manganite La2/3Ba1/3MnO3 at various temperatures

International Nuclear Information System (INIS)

Hu Jifan; Qin Hongwei; Niu Hongdong; Zhu Luming; Chen Juan; Xiao Weiwei; Pei Yu

2003-01-01

In the present work, the magnetoimpedance (MI) effect for the manganite La 2/3 Ba 1/3 MnO 3 at various temperatures was reported. At a lower frequency such as f=100 kHz, the metal-insulator transition temperature T MI deduced from the peak in the temperature dependence of the AC impedance Z is very close to the value obtained from the DC resistance case, meanwhile there exists a peak of the MI ΔZ/Z 0 near the T MI . Similar to the case of DC colossal magnetoresistance effect, the T MI in MI effect can be shifted to a high temperature under application of a DC field. At a higher frequency such as f=23 MHz, a valley of the impedance Z dominated by the term of the reactance X occurs at the T MI , which can be moved by a field. The impedance Z increases with increasing AC frequency due to the skin effect. The variation of the resistance R with AC frequency strongly depends on the temperature. Below the T MI , the R increases with frequency. Above the T MI , with increasing AC frequency the R increases slightly at first, undergoes a valley, and finally increases again. Our present results imply that the interplay between the double-exchange effect and the electron-phonon coupling may also involve in the MI effect of the manganites, in addition to the variation of penetration depth via the permeability and conductivity under the application of DC fields

Magneto-caloric and magneto-resistive properties of La0.67Ca0.33-xSrxMnO3

International Nuclear Information System (INIS)

Reves Dinesen, Anders

2004-08-01

This thesis presents results of an experimental investigation of magneto-caloric and magneto-resistive properties of a series of polycrystalline Ca- and Sr-doped lanthanum manganites, La 0.67 Ca 0.33-x Sr x MnO 3 (0≤ x ≤ 0.33), with the perovskite structure. The samples consisted of sintered oxide powders prepared the glycine-nitrate combustion technique. The compounds were ferromagnetic and showed a Curie transition in the temperature range 267370 K (T C increased with increasing x). An analysis of the structural properties was carried out by means of x-ray diffraction and the Rietveld technique. The variation of the Ca/Sr ratio was found to cause a transition from orthorhombic to rhombohedral symmetry in the composition range 0.110 0.67 Ca 0.33-x Sr x MnO 3 samples was measured directly and indirectly (by means of magnetization measurements). All the samples showed a magnetocaloric effect in the vicinity of T C . A model for the mag-netocaloric effect based on Weiss mean field theory and classical theories for heat capacities was developed. The model provided reasonable predictions of the magneto-caloric properties of the samples. The compounds with low Sr content showed a magnetocaloric effect comparable to that of Gadolinium, the prototypical working material for magnetic refrigeration at room temperature. A less comprehensive part of the investigation regarded the magneto-resistive properties of the La 0.67 Ca 0.33-x Sr x MnO 3 system. It was found that th polycrystalline nature of the compounds played a decisive role for the magnetotransport properties. Characteristic grain boundary effects, such as a low-field magnetoresistance, which is absent in single-crystalline perovskites, were observed. The low-field effect is usually ascribed to spin-dependent scattering in grain boundaries. Qualitatively the results obtained for the La 0.67 Ca 0.33-x Sr x MnO 3 samples were consistent with this model. The resistivity contribution arising from the presence of

Current perpendicular to plane giant magnetoresistance and tunneling magnetoresistance treated with unified model

NARCIS (Netherlands)

Jonkers, PAE

2002-01-01

The conceptual similarity between current perpendicular to plane giant magnetoresistance (CPP-GMR) and tunneling magnetoresistance (TMR) is exploited by utilizing a unified single-particle model accounting for both types of magnetoresistance. By defining structures composed of ferromagnetic,

Transport-entropy correlations in La0.7Ca0.3MnO3 manganite

International Nuclear Information System (INIS)

Debnath, J.C.; Strydom, A.M.

2014-01-01

An investigation of the magnetic entropy change ΔS M and resistivity ρ, and the relation between them, for La 0.7 Ca 0.3 MnO 3 (LCMO) material has been presented. By using an equation of the form ΔS M =−α∫ 0 H [(δln(ρ))/(δT) ] H dH (α=9.98 emu/g), which relates magnetic order to transport behavior of the compounds, we measure the magnetic entropy change ΔS M from the resistivity measurement, where the resistivity results agree quite well with the fitting parameter α=9.98 emu/g in the intermediate temperature range. This result reveals the predominant role of magnetic polarons on the magnetoresistive property of manganites. It is obvious that magnetic disorder, characterized by ΔS M , affects the magnetic polarons, while the magnetic polarons influence the electronic transport properties, which may be the underlying reason for a salient ΔS M −ρ relation. It also provides an alternative method to determine magnetic entropy change on the basis of resistive measurements

Quasi-Particle Relaxation and Quantum Femtosecond Magnetism in Non-Equilibrium Phases of Insulating Manganites

Science.gov (United States)

Perakis, Ilias; Kapetanakis, Myron; Lingos, Panagiotis; Barmparis, George; Patz, A.; Li, T.; Wang, Jigang

We study the role of spin quantum fluctuations driven by photoelectrons during 100fs photo-excitation of colossal magneto-resistive manganites in anti-ferromagnetic (AFM) charge-ordered insulating states with Jahn-Teller distortions. Our mean-field calculation of composite fermion excitations demonstrates that spin fluctuations reduce the energy gap by quasi-instantaneously deforming the AFM background, thus opening a conductive electronic pathway via FM correlation. We obtain two quasi-particle bands with distinct spin-charge dynamics and dependence on lattice distortions. To connect with fs-resolved spectroscopy experiments, we note the emergence of fs magnetization in the low-temperature magneto-optical signal, with threshold dependence on laser intensity characteristic of a photo-induced phase transition. Simultaneously, the differential reflectivity shows bi-exponential relaxation, with fs component, small at low intensity, exceeding ps component above threshold for fs AFM-to-FM switching. This suggests the emergence of a non-equilibrium metallic FM phase prior to establishment of a new lattice structure, linked with quantum magnetism via spin/charge/lattice couplings for weak magnetic fields.

Low field magnetoresistance in a 2D topological insulator based on wide HgTe quantum well.

Science.gov (United States)

Olshanetsky, E B; Kvon, Z D; Gusev, G M; Mikhailov, N N; Dvoretsky, S A

2016-09-01

Low field magnetoresistance is experimentally studied in a two-dimensional topological insulator (TI) in both diffusive and quasiballistic samples fabricated on top of a wide (14 nm) HgTe quantum well. In all cases a pronounced quasi-linear positive magnetoresistance is observed similar to that found previously in diffusive samples based on a narrow (8 nm) HgTe well. The experimental results are compared with the main existing theoretical models based on different types of disorder: sample edge roughness, nonmagnetic disorder in an otherwise coherent TI and metallic puddles due to locally trapped charges that act like local gate on the sample. The quasiballistic samples with resistance close to the expected quantized values also show a positive low-field magnetoresistance but with a pronounced admixture of mesoscopic effects.

Tunneling anisotropic magnetoresistance driven by magnetic phase transition.

Science.gov (United States)

Chen, X Z; Feng, J F; Wang, Z C; Zhang, J; Zhong, X Y; Song, C; Jin, L; Zhang, B; Li, F; Jiang, M; Tan, Y Z; Zhou, X J; Shi, G Y; Zhou, X F; Han, X D; Mao, S C; Chen, Y H; Han, X F; Pan, F

2017-09-06

The independent control of two magnetic electrodes and spin-coherent transport in magnetic tunnel junctions are strictly required for tunneling magnetoresistance, while junctions with only one ferromagnetic electrode exhibit tunneling anisotropic magnetoresistance dependent on the anisotropic density of states with no room temperature performance so far. Here, we report an alternative approach to obtaining tunneling anisotropic magnetoresistance in α'-FeRh-based junctions driven by the magnetic phase transition of α'-FeRh and resultantly large variation of the density of states in the vicinity of MgO tunneling barrier, referred to as phase transition tunneling anisotropic magnetoresistance. The junctions with only one α'-FeRh magnetic electrode show a magnetoresistance ratio up to 20% at room temperature. Both the polarity and magnitude of the phase transition tunneling anisotropic magnetoresistance can be modulated by interfacial engineering at the α'-FeRh/MgO interface. Besides the fundamental significance, our finding might add a different dimension to magnetic random access memory and antiferromagnet spintronics.Tunneling anisotropic magnetoresistance is promising for next generation memory devices but limited by the low efficiency and functioning temperature. Here the authors achieved 20% tunneling anisotropic magnetoresistance at room temperature in magnetic tunnel junctions with one α'-FeRh magnetic electrode.

Magnetic anisotropy and magnetoresistance in Co-based multilayers: a polarised neutron reflectivity study

International Nuclear Information System (INIS)

Yusuf, S.M.

2000-01-01

We have studied giant magnetoresistance (GMR) and anisotropic magnetoresistance (AMR) effects by carrying out magnetization, magnetoresistance and polarized neutron reflectivity measurements on epitaxial Co/Re multilayers. Polarized neutron reflectivity study with polarization analysis gives a direct way to sense the direction of sublattice magnetization and coupling between magnetic layers. The evolution of magnetic structure as a function of the strength and direction of the applied magnetic field has been studied. The AMR effect observed in magnetoresistance study has been explained in the light of observed magnetic structure. (author)

Anisotropic magnetoresistance and spin polarization of La0.7Sr0.3MnO3/SrTiO3 superlattices

International Nuclear Information System (INIS)

Wang, L.M.; Guo, C.-C.

2005-01-01

The crystalline structure, anisotropic magnetoresistance (AMR), and magnetization of La 0.7 Sr 0.3 MnO 3 /SrTiO 3 (LSMO/STO) superlattices grown by a rf sputtering system are systematically analyzed to study the spin polarization of manganite at interfaces. The presence of positive low-temperature AMR in LSMO/STO superlattices implies that two bands of majority and minority character contribute to the transport properties, leading to a reduced spin polarization. Furthermore, the magnetization of superlattices follows the T 3/2 law and decays more quickly as the thickness ratio d STO /d LSMO increases, corresponding to a reduced exchange coupling. The results clearly show that the spin polarization is strongly correlated with the influence of interface-induced strain on the structure

Wheatstone bridge giant-magnetoresistance based cell counter.

Science.gov (United States)

Lee, Chiun-Peng; Lai, Mei-Feng; Huang, Hao-Ting; Lin, Chi-Wen; Wei, Zung-Hang

2014-07-15

A Wheatstone bridge giant magnetoresistance (GMR) biosensor was proposed here for the detection and counting of magnetic cells. The biosensor was made of a top-pinned spin-valve layer structure, and it was integrated with a microchannel possessing the function of hydrodynamic focusing that allowed the cells to flow in series one by one and ensured the accuracy of detection. Through measuring the magnetoresistance variation caused by the stray field of the magnetic cells that flowed through the microchannel above the GMR biosensor, we can not only detect and count the cells but we can also recognize cells with different magnetic moments. In addition, a magnetic field gradient was applied for the separation of different cells into different channels. Copyright © 2014 Elsevier B.V. All rights reserved.

Probing giant magnetoresistance with THz spectroscopy

DEFF Research Database (Denmark)

Jin, Zuanming; Tkach, Alexander; Casper, Frederick

2014-01-01

We observe a giant magnetoresistance effect in CoFe/Cu-based multistack using THz time-domain spectroscopy. The magnetic field-dependent dc conductivity, electron scattering time, as well as spin-asymmetry parameter of the structure are successfully determined. © 2014 OSA.......We observe a giant magnetoresistance effect in CoFe/Cu-based multistack using THz time-domain spectroscopy. The magnetic field-dependent dc conductivity, electron scattering time, as well as spin-asymmetry parameter of the structure are successfully determined. © 2014 OSA....

Magnetoresistance anisotropy of ultrathin epitaxial La0.83Sr0.17MnO3 films

Science.gov (United States)

Balevičius, Saulius; Tornau, Evaldas E.; ŽurauskienÄ--, Nerija; Stankevič, Voitech; Šimkevičius, Česlovas; TolvaišienÄ--, Sonata; PlaušinaitienÄ--, Valentina; Abrutis, Adulfas

2017-12-01

We present the study of temperature dependence of resistivity (ρ), magnetoresistance (MR), and magnetoresistance anisotropy (AMR) of thin epitaxial La0.83Sr0.17MnO3 films. The films with thickness from 4 nm to 140 nm were grown on an NdGaO3 (001) substrate by a pulsed injection metal organic chemical vapor deposition technique. We demonstrate that the resistivity of these films significantly increases and the temperature Tm of the resistivity maximum in ρ(T) dependence decreases with the decrease of film thickness. The anisotropy of ρ(T) dependence with respect to the electrical current direction along the [100] or [010] crystallographic axis of the film is found for ultrathin films (4-8 nm) at temperatures close to Tm. Both MR and AMR, measured in magnetic fields up to 0.7 T applied in the film plane parallel and perpendicular to the current direction, have shown strong dependence on the film thickness. It was also found that the anisotropy of magnetoresistance could change its sign from positive (thicker films) to negative (ultrathin films) and obtain very small values at a certain intermediate thickness (20 nm) when the current is flowing perpendicular to the easy magnetization axis [010]. While the positive AMR effect was assigned to the conventional magnetic ordering of manganites, the AMR of ultrathin films was influenced by the pinning of magnetization to the easy axis. The temperature dependence and change of the AMR sign with film thickness is shown to be well described by the two-region model (more strained closer to the film substrate and more relaxed further from it) assuming that the relative concentration of both regions changes with the film thickness. The possibility to use the effect of the AMR compensation for the development of scalar in-plane magnetic field sensors is discussed.

Characteristic features of the magnetoresistance in the ferrimagnetic (Sr2FeMoO6-δ) - dielectric (SrMoO4) nanocomposite

Science.gov (United States)

Demyanov, S.; Kalanda, N.; Yarmolich, M.; Petrov, A.; Lee, S.-H.; Yu, S.-C.; Oh, S. K.; Kim, D.-H.

2018-05-01

Magnetic metal-oxide compounds with high values of magnetoresistance (MR) have attracted huge interest for spintronic applications, among which Sr2FeMoO6-δ (SFMO) has been relatively less known compared to the cobaltites and manganites, despite 100% electrons spin-polarization degree and a high Curie temperature. Here, stable fabrication and systematic analysis of nanocomposites based on SFMO with SrMoO4 dielectric sheaths are presented. SFMO-SrMoO4 nanocomposites were fabricated as follows: synthesis of the SFMO single-phase nanopowders by the modified citrate-gel technique; compaction under high pressure; thermal treatment for sheaths formation around grains. The nanocomposite is observed to exhibit a transitional behavior of conductivity from metallic, which is characteristic for the SFMO to semiconductor one in the temperature range 4 - 300K under magnetic fields up to 10T. A negative MR is observed due to the spin-polarized charge carriers tunneling through dielectric sheaths. MR value reaches 43% under 8T at 10κ. The dielectric sheaths thickness was determined to be about 10 nm by electric breakdown voltage value at current-voltage characteristics curves. The breakdown is found to be a reversible process determined by collisional ionization of dielectric atoms in strong electric field depending on knocked-out electrons from the SrMoO4. It was found that MR changes sign in electric breakdown region, revealing the giant magnetoresistive properties.

Magnetic phase transitions in the anion-deficient La sub 1 sub - sub x Ba sub x MnO sub 3 sub - sub x sub / sub 2 (0 <= x <= 0.50) manganites

CERN Document Server

Trukhanov, S V; Bushinsky, M V; Troyanchuk, I O; Szymczak, H

2003-01-01

The crystal structure, magnetization and electrical resistivity properties of the anion-deficient La sub 1 sub - sub x Ba sub x MnO sub 3 sub - sub x sub / sub 2 (0 = 0.03) being a mixture of antiferromagnetic and ferromagnetic phases. At x >= 0.12 competition between antiferromagnetic and ferromagnetic interactions leads to a cluster spin glass state appearance with a magnetic moment freezing temperature of approx 45 K. The dominant magnetic phase for x >= 0.22 is supposed to be antiferromagnetic. All the reduced samples are semiconductors and show considerable magnetoresistance over a wide temperature range in a magnetically ordered state. The largest magnetoresistance (approx 34% in a 9 kOe field at liquid nitrogen temperatures) is observed for an x = 0.30 sample. The magnetic phase diagram of La sub 1 sub - sub x sup 3 sup + Ba sub x sup 2 sup + Mn sup 3 sup + O sub 3 sub - sub x sub / sub 2 sup 2 sup - manganites has been established by combining the results of magnetic and electrical measurements. The r...

Structural phase transition at the percolation threshold in epitaxial (La0.7Ca0.3MnO3)1-x:(MgO)x nanocomposite films.

Science.gov (United States)

Moshnyaga, V; Damaschke, B; Shapoval, O; Belenchuk, A; Faupel, J; Lebedev, O I; Verbeeck, J; van Tendeloo, G; Mücksch, M; Tsurkan, V; Tidecks, R; Samwer, K

2003-04-01

'Colossal magnetoresistance' in perovskite manganites such as La0.7Ca0.3MnO3 (LCMO), is caused by the interplay of ferro-paramagnetic, metal-insulator and structural phase transitions. Moreover, different electronic phases can coexist on a very fine scale resulting in percolative electron transport. Here we report on (LCMO)1-x:(MgO)x (0 strain. The largest colossal magnetoresistance of 10(5)% was observed at the percolation threshold in the conductivity at xc 0.3, which is coupled to a structural phase transition from orthorhombic (0 < x < or 0.1) to rhombohedral R3c structure (0.33 < or = x < or = 0.8). An increase of the Curie temperature for the Rc phase was observed. These results may provide a general method for controlling the magnetotransport properties of manganite-based composite films by appropriate choice of the second phase.

Solid oxide fuel cell (SOFC) materials

CERN Document Server

Saravanan, R

2018-01-01

Developing materials for SOFC applications is one of the key topics in energy research. The book focuses on manganite structured materials, such as doped lanthanum chromites and lanthanum manganites, which have interesting properties: thermal and chemical stability, mixed ionic and electrical conductivity, electrocatalytic activity, magnetocaloric property and colossal magnetoresistance (CMR).

Magnetocaloric and magnetoresistive properties of La0.67Ca0.33-xSrxMnO3

DEFF Research Database (Denmark)

Dinesen, Anders Reves

This thesis presents results of an experimental investigation of magneto-caloric and magnetoresistive properties of a series of polycrystalline Ca- and Sr-doped lanthanum manganites, La0.67Ca0.33-xSrxMnO3 (0=x=0.33 ), with the perovskite structure. The samples consisted of sintered oxide powders...... prepared the glycine-nitrate combustion technique. The compounds were ferromagnetic and showed a Curie transition in the temperature range 267–370 K (TC increased with increasing x). An analysis of the structural properties was carried out by means of x-ray diffraction and the Rietveld technique...... and the Curie temperature. The Mn–O–Mn bonds mediate ferromagnetism and electrical transport in these materials via the double-exchange mechanism. The magnetocaloric effect of the La0.67Ca0.33-xSrxMnO3 samples was measured directly and indirectly (by means of magnetization measurements). All the samples showed...

Extremely large magnetoresistance in few-layer graphene/boron-nitride heterostructures.

Science.gov (United States)

Gopinadhan, Kalon; Shin, Young Jun; Jalil, Rashid; Venkatesan, Thirumalai; Geim, Andre K; Castro Neto, Antonio H; Yang, Hyunsoo

2015-09-21

Understanding magnetoresistance, the change in electrical resistance under an external magnetic field, at the atomic level is of great interest both fundamentally and technologically. Graphene and other two-dimensional layered materials provide an unprecedented opportunity to explore magnetoresistance at its nascent stage of structural formation. Here we report an extremely large local magnetoresistance of ∼2,000% at 400 K and a non-local magnetoresistance of >90,000% in an applied magnetic field of 9 T at 300 K in few-layer graphene/boron-nitride heterostructures. The local magnetoresistance is understood to arise from large differential transport parameters, such as the carrier mobility, across various layers of few-layer graphene upon a normal magnetic field, whereas the non-local magnetoresistance is due to the magnetic field induced Ettingshausen-Nernst effect. Non-local magnetoresistance suggests the possibility of a graphene-based gate tunable thermal switch. In addition, our results demonstrate that graphene heterostructures may be promising for magnetic field sensing applications.

Transverse thermal magnetoresistance of potassium

International Nuclear Information System (INIS)

Newrock, R.S.; Maxfield, B.W.

1976-01-01

Results are presented of extensive thermal magnetoresistance measurements on single-crystal and polycrystalline specimens of potassium having residual resistance ratios (RRR) ranging from 1100 to 5300. Measurements were made between 2 and 9 0 K for magnetic fields up to 1.8 T. The observed thermal magnetoresistance cannot be understood on the basis of either semiclassical theories or from the electrical magnetoresistance and the Wiedemann-Franz law. A number of relationships are observed between the thermal and electrical magnetoresistances, many of which are not immediately obvious when comparing direct experimental observations. The thermal magnetoresistance W(T,H) is given reasonably well by W(T,H)T = W(T,0)T + AH + BH 2 , where both A and B are temperature-dependent coefficients. Results show that A = A 0 + A 1 T 3 , while B(T) cannot be expressed as any simple power law. A 0 is dependent on the RRR, while A 1 is independent of the RRR. Two relationships are found between corresponding coefficients in the electrical and thermal magnetoresistance: (i) the Wiedmann--Franz law relates A 0 to the Kohler slope of the electrical magnetoresistance and (ii) the temperature-dependent portions of the electrical and thermal Kohler slopes are both proportional to the electron--phonon scattering contribution to the corresponding zero-field resistance. The latter provides evidence that inelastic scattering is very important in determining the temperature-dependent linear magnetoresistances. Part, but by no means all, of the quadratic thermal resistance is accounted for by lattice thermal conduction. It is concluded that at least a portion of the anomalous electrical and thermal magnetoresistances is due to intrinsic causes and not inhomogeneities or other macroscopic defects

Pramana – Journal of Physics | Indian Academy of Sciences

Indian Academy of Sciences (India)

Rare earth manganites doped with alkaline earths, namely Re1-AMnO3, exhibit colossal magnetoresistance, metal insulator transitions, competing magnetic, orbital and charge ordering, and many other interesting but poorly understood phenomena. In this article I outline our recent theory based on the idea that in the ...

Microscopic theory of longitudinal sound velocity in charge ordered manganites

International Nuclear Information System (INIS)

Rout, G C; Panda, S

2009-01-01

A microscopic theory of longitudinal sound velocity in a manganite system is reported here. The manganite system is described by a model Hamiltonian consisting of charge density wave (CDW) interaction in the e g band, an exchange interaction between spins of the itinerant e g band electrons and the core t 2g electrons, and the Heisenberg interaction of the core level spins. The magnetization and the CDW order parameters are considered within mean-field approximations. The phonon Green's function was calculated by Zubarev's technique and hence the longitudinal velocity of sound was finally calculated for the manganite system. The results show that the elastic spring involved in the velocity of sound exhibits strong stiffening in the CDW phase with a decrease in temperature as observed in experiments.

Microscopic theory of longitudinal sound velocity in charge ordered manganites

Energy Technology Data Exchange (ETDEWEB)

Rout, G C [Condensed Matter Physics Group, PG Department of Applied Physics and Ballistics, FM University, Balasore 756 019 (India); Panda, S, E-mail: gcr@iopb.res.i [Trident Academy of Technology, F2/A, Chandaka Industrial Estate, Bhubaneswar 751 024 (India)

2009-10-14

A microscopic theory of longitudinal sound velocity in a manganite system is reported here. The manganite system is described by a model Hamiltonian consisting of charge density wave (CDW) interaction in the e{sub g} band, an exchange interaction between spins of the itinerant e{sub g} band electrons and the core t{sub 2g} electrons, and the Heisenberg interaction of the core level spins. The magnetization and the CDW order parameters are considered within mean-field approximations. The phonon Green's function was calculated by Zubarev's technique and hence the longitudinal velocity of sound was finally calculated for the manganite system. The results show that the elastic spring involved in the velocity of sound exhibits strong stiffening in the CDW phase with a decrease in temperature as observed in experiments.

Multiferroic nature of charge-ordered rare earth manganites

International Nuclear Information System (INIS)

Serrao, Claudy Rayan; Sundaresan, A; Rao, C N R

2007-01-01

Charge-ordered rare earth manganites Nd 0.5 Ca 0.5 MnO 3 ,La 0.25 Nd 0.25 Ca 0.5 MnO 3 , Pr 0.7 Ca 0.3 MnO 3 and Pr 0.6 Ca 0.4 MnO 3 are found to exhibit dielectric constant anomalies around the charge-ordering or the antiferromagnetic transition temperatures. Magnetic fields have a marked effect on the dielectric properties, indicating the presence of coupling between the magnetic and electrical order parameters. The observation of magnetoferroelectricity in these manganites is in accord with the recent theoretical predictions of Khomskii and co-workers

Gate-tunable large magnetoresistance in an all-semiconductor spin valve device.

Science.gov (United States)

Oltscher, M; Eberle, F; Kuczmik, T; Bayer, A; Schuh, D; Bougeard, D; Ciorga, M; Weiss, D

2017-11-27

A large spin-dependent and electric field-tunable magnetoresistance of a two-dimensional electron system is a key ingredient for the realization of many novel concepts for spin-based electronic devices. The low magnetoresistance observed during the last few decades in devices with lateral semiconducting transport channels between ferromagnetic source and drain contacts has been the main obstacle for realizing spin field effect transistor proposals. Here, we show both a large two-terminal magnetoresistance in a lateral spin valve device with a two-dimensional channel, with up to 80% resistance change, and tunability of the magnetoresistance by an electric gate. The enhanced magnetoresistance is due to finite electric field effects at the contact interface, which boost spin-to-charge conversion. The gating scheme that we use is based on switching between uni- and bidirectional spin diffusion, without resorting to spin-orbit coupling. Therefore, it can also be employed in materials with low spin-orbit coupling.

Rashba-Edelstein Magnetoresistance in Metallic Heterostructures.

Science.gov (United States)

Nakayama, Hiroyasu; Kanno, Yusuke; An, Hongyu; Tashiro, Takaharu; Haku, Satoshi; Nomura, Akiyo; Ando, Kazuya

2016-09-09

We report the observation of magnetoresistance originating from Rashba spin-orbit coupling (SOC) in a metallic heterostructure: the Rashba-Edelstein (RE) magnetoresistance. We show that the simultaneous action of the direct and inverse RE effects in a Bi/Ag/CoFeB trilayer couples current-induced spin accumulation to the electric resistance. The electric resistance changes with the magnetic-field angle, reminiscent of the spin Hall magnetoresistance, despite the fact that bulk SOC is not responsible for the magnetoresistance. We further found that, even when the magnetization is saturated, the resistance increases with increasing the magnetic-field strength, which is attributed to the Hanle magnetoresistance in this system.

Highly Sensitive Flexible Magnetic Sensor Based on Anisotropic Magnetoresistance Effect.

Science.gov (United States)

Wang, Zhiguang; Wang, Xinjun; Li, Menghui; Gao, Yuan; Hu, Zhongqiang; Nan, Tianxiang; Liang, Xianfeng; Chen, Huaihao; Yang, Jia; Cash, Syd; Sun, Nian-Xiang

2016-11-01

A highly sensitive flexible magnetic sensor based on the anisotropic magnetoresistance effect is fabricated. A limit of detection of 150 nT is observed and excellent deformation stability is achieved after wrapping of the flexible sensor, with bending radii down to 5 mm. The flexible AMR sensor is used to read a magnetic pattern with a thickness of 10 μm that is formed by ferrite magnetic inks. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fast Magnetoresistive Random-Access Memory

Science.gov (United States)

Wu, Jiin-Chuan; Stadler, Henry L.; Katti, Romney R.

1991-01-01

Magnetoresistive binary digital memories of proposed new type expected to feature high speed, nonvolatility, ability to withstand ionizing radiation, high density, and low power. In memory cell, magnetoresistive effect exploited more efficiently by use of ferromagnetic material to store datum and adjacent magnetoresistive material to sense datum for readout. Because relative change in sensed resistance between "zero" and "one" states greater, shorter sampling and readout access times achievable.

Anomalous magnetoresistance in amorphous metals

International Nuclear Information System (INIS)

Kuz'menko, V.M.; Vladychkin, A.N.; Mel'nikov, V.I.; Sudovtsev, A.I.

1984-01-01

The magnetoresistance of amorphous Bi, Ca, V and Yb films is investigated in fields up to 4 T at low temperatures. For all metals the magnetoresistance is positive, sharply decreases with growth of temperature and depends anomalously on the magnetic field strength. For amorphous superconductors the results agree satisfactorily with the theory of anomalous magnetoresistance in which allowance is made for scattering of electrons by the superconducting fluctuations

Giant magnetoresistance through a single molecule.

Science.gov (United States)

Schmaus, Stefan; Bagrets, Alexei; Nahas, Yasmine; Yamada, Toyo K; Bork, Annika; Bowen, Martin; Beaurepaire, Eric; Evers, Ferdinand; Wulfhekel, Wulf

2011-03-01

Magnetoresistance is a change in the resistance of a material system caused by an applied magnetic field. Giant magnetoresistance occurs in structures containing ferromagnetic contacts separated by a metallic non-magnetic spacer, and is now the basis of read heads for hard drives and for new forms of random access memory. Using an insulator (for example, a molecular thin film) rather than a metal as the spacer gives rise to tunnelling magnetoresistance, which typically produces a larger change in resistance for a given magnetic field strength, but also yields higher resistances, which are a disadvantage for real device operation. Here, we demonstrate giant magnetoresistance across a single, non-magnetic hydrogen phthalocyanine molecule contacted by the ferromagnetic tip of a scanning tunnelling microscope. We measure the magnetoresistance to be 60% and the conductance to be 0.26G(0), where G(0) is the quantum of conductance. Theoretical analysis identifies spin-dependent hybridization of molecular and electrode orbitals as the cause of the large magnetoresistance.

Magnetically induced electrical transport and dielectric properties of 3d transition elemental substitution at the Mn-site in Nd0.67Ba0.33MnO3 manganites

Science.gov (United States)

Sudakshina, B.; Arun, B.; Chandrasekhar, K. Devi; Yang, H. D.; Vasundhara, M.

2018-05-01

We have investigated the temperature dependence of electrical transport and dielectric properties along with magnetoresistance and magneto dielectric behavior in Nd0.67Ba0.33Mn0.9TR0.1O3 (TR= Cr, Fe, Co, Ni, Cu) manganites. All the compounds crystallized into an orthorhombic structure with Imma space group. Nd0.67Ba0.33MnO3 shows insulating to metallic behavior at intermediate temperatures, but, with the substitution of transitional elements it shows insulating in nature, down to lowest temperature measured for all the compounds. Dielectric measurement shows the intrinsic behavior of these lossy materials. A large value of magneto resistance is obtained for all the compounds and considerable amount of magneto-dielectric effect is shown for all the substituted compounds at lower temperatures.

Controlled lateral anisotropy in correlated manganite heterostructures by interface-engineered oxygen octahedral coupling

NARCIS (Netherlands)

Liao, Zhaoliang; Huijben, Mark; Zhong, Z.; Gauquelin, N.; Macke, S.; Green, R.J.; van Aert, S.; Verbeeck, J.; van Tendeloo, G.; Held, K.; Sawatzky, G.A.; Koster, Gertjan; Rijnders, Augustinus J.H.M.

2016-01-01

Controlled in-plane rotation of the magnetic easy axis in manganite heterostructures by tailoring the interface oxygen network could allow the development of correlated oxide-based magnetic tunnelling junctions with non-collinear magnetization, with possible practical applications as miniaturized

Electric field tuning of phase separation in manganite thin films

KAUST Repository

Lourembam, James; Wu, Jianchun; Ding, Junfeng; Lin, Weinan; Wu, Tao

2014-01-01

In this paper, we investigate the electric field effect on epitaxial Pr0.65(Ca0.75Sr0.25)0.35MnO3 thin films in electric double-layer transistors. Different from the conventional transistors with semiconducting channels, the sub(micrometer)-scale phase separation in the manganite channels is expected to result in inhomogeneous distribution of mobile carriers and local enhancement of electric field. The field effect is much larger in the low-temperature phase separation region compared to that in the high-temperature polaron transport region. Further enhancement of electroresistance is achieved by applying a magnetic field, and a 250% modulation of resistance is observed at 80 K, equivalent to an increase of the ferromagnetic metallic phase fraction by 0.51%, as estimated by the general effective medium model. Our results illustrate the complementary nature of electric and magnetic field effects in phase-separated manganites, providing insights on such novel electronic devices based on complex oxides.

Electric field tuning of phase separation in manganite thin films

KAUST Repository

Lourembam, James

2014-01-29

In this paper, we investigate the electric field effect on epitaxial Pr0.65(Ca0.75Sr0.25)0.35MnO3 thin films in electric double-layer transistors. Different from the conventional transistors with semiconducting channels, the sub(micrometer)-scale phase separation in the manganite channels is expected to result in inhomogeneous distribution of mobile carriers and local enhancement of electric field. The field effect is much larger in the low-temperature phase separation region compared to that in the high-temperature polaron transport region. Further enhancement of electroresistance is achieved by applying a magnetic field, and a 250% modulation of resistance is observed at 80 K, equivalent to an increase of the ferromagnetic metallic phase fraction by 0.51%, as estimated by the general effective medium model. Our results illustrate the complementary nature of electric and magnetic field effects in phase-separated manganites, providing insights on such novel electronic devices based on complex oxides.

Optically Tunable Magnetoresistance Effect: From Mechanism to Novel Device Application.

Science.gov (United States)

Liu, Pan; Lin, Xiaoyang; Xu, Yong; Zhang, Boyu; Si, Zhizhong; Cao, Kaihua; Wei, Jiaqi; Zhao, Weisheng

2017-12-28

The magnetoresistance effect in sandwiched structure describes the appreciable magnetoresistance effect of a device with a stacking of two ferromagnetic layers separated by a non-magnetic layer (i.e., a sandwiched structure). The development of this effect has led to the revolution of memory applications during the past decades. In this review, we revisited the magnetoresistance effect and the interlayer exchange coupling (IEC) effect in magnetic sandwiched structures with a spacer layer of non-magnetic metal, semiconductor or organic thin film. We then discussed the optical modulation of this effect via different methods. Finally, we discuss various applications of these effects and present a perspective to realize ultralow-power, high-speed data writing and inter-chip connection based on this tunable magnetoresistance effect.

Electrically tuned magnetic order and magnetoresistance in a topological insulator.

Science.gov (United States)

Zhang, Zuocheng; Feng, Xiao; Guo, Minghua; Li, Kang; Zhang, Jinsong; Ou, Yunbo; Feng, Yang; Wang, Lili; Chen, Xi; He, Ke; Ma, Xucun; Xue, Qikun; Wang, Yayu

2014-09-15

The interplay between topological protection and broken time reversal symmetry in topological insulators may lead to highly unconventional magnetoresistance behaviour that can find unique applications in magnetic sensing and data storage. However, the magnetoresistance of topological insulators with spontaneously broken time reversal symmetry is still poorly understood. In this work, we investigate the transport properties of a ferromagnetic topological insulator thin film fabricated into a field effect transistor device. We observe a complex evolution of gate-tuned magnetoresistance, which is positive when the Fermi level lies close to the Dirac point but becomes negative at higher energies. This trend is opposite to that expected from the Berry phase picture, but is intimately correlated with the gate-tuned magnetic order. The underlying physics is the competition between the topology-induced weak antilocalization and magnetism-induced negative magnetoresistance. The simultaneous electrical control of magnetic order and magnetoresistance facilitates future topological insulator based spintronic devices.

Synthesis of calcium doped lanthanum manganite by mechanosynthesis

International Nuclear Information System (INIS)

Bolarin, A.M.; Sanchez, F.; Palomares, S.; Aguilar, J.A.; Torres-Villasenor, G.

2007-01-01

Lanthanum manganite doped with calcium, Ca 1/3 La 2/3 MnO 3-δ , was prepared by a high-energy ball milling. The precursors used were Mn 2 O 3 , La 2 O 3 and CaO, mixed in the stoichiometric ratio to obtain this manganite. The mechano-chemical process was performed at room temperature in a SPEX 8000D mixer/mill, using hardened steel balls and stainless steel vials, in air atmosphere. X-ray diffraction was used to elucidate the phase transformation as a function of the milling time. The Rietveld refinement was used in order to characterize structurally the manganites. The morphology and particle size of powder compound obtained were characterized by scanning electron microscope. The particle size of this powder material was measured with zeta size analyzer, and selected area electron diffraction (SAED) from TEM was used to elucidate the crystalline structure of this powder compound. The results showed that it is possible to obtain calcium doped lanthanum manganite by mechano-synthesis, using a weight ratio of ball to powder of 12:1, after 3 h of milling. The evolution of the phase transformation during the milling time is reported. Increases in milling time produce exponential decrease in the particle size, up to 680 nm after 1 h of milling. After the milling process it is obtained a powder compound with an orthorhombic structure (S.G. Pbnm). A prolonged milling time (>9 h) produce an important reduction in the particle size but this is accompanied with a high iron contamination caused by metallic residues originated from vial and balls and also, after 9 h of milling time, it was found an important distortion in orthorhombic structure, obtaining two types of parameters

Mutual influence between current-induced giant magnetoresistance and radiation-induced magnetoresistance oscillations in the GaAs/AlGaAs 2DES.

Science.gov (United States)

Samaraweera, R L; Liu, H-C; Wang, Z; Reichl, C; Wegscheider, W; Mani, R G

2017-07-11

Radiation-induced magnetoresistance oscillations are examined in the GaAs/AlGaAs 2D system in the regime where an observed concurrent giant magnetoresistance is systematically varied with a supplementary dc-current, I dc . The I dc tuned giant magnetoresistance is subsequently separated from the photo-excited oscillatory resistance using a multi-conduction model in order to examine the interplay between the two effects. The results show that the invoked multiconduction model describes the observed giant magnetoresistance effect even in the presence of radiation-induced magnetoresistance oscillations, the magnetoresistance oscillations do not modify the giant magnetoresistance, and the magnetoresistance oscillatory extrema, i.e., maxima and minima, disappear rather asymmetrically with increasing I dc . The results suggest the interpretation that the I dc serves to suppress scattering between states near the Fermi level in a strong magnetic field limit.

Multiferroic nature of charge-ordered rare earth manganites

Energy Technology Data Exchange (ETDEWEB)

Serrao, Claudy Rayan [Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur PO, Bangalore-560064 (India); Sundaresan, A [Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur PO, Bangalore-560064 (India); Rao, C N R [Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur PO, Bangalore-560064 (India)

2007-12-12

Charge-ordered rare earth manganites Nd{sub 0.5}Ca{sub 0.5}MnO{sub 3},La{sub 0.25}Nd{sub 0.25}Ca{sub 0.5}MnO{sub 3}, Pr{sub 0.7}Ca{sub 0.3}MnO{sub 3} and Pr{sub 0.6}Ca{sub 0.4}MnO{sub 3} are found to exhibit dielectric constant anomalies around the charge-ordering or the antiferromagnetic transition temperatures. Magnetic fields have a marked effect on the dielectric properties, indicating the presence of coupling between the magnetic and electrical order parameters. The observation of magnetoferroelectricity in these manganites is in accord with the recent theoretical predictions of Khomskii and co-workers.

Linear negative magnetoresistance in two-dimensional Lorentz gases

Science.gov (United States)

Schluck, J.; Hund, M.; Heckenthaler, T.; Heinzel, T.; Siboni, N. H.; Horbach, J.; Pierz, K.; Schumacher, H. W.; Kazazis, D.; Gennser, U.; Mailly, D.

2018-03-01

Two-dimensional Lorentz gases formed by obstacles in the shape of circles, squares, and retroreflectors are reported to show a pronounced linear negative magnetoresistance at small magnetic fields. For circular obstacles at low number densities, our results agree with the predictions of a model based on classical retroreflection. In extension to the existing theoretical models, we find that the normalized magnetoresistance slope depends on the obstacle shape and increases as the number density of the obstacles is increased. The peaks are furthermore suppressed by in-plane magnetic fields as well as by elevated temperatures. These results suggest that classical retroreflection can form a significant contribution to the magnetoresistivity of two-dimensional Lorentz gases, while contributions from weak localization cannot be excluded, in particular for large obstacle densities.

Colossal magnetoresistance of bulk Ag-doped Nd{sub 0.7}Sr{sub 0.3}MnO{sub 3} two-phase composites

Energy Technology Data Exchange (ETDEWEB)

Cui Xugao [National Laboratory of Solid State Microstructures, Department of Physics, Nanjing University, Nanjing 210093 (China); Hu Xiukun [National Laboratory of Solid State Microstructures, Department of Physics, Nanjing University, Nanjing 210093 (China); Xia Hongxu [National Laboratory of Solid State Microstructures, Department of Physics, Nanjing University, Nanjing 210093 (China); Yu Jiangying [National Laboratory of Solid State Microstructures, Department of Physics, Nanjing University, Nanjing 210093 (China); Zhang Shiyuan [National Laboratory of Solid State Microstructures, Department of Physics, Nanjing University, Nanjing 210093 (China)]. E-mail: zsy@netra.nju.edu.cn

2005-05-17

We have prepared a series of bulk polycrystalline manganites with the nominal compositions, Nd{sub 0.7}Sr{sub 0.3}MnO{sub 3}-Ag {sub x} (x is the molar fraction) with x = 0.1, 0.2, 0.3, 0.4, 0.5 by conventional solid-state reaction. The X-ray diffraction patterns show that the sample Nd{sub 0.7}Sr{sub 0.3}MnO{sub 3} (x = 0) is a single-phase compound with the pseudocubic perovskite structure, while the Ag-doped samples are two-phase composites consisting of a ferromagnetic perovskite phase and a nonmagnetic Ag metal phase. For all the samples, the Curie temperature, T {sub C}, remains nearly the same (228 {+-} 2 K), but the maximum magnetoresistance in a magnetic field of 1 T at 222 K is enhanced strongly due to the addition of Ag, namely, from 45% for the Nd{sub 0.7}Sr{sub 0.3}MnO{sub 3} sample to 188, 277, 142, 158 and 151% for the Nd{sub 0.7}Sr{sub 0.3}MnO{sub 3}-Ag {sub x} samples with x = 0.1, 0.2, 0.3, 0.4, and 0.5, respectively. This magnetoresistance-enhancement phenomenon can be attributed to the spin-dependent scattering of the spin-polarized electrons at the interfaces between the perovskite grains and the Ag granules.

Recovery of oscillatory magneto-resistance in phase separated La0.3Pr0.4Ca0.3MnO3 epitaxial thin films

International Nuclear Information System (INIS)

Alagoz, H. S.; Jeon, J.; Mahmud, S. T.; Saber, M. M.; Chow, K. H.; Jung, J.; Prasad, B.; Egilmez, M.

2013-01-01

In-plane angular dependent magneto-resistance has been studied in La 0.3 Pr 0.4 Ca 0.3 MnO 3 (LPCMO) manganite thin films deposited on the (100) oriented NdGaO 3 , and (001) oriented SrTiO 3 and LaAlO 3 substrates. At temperatures where the electronic phase separation is the strongest, a metastable irreversible state exists in the films whose resistivity ρ attains a large time dependent value. The ρ decreases sharply with an increasing angle θ between the magnetic field and the current, and does not display an expected oscillatory cos 2 θ/sin 2 θ dependence for all films. The regular oscillations are recovered during repetitive sweeping of θ between 0° and 180°. We discuss possible factors that could produce these unusual changes in the resistivity

Two-phase behavior in strained thin films of hole-doped manganites

OpenAIRE

Biswas, Amlan; Rajeswari, M.; Srivastava, R. C.; Li, Y. H.; Venkatesan, T.; Greene, R. L.; Millis, A. J.

1999-01-01

We present a study of the effect of biaxial strain on the electrical and magnetic properties of thin films of manganites. We observe that manganite films grown under biaxial compressive strain exhibit island growth morphology which leads to a non-uniform distribution of the strain. Transport and magnetic properties of these films suggest the coexistence of two different phases, a metallic ferromagnet and an insulating antiferromagnet. We suggest that the high strain regions are insulating whi...

Non-local magnetoresistance in YIG/Pt nanostructures

Energy Technology Data Exchange (ETDEWEB)

Goennenwein, Sebastian T. B., E-mail: goennenwein@wmi.badw.de; Pernpeintner, Matthias; Gross, Rudolf; Huebl, Hans [Walther-Meißner-Institut, Bayerische Akademie der Wissenschaften, Walther-Meißner-Str. 8, 85748 Garching (Germany); Nanosystems Initiative Munich (NIM), Schellingstraße 4, 80799 München (Germany); Physik-Department, Technische Universität München, James-Franck-Str. 1, 85748 Garching (Germany); Schlitz, Richard; Ganzhorn, Kathrin [Walther-Meißner-Institut, Bayerische Akademie der Wissenschaften, Walther-Meißner-Str. 8, 85748 Garching (Germany); Physik-Department, Technische Universität München, James-Franck-Str. 1, 85748 Garching (Germany); Althammer, Matthias [Walther-Meißner-Institut, Bayerische Akademie der Wissenschaften, Walther-Meißner-Str. 8, 85748 Garching (Germany)

2015-10-26

We study the local and non-local magnetoresistance of thin Pt strips deposited onto yttrium iron garnet. The local magnetoresistive response, inferred from the voltage drop measured along one given Pt strip upon current-biasing it, shows the characteristic magnetization orientation dependence of the spin Hall magnetoresistance. We simultaneously also record the non-local voltage appearing along a second, electrically isolated, Pt strip, separated from the current carrying one by a gap of a few 100 nm. The corresponding non-local magnetoresistance exhibits the symmetry expected for a magnon spin accumulation-driven process, confirming the results recently put forward by Cornelissen et al. [“Long-distance transport of magnon spin information in a magnetic insulator at room temperature,” Nat. Phys. (published online 14 September 2015)]. Our magnetotransport data, taken at a series of different temperatures as a function of magnetic field orientation, rotating the externally applied field in three mutually orthogonal planes, show that the mechanisms behind the spin Hall and the non-local magnetoresistance are qualitatively different. In particular, the non-local magnetoresistance vanishes at liquid Helium temperatures, while the spin Hall magnetoresistance prevails.

Effect of high pressure on the ground state of low doped manganite: a neutron diffraction and transport property study

International Nuclear Information System (INIS)

Ghosh, Barnali; Raychaudhuri, A.K.; Siruguri, V.; Chatterji, Tapan; Thomas, Hansen; Mukovskii, Ya.M.

2013-01-01

Depending on the doping level x the hole-doped perovskite manganites, like La 1-x Ca x MnO 3 exhibit a wide variety of physical properties. These compounds lead their high sensitivity to thermodynamic variables like temperature, magnetic field and pressure. The structure can be modified by application of high pressure and it can be quantitative that changes the Mn-O bond length and increases the Mn-O-Mn bond angle. In some cases the pressure can bring about qualitative changes in the structure like change in the lattice structure or its symmetry. These structural factors can contribute to the effective electron transfer integral between Mn ions, which in turn can change the magnetic exchanges like the double-exchange as well as the super exchange. For low hole doping (0.15 ≤ x ≤ 0.2), the low temperature ground state is Ferromagnetic insulator (FMI). The ground state of the low doped manganite La 0.79 Ca 0.21 MnO 3 (LCMO) can be destabilized by external hydrostatic pressure. We have done electrical transport measurement under magnetic field and under high pressure for understanding the nature of the resulting phase(s) that arise from the applied hydrostatic pressure. We find that the metallic phase so created under pressure has no appreciable magnetoresistance (MR). The Neutron powder diffraction measurement done on D20 diffractometer (λ=1.3Å) at ILL, Grenoble, France under high hydrostatic pressure up to 10GPa shows that the pressure leads to a change in the crystal structure from orthorhombic to rhombohedral and leading to a change in magnetic structure also; and most importantly collapse of the magnetic moment to a low value that leads to absence of any MR under pressure induced metallization. (author)

Magnetoresistance of individual ferromagnetic GaAs/(Ga,Mn)As core-shell nanowires

OpenAIRE

Butschkow, Christian H.; Reiger, Elisabeth; Geißler, Stefan; Rudolph, Andreas; Soda, Marcello; Schuh, Dieter; Woltersdorf, Georg; Wegscheider, Werner; Weiss, Dieter

2011-01-01

We investigate, angle dependent, the magnetoresistance (MR) of individual self-assembled ferromagnetic GaAs/(Ga,Mn)As core-shell nanowires at cryogenic temperatures. The shape of the MR traces and the observed strong anisotropies in transport can be ascribed to the interplay of the negative magnetoresistance effect and a strong uniaxial anisotropy with the magnetic easy direction pointing along the wire axis. The magnetoresistance can be well described by a quantitative analysis based on the ...

Magnetoresistance in RCo2 spin-fluctuation systems

International Nuclear Information System (INIS)

Gratz, E.; Nowotny, H.; Enser, J.; Bauer, E.; Hense, K.

2004-01-01

The effect of the spin fluctuations on the field and temperature dependence of the magnetoresistance in ScCo 2 and LuCo 2 was studied. The experimental data where explained assuming two competing mechanisms determining the magnetoresistance of these substances. One is the 'normal magnetoresistance' caused by the influence of the Lorentz force on conduction electron trajectories. The other is due to the suppression of the spin fluctuations caused by an external magnetic field. This interplay give rise to a pronounced drop of the magnetoresistance towards the lower temperature range

Deposition temperature influence on sputtered nanogranular magnetoresistive composites

International Nuclear Information System (INIS)

Mujika, M.; Arana, S.; Castano, E.

2007-01-01

Among different physical principles magnetic sensors for low magnetic field detection can be based on, granular giant magnetoresistances have been studied due to their high sensitivity to small field changes and gradual magnetoresistance change at low fields. Following this aim, nanogranular Ag-Co thin films, deposited by DC co-sputtering from Ag and Co targets at different deposition temperatures have been tested. Samples have been grown at room temperature, 100 and 200 deg. C and annealed in a mixture of N 2 and H 2 at 200 and 300 deg. C for 45 min. The samples that have shown the best performance have been subjected to two sets of measurements where an external field has been applied in-plane and perpendicular to the film plane. The best performance has been shown by the samples deposited at room temperature and annealed at 300 deg. C, reporting a maximum value of magnetoresistance of 16.7% at 1.4 T and a linear sensitivity of 63%/T between 0.04 and 0.07 T within a magnetoresistance range varying from 1.5% to 3% when subjected to an in-plane external field

Engineering magnetism at functional oxides interfaces: manganites and beyond.

Science.gov (United States)

Yi, Di; Lu, Nianpeng; Chen, Xuegang; Shen, Shengchun; Yu, Pu

2017-11-08

The family of transition metal oxides (TMOs) is a large class of magnetic materials that has been intensively studied due to the rich physics involved as well as the promising potential applications in next generation electronic devices. In TMOs, the spin, charge, orbital and lattice are strongly coupled, and significant advances have been achieved to engineer the magnetism by different routes that manipulate these degrees of freedom. The family of manganites is a model system of strongly correlated magnetic TMOs. In this review, using manganites thin films and the heterostructures in conjunction with other TMOs as model systems, we review the recent progress of engineering magnetism in TMOs. We first discuss the role of the lattice that includes the epitaxial strain and the interface structural coupling. Then we look into the role of charge, focusing on the interface charge modulation. Having demonstrated the static effects, we continue to review the research on dynamical control of magnetism by electric field. Next, we review recent advances in heterostructures comprised of high T c cuprate superconductors and manganites. Following that, we discuss the emergent magnetic phenomena at interfaces between 3d TMOs and 5d TMOs with strong spin-orbit coupling. Finally, we provide our outlook for prospective future directions.

On magnetic ordering in heavily sodium substituted hole doped lanthanum manganites

Energy Technology Data Exchange (ETDEWEB)

Sethulakshmi, N. [Department of Physics, Cochin University of Science and Technology, Cochin 682022, Kerala (India); Unnimaya, A.N. [Centre for Materials for Electronic Technology (CMET), Thrissur 680581, Kerala (India); Al-Omari, I.A.; Al-Harthi, Salim [Department of Physics, Sultan Qaboos University, PC 123 Muscat (Oman); Sagar, S. [Government College for Women, Thiruvananthapuram 695014, Kerala (India); Thomas, Senoy [Materials Science and Technology Division, National Institute for Interdisciplinary Science and Technology, Thiruvananthapuram 695019, Kerala (India); Srinivasan, G. [Department of Physics, Oakland University, Rochester (United States); Anantharaman, M.R., E-mail: mraiyer@yahoo.com [Department of Physics, Cochin University of Science and Technology, Cochin 682022, Kerala (India)

2015-10-01

Mixed valence manganite system with monovalent sodium substituted lanthanum manganites form the basis of the present work. Lanthanum manganites belonging to the series La{sub 1−x}Na{sub x}MnO{sub 3} with x=0.5–0.9 were synthesized using modified citrate gel method. Variation of lattice parameters and unit cell volume with Na concentration were analyzed and the magnetization measurements indicated ferromagnetic ordering in all samples at room temperature. Low temperature magnetization behavior indicated that all samples exhibit antiferromagnetism along with ferromagnetism and it has also been observed that antiferromagnetic ordering dominates ferromagnetic ordering as concentration is increased. Evidence for such a magnetic inhomogeneity in these samples has been confirmed from the variation in Mn{sup 3+}/Mn{sup 4+} ion ratio from X-ray Photoelectron Spectroscopy and from the absorption peak studies using Ferromagnetic Resonance Spectroscopy. - Highlights: • Higher substitution of more than 50 percent of monovalent ion, sodium for La sites in lanthanum manganites scarce in literature. • Structural studies using XRD and further structure refinement by Rietveld refinement confirmed orthorhombic pbnm spacegroup. • Ferromagnetic behavior at room temperature with saturation magnetization decreasing with increase in sodium concentration. • M vs T measurements using FC ZFC proved coexisting FM/AFM behavior arising from exchange interactions between different valence states of Mn ions. • Disparity in ratio of Mn valence ions indicated presence of vacancies providing the role of vacancies and oxygen stoichiometry in deciding magnetic inhomogeneity.

Cold-Rolled Strip Steel Stress Detection Technology Based on a Magnetoresistance Sensor and the Magnetoelastic Effect.

Science.gov (United States)

Guan, Ben; Zang, Yong; Han, Xiaohui; Zheng, Kailun

2018-05-21

Driven by the demands for contactless stress detection, technologies are being used for shape control when producing cold-rolled strips. This paper presents a novel contactless stress detection technology based on a magnetoresistance sensor and the magnetoelastic effect, enabling the detection of internal stress in manufactured cold-rolled strips. An experimental device was designed and produced. Characteristics of this detection technology were investigated through experiments assisted by theoretical analysis. Theoretically, a linear correlation exists between the internal stress of strip steel and the voltage output of a magneto-resistive sensor. Therefore, for this stress detection system, the sensitivity of the stress detection was adjusted by adjusting the supply voltage of the magnetoresistance sensor, detection distance, and other relevant parameters. The stress detection experimental results showed that this detection system has good repeatability and linearity. The detection error was controlled within 1.5%. Moreover, the intrinsic factors of the detected strip steel, including thickness, carbon percentage, and crystal orientation, also affected the sensitivity of the detection system. The detection technology proposed in this research enables online contactless detection and meets the requirements for cold-rolled steel strips.

Magnetoresistances in Ni80Fe20-ITO granular film

International Nuclear Information System (INIS)

Gao Chunhong; Chen Ke; Yang Yanxia; Xiong Yuanqiang; Chen Peng

2012-01-01

Highlights: ► Magnetoresistance (MR) in Ni 80 Fe 20 -ITO granular film are investigated. ► MR is positive at high temperature, and is negative at low temperature. ► MR results from the competition among three mechanisms. - Abstract: The magnetic properties, electrical properties and magnetoresistance are investigated in Ni 80 Fe 20 -ITO granular film with various volume fractions V NF of Ni 80 Fe 20 . The room temperature magnetization hysteresis of sample with V NF = 25% shows superparamagnetic behavior. Current-voltage curve of sample with V NF = 25% at 175 K shows typical tunneling-type behavior. The magnetoresistances of samples with low V NF are positive at high temperature, and are negative at low temperature. The temperature-dependent magnetoresistances result from the competition among ordinary magnetoresistances, the granular-typed tunneling magnetoresistance and the spin-mixing induced magnetoresistances.

Large magnetoresistance in non-magnetic silver chalcogenides and new class of magnetoresistive compounds

Science.gov (United States)

Saboungi, Marie-Louis; Price, David C. L.; Rosenbaum, Thomas F.; Xu, Rong; Husmann, Anke

2001-01-01

The heavily-doped silver chalcogenides, Ag.sub.2+.delta. Se and Ag.sub.2+.delta. Te, show magnetoresistance effects on a scale comparable to the "colossal" magnetoresistance (CMR) compounds. Hall coefficient, magnetoconductivity, and hydrostatic pressure experiments establish that elements of narrow-gap semiconductor physics apply, but both the size of the effects at room temperature and the linear field dependence down to fields of a few Oersteds are surprising new features.

Huge magnetoresistance effect of highly oriented pyrolytic graphite

International Nuclear Information System (INIS)

Du Youwei; Wang Zhiming; Ni Gang; Xing Dingyu; Xu Qingyu

2004-01-01

Graphite is a quasi-two-dimensional semimetal. However, for usual graphite the magnetoresistance is not so high due to its small crystal size and no preferred orientation. Huge positive magnetoresistance up to 85300% at 4.2 K and 4950% at 300 K under 8.15 T magnetic field was found in highly oriented pyrolytic graphite. The mechanism of huge positive magnetoresistance is not only due to ordinary magnetoresistance but also due to magnetic-field-driven semimetal-insulator transition

Spin Hall magnetoresistance in antiferromagnet/normal metal bilayers

KAUST Repository

Manchon, Aurelien

2017-01-01

We investigate the emergence of spin Hall magnetoresistance in a magnetic bilayer composed of a normal metal adjacent to an antiferromagnet. Based on a recently derived drift diffusion equation, we show that the resistance of the bilayer depends on the relative angle between the direction transverse to the current flow and the Néel order parameter. While this effect presents striking similarities with the spin Hall magnetoresistance recently reported in ferromagnetic bilayers, its physical origin is attributed to the anisotropic spin relaxation of itinerant spins in the antiferromagnet.

Dramatically decreased magnetoresistance in non-stoichiometric WTe2 crystals.

Science.gov (United States)

Lv, Yang-Yang; Zhang, Bin-Bin; Li, Xiao; Pang, Bin; Zhang, Fan; Lin, Da-Jun; Zhou, Jian; Yao, Shu-Hua; Chen, Y B; Zhang, Shan-Tao; Lu, Minghui; Liu, Zhongkai; Chen, Yulin; Chen, Yan-Feng

2016-05-27

Recently, the layered semimetal WTe2 has attracted renewed interest owing to the observation of a non-saturating and giant positive magnetoresistance (~10(5)%), which can be useful for magnetic memory and spintronic devices. However, the underlying mechanisms of the giant magnetoresistance are still under hot debate. Herein, we grew the stoichiometric and non-stoichiometric WTe2 crystals to test the robustness of giant magnetoresistance. The stoichiometric WTe2 crystals have magnetoresistance as large as 3100% at 2 K and 9-Tesla magnetic field. However, only 71% and 13% magnetoresistance in the most non-stoichiometry (WTe1.80) and the highest Mo isovalent substitution samples (W0.7Mo0.3Te2) are observed, respectively. Analysis of the magnetic-field dependent magnetoresistance of non-stoichiometric WTe2 crystals substantiates that both the large electron-hole concentration asymmetry and decreased carrier mobility, induced by non-stoichiometry, synergistically lead to the decreased magnetoresistance. This work sheds more light on the origin of giant magnetoresistance observed in WTe2.

Above room-temperature ferromagnetism in La1-xCaxMnO3 epitaxial thin films on SrTiO3(001) substrates

Science.gov (United States)

Kou, Yunfang; Wang, Hui; Miao, Tian; Wang, Yanmei; Xie, Lin; Wang, Shasha; Liu, Hao; Lin, Hanxuan; Zhu, Yinyan; Wang, Wenbin; Du, Haifeng; Pan, Xiaoqing; Wu, Ruqian; Yin, Lifeng; Shen, Jian

The colossal magnetoresistive (CMR) manganites are popular materials for spintronics applications due to their high spin polarization. Only a couple of manganites like La1-xSrxMnO3 have a Curie temperature (Tc) that is higher than room temperature. Finding methods to raise the Tc of manganites over room temperature is useful but challenging. In this work, we use the most intensively studied La1-xCaxMnO3 (LCMO) as the prototype system to demonstrate that Tc can be greatly enhanced by carefully tuning the electronic structure using doping and strain. Specifically, we grow LCMO films on SrTiO3 (001) substrates using pulsed laser deposition. Magnetic and transport measurements indicate a great enhancement of Tc over room temperature at x =0.2 doping. Theoretical calculations indicate that the combined effects from doping and strain give rise to a new electronic structure favoring ferromagnetism in LCMO system. Furthermore, using the La0.8Ca0.2MnO3 as ferromagnetic electrodes, we achieve finite tunneling magnetoresistance (TMR) above room temperature.

Strontium-90 sorption from fresh waters in the process of barium manganite modification

International Nuclear Information System (INIS)

Ryzhen'kov, A.P.; Egorov, Yu.V.

1995-01-01

Strontium-90 extraction by barium manganite from fresh water (natural non-salty water in open ponds) may be increased adding to the solution the sulfate anion containing reagents that modify a sorbent and chemically bind a sorbate. Heterogeneous anion-exchanging reaction of barium manganite transformation into barium sulfate-manganese dioxide and simultaneous coprecipitation of strontium sulfate (microelement) occur as a result of it. 9 refs., 4 figs., 1 tab

Tailoring the physical properties of manganite thin films by tuning the epitaxial strain

International Nuclear Information System (INIS)

Zhang, P.X.; Zhang, H.; Cha, L.M.; Habermeier, H.-U.

2003-01-01

Through a proper choice of the mismatch between substrate and films, the physical properties of manganite thin films can be tailored We show that two types of manganite thin films of the Ruddlesden-Popper family, n=∞ and n=2, demonstrate a dramatic variation of their physical properties. It is proved that the property variation can be tuned precisely by controlling the lattice mismatch and/or the film thickness

Anisotropic magnetoresistance in a Fermi glass

International Nuclear Information System (INIS)

Ovadyahu, Z.; Physics Department, Ben-Gurion University of the Negev, Beer-Sheva, Israel 84120)

1986-01-01

Insulating thin films of indium oxide exhibit negative, anisotropic magnetoresistance. The systematics of these results imply that the magnetoresistance mechanism may give different weight to the distribution of the localization lengths than that given by the hopping conductivity

Magnetoresistance through spin-polarized p states

International Nuclear Information System (INIS)

Papanikolaou, Nikos

2003-01-01

We present a theoretical study of the ballistic magnetoresistance in Ni contacts using first-principles, atomistic, electronic structure calculations. In particular we investigate the role of defects in the contact region with the aim of explaining the recently observed spectacular magnetoresistance ratio. Our results predict that the possible presence of spin-polarized oxygen in the contact region could explain conductance changes by an order of magnitude. Electronic transport essentially occurs through spin-polarized oxygen p states, and this mechanism gives a much higher magnetoresistance than that obtained assuming clean atomically sharp domain walls alone

On-chip magnetic bead-based DNA melting curve analysis using a magnetoresistive sensor

International Nuclear Information System (INIS)

Rizzi, Giovanni; Østerberg, Frederik W.; Henriksen, Anders D.; Dufva, Martin; Hansen, Mikkel F.

2015-01-01

We present real-time measurements of DNA melting curves in a chip-based system that detects the amount of surface-bound magnetic beads using magnetoresistive magnetic field sensors. The sensors detect the difference between the amount of beads bound to the top and bottom sensor branches of the differential sensor geometry. The sensor surfaces are functionalized with wild type (WT) and mutant type (MT) capture probes, differing by a single base insertion (a single nucleotide polymorphism, SNP). Complementary biotinylated targets in suspension couple streptavidin magnetic beads to the sensor surface. The beads are magnetized by the field arising from the bias current passed through the sensors. We demonstrate the first on-chip measurements of the melting of DNA hybrids upon a ramping of the temperature. This overcomes the limitation of using a single washing condition at constant temperature. Moreover, we demonstrate that a single sensor bridge can be used to genotype a SNP. - Highlights: • We apply magnetoresistive sensors to study solid-surface hybridization kinetics of DNA. • We measure DNA melting profiles for perfectly matching DNA duplexes and for a single base mismatch. • We present a procedure to correct for temperature dependencies of the sensor output. • We reliably extract melting temperatures for the DNA hybrids. • We demonstrate direct measurement of differential binding signal for two probes on a single sensor

Magnetoresistance of magnetically doped ZnO films

Energy Technology Data Exchange (ETDEWEB)

Behan, A J; Mokhtari, A; Blythe, H J; Fox, A M; Gehring, G A [Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH (United Kingdom); Ziese, M, E-mail: G.A.Gehring@sheffield.ac.u [Division of Superconductivity and Magnetism, University of Leipzig, D-04103, Leipzig (Germany)

2009-08-26

Magnetoresistance measurements have been made at 5 K on doped ZnO thin films grown by pulsed laser deposition. ZnCoO, ZnCoAlO and ZnMnAlO samples have been investigated and compared to similar films containing no transition metal dopants. It is found that the Co-doped samples with a high carrier concentration have a small negative magnetoresistance, irrespective of their magnetic moment. On decreasing the carrier concentration, a positive contribution to the magnetoresistance appears and a further negative contribution. This second, negative contribution, which occurs at very low carrier densities, correlates with the onset of ferromagnetism due to bound magnetic polarons suggesting that the negative magnetoresistance results from the destruction of polarons by a magnetic field. An investigation of the anisotropic magnetoresistance showed that the orientation of the applied magnetic field, relative to the sample, had a large effect. The results for the ZnMnAlO samples showed less consistent trends.

Superconducting magnetoresistance in ferromagnet/superconductor/ferromagnet trilayers.

Science.gov (United States)

Stamopoulos, D; Aristomenopoulou, E

2015-08-26

Magnetoresistance is a multifaceted effect reflecting the diverse transport mechanisms exhibited by different kinds of plain materials and hybrid nanostructures; among other, giant, colossal, and extraordinary magnetoresistance versions exist, with the notation indicative of the intensity. Here we report on the superconducting magnetoresistance observed in ferromagnet/superconductor/ferromagnet trilayers, namely Co/Nb/Co trilayers, subjected to a parallel external magnetic field equal to the coercive field. By manipulating the transverse stray dipolar fields that originate from the out-of-plane magnetic domains of the outer layers that develop at coercivity, we can suppress the supercurrent of the interlayer. We experimentally demonstrate a scaling of the magnetoresistance magnitude that we reproduce with a closed-form phenomenological formula that incorporates relevant macroscopic parameters and microscopic length scales of the superconducting and ferromagnetic structural units. The generic approach introduced here can be used to design novel cryogenic devices that completely switch the supercurrent 'on' and 'off', thus exhibiting the ultimate magnetoresistance magnitude 100% on a regular basis.

Evolution and control of the phase competition morphology in a manganite film

Science.gov (United States)

Zhou, Haibiao; Wang, Lingfei; Hou, Yubin; Huang, Zhen; Lu, Qingyou; Wu, Wenbin

2015-11-01

The competition among different phases in perovskite manganites is pronounced since their energies are very close under the interplay of charge, spin, orbital and lattice degrees of freedom. To reveal the roles of underlying interactions, many efforts have been devoted towards directly imaging phase transitions at microscopic scales. Here we show images of the charge-ordered insulator (COI) phase transition from a pure ferromagnetic metal with reducing field or increasing temperature in a strained phase-separated manganite film, using a home-built magnetic force microscope. Compared with the COI melting transition, this reverse transition is sharp, cooperative and martensitic-like with astonishingly unique yet diverse morphologies. The COI domains show variable-dimensional growth at different temperatures and their distribution can illustrate the delicate balance of the underlying interactions in manganites. Our findings also display how phase domain engineering is possible and how the phase competition can be tuned in a controllable manner.

Large rectification magnetoresistance in nonmagnetic Al/Ge/Al heterojunctions

OpenAIRE

Zhang, Kun; Li, Huan-huan; Grünberg, Peter; Li, Qiang; Ye, Sheng-tao; Tian, Yu-feng; Yan, Shi-shen; Lin, Zhao-jun; Kang, Shi-shou; Chen, Yan-xue; Liu, Guo-lei; Mei, and Liang-mo

2015-01-01

Magnetoresistance and rectification are two fundamental physical properties of heterojunctions and respectively have wide applications in spintronics devices. Being different from the well known various magnetoresistance effects, here we report a brand new large magnetoresistance that can be regarded as rectification magnetoresistance: the application of a pure small sinusoidal alternating-current to the nonmagnetic Al/Ge Schottky heterojunctions can generate a significant direct-current volt...

The tunneling magnetoresistance current dependence on cross sectional area, angle and temperature

Directory of Open Access Journals (Sweden)

Z. H. Zhang

2015-03-01

Full Text Available The magnetoresistance of a MgO-based magnetic tunnel junction (MTJ was studied experimentally. The magnetoresistance as a function of current was measured systematically on MTJs for various MgO cross sectional areas and at various temperatures from 7.5 to 290.1 K. The resistance current dependence of the MTJ was also measured for different angles between the two ferromagnetic layers. By considering particle and angular momentum conservation of transport electrons, the current dependence of magnetoresistance can be explained by the changing of spin polarization in the free magnetic layer of the MTJ. The changing of spin polarization is related to the magnetoresistance, its angular dependence and the threshold current where TMR ratio equals zero. A phenomenological model is used which avoid the complicated barrier details and also describes the data.

Tunneling magnetoresistance in Si nanowires

KAUST Repository

Montes Muñoz, Enrique

2016-11-09

We investigate the tunneling magnetoresistance of small diameter semiconducting Si nanowires attached to ferromagnetic Fe electrodes, using first principles density functional theory combined with the non-equilibrium Green\\'s functions method for quantum transport. Silicon nanowires represent an interesting platform for spin devices. They are compatible with mature silicon technology and their intrinsic electronic properties can be controlled by modifying the diameter and length. Here we systematically study the spin transport properties for neutral nanowires and both n and p doping conditions. We find a substantial low bias magnetoresistance for the neutral case, which halves for an applied voltage of about 0.35 V and persists up to 1 V. Doping in general decreases the magnetoresistance, as soon as the conductance is no longer dominated by tunneling.

Magneto-caloric and magneto-resistive properties of La{sub 0.67}Ca{sub 0.33-x}Sr{sub x}MnO{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Reves Dinesen, Anders

2004-08-01

This thesis presents results of an experimental investigation of magneto-caloric and magneto-resistive properties of a series of polycrystalline Ca- and Sr-doped lanthanum manganites, La{sub 0.67}Ca{sub 0.33-x}Sr{sub x}MnO{sub 3} (0{<=} x {<=} 0.33), with the perovskite structure. The samples consisted of sintered oxide powders prepared the glycine-nitrate combustion technique. The compounds were ferromagnetic and showed a Curie transition in the temperature range 267370 K (T{sub C} increased with increasing x). An analysis of the structural properties was carried out by means of x-ray diffraction and the Rietveld technique. The variation of the Ca/Sr ratio was found to cause a transition from orthorhombic to rhombohedral symmetry in the composition range 0.110 < x < 0.165. The analysis suggested a strong correlation between structural properties and magnetism, for instance a relationship between the mean MnOMn bond angle and the Curie temperature. The MnOMn bonds mediate ferromagnetism and electrical transport in these materials via the double-exchange mechanism. The magnetocaloric effect of the La{sub 0.67}Ca{sub 0.33-x}Sr{sub x}MnO{sub 3} samples was measured directly and indirectly (by means of magnetization measurements). All the samples showed a magnetocaloric effect in the vicinity of T{sub C}. A model for the mag-netocaloric effect based on Weiss mean field theory and classical theories for heat capacities was developed. The model provided reasonable predictions of the magneto-caloric properties of the samples. The compounds with low Sr content showed a magnetocaloric effect comparable to that of Gadolinium, the prototypical working material for magnetic refrigeration at room temperature. A less comprehensive part of the investigation regarded the magneto-resistive properties of the La{sub 0.67}Ca{sub 0.33-x}Sr{sub x}MnO{sub 3} system. It was found that th polycrystalline nature of the compounds played a decisive role for the magnetotransport properties

Silica-coated manganite and Mn-based ferrite nanoparticles: a comparative study focused on cytotoxicity

Czech Academy of Sciences Publication Activity Database

Kaman, Ondřej; Dědourková, T.; Koktan, Jakub; Kuličková, Jarmila; Maryško, Miroslav; Veverka, Pavel; Havelek, R.; Královec, K.; Turnovcová, Karolína; Jendelová, Pavla; Schröfel, A.; Svoboda, L.

2016-01-01

Roč. 18, č. 4 (2016), 1-18, č. článku 100. ISSN 1388-0764 R&D Projects: GA ČR GA15-10088S Institutional support: RVO:68378271 ; RVO:68378041 Keywords : magnetic nanoparticles * manganite * ferrite * in vitro toxicity * stem cells Subject RIV: BM - Solid Matter Physics ; Magnetism; EB - Genetics ; Molecular Biology (UEM-P) OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.); Acoustics (UEM-P) Impact factor: 2.020, year: 2016

Manganite/Cuprate Superlattice as Artificial Reentrant Spin Glass

KAUST Repository

Ding, Junfeng; Cossu, Fabrizio; Lebedev, Oleg I.; Zhang, Yuqin; Zhang, Zhidong; Schwingenschlö gl, Udo; Wu, Tao

2016-01-01

magnetic memory effect discovered in oxide heterostructures composed of ultrathin manganite La0.7Sr0.3MnO3 (LSMO) and cuprate La2CuO4 (LCO) layers. These heterostructures are featured with enhanced ferromagnetism before entering the spin glass state: a

Resistivity dependence of magnetoresistance in Co/ZnO films.

Science.gov (United States)

Quan, Zhi-Yong; Zhang, Li; Liu, Wei; Zeng, Hao; Xu, Xiao-Hong

2014-01-06

We report the dependence of magnetoresistance effect on resistivity (ρ) in Co/ZnO films deposited by magnetron sputtering at different sputtering pressures with different ZnO contents. The magnitude of the resistivity reflects different carrier transport regimes ranging from metallic to hopping behaviors. Large room-temperature magnetoresistance greater than 8% is obtained in the resistivity range from 0.08 to 0.5 Ω · cm. The magnetoresistance value decreases markedly when the resistivity of the films is less than 0.08 Ω · cm or greater than 0.5 Ω · cm. When 0.08 Ω · cm magnetoresistance effect. When ρ > 0.5 Ω · cm, the spin-independent higher-order hopping (N > 2) comes into play and decreases the tunneling magnetoresistance value. For the samples with ρ magnetoresistance is mainly ascribed to the formation of percolation paths through interconnected elongated metallic Co particles. This observation is significant for the improvement of room-temperature magnetoresistance value for future spintronic devices.

Enhanced Magnetoresistance in Molecular Junctions by Geometrical Optimization of Spin-Selective Orbital Hybridization.

Science.gov (United States)

Rakhmilevitch, David; Sarkar, Soumyajit; Bitton, Ora; Kronik, Leeor; Tal, Oren

2016-03-09

Molecular junctions based on ferromagnetic electrodes allow the study of electronic spin transport near the limit of spintronics miniaturization. However, these junctions reveal moderate magnetoresistance that is sensitive to the orbital structure at their ferromagnet-molecule interfaces. The key structural parameters that should be controlled in order to gain high magnetoresistance have not been established, despite their importance for efficient manipulation of spin transport at the nanoscale. Here, we show that single-molecule junctions based on nickel electrodes and benzene molecules can yield a significant anisotropic magnetoresistance of up to ∼200% near the conductance quantum G0. The measured magnetoresistance is mechanically tuned by changing the distance between the electrodes, revealing a nonmonotonic response to junction elongation. These findings are ascribed with the aid of first-principles calculations to variations in the metal-molecule orientation that can be adjusted to obtain highly spin-selective orbital hybridization. Our results demonstrate the important role of geometrical considerations in determining the spin transport properties of metal-molecule interfaces.

Giant magnetoresistance in CrFeMn alloys

International Nuclear Information System (INIS)

Xu, W.M.; Zheng, P.; Chen, Z.J.

1997-01-01

The electrical resistance and longitudinal magnetoresistance of Cr 75 (Fe x Mn 1-x ) 25 alloys, x=0.64, 0.72, are studied in the temperature range 1.5-270 K in applied field up to 7.5 T. The magnetoresistance is negative and strongly correlated with the spin reorientation. In the temperature range where the antiferromagnetic and ferromagnetic domains coexist, the samples display giant magnetoresistance which follows a H n -law at high field. (orig.)

Temperature-Dependent Asymmetry of Anisotropic Magnetoresistance in Silicon p-n Junctions.

Science.gov (United States)

Yang, D Z; Wang, T; Sui, W B; Si, M S; Guo, D W; Shi, Z; Wang, F C; Xue, D S

2015-09-01

We report a large but asymmetric magnetoresistance in silicon p-n junctions, which contrasts with the fact of magnetoresistance being symmetric in magnetic metals and semiconductors. With temperature decreasing from 293 K to 100 K, the magnetoresistance sharply increases from 50% to 150% under a magnetic field of 2 T. At the same time, an asymmetric magnetoresistance, which manifests itself as a magnetoresistance voltage offset with respect to the sign of magnetic field, occurs and linearly increases with magnetoresistance. More interestingly, in contrast with other materials, the lineshape of anisotropic magnetoresistance in silicon p-n junctions significantly depends on temperature. As temperature decreases from 293 K to 100 K, the width of peak shrinks from 90° to 70°. We ascribe these novel magnetoresistance to the asymmetric geometry of the space charge region in p-n junction induced by the magnetic field. In the vicinity of the space charge region the current paths are deflected, contributing the Hall field to the asymmetric magnetoresistance. Therefore, the observed temperature-dependent asymmetry of magnetoresistance is proved to be a direct consequence of the spatial configuration evolution of space charge region with temperature.

Large, Tunable Magnetoresistance in Nonmagnetic III-V Nanowires.

Science.gov (United States)

Li, Sichao; Luo, Wei; Gu, Jiangjiang; Cheng, Xiang; Ye, Peide D; Wu, Yanqing

2015-12-09

Magnetoresistance, the modulation of resistance by magnetic fields, has been adopted and continues to evolve in many device applications including hard-disk, memory, and sensors. Magnetoresistance in nonmagnetic semiconductors has recently raised much attention and shows great potential due to its large magnitude that is comparable or even larger than magnetic materials. However, most of the previous work focus on two terminal devices with large dimensions, typically of micrometer scales, which severely limit their performance potential and more importantly, scalability in commercial applications. Here, we investigate magnetoresistance in the impact ionization region in InGaAs nanowires with 20 nm diameter and 40 nm gate length. The deeply scaled dimensions of these nanowires enable high sensibility with less power consumption. Moreover, in these three terminal devices, the magnitude of magnetoresistance can be tuned by the transverse electric field controlled by gate voltage. Large magnetoresistance between 100% at room temperature and 2000% at 4.3 K can be achieved at 2.5 T. These nanoscale devices with large magnetoresistance offer excellent opportunity for future high-density large-scale magneto-electric devices using top-down fabrication approaches, which are compatible with commercial silicon platform.

Extreme magnetoresistance in magnetic rare-earth monopnictides

Science.gov (United States)

Ye, Linda; Suzuki, Takehito; Wicker, Christina R.; Checkelsky, Joseph G.

2018-02-01

The acute sensitivity of the electrical resistance of certain systems to magnetic fields known as extreme magnetoresistance (XMR) has recently been explored in a new materials context with topological semimetals. Exemplified by WTe2 and rare-earth monopnictide La(Sb,Bi), these systems tend to be nonmagnetic, nearly compensated semimetals and represent a platform for large magnetoresistance driven by intrinsic electronic structure. Here we explore electronic transport in magnetic members of the latter family of semimetals and find that XMR is strongly modulated by magnetic order. In particular, CeSb exhibits XMR in excess of 1.6 ×106% at fields of 9 T whereas the magnetoresistance itself is nonmonotonic across the various magnetic phases and shows a transition from negative magnetoresistance to XMR with fields above magnetic ordering temperature TN. The magnitude of the XMR is larger than in other rare-earth monopnictides including the nonmagnetic members and follows a nonsaturating power law to fields above 30 T. We show that the overall response can be understood as the modulation of conductivity by the Ce orbital state and for intermediate temperatures can be characterized by an effective medium model. Comparison to the orbitally quenched compound GdBi supports the correlation of XMR with the onset of magnetic ordering and compensation and highlights the unique combination of orbital inversion and type-I magnetic ordering in CeSb in determining its large response. These findings suggest a paradigm for magneto-orbital control of XMR and are relevant to the understanding of rare-earth-based correlated topological materials.

Thin-film magnetoresistive absolute position detector

NARCIS (Netherlands)

Groenland, J.P.J.

1990-01-01

The subject of this thesis is the investigation of a digital absolute posi- tion-detection system, which is based on a position-information carrier (i.e. a magnetic tape) with one single code track on the one hand, and an array of magnetoresistive sensors for the detection of the information on the

Systematic study of doping dependence on linear magnetoresistance in p-PbTe

International Nuclear Information System (INIS)

Schneider, J. M.; Chitta, V. A.; Oliveira, N. F.; Peres, M. L.; Castro, S. de; Soares, D. A. W.; Wiedmann, S.; Zeitler, U.; Abramof, E.; Rappl, P. H. O.; Mengui, U. A.

2014-01-01

We report on a large linear magnetoresistance effect observed in doped p-PbTe films. While undoped p-PbTe reveals a sublinear magnetoresistance, p-PbTe films doped with BaF 2 exhibit a transition to a nearly perfect linear magnetoresistance behaviour that is persistent up to 30 T. The linear magnetoresistance slope ΔR/ΔB is to a good approximation, independent of temperature. This is in agreement with the theory of Quantum Linear Magnetoresistance. We also performed magnetoresistance simulations using a classical model of linear magnetoresistance. We found that this model fails to explain the experimental data. A systematic study of the doping dependence reveals that the linear magnetoresistance response has a maximum for small BaF 2 doping levels and diminishes rapidly for increasing doping levels. Exploiting the huge impact of doping on the linear magnetoresistance signal could lead to new classes of devices with giant magnetoresistance behavior.

Large linear magnetoresistance and magnetothermopower in layered SrZnSb$_2$

OpenAIRE

Wang, Kefeng; Petrovic, C.

2016-01-01

We report the large linear magnetoresistance ($\\sim 300\\%$ in 9 T field at 2 K) and magnetothermopower in layered SrZnSb$_2$ crystal with quasi-two-dimensional Sb layers. A crossover from the semiclassical parabolic field dependent magnetoresistance to linear field dependent magnetoresistance with increasing magnetic field is observed. The magnetoresistance behavior can be described very well by combining the semiclassical cyclotron contribution and the quantum limit magnetoresistance. Magnet...

Magnetoresistance in terbium and holmium single crystals

International Nuclear Information System (INIS)

Singh, R.L.; Jericho, M.H.; Geldart, D.J.W.

1976-01-01

The longitudinal magnetoresistance of single crystals of terbium and holmium metals in their low-temperature ferromagnetic phase has been investigated in magnetic fields up to 80 kOe. Typical magnetoresistance isotherms exhibit a minimum which increases in depth and moves to higher fields as the temperature increases. The magnetoresistance around 1 0 K, where inelastic scattering is negligible, has been interpreted as the sum of a negative contribution due to changes in the domain structure and a positive contribution due to normal magnetoresistance. At higher temperatures, a phenomenological approach has been developed to extract the inelastic phonon and spin-wave components from the total measured magnetoresistance. In the temperature range 4--20 0 K (approximately), the phonon resistivity varies as T 3 . 7 for all samples. Approximate upper and lower bounds have been placed on the spin-wave resistivity which is also found to be described by a simple power law in this temperature range. The implications of this result for theoretical treatments of spin-wave resistivity due to s-f exchange interactions are considered. It is concluded that the role played by the magnon energy gap is far less transparent than previously suggested

Tunneling magnetoresistance sensor with pT level 1/f magnetic noise

Science.gov (United States)

Deak, James G.; Zhou, Zhimin; Shen, Weifeng

2017-05-01

Magnetoresistive devices are important components in a large number of commercial electronic products in a wide range of applications including industrial position sensors, automotive sensors, hard disk read heads, cell phone compasses, and solid state memories. These devices are commonly based on anisotropic magnetoresistance (AMR) and giant magnetoresistance (GMR), but over the past few years tunneling magnetoresistance (TMR) has been emerging in more applications. Here we focus on recent work that has enabled the development of TMR magnetic field sensors with 1/f noise of less than 100 pT/rtHz at 1 Hz. Of the commercially available sensors, the lowest noise devices have typically been AMR, but they generally have the largest die size. Based on this observation and modeling of experimental data size and geometry dependence, we find that there is an optimal design rule that produces minimum 1/f noise. This design rule requires maximizing the areal coverage of an on-chip flux concentrator, providing it with a minimum possible total gap width, and tightly packing the gaps with MTJ elements, which increases the effective volume and decreases the saturation field of the MTJ freelayers. When properly optimized using this rule, these sensors have noise below 60 pT/rtHz, and could possibly replace fluxgate magnetometers in some applications.

Microstructural and electrical changes in nickel manganite powder induced by mechanical activation

International Nuclear Information System (INIS)

Savic, S.M.; Mancic, L.; Vojisavljevic, K.; Stojanovic, G.; Brankovic, Z.; Aleksic, O.S.; Brankovic, G.

2011-01-01

Highlights: → The influence of mechanical activation on microstructure evolution in the nickel manganite powder was investigated as well as electrical properties of the sintered samples. → Structural refinement obtained by Topas-Academic software based on Rietveld analysis showed that the milling process remarkably changed the powder morphology and microstructure. → SEM studies of sintered samples also revealed the strong influence of milling time on ceramics density (increases with milling time). → The electrical properties of ceramic samples are clearly conditioned by terms of synthesis, in our case the time of mechanical activation. → The highest density and higher values of dielectric constant were achieved at the sample activated for 45 min. -- Abstract: Nickel manganite powder synthesized by calcination of a stoichiometric mixture of manganese and nickel oxide was additionally mechanically activated in a high energy planetary ball mill for 5-60 min in order to obtain a pure NiMn 2 O 4 phase. The as-prepared powders were uniaxially pressed into disc shape pellets and then sintered for 60 min at 1200 o C. Changes in the particle morphology induced by mechanical activation were monitored using scanning electron microscopy, while changes in powder structural characteristics were followed using X-ray powder diffraction. The ac impedance spectroscopy was performed on sintered nickel manganite samples at 25 o C, 50 o C and 80 o C. It was shown that mechanical activation intensifies transport processes causing a decrease in the average crystallites size, while longer activation times can lead to the formation of aggregates, defects and increase of lattice microstrains. The observed changes in microstructures were correlated with measured electrical properties in order to define optimal processing conditions.

Magnetoresistance anomaly in DyFeCo thin films

International Nuclear Information System (INIS)

Wu, J. C.; Wu, C. S.; Wu, Te-ho; Chen, Bing-Mau; Shieh, Han-Ping D.

2001-01-01

Microstructured rare-earth - transition-metal DyFeCo films have been investigated using magnetoresistance and extraordinary Hall-effect measurements. The Hall loops reveal variation of coercive fields depending on the linewidth and the composition of the films. The magnetoresistance curves, with changes up to as high as 1.3%, show positive/negative magnetoresistance peaks centered on the coercive fields depending on the linewidth of the films only. The variation of the coercivity can be attributed to the magnetic moment canting between the Dy and FeCo subcomponents and the existence of the diverged magnetization on the edges, and the anomalous magnetoresistance peaks observed are discussed with the existing theories. [copyright] 2001 American Institute of Physics

Study of dependence upon the magnetic field and transport current of the magnetoresistive effect in YBCO-based bulk composites

International Nuclear Information System (INIS)

Balaev, D A; Prus, A G; Shaykhutdinov, K A; Gokhfeld, D M; Petrov, M I

2007-01-01

The magnetoresistive properties of bulk YBCO + CuO and YBCO+BaPb 0.75 Sn 0.25 O 3 composites for different orientations of external magnetic field H and macroscopic transport current j have been measured. These composites exhibit large magnetoresistance in weak magnetic fields ( 2 θ. This fact suggests that the flux flow in the intergrain boundaries is responsible for the large magnetoresistive effect observed in the composites

Spin-flip induced magnetoresistance in positionally disordered organic solids.

Science.gov (United States)

Harmon, N J; Flatté, M E

2012-05-04

A model for magnetoresistance in positionally disordered organic materials is presented and solved using percolation theory. The model describes the effects of spin dynamics on hopping transport by considering changes in the effective density of hopping sites, a key quantity determining the properties of percolative transport. Faster spin-flip transitions open up "spin-blocked" pathways to become viable conduction channels and hence produce magnetoresistance. Features of this percolative magnetoresistance can be found analytically in several regimes, and agree with previous measurements, including the sensitive dependence of the magnetic-field dependence of the magnetoresistance on the ratio of the carrier hopping time to the hyperfine-induced carrier spin precession time. Studies of magnetoresistance in known systems with controllable positional disorder would provide an additional stringent test of this theory.

Recovery of oscillatory magneto-resistance in phase separated La{sub 0.3}Pr{sub 0.4}Ca{sub 0.3}MnO{sub 3} epitaxial thin films

Energy Technology Data Exchange (ETDEWEB)

Alagoz, H. S., E-mail: alagoz@ualberta.ca; Jeon, J.; Mahmud, S. T.; Saber, M. M.; Chow, K. H., E-mail: khchow@ualberta.ca; Jung, J., E-mail: jjung@ualberta.ca [Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1 (Canada); Prasad, B. [Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB2 3QZ (United Kingdom); Egilmez, M. [Department of Physics, American University of Sharjah, Sharjah (United Arab Emirates)

2013-12-02

In-plane angular dependent magneto-resistance has been studied in La{sub 0.3}Pr{sub 0.4}Ca{sub 0.3}MnO{sub 3} (LPCMO) manganite thin films deposited on the (100) oriented NdGaO{sub 3}, and (001) oriented SrTiO{sub 3} and LaAlO{sub 3} substrates. At temperatures where the electronic phase separation is the strongest, a metastable irreversible state exists in the films whose resistivity ρ attains a large time dependent value. The ρ decreases sharply with an increasing angle θ between the magnetic field and the current, and does not display an expected oscillatory cos{sup 2}θ/sin{sup 2}θ dependence for all films. The regular oscillations are recovered during repetitive sweeping of θ between 0° and 180°. We discuss possible factors that could produce these unusual changes in the resistivity.

Charge Ordering, Competing Magnetic Interactions, and Magneto-Resistance Effects in Layered Iron(IV)-Based Oxides

International Nuclear Information System (INIS)

Adler, P.; Ghosh, S.

2002-01-01

Iron(IV)-based Ruddlesden-Popper-type oxides Sr 3 Fe 2-x Co x O 7-y (0≤x≤1) have been synthesized and studied by various techniques. It is shown that iron-57 Moessbauer spectroscopy is a powerful tool for elucidating the intimate correlations between chemical composition, electron-transport properties, electronic state, magnetism, and the large magneto-resistance effects in this system.

Magnetoresistance of galfenol-based magnetic tunnel junction

International Nuclear Information System (INIS)

Gobaut, B.; Vinai, G.; Castán-Guerrero, C.; Krizmancic, D.; Panaccione, G.; Torelli, P.; Rafaqat, H.; Roddaro, S.; Rossi, G.; Eddrief, M.; Marangolo, M.

2015-01-01

The manipulation of ferromagnetic layer magnetization via electrical pulse is driving an intense research due to the important applications that this result will have on memory devices and sensors. In this study we realized a magnetotunnel junction in which one layer is made of Galfenol (Fe 1-x Ga x ) which possesses one of the highest magnetostrictive coefficient known. The multilayer stack has been grown by molecular beam epitaxy and e-beam evaporation. Optical lithography and physical etching have been combined to obtain 20x20 micron sized pillars. The obtained structures show tunneling conductivity across the junction and a tunnel magnetoresistance (TMR) effect of up to 11.5% in amplitude

Magnetoresistive multilayers deposited on the AAO membranes

International Nuclear Information System (INIS)

Malkinski, Leszek M.; Chalastaras, Athanasios; Vovk, Andriy; Jung, Jin-Seung; Kim, Eun-Mee; Jun, Jong-Ho; Ventrice, Carl A.

2005-01-01

Silicon and GaAs wafers are the most commonly used substrates for deposition of giant magnetoresistive (GMR) multilayers. We explored a new type of a substrate, prepared electrochemically by anodization of aluminum sheets, for deposition of GMR multilayers. The surface of this AAO substrate consists of nanosized hemispheres organized in a regular hexagonal array. The current applied along the substrate surface intersects many magnetic layers in the multilayered structure, which results in enhancement of giant magnetoresistance effect. The GMR effect in uncoupled Co/Cu multilayers was significantly larger than the magnetoresistance of similar structures deposited on Si

New type magnetoresistance in Co/Si systems

International Nuclear Information System (INIS)

Honda, S.; Ishikawa, T.; Takai, K.; Mitarai, Y.; Harada, H.

2005-01-01

The magnetoresistance (MR) properties in both the sputter-deposited Co/Si multilayers and the system consisting of Co evaporated on the anodized Si have been examined. In the Co/Si multilayers, at room temperature both the sharp ordinary magnetoresistance (OMR) and the negative granular-type giant magnetoresistance (GMR) appear, while at low temperatures only the large OMR of about 3.5% is observed for in-plane field. In the Co/anodized-Si system, at room temperature the MR is negligibly small, while it increases steeply with decreasing temperature and very large OMR of about 22% is obtained at 110 K for perpendicular field

Semiclassical theory of magnetoresistance in positionally disordered organic semiconductors

Science.gov (United States)

Harmon, N. J.; Flatté, M. E.

2012-02-01

A recently introduced percolative theory of unipolar organic magnetoresistance is generalized by treating the hyperfine interaction semiclassically for an arbitrary hopping rate. Compact analytic results for the magnetoresistance are achievable when carrier hopping occurs much more frequently than the hyperfine field precession period. In other regimes the magnetoresistance can be straightforwardly evaluated numerically. Slow and fast hopping magnetoresistance are found to be uniquely characterized by their line shapes. We find that the threshold hopping distance is analogous a phenomenological two-site model's branching parameter, and that the distinction between slow and fast hopping is contingent on the threshold hopping distance.

Magnetic tunnel structures: Transport properties controlled by bias, magnetic field, and microwave and optical radiation

International Nuclear Information System (INIS)

Volkov, N.V.; Eremin, E.V.; Tarasov, A.S.; Rautskii, M.V.; Varnakov, S.N.; Ovchinnikov, S.G.; Patrin, G.S.

2012-01-01

Different phenomena that give rise to a spin-polarized current in some systems with magnetic tunnel junctions are considered. In a manganite-based magnetic tunnel structure in CIP geometry, the effect of current-channel switching was observed, which causes bias-driven magnetoresistance, rf rectification, and the photoelectric effect. The second system under study, ferromagnetic/insulator/semiconductor, exhibits the features of the transport properties in CIP geometry that are also related to the current-channel switching effect. The described properties can be controlled by a bias, a magnetic field, and optical radiation. At last, the third system under consideration is a cooperative assembly of magnetic tunnel junctions. This system exhibits tunnel magnetoresistance and the magnetic-field-driven microwave detection effect.

Fabrication of Polycrystalline Lanthanum Manganite (La0.99 Mn0.01 O3) Powder and Fibres by Electrospinning Method

International Nuclear Information System (INIS)

Yin Yin Win; That Htar Lwin; Than Than Win; Yin Maung Maung; Ko Ko Kyaw Soe

2011-12-01

Lanthanum manganite (La0.99 Mn0.01 O3) powder have been prepared by using pyrolysis methods. Lanthanum manganite fibres were successfully fabricated by electro-spinning utilizing precursors. Polycrystalline perovskite structure lanthanum manganite powder and fibres showed that the grain size and crystal grain increased significantly with the increase in calcination temperature. A variety of techniques (SEM, FT-IR and TG-DTA) were employed to study the morphology and fibre quality, crystal structure, and thermal analysis of La0.99 Mn0.01 O3 specimen respectively.

Quasilinear quantum magnetoresistance in pressure-induced nonsymmorphic superconductor chromium arsenide.

Science.gov (United States)

Niu, Q; Yu, W C; Yip, K Y; Lim, Z L; Kotegawa, H; Matsuoka, E; Sugawara, H; Tou, H; Yanase, Y; Goh, Swee K

2017-06-05

In conventional metals, modification of electron trajectories under magnetic field gives rise to a magnetoresistance that varies quadratically at low field, followed by a saturation at high field for closed orbits on the Fermi surface. Deviations from the conventional behaviour, for example, the observation of a linear magnetoresistance, or a non-saturating magnetoresistance, have been attributed to exotic electron scattering mechanisms. Recently, linear magnetoresistance has been observed in many Dirac materials, in which the electron-electron correlation is relatively weak. The strongly correlated helimagnet CrAs undergoes a quantum phase transition to a nonmagnetic superconductor under pressure. Here we observe, near the magnetic instability, a large and non-saturating quasilinear magnetoresistance from the upper critical field to 14 T at low temperatures. We show that the quasilinear magnetoresistance may arise from an intricate interplay between a nontrivial band crossing protected by nonsymmorphic crystal symmetry and strong magnetic fluctuations.

Spin glass behavior in nanogranular La0.25Ca0.75MnO3 manganites

International Nuclear Information System (INIS)

2UB, Universitat de Barcelona, Martí i Franquès 1, planta 3, edifici nou, 08028 Barcelona (Spain))" data-affiliation=" (Grup de Magnetisme, Dept. Física Fonamental, Facultat de Física, Universitat de Barcelona, Martí i Franquès 1, planta 4, edifici nou, 08028 Barcelona (Spain); Institut de Nanociència i Nanotecnologia IN2UB, Universitat de Barcelona, Martí i Franquès 1, planta 3, edifici nou, 08028 Barcelona (Spain))" >Fernández-Martínez, Antoni; 2UB, Universitat de Barcelona, Martí i Franquès 1, planta 3, edifici nou, 08028 Barcelona (Spain))" data-affiliation=" (Grup de Magnetisme, Dept. Física Fonamental, Facultat de Física, Universitat de Barcelona, Martí i Franquès 1, planta 4, edifici nou, 08028 Barcelona (Spain); Institut de Nanociència i Nanotecnologia IN2UB, Universitat de Barcelona, Martí i Franquès 1, planta 3, edifici nou, 08028 Barcelona (Spain))" >García-Santiago, Antoni; 2UB, Universitat de Barcelona, Martí i Franquès 1, planta 3, edifici nou, 08028 Barcelona (Spain))" data-affiliation=" (Grup de Magnetisme, Dept. Física Fonamental, Facultat de Física, Universitat de Barcelona, Martí i Franquès 1, planta 4, edifici nou, 08028 Barcelona (Spain); Institut de Nanociència i Nanotecnologia IN2UB, Universitat de Barcelona, Martí i Franquès 1, planta 3, edifici nou, 08028 Barcelona (Spain))" >Hernàndez, Joan Manel; Zhang, Tao

2014-01-01

The magnetic properties of two nanogranular La 0.25 Ca 0.75 MnO 3 manganites with different average grain sizes have been studied. Besides the well-known exchange bias effect and the appearance of ferromagnetic clusters in the grains of both samples, the results show the occurrence of an antiferromagnetic transition and spin-glass properties. Both samples are described as core–shell magnetic systems, whose main difference is found in the interface between the outer ferromagnetic and the inner antiferromagnetic phases of the grains. - Highlights: • Nanogranular manganites show antiferromagnetism in magnetic measurements. • Exchange bias effect was observed in magnetic hysteresis cycles. • Spin-glass properties were detected at low temperatures. • A core-shell model was applied to describe the results in both samples. • These features have nothing to do with usual properties of nanoparticle manganites

The magnetoresistivity of some rare-earth metals

International Nuclear Information System (INIS)

Webber, G.D.

1978-10-01

The thesis describes measurements of the low temperature transverse magnetoresistivities of single crystals of rare-earth metals in magnetic fields up to 8 Tesla. A general introduction to the rare-earths, their magnetic properties and a review of the basic theory and mechanism of magnetoresistivity is given. Details of the crystal structure, growth of single crystals and sample mounting method follow. The experimental equipment and measuring techniques are then described. The low temperature transverse magnetoresistivity of polycrystalline lanthanum and single crystal praseodymium for the temperature range 4.2 - 30K is measured. The separation of the spin-disorder and Fermi-surface orbital effect contributions are described and the theoretical and experimental spin-disorder values compared. Magnetoresistivity measurements for neodymium single crystals (4.2 - 30K) are compared with the magnetic properties determined from neutron diffraction studies. Results for gadolinium single crystals (4.2 - 200K) are compared for two different impurity levels and with previous work. (UK)

Mutual influence between current-induced giant magnetoresistance and radiation-induced magnetoresistance oscillations in the GaAs/AlGaAs 2DES

OpenAIRE

Samaraweera, R. L.; Liu, H.-C.; Wang, Z.; Reichl, C.; Wegscheider, W.; Mani, R. G.

2017-01-01

Radiation-induced magnetoresistance oscillations are examined in the GaAs/AlGaAs 2D system in the regime where an observed concurrent giant magnetoresistance is systematically varied with a supplementary dc-current, I dc . The I dc tuned giant magnetoresistance is subsequently separated from the photo-excited oscillatory resistance using a multi-conduction model in order to examine the interplay between the two effects. The results show that the invoked multiconduction model describes the obs...

Magnetoresistance in molybdenite (MoS2) crystals

International Nuclear Information System (INIS)

Chakraborty, B.R.; Dutta, A.K.

1975-01-01

The principal magnetoresistance ratios of molybdenite (MoS 2 ), the naturally occurring semiconducting crystal, have been investigated at magnetic fields ranging from 4.5 KOe and within the temperature range 300 0 K to 700 0 K. Unlike some previous observations, magnetoresistance has been found to be negative. (author)

Microstructural and electrical changes in nickel manganite powder induced by mechanical activation

Energy Technology Data Exchange (ETDEWEB)

Savic, S.M., E-mail: slavicas@cms.bg.ac.rs [Institute for Multidisciplinary Research-University of Belgrade, Kneza Viseslava 1a, 11030 Belgrade (Serbia); Mancic, L. [Institute of Technical Sciences SASA, Knez Mihailova 35/IV, 11000 Belgrade (Serbia); Vojisavljevic, K. [Institute for Multidisciplinary Research-University of Belgrade, Kneza Viseslava 1a, 11030 Belgrade (Serbia); Stojanovic, G. [Faculty of Technical Sciences University of Novi Sad, Trg Dositeja Obradovica 6, 21000 Novi Sad (Serbia); Brankovic, Z.; Aleksic, O.S.; Brankovic, G. [Institute for Multidisciplinary Research-University of Belgrade, Kneza Viseslava 1a, 11030 Belgrade (Serbia)

2011-07-15

Highlights: {yields} The influence of mechanical activation on microstructure evolution in the nickel manganite powder was investigated as well as electrical properties of the sintered samples. {yields} Structural refinement obtained by Topas-Academic software based on Rietveld analysis showed that the milling process remarkably changed the powder morphology and microstructure. {yields} SEM studies of sintered samples also revealed the strong influence of milling time on ceramics density (increases with milling time). {yields} The electrical properties of ceramic samples are clearly conditioned by terms of synthesis, in our case the time of mechanical activation. {yields} The highest density and higher values of dielectric constant were achieved at the sample activated for 45 min. -- Abstract: Nickel manganite powder synthesized by calcination of a stoichiometric mixture of manganese and nickel oxide was additionally mechanically activated in a high energy planetary ball mill for 5-60 min in order to obtain a pure NiMn{sub 2}O{sub 4} phase. The as-prepared powders were uniaxially pressed into disc shape pellets and then sintered for 60 min at 1200 {sup o}C. Changes in the particle morphology induced by mechanical activation were monitored using scanning electron microscopy, while changes in powder structural characteristics were followed using X-ray powder diffraction. The ac impedance spectroscopy was performed on sintered nickel manganite samples at 25 {sup o}C, 50 {sup o}C and 80 {sup o}C. It was shown that mechanical activation intensifies transport processes causing a decrease in the average crystallites size, while longer activation times can lead to the formation of aggregates, defects and increase of lattice microstrains. The observed changes in microstructures were correlated with measured electrical properties in order to define optimal processing conditions.

On-chip magnetic bead-based DNA melting curve analysis using a magnetoresistive sensor

DEFF Research Database (Denmark)

Rizzi, Giovanni; Østerberg, Frederik Westergaard; Henriksen, Anders Dahl

2014-01-01

We present real-time measurements of DNA melting curves in a chip-based system that detects the amount of surface-bound magnetic beads using magnetoresistive magnetic field sensors. The sensors detect the difference between the amount of beads bound to the top and bottom sensor branches....... The beads are magnetized by the field arising from the bias current passed through the sensors. We demonstrate the first on-chip measurements of the melting of DNA hybrids upon a ramping of the temperature. This overcomes the limitation of using a single washing condition at constant temperature. Moreover...

Spin Hall magnetoresistance at high temperatures

International Nuclear Information System (INIS)

Uchida, Ken-ichi; Qiu, Zhiyong; Kikkawa, Takashi; Iguchi, Ryo; Saitoh, Eiji

2015-01-01

The temperature dependence of spin Hall magnetoresistance (SMR) in Pt/Y 3 Fe 5 O 12 (YIG) bilayer films has been investigated in a high temperature range from room temperature to near the Curie temperature of YIG. The experimental results show that the magnitude of the magnetoresistance ratio induced by the SMR monotonically decreases with increasing the temperature and almost disappears near the Curie temperature. We found that, near the Curie temperature, the temperature dependence of the SMR in the Pt/YIG film is steeper than that of a magnetization curve of the YIG; the critical exponent of the magnetoresistance ratio is estimated to be 0.9. This critical behavior of the SMR is attributed mainly to the temperature dependence of the spin-mixing conductance at the Pt/YIG interface

Magnetoresistance of galfenol-based magnetic tunnel junction

Energy Technology Data Exchange (ETDEWEB)

Gobaut, B., E-mail: benoit.gobaut@elettra.eu [Sincrotrone Trieste S.C.p.A., S.S. 14 Km 163.5, Area Science Park, 34149 Trieste (Italy); Vinai, G.; Castán-Guerrero, C.; Krizmancic, D.; Panaccione, G.; Torelli, P. [Laboratorio TASC, IOM-CNR, S.S. 14km 163.5, Basovizza, 34149 Trieste (Italy); Rafaqat, H. [Laboratorio TASC, IOM-CNR, S.S. 14km 163.5, Basovizza, 34149 Trieste (Italy); ICTP, Trieste (Italy); Roddaro, S. [Laboratorio TASC, IOM-CNR, S.S. 14km 163.5, Basovizza, 34149 Trieste (Italy); NEST, Scuola Normale Superiore and Istituto Nanoscienze-CNR, Piazza S. Silvestro 12, 56127 Pisa (Italy); Rossi, G. [Laboratorio TASC, IOM-CNR, S.S. 14km 163.5, Basovizza, 34149 Trieste (Italy); Dipartimento di Fisica, Università di Milano, via Celoria 16, 20133 Milano (Italy); Eddrief, M.; Marangolo, M. [Sorbonne Universités, UPMC Paris 06, CNRS-UMR 7588, Institut des Nanosciences de Paris, 75005, Paris (France)

2015-12-15

The manipulation of ferromagnetic layer magnetization via electrical pulse is driving an intense research due to the important applications that this result will have on memory devices and sensors. In this study we realized a magnetotunnel junction in which one layer is made of Galfenol (Fe{sub 1-x}Ga{sub x}) which possesses one of the highest magnetostrictive coefficient known. The multilayer stack has been grown by molecular beam epitaxy and e-beam evaporation. Optical lithography and physical etching have been combined to obtain 20x20 micron sized pillars. The obtained structures show tunneling conductivity across the junction and a tunnel magnetoresistance (TMR) effect of up to 11.5% in amplitude.

Magnetoresistance effect in a both magnetically and electrically modulated nanostructure

International Nuclear Information System (INIS)

Lu, Mao-Wang; Yang, Guo-Jian

2007-01-01

We propose a magnetoresistance device in a both magnetically and electrically modulated two-dimensional electron gas, which can be realized experimentally by the deposition, on the top and bottom of a semiconductor heterostructure, of two parallel metallic ferromagnetic strips under an applied voltage. It is shown that a considerable magnetoresistance effect can be achieved in such a device due to the significant transmission difference for electrons through parallel and antiparallel magnetization configurations. It is also shown that the magnetoresistance ratio depends strongly on the applied voltage to the stripe in the device. These interesting properties may provide an alternative scheme to realize magnetoresistance effect in hybrid ferromagnetic/semiconductor nanosystems, and this system may be used as a voltage-tunable magnetoresistance device

Two-dimensional salt and temperature DNA denaturation analysis using a magnetoresistive sensor

DEFF Research Database (Denmark)

Rizzi, Giovanni; Dufva, Martin; Hansen, Mikkel Fougt

2017-01-01

We present a microfluidic system and its use to measure DNA denaturation curves by varying the temperature or salt (Na+) concentration. The readout is based on real-time measurements of DNA hybridization using magnetoresistive sensors and magnetic nanoparticles (MNPs) as labels. We report the first...... melting curves of DNA hybrids measured as a function of continuously decreasing salt concentration at fixed temperature and compare them to the corresponding curves obtained vs. temperature at fixed salt concentration. The magnetoresistive sensor platform provided reliable results under varying....... The results demonstrate that concentration melting provides an attractive alternative to temperature melting in on-chip DNA denaturation experiments and further show that the magnetoresistive platform is attractive due to its low cross-sensitivity to temperature and liquid composition....

Unidirectional spin-Hall and Rashba-Edelstein magnetoresistance in topological insulator-ferromagnet layer heterostructures.

Science.gov (United States)

Lv, Yang; Kally, James; Zhang, Delin; Lee, Joon Sue; Jamali, Mahdi; Samarth, Nitin; Wang, Jian-Ping

2018-01-09

The large spin-orbit coupling in topological insulators results in helical spin-textured Dirac surface states that are attractive for topological spintronics. These states generate an efficient spin-orbit torque on proximal magnetic moments. However, memory or logic spin devices based upon such switching require a non-optimal three-terminal geometry, with two terminals for the writing current and one for reading the state of the device. An alternative two-terminal device geometry is now possible by exploiting the recent discovery of the unidirectional spin Hall magnetoresistance in heavy metal/ferromagnet bilayers and unidirectional magnetoresistance in magnetic topological insulators. Here, we report the observation of such unidirectional magnetoresistance in a technologically relevant device geometry that combines a topological insulator with a conventional ferromagnetic metal. Our devices show a figure of merit (magnetoresistance per current density per total resistance) that is more than twice as large as the highest reported values in all-metal Ta/Co bilayers.

Colossal magnetoresistance manganites: A new approach

Indian Academy of Sciences (India)

Unknown

hopping, and band-like, nonpolaronic states b, leading to a new 2-band .... implications of the model, we have ignored spatial correlations of the orbital structure or .... induced t2g spin alignment (maximum near Tc) increasing D and thus b.

The effect of spin-orbit coupling on magnetoresistance in nonmagnetic organic semiconductors

International Nuclear Information System (INIS)

Zhao Jun-Qing; Ding Meng; Zhang Tian-You; Zhang Ning-Yu; Pang Yan-Tao; Ji Yan-Ju; Chen Ying; Wang Feng-Xiang; Fu Gang

2012-01-01

We investigated the effect of spin-orbit coupling on magnetoresistance in nonmagnetic organic semiconductors. A Lorentz-type magnetoresistance is obtained from spin-orbit coupling-dependent spin precession under the condition of a space-charge-limited current. The magnetoresistance depends on the initial spin orientation of the electron with respect to the hole in electron—hole pairs, and the increasing spin-orbit coupling slows down the change in magnetoresistance with magnetic field. The field dependence, the sign and the saturation value of the magnetoresistance are composite effects of recombination and dissociation rate constants of singlet and triplet electron—hole pairs. The simulated magnetoresistance shows good consistency with the experimental results. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Effect of quantum tunneling on spin Hall magnetoresistance.

Science.gov (United States)

Ok, Seulgi; Chen, Wei; Sigrist, Manfred; Manske, Dirk

2017-02-22

We present a formalism that simultaneously incorporates the effect of quantum tunneling and spin diffusion on the spin Hall magnetoresistance observed in normal metal/ferromagnetic insulator bilayers (such as Pt/Y 3 Fe 5 O 12 ) and normal metal/ferromagnetic metal bilayers (such as Pt/Co), in which the angle of magnetization influences the magnetoresistance of the normal metal. In the normal metal side the spin diffusion is known to affect the landscape of the spin accumulation caused by spin Hall effect and subsequently the magnetoresistance, while on the ferromagnet side the quantum tunneling effect is detrimental to the interface spin current which also affects the spin accumulation. The influence of generic material properties such as spin diffusion length, layer thickness, interface coupling, and insulating gap can be quantified in a unified manner, and experiments that reveal the quantum feature of the magnetoresistance are suggested.

Hopping magnetotransport via nonzero orbital momentum states and organic magnetoresistance.

Science.gov (United States)

Alexandrov, Alexandre S; Dediu, Valentin A; Kabanov, Victor V

2012-05-04

In hopping magnetoresistance of doped insulators, an applied magnetic field shrinks the electron (hole) s-wave function of a donor or an acceptor and this reduces the overlap between hopping sites resulting in the positive magnetoresistance quadratic in a weak magnetic field, B. We extend the theory of hopping magnetoresistance to states with nonzero orbital momenta. Different from s states, a weak magnetic field expands the electron (hole) wave functions with positive magnetic quantum numbers, m>0, and shrinks the states with negative m in a wide region outside the point defect. This together with a magnetic-field dependence of injection/ionization rates results in a negative weak-field magnetoresistance, which is linear in B when the orbital degeneracy is lifted. The theory provides a possible explanation of a large low-field magnetoresistance in disordered π-conjugated organic materials.

Large magnetoresistance in La-Ca-Mn-O films

International Nuclear Information System (INIS)

Chen, L.H.; Jin, S.; Tiefel, T.H.; Ramesh, R.; Schurig, D.

1995-01-01

A very large magnetoresistance value in excess of 10 6 % has been obtained at 110 K, H = 6 T in La-Ca-Mn-O thin films epitaxially grown on LaAlO 3 substrates by pulsed laser deposition. The as-deposited film exhibits a substantial magnetoresistance value of 39,000%, which is further improved by heat treatment. A strong dependence of the magnetoresistance on film thickness was observed, with the value reduced by orders of magnitude when the film is made thicker than ∼2,000 angstrom. This behavior is interpreted in terms of lattice strain in the La-Ca-Mn-O films

Fractional Modeling of the AC Large-Signal Frequency Response in Magnetoresistive Current Sensors

Directory of Open Access Journals (Sweden)

Sergio Iván Ravelo Arias

2013-12-01

Full Text Available Fractional calculus is considered when derivatives and integrals of non-integer order are applied over a specific function. In the electrical and electronic domain, the transfer function dependence of a fractional filter not only by the filter order n, but additionally, of the fractional order α is an example of a great number of systems where its input-output behavior could be more exactly modeled by a fractional behavior. Following this aim, the present work shows the experimental ac large-signal frequency response of a family of electrical current sensors based in different spintronic conduction mechanisms. Using an ac characterization set-up the sensor transimpedance function  is obtained considering it as the relationship between sensor output voltage and input sensing current,[PLEASE CHECK FORMULA IN THE PDF]. The study has been extended to various magnetoresistance sensors based in different technologies like anisotropic magnetoresistance (AMR, giant magnetoresistance (GMR, spin-valve (GMR-SV and tunnel magnetoresistance (TMR. The resulting modeling shows two predominant behaviors, the low-pass and the inverse low-pass with fractional index different from the classical integer response. The TMR technology with internal magnetization offers the best dynamic and sensitivity properties opening the way to develop actual industrial applications.

Electrical behaviour of strontium-doped lanthanum manganite interfaces

DEFF Research Database (Denmark)

Koch, Søren; Hendriksen, P.V.; Jacobsen, Torben

2005-01-01

The contact resistance of strontium-doped lanthanum manganite (LSM) contact pairs is investigated by polarisation analysis at different temperatures and atmospheres. The ceramic contacts have a high contact resistance, and strongly nonlinear current–voltage behaviour is observed at low temperatur....... The nonlinear behaviour is ascribed to the presence of energy barriers at the contact interface. Generally, point contacts showed a more linear behaviour than plane contact interfaces....

Influence of voltage on magnetization of ferromagnetic semiconductors with colossal magnetoresistance

International Nuclear Information System (INIS)

Povzner, A.A.; Volkov, A.G.

2017-01-01

Graphical abstract: We investigate nonequilibrium states of strongly correlated electron subsystem of lanthanum manganite, resulting in an external electric field. It is shown that the Joule heat leads to localization of electrons. As result, electric resistance, magnetization and other characteristics of the electronic system are depending on the applied voltage. This leads to the formation of the bistable state of the electronic system in the vicinity of the Curie point in an external electric field. This manifests itself in non-linear current-voltage characteristics of these substances, and should lead to oscillations of the magnetization and current. - Abstract: The nonequilibrium processes of “self-heating” arising during the flow of electric current are studied for ferromagnetic semiconductors with colossal magnetoresistance near the Curie temperature. These processes lead to the emergence of “hot” paramagnons and the destruction of ferromagnetic order. The solution to the heat balance equation takes into account the temperature dependence of the electrical conductivity caused by Anderson localization of electrons due to their scattering on magnetic inhomogeneities. Description of delocalized electrons subsystem takes into account the spin-flip processes leading to the double exchange. At that, the value of the Anderson percolation threshold and the double exchange depends on the amplitude of spin fluctuations. It was found that N-shaped current-voltage characteristics and hysteresis dependencies of magnetization on the voltage arise in a steady state due to the emergence of “hot” (by internal sample temperature) semiconductor paramagnetic phase. It is shown that the occurrence of self-oscillations of current and magnetization there may be.

Influence of voltage on magnetization of ferromagnetic semiconductors with colossal magnetoresistance

Energy Technology Data Exchange (ETDEWEB)

Povzner, A.A., E-mail: a.a.povzner@urfu.ru; Volkov, A.G., E-mail: agvolkov@yandex.ru

2017-06-15

Graphical abstract: We investigate nonequilibrium states of strongly correlated electron subsystem of lanthanum manganite, resulting in an external electric field. It is shown that the Joule heat leads to localization of electrons. As result, electric resistance, magnetization and other characteristics of the electronic system are depending on the applied voltage. This leads to the formation of the bistable state of the electronic system in the vicinity of the Curie point in an external electric field. This manifests itself in non-linear current-voltage characteristics of these substances, and should lead to oscillations of the magnetization and current. - Abstract: The nonequilibrium processes of “self-heating” arising during the flow of electric current are studied for ferromagnetic semiconductors with colossal magnetoresistance near the Curie temperature. These processes lead to the emergence of “hot” paramagnons and the destruction of ferromagnetic order. The solution to the heat balance equation takes into account the temperature dependence of the electrical conductivity caused by Anderson localization of electrons due to their scattering on magnetic inhomogeneities. Description of delocalized electrons subsystem takes into account the spin-flip processes leading to the double exchange. At that, the value of the Anderson percolation threshold and the double exchange depends on the amplitude of spin fluctuations. It was found that N-shaped current-voltage characteristics and hysteresis dependencies of magnetization on the voltage arise in a steady state due to the emergence of “hot” (by internal sample temperature) semiconductor paramagnetic phase. It is shown that the occurrence of self-oscillations of current and magnetization there may be.

Anisotropic magnetoresistance and thermodynamic fluctuations in high-temperature superconductors

International Nuclear Information System (INIS)

Heine, G.

1999-05-01

Measurements of the in-plane and out-of-plane resistivity and the transverse and longitudinal in-plane and out-of-plane magnetoresistance above T, are reported in the high-temperature superconductors Bi2Sr2CaCu208+' and YBa2CU307 b . The carrier concentration of the Bi2Sr2CaCu208+' single crystals covers a broad range of the phase diagram from the slightly under doped to the moderately over doped region. The doping concentration of the thin films ranges from strongly under doped to optimally doped. The in-plane resistivities obey a metallic-like temperature dependence with a positive magnetoresistance in the transverse and the longitudinal orientation of the magnetic field. The out-of-plane resistivities show an activated behavior above T, with a metallic region at higher temperatures and negative magnetoresistance. The data were analyzed in the framework of a model for superconducting order parameter fluctuations. The positive in-plane magnetoresistance of the highly anisotropic Bi2Sr2CaCu208+x single crystals is interpreted as the suppression of the fluctuation-conductivity enhancement including orbital and spin contributions, whereas the negative magnetoresistance arises from the reduction of the fluctuation-induced pseudogap in the single-electron density-of-states by the magnetic field. For higher temperatures a transition to the normal-state magnetoresistance occurs for the in-plane transport. In the less anisotropic YBa2CU307 b thin films the positive out-of-plane magnetoresistance near T, changes sign to a negative magnetoresistance at higher temperatures. This behavior is also consistent with predictions from the theory of thermodynamic order-parameter fluctuations. The agreement of the fluctuation theory with the experimental findings is excellent for samples from the over doped side of the phase diagram, but deteriorate with decreasing carrier concentration. This behavior is interpreted by the dominating d-wave symmetry of the superconducting order

Magnetoresistance and magnetic ordering in praseodymium and neodymium hexaborides

International Nuclear Information System (INIS)

Anisimov, M. A.; Bogach, A. V.; Glushkov, V. V.; Demishev, S. V.; Samarin, N. A.; Filipov, V. B.; Shitsevalova, N. Yu.; Kuznetsov, A. V.; Sluchanko, N. E.

2009-01-01

The magnetoresistance Δρ/ρ of single-crystal samples of praseodymium and neodymium hexaborides (PrB 6 and NdB 6 ) has been measured at temperatures ranging from 2 to 20 K in a magnetic field of up to 80 kOe. The results obtained have revealed a crossover of the regime from a small negative magnetoresistance in the paramagnetic state to a large positive magnetoresistive effect in magnetically ordered phases of the PrB 6 and NdB 6 compounds. An analysis of the dependences Δρ(H)/ρ has made it possible to separate three contributions to the magnetoresistance for the compounds under investigation. In addition to the main negative contribution, which is quadratic in the magnetic field (-Δρ/ρ ∝ H 2 ), a linear positive contribution (Δρ/ρ ∝ H) and a nonlinear ferromagnetic contribution have been found. Upon transition to a magnetically ordered state, the linear positive component in the magnetoresistance of the PrB 6 and NdB 6 compounds becomes dominant, whereas the quadratic contribution to the negative magnetoresistance is completely suppressed in the commensurate magnetic phase of these compounds. The presence of several components in the magnetoresistance has been explained by assuming that, in the antiferromagnetic phases of PrB 6 and NdB 6 , ferromagnetic nanoregions (ferrons) are formed in the 5d band in the vicinity of the rareearth ions. The origin of the quadratic contribution to the negative magnetoresistance is interpreted in terms of the Yosida model, which takes into account scattering of conduction electrons by localized magnetic moments of rare-earth ions. Within the approach used, the local magnetic susceptibility χ loc has been estimated. It has been demonstrated that, in the temperature range T N loc for the compounds under investigation can be described with good accuracy by the Curie-Weiss dependence χ loc ∝ (T - Θ p ) -1 .

Thermoelectric power and electrical conductivity of strontium-doped lanthanum manganite

DEFF Research Database (Denmark)

Ahlgren, E.O.; Poulsen, F.W.

1996-01-01

Thermoelectric power and electrical conductivity of pure and 5, 10 and 20% strontium-doped lanthanum manganite are determined as function of temperature in air and of P-O2 at 1000 degrees C. At high temperatures the thermoelectric power is negative. Both thermoelectric power and conductivity...

3000% high-field magnetoresistance in super-lattices of CoFe nanoparticles

International Nuclear Information System (INIS)

Tan, Reasmey P.; Carrey, Julian; Respaud, Marc; Desvaux, Celine; Renaud, Philippe; Chaudret, Bruno

2008-01-01

We report on magnetotransport measurements on millimeter-large super-lattices of CoFe nanoparticles surrounded by an organic layer. Electrical properties are typical of Coulomb blockade in three-dimensional arrays of nanoparticles. A large high-field magnetoresistance, reaching up to 3000%, is measured between 1.8 and 10 K. This exceeds by two orders of magnitude magnetoresistance values generally measured in arrays of 3d transition metal ferromagnetic nanoparticles. The magnetoresistance amplitude scales with the magnetic field/temperature ratio and displays an unusual exponential dependency with the applied voltage. The magnetoresistance abruptly disappears below 1.8 K. We propose that the magnetoresistance is due to some individual paramagnetic moments localized between the metallic cores of the nanoparticles, the origin of which is discussed

Big magnetoresistance: magnetic polarons

International Nuclear Information System (INIS)

Teresa, J.M. de; Ibarra, M.R.

1997-01-01

By using several macro and microscopic experimental techniques we have given evidence for magnetoresistance in manganese oxides caused by the effect of the magnetic field on the magnetic polarons. (Author) 3 refs

Transverse magnetoresistance induced by electron-surface scattering on thin gold films: Experiment and theory

International Nuclear Information System (INIS)

Oyarzún, Simón; Henríquez, Ricardo; Suárez, Marco Antonio; Moraga, Luis; Kremer, Germán; Munoz, Raúl C.

2014-01-01

We report new experimental data regarding the transverse magnetoresistance measured in a family of thin gold films of different thickness with the electric field E oriented perpendicular to the magnetic field B (both fields contained within the plane of the film), as well as a theoretical description of size effects based upon a solution of Boltzmann Transport Equation. The measurements were performed at low temperatures T (4 K ≤ T ≤ 50 K) under magnetic field strengths B (1.5 T ≤ B ≤ 9 T). The magnetoresistance signal can be univocally identified as arising from electron-surface scattering, for the Hall mobility at 4 K depends linearly on film thickness. The magnetoresistance signal exhibits a marked thickness dependence, and its curvature as a function of magnetic field B varies with film thickness. The theoretical description of the magnetic field dependence of the magnetoresistance requires a Hall field that varies with the thickness of the film; this Hall field is tuned to reproduce the experimental data.

Transverse magnetoresistance induced by electron-surface scattering on thin gold films: Experiment and theory

Energy Technology Data Exchange (ETDEWEB)

Oyarzún, Simón [Institut Lumière Matière, UMR5306 Université Lyon 1-CNRS, Université de Lyon, 69622 Villeurbanne CEDEX (France); Henríquez, Ricardo [Departamento de Física, Universidad Técnica Federico Santa María, Av. España 1680, Casilla 110-V, Valparaíso (Chile); Suárez, Marco Antonio; Moraga, Luis [Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Blanco Encalada 2008, Casilla 487-3, Santiago 8370449 (Chile); Kremer, Germán [Bachillerato, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Santiago 7800024 (Chile); Munoz, Raúl C., E-mail: ramunoz@ing.uchile.cl [Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Blanco Encalada 2008, Casilla 487-3, Santiago 8370449 (Chile)

2014-01-15

We report new experimental data regarding the transverse magnetoresistance measured in a family of thin gold films of different thickness with the electric field E oriented perpendicular to the magnetic field B (both fields contained within the plane of the film), as well as a theoretical description of size effects based upon a solution of Boltzmann Transport Equation. The measurements were performed at low temperatures T (4 K ≤ T ≤ 50 K) under magnetic field strengths B (1.5 T ≤ B ≤ 9 T). The magnetoresistance signal can be univocally identified as arising from electron-surface scattering, for the Hall mobility at 4 K depends linearly on film thickness. The magnetoresistance signal exhibits a marked thickness dependence, and its curvature as a function of magnetic field B varies with film thickness. The theoretical description of the magnetic field dependence of the magnetoresistance requires a Hall field that varies with the thickness of the film; this Hall field is tuned to reproduce the experimental data.

Giant magneto-resistance devices

CERN Document Server

Hirota, Eiichi; Inomata, Koichiro

2002-01-01

This book deals with the application of giant magneto-resistance (GMR) effects to electronic devices. It will appeal to engineers and graduate students in the fields of electronic devices and materials. The main subjects are magnetic sensors with high resolution and magnetic read heads with high sensitivity, required for hard-disk drives with recording densities of several gigabytes. Another important subject is novel magnetic random-access memories (MRAM) with non-volatile non-destructive and radiation-resistant characteristics. Other topics include future GMR devices based on bipolar spin transistors, spin field-effect transistors (FETs) and double-tunnel junctions.

Surface Spin Glass Ordering and Exchange Bias in Nanometric Sm0.09Ca0.91MnO3 Manganites

Science.gov (United States)

Giri, S. K.; Nath, T. K.

2011-07-01

We have thoroughly investigated the entire magnetic state of under doped ferromagnetic insulating manganite Sm0.09Ca0.91MnO3 through temperature dependent linear and non-linear ac magnetic susceptibility and magnetization measurements. This ferromagnetic insulating manganite is found to have frequency dependent ferromagnetic to paramagnetic transition temperature at around 108 K. Exchange- bias effect are observed in field -cooled magnetic hysteresis loops for this nanoparticle. We have attributed our observation to the formation of ferromagnetic cluster which are formed as a consequence of intrinsic phase separation below certain temperature in this under doped manganites. We have carried out electronic- and magneto-transport measurements to support these observed results.

Anisotropy of magnetoresistance on trapping magnetic fields in granular HTSC

CERN Document Server

Sukhanov, A A

2003-01-01

The features of magnetoresistance in Bi (Pb)-HTSC ceramics with the magnetic fields trapped are investigated. It is found that on trapping magnetic flux the magnetoresistance in granular HTSC becomes anisotropic. Moreover, for magnetic fields H parallel and currents perpendicular to field H sub i which induces the trapping the magnetoresistance field dependence DELTA R(H) is nonmonotonic and the magnetoresistance is negative for small fields H < Hinv. The effect of trapped field and transport current and their orientations on the dependence DELTA R(H) is investigated. In particular, it is found that the field of magnetoresistance sign inversion Hinv almost linearly grows with increase of the effective trapped magnetic fields. Hinv decreases down to zero as the angle between fields H and H sub i increases up to pi/2 and slightly decreases with increasing transport current. The results are treated in terms of the model of magnetic flux trapping in superconducting grains or 'loops' embedded in a matrix of wea...

Magnetoresistive waves in plasmas

International Nuclear Information System (INIS)

Felber, F.S.; Hunter, R.O. Jr.; Pereira, N.R.; Tajima, T.

1982-01-01

The self-generated magnetic field of a current diffusing into a plasma between conductors can magnetically insulate the plasma. Propagation of magnetoresistive waves in plasmas is analyzed. Applications to plasma opening switches are discussed

Fusion neutron effects on magnetoresistivity of copper stabilizer materials

International Nuclear Information System (INIS)

Guinan, M.W.; Van Konynenburg, R.A.

1983-01-01

Eight copper wires were repeatedly irradiated at 4.2 to 4.4 K with 14.8 MV neutrons and isochronally annealed at temperatures up to 34 0 C for a total of five cycles. Their electrical resistances were monitored during irradiation under zero applied magnetic field. After each irradiation the magnetoresistances were measured in applied transverse magnetic fields of up to 12 T. Then the samples were isochronally annealed to observe the recovery of the resistivity and magnetoresistivity. After each anneal at the highest temperature (34 0 C), some of the damage remained and contributed to the damage state observed following the subsequent irradiation. In this way, we were able to observe how the changes in magnetoresistance would accumulate during the repeated irradiations and anneals expected to be characteristic of fusion reactor magnets. For each succeeding irradiation the fluence was chosen to produce approximately the same final magnetoresistance at 12 T, taking account of the accumulating residual radiation damage. The increment of magnetoresistivity added by the irradiation varied from 35 to 65% at 12 T and from 50 to 90% at 8 T for the various samples

Gadolinium- and manganite-based contrast agents with fluorescent probes for both magnetic resonance and fluorescence imaging of pancreatic islets: a comparative study

Czech Academy of Sciences Publication Activity Database

Berková, Z.; Jirák, D.; Zacharovová, K.; Lukeš, I.; Kotková, Z.; Kotek, J.; Kačenka, M.; Kaman, Ondřej; Řehoř, I.; Hájek, M.; Saudek, F.

2013-01-01

Roč. 8, č. 4 (2013), s. 614-621 ISSN 1860-7179 Institutional support: RVO:68378271 Keywords : contrast agents * gadolinium * magnetic resonance imaging * manganite * pancreatic islet s Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.046, year: 2013

A giant magnetoresistance ring-sensor based microsystem for magnetic bead manipulation and detection

KAUST Repository

Gooneratne, Chinthaka P.

2011-03-28

In this paper a novel spin valvegiant magnetoresistance(GMR) ring-sensor integrated with a microstructure is proposed for concentrating, trapping, and detecting superparamagnetic beads (SPBs). Taking advantage of the fact that SPBs can be manipulated by an external magnetic field, a unique arrangement of conducting microrings is utilized to manipulate the SPBs toward the GMR sensing area in order to increase the reliability of detection. The microrings are arranged and activated in such a manner so as to enable the detection of minute concentrations of SPBs in a sample. Precise manipulation is achieved by applying current sequentially to the microrings. The fabricated ring-shaped GMR element is located underneath the innermost ring and has a magnetoresistance of approximately 5.9%. By the performed experiments it was shown that SPBs could be successfully manipulated toward the GMR sensing zone.

A giant magnetoresistance ring-sensor based microsystem for magnetic bead manipulation and detection

KAUST Repository

Gooneratne, Chinthaka P.; Giouroudi, Ioanna; Liang, Cai; Kosel, Jü rgen

2011-01-01

In this paper a novel spin valvegiant magnetoresistance(GMR) ring-sensor integrated with a microstructure is proposed for concentrating, trapping, and detecting superparamagnetic beads (SPBs). Taking advantage of the fact that SPBs can be manipulated by an external magnetic field, a unique arrangement of conducting microrings is utilized to manipulate the SPBs toward the GMR sensing area in order to increase the reliability of detection. The microrings are arranged and activated in such a manner so as to enable the detection of minute concentrations of SPBs in a sample. Precise manipulation is achieved by applying current sequentially to the microrings. The fabricated ring-shaped GMR element is located underneath the innermost ring and has a magnetoresistance of approximately 5.9%. By the performed experiments it was shown that SPBs could be successfully manipulated toward the GMR sensing zone.

Experimental investigation of the nature of the magnetoresistance effects in Pd-YIG hybrid structures.

Science.gov (United States)

Lin, Tao; Tang, Chi; Alyahayaei, Hamad M; Shi, Jing

2014-07-18

In bilayers consisting of Pd and yttrium iron garnet (Y(3)Fe(5)O(12) or YIG), we observe vanishingly small room-temperature conventional anisotropic magnetoresistance but large new magnetoresistance that is similar to the spin Hall magnetoresistance previously reported in Pt-YIG bilayers. We report a temperature dependence study of the two magnetoresistance effects in Pt-YIG bilayers. As the temperature is decreased, the new magnetoresistance shows a peak, whereas the anisotropic magnetoresistance effect starts to appear and increases monotonically. We find that the magnetoresistance peak shifts to lower temperatures in thicker Pd samples, a feature characteristic of the spin current effect. The distinct temperature dependence reveals fundamentally different mechanisms responsible for the two effects in such hybrid structures.

Tunnelling anisotropic magnetoresistance at La_0_._6_7Sr_0_._3_3MnO_3-graphene interfaces

International Nuclear Information System (INIS)

Phillips, L. C.; Yan, W.; Kar-Narayan, S.; Mathur, N. D.; Lombardo, A.; Barbone, M.; Milana, S.; Ferrari, A. C.; Ghidini, M.; Hämäläinen, S. J.; Dijken, S. van

2016-01-01

Using ferromagnetic La_0_._6_7Sr_0_._3_3MnO_3 electrodes bridged by single-layer graphene, we observe magnetoresistive changes of ∼32–35 MΩ at 5 K. Magneto-optical Kerr effect microscopy at the same temperature reveals that the magnetoresistance arises from in-plane reorientations of electrode magnetization, evidencing tunnelling anisotropic magnetoresistance at the La_0_._6_7Sr_0_._3_3MnO_3-graphene interfaces. Large resistance switching without spin transport through the non-magnetic channel could be attractive for graphene-based magnetic-sensing applications.

Anomalous magnetoresistance effect in sputtered TbFeCo relating to dispersed magnetic moment

International Nuclear Information System (INIS)

Yumoto, S.; Toki, K.; Okada, O.; Gokan, H.

1988-01-01

The electric resistance is sputtered TbFeCo has been measured at room temperature as a function of magnetic field perpendicular to the film plane. Two kinds of anomalous magnetoresistance have been observed. One is a magnetoresistance peak in the magnetization reversal region. The other is reversible change proportional to the applied magnetic field, appearing in the other region. The magnetoresistance peak agrees well with a curve calculated from experimental Hall loop, using a phenomenological relation between anomalous magnetoresistance and anomalous Hall voltage. The magnetoresistance peak is found to originate from magnetic domain walls. The linear magnetoresistance change for TM dominant samples appears in a direction opposite to that for RE dominant samples. The linear change can't be derived from Hall loop

Ballistic Anisotropic Magnetoresistance of Single-Atom Contacts.

Science.gov (United States)

Schöneberg, J; Otte, F; Néel, N; Weismann, A; Mokrousov, Y; Kröger, J; Berndt, R; Heinze, S

2016-02-10

Anisotropic magnetoresistance, that is, the sensitivity of the electrical resistance of magnetic materials on the magnetization direction, is expected to be strongly enhanced in ballistic transport through nanoscale junctions. However, unambiguous experimental evidence of this effect is difficult to achieve. We utilize single-atom junctions to measure this ballistic anisotropic magnetoresistance (AMR). Single Co and Ir atoms are deposited on domains and domain walls of ferromagnetic Fe layers on W(110) to control their magnetization directions. They are contacted with nonmagnetic tips in a low-temperature scanning tunneling microscope to measure the junction conductances. Large changes of the magnetoresistance occur from the tunneling to the ballistic regime due to the competition of localized and delocalized d-orbitals, which are differently affected by spin-orbit coupling. This work shows that engineering the AMR at the single atom level is feasible.

Microstructural and magnetotransport studies of novel manganite–sebacic acid nanocomposites prepared at low temperature

International Nuclear Information System (INIS)

Romero, Mariano; Faccio, Ricardo; Pardo, Helena; Tumelero, Milton A.; Pasa, André A.; Mombrú, Álvaro W.

2015-01-01

Novel La 2/3 Sr 1/3 MnO 3 :sebacic acid nanocomposites (LSMO–SA-X) were prepared for different fraction additions (X) of sebacic acid (SA). The preparation of these nanocomposites was performed at low temperatures (T∼130 °C) avoiding partial decomposition of the organic matrix. The microstructure of these LSMO–SA-X nanocomposites was studied by small angle X-ray scattering (SAXS) technique and both nanoparticles size and inter-particle distances were estimated. The magnetic, electrical and magnetotransport properties were also investigated. An enhancement in the low-field magnetoresistance (LFMR) for lower fractions of SA was obtained with respect to pure LSMO and higher fraction additions showed a decrease in the LFMR due to the higher separation distance between LSMO nanoparticles. The tunnel barrier thickness observed in these nanocomposites was correlated with the interparticle distance obtained by SAXS. The enhancement of magnetoresistance was attributed to the increase in the extrinsic disorder promoted by the SA addition and no enhancement due to intrinsic magnetoresistance of LSMO was evidenced. - Highlights: • The synthesis of novel manganite-sebacic acid nanocomposites is reported. • Microstructural trends are shown using the GISAXS technique. • An enhancement on the LFMR in the nanocomposites with respect to pure manganite was evidenced. • Correlation between microstructure and magnetotransport is discussed

Effect of crystallinity on the magnetoresistance in perovskite manganese oxide thin films

International Nuclear Information System (INIS)

Shreekala, R.; Rajeswari, M.; Ghosh, K.; Goyal, A.; Gu, J.Y.; Kwon, C.; Trajanovic, Z.; Boettcher, T.; Greene, R.L.; Ramesh, R.; Venkatesan, T.

1997-01-01

We report our study of the effect of crystallinity on the magnetoresistance in epitaxial and polycrystalline La 2/3 Ba 1/3 MnO 3 and La 2/3 Ca 1/3 MnO 3 thin films. Magnetoresistance in epitaxial films exhibits field dependence and temperature dependence similar to bulk single crystals and sintered bulk ceramics. The polycrystalline films exhibit a markedly different behavior. The magnetoresistance in this case shows either a monotonic increase or saturation with decreasing temperature in contrast to that of epitaxial films in which the magnetoresistance peaks close to the ferromagnetic transition temperature. The field dependence in the polycrystalline films is also remarkably different. At low fields, we observe a sharp drop in resistance followed by a more gradual decrease at higher fields. Our data suggest that in addition to the intrinsic magnetoresistance, grain-boundary transport contributes significantly to the magnetoresistance in polycrystalline films. copyright 1997 American Institute of Physics

Giant Magnetoresistance-based Biosensor for Detection of Influenza A Virus.

Science.gov (United States)

Krishna, Venkatramana D; Wu, Kai; Perez, Andres M; Wang, Jian-Ping

2016-01-01

We have developed a simple and sensitive method for the detection of influenza A virus based on giant magnetoresistance (GMR) biosensor. This assay employs monoclonal antibodies to viral nucleoprotein (NP) in combination with magnetic nanoparticles (MNPs). Presence of influenza virus allows the binding of MNPs to the GMR sensor and the binding is proportional to the concentration of virus. Binding of MNPs onto the GMR sensor causes change in the resistance of sensor, which is measured in a real time electrical readout. GMR biosensor detected as low as 1.5 × 10(2) TCID50/mL virus and the signal intensity increased with increasing concentration of virus up to 1.0 × 10(5) TCID50/mL. This study showed that the GMR biosensor assay is relevant for diagnostic application since the virus concentration in nasal samples of influenza virus infected swine was reported to be in the range of 10(3) to 10(5) TCID50/mL.

Tunnelling anisotropic magnetoresistance due to antiferromagnetic CoO tunnel barriers

NARCIS (Netherlands)

Wang, Kai; Sanderink, Johannes G.M.; Bolhuis, Thijs; van der Wiel, Wilfred Gerard; de Jong, Machiel Pieter

2015-01-01

A new approach in spintronics is based on spin-polarized charge transport phenomena governed by antiferromagnetic (AFM) materials. Recent studies have demonstrated the feasibility of this approach for AFM metals and semiconductors. We report tunneling anisotropic magnetoresistance (TAMR) due to the

Giant magnetoresistance in lateral metallic nanostructures for spintronic applications.

Science.gov (United States)

Zahnd, G; Vila, L; Pham, V T; Marty, A; Beigné, C; Vergnaud, C; Attané, J P

2017-08-25

In this letter, we discuss the shift observed in spintronics from the current-perpendicular-to-plane geometry towards lateral geometries, illustrating the new opportunities offered by this configuration. Using CoFe-based all-metallic LSVs, we show that giant magnetoresistance variations of more than 10% can be obtained, competitive with the current-perpendicular-to-plane giant magnetoresistance. We then focus on the interest of being able to tailor freely the geometries. On the one hand, by tailoring the non-magnetic parts, we show that it is possible to enhance the spin signal of giant magnetoresistance structures. On the other hand, we show that tailoring the geometry of lateral structures allows creating a multilevel memory with high spin signals, by controlling the coercivity and shape anisotropy of the magnetic parts. Furthermore, we study a new device in which the magnetization direction of a nanodisk can be detected. We thus show that the ability to control the magnetic properties can be used to take advantage of all the spin degrees of freedom, which are usually occulted in current-perpendicular-to-plane devices. This flexibility of lateral structures relatively to current-perpendicular-to-plane structures is thus found to offer a new playground for the development of spintronic applications.

Spin glass behavior in nanogranular La{sub 0.25}Ca{sub 0.75}MnO{sub 3} manganites

Energy Technology Data Exchange (ETDEWEB)

Fernández-Martínez, Antoni [Grup de Magnetisme, Dept. Física Fonamental, Facultat de Física, Universitat de Barcelona, Martí i Franquès 1, planta 4, edifici nou, 08028 Barcelona (Spain); Institut de Nanociència i Nanotecnologia IN" 2UB, Universitat de Barcelona, Martí i Franquès 1, planta 3, edifici nou, 08028 Barcelona (Spain); García-Santiago, Antoni, E-mail: agarciasan@ub.edu [Grup de Magnetisme, Dept. Física Fonamental, Facultat de Física, Universitat de Barcelona, Martí i Franquès 1, planta 4, edifici nou, 08028 Barcelona (Spain); Institut de Nanociència i Nanotecnologia IN" 2UB, Universitat de Barcelona, Martí i Franquès 1, planta 3, edifici nou, 08028 Barcelona (Spain); Hernàndez, Joan Manel [Grup de Magnetisme, Dept. Física Fonamental, Facultat de Física, Universitat de Barcelona, Martí i Franquès 1, planta 4, edifici nou, 08028 Barcelona (Spain); Institut de Nanociència i Nanotecnologia IN" 2UB, Universitat de Barcelona, Martí i Franquès 1, planta 3, edifici nou, 08028 Barcelona (Spain); Zhang, Tao [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China)

2014-06-01

The magnetic properties of two nanogranular La{sub 0.25}Ca{sub 0.75}MnO{sub 3} manganites with different average grain sizes have been studied. Besides the well-known exchange bias effect and the appearance of ferromagnetic clusters in the grains of both samples, the results show the occurrence of an antiferromagnetic transition and spin-glass properties. Both samples are described as core–shell magnetic systems, whose main difference is found in the interface between the outer ferromagnetic and the inner antiferromagnetic phases of the grains. - Highlights: • Nanogranular manganites show antiferromagnetism in magnetic measurements. • Exchange bias effect was observed in magnetic hysteresis cycles. • Spin-glass properties were detected at low temperatures. • A core-shell model was applied to describe the results in both samples. • These features have nothing to do with usual properties of nanoparticle manganites.

Giant magnetorefractive effect in La{sub 0.7}Ca{sub 0.3}MnO{sub 3} films

Energy Technology Data Exchange (ETDEWEB)

Granovskii, A. B., E-mail: granov@magn.ru [Moscow State University (Russian Federation); Sukhorukov, Yu. P., E-mail: suhorukov@imp.uran.ru; Telegin, A. V.; Bessonov, V. D. [Russian Academy of Sciences, Institute of Metal Physics, Ural Branch (Russian Federation); Gan' shina, E. A.; Kaul' , A. R.; Korsakov, I. E.; Gorbenko, O. Yu. [Moscow State University (Russian Federation); Gonzalez, J. [Universidad del Pais Vasco, Departamento Fisica de Materiales, Facultad de Quimica (Spain)

2011-01-15

Complex experimental investigations of the structural, optical, and magneto-optical properties (magnetotransmission, magnetoreflection, and transversal Kerr effect, as well as the magnetoresistance, of La{sub 0.7}Ca{sub 0.3}MnO{sub 3} epitaxial films indicate that magnetoreflection and magnetotransmission in manganite films can reach giant values and depend strongly on the magnetic and charge homogeneity of the films, their thickness, and spectral range under investigation. It has been shown that the optical enhancement of the magnetorefractive effect occurs in thin films as compared to manganite crystals. In the region of the minimum of the reflectance near the first phonon band, the resonance-like magnetorefractive effect has been observed, which is accompanied by change of the sign of the magnetoreflection. A model based on the theory of the magnetorefractive effect has been proposed to qualitatively explain this behavior.

Magnetocaloric effect in potassium doped lanthanum manganite perovskites prepared by a pyrophoric method

Science.gov (United States)

Das, Soma; Dey, T. K.

2006-08-01

The magnetocaloric effect (MCE) in fine grained perovskite manganites of the type La1-xKxMnO3 (0value of 3.00 J kg-1 K-1 at 310 K amongst the compounds investigated. Moreover, the maximum magnetic entropy change exhibits a linear dependence with applied magnetic field. The estimated adiabatic temperature change at TC and at 1 T field also increases with K doping, being a maximum of 2.1 K for the La0.85K0.15MnO3 compound. The relative cooling power (RCP) of La1-xKxMnO3 compounds is estimated to be about one-third of that of the prototype magnetic refrigerant material (pure Gd). However, La1-xKxMnO3 compounds possess an MCE around room temperature, which is comparable to that of Gd. Further, tailoring of their TC, higher chemical stability, lower eddy current heating and lower cost of synthesis are some of the attractive features of K doped lanthanum manganites that are advantageous for a magnetic refrigerant. The temperature dependence of the magnetic entropy change (ΔSM) measured under various magnetic fields is explained fairly well using the Landau theory of phase transitions. Contributions of magnetoelastic and electron interaction are found to have a strong influence in the magnetocaloric effect of manganites.

Magnetoresistance in two-dimensional array of Ge/Si quantum dots

Science.gov (United States)

Stepina, N. P.; Koptev, E. S.; Pogosov, A. G.; Dvurechenskii, A. V.; Nikiforov, A. I.; Zhdanov, E. Yu

2012-07-01

Magnetoresistance in two-dimensional array of Ge/Si was studied for a wide range of the conductance, where the transport regime changes from hopping to diffusive one. The behavior of magnetoresistance is similar for all samples; it is negative in weak fields and becomes positive with increasing of magnetic field. Negative magnetoresistance can be described in the frame of weak localization approach with suggestion that quantum interference contribution to the conductance is restricted not only by the phase breaking length but also by the localization length.

Magnetoresistance in two-dimensional array of Ge/Si quantum dots

International Nuclear Information System (INIS)

Stepina, N P; Koptev, E S; Pogosov, A G; Dvurechenskii, A V; Nikiforov, A I; Zhdanov, E Yu

2012-01-01

Magnetoresistance in two-dimensional array of Ge/Si was studied for a wide range of the conductance, where the transport regime changes from hopping to diffusive one. The behavior of magnetoresistance is similar for all samples; it is negative in weak fields and becomes positive with increasing of magnetic field. Negative magnetoresistance can be described in the frame of weak localization approach with suggestion that quantum interference contribution to the conductance is restricted not only by the phase breaking length but also by the localization length.

Diluted magnetic semiconductor nanowires exhibiting magnetoresistance

Science.gov (United States)

Yang, Peidong [El Cerrito, CA; Choi, Heonjin [Seoul, KR; Lee, Sangkwon [Daejeon, KR; He, Rongrui [Albany, CA; Zhang, Yanfeng [El Cerrito, CA; Kuykendal, Tevye [Berkeley, CA; Pauzauskie, Peter [Berkeley, CA

2011-08-23

A method for is disclosed for fabricating diluted magnetic semiconductor (DMS) nanowires by providing a catalyst-coated substrate and subjecting at least a portion of the substrate to a semiconductor, and dopant via chloride-based vapor transport to synthesize the nanowires. Using this novel chloride-based chemical vapor transport process, single crystalline diluted magnetic semiconductor nanowires Ga.sub.1-xMn.sub.xN (x=0.07) were synthesized. The nanowires, which have diameters of .about.10 nm to 100 nm and lengths of up to tens of micrometers, show ferromagnetism with Curie temperature above room temperature, and magnetoresistance up to 250 Kelvin.

High Field Linear Magnetoresistance Sensors with Perpendicular Anisotropy L10-FePt Reference Layer

Directory of Open Access Journals (Sweden)

X. Liu

2016-01-01

Full Text Available High field linear magnetoresistance is an important feature for magnetic sensors applied in magnetic levitating train and high field positioning measurements. Here, we investigate linear magnetoresistance in Pt/FePt/ZnO/Fe/Pt multilayer magnetic sensor, where FePt and Fe ferromagnetic layers exhibit out-of-plane and in-plane magnetic anisotropy, respectively. Perpendicular anisotropy L10-FePt reference layer with large coercivity and high squareness ratio was obtained by in situ substrate heating. Linear magnetoresistance is observed in this sensor in a large range between +5 kOe and −5 kOe with the current parallel to the film plane. This L10-FePt based sensor is significant for the expansion of linear range and the simplification of preparation for future high field magnetic sensors.

Tunneling magnetoresistance in nanogranular La1-xSrxMnO3 (x∼0.5

Directory of Open Access Journals (Sweden)

Jiří Hejtmánek

2017-05-01

Full Text Available Electric transport and magnetic studies were performed on the La1-xSrxMnO3 (x=0.45-0.55 perovskite manganites. The main focus was given to the nanogranular ceramics of average x=0.47 composition, compacted by spark plasma sintering of molten salt synthesized nanoparticles. This sample can be viewed as a two-phase composite where FM manganite granules are embedded in AFM manganite matrix. The magnetoconductance data observed on this sample reveal a coexistence of distinct low- and high-field contributions, related to the field-induced alignment of ferromagnetic (FM granules and the spin canting in antiferromagnetic (AFM matrix, respectively. Their analysis confirms the theoretically predicted scaling of the low-field effect with squared reduced magnetization and provides also a quantitative comparison between the linear coefficient of high-field magnetoconductance and paraprocess seen in the magnetization measurement.

Hanle Magnetoresistance in Thin Metal Films with Strong Spin-Orbit Coupling.

Science.gov (United States)

Vélez, Saül; Golovach, Vitaly N; Bedoya-Pinto, Amilcar; Isasa, Miren; Sagasta, Edurne; Abadia, Mikel; Rogero, Celia; Hueso, Luis E; Bergeret, F Sebastian; Casanova, Fèlix

2016-01-08

We report measurements of a new type of magnetoresistance in Pt and Ta thin films. The spin accumulation created at the surfaces of the film by the spin Hall effect decreases in a magnetic field because of the Hanle effect, resulting in an increase of the electrical resistance as predicted by Dyakonov [Phys. Rev. Lett. 99, 126601 (2007)]. The angular dependence of this magnetoresistance resembles the recently discovered spin Hall magnetoresistance in Pt/Y(3)Fe(5)O(12) bilayers, although the presence of a ferromagnetic insulator is not required. We show that this Hanle magnetoresistance is an alternative simple way to quantitatively study the coupling between charge and spin currents in metals with strong spin-orbit coupling.

Quantum and classical contributions to linear magnetoresistance in topological insulator thin films

International Nuclear Information System (INIS)

Singh, Sourabh; Gopal, R. K.; Sarkar, Jit; Mitra, Chiranjib

2016-01-01

Three dimensional topological insulators possess backscattering immune relativistic Dirac fermions on their surface due to nontrivial topology of the bulk band structure. Both metallic and bulk insulating topological insulators exhibit weak-antilocalization in the low magnetic field and linear like magnetoresistance in higher fields. We explore the linear magnetoresistance in bulk insulating topological insulator Bi 2-x Sb x Te 3-y Se y thin films grown by pulsed laser deposition technique. Thin films of Bi 2-x Sb x Te 3-y Se y were found to be insulating in nature, which conclusively establishes the origin of linear magnetoresistance from surface Dirac states. The films were thoroughly characterized for their crystallinity and composition and then subjected to transport measurements. We present a careful analysis taking into considerations all the existing models of linear magnetoresistance. We comprehend that the competition between classical and quantum contributions to magnetoresistance results in linear magnetoresistance in high fields. We observe that the cross-over field decreases with increasing temperature and the physical argument for this behavior is explained.

Frozen magnetoresistance at magnetization reversal of granular Bi(Pb)-HTSC

International Nuclear Information System (INIS)

Sukhanov, A.A.; Omelchenko, V.I.

2004-01-01

The frozen magnetoresistance dependences of granular Bi(Pb)-HTSC samples on fields initiating a magnetic flux trapping and on magnetic reversal fields Rt(Hi, Hr) are investigated. It is found that the Rt (Hr) dependences are nonmonotonous. The frozen magnetoresistance decreases substantially after the first pulse Hr applied (Hr < Hi) but remains practically unchanged at subsequent remagnetization by magnetic pulses of alternating polarity and of the same amplitude. The effect of magnetic reversal on magnetoresistance anisotropy and the negative magnetoresistance phenomenon are studied. Is shown that the results obtained are inconsistent with the model of critical state for SC grains and the model of SC loops but are well described quantitatively by the proposed Bi(Pb)-HTSC model according to which the magnetic flux trapping occurs in normal grains with HTSC shells and the sample resistance is determined by weak link chains

Pramana – Journal of Physics | Indian Academy of Sciences

Indian Academy of Sciences (India)

Keywords. Spin waves; neutron scattering; colossal magnetoresistance. Abstract. The results of inelastic and quasi-elastic neutron scattering investigations on the 40% hole-doped quasi-2D bilayer manganites La1.2Sr1.8Mn2O7 have been reviewed. The complete set of exchange interactions have been determined on the ...

Manganite/Cuprate Superlattice as Artificial Reentrant Spin Glass

KAUST Repository

Ding, Junfeng

2016-05-04

Emerging physical phenomena at the unit-cell-controlled interfaces of transition-metal oxides have attracted lots of interest because of the rich physics and application opportunities. This work reports a reentrant spin glass behavior with strong magnetic memory effect discovered in oxide heterostructures composed of ultrathin manganite La0.7Sr0.3MnO3 (LSMO) and cuprate La2CuO4 (LCO) layers. These heterostructures are featured with enhanced ferromagnetism before entering the spin glass state: a Curie temperature of 246 K is observed in the superlattice with six-unit-cell LSMO layers, while the reference LSMO film with the same thickness shows much weaker magnetism. Furthermore, an insulator-metal transition emerges at the Curie temperature, and below the freezing temperature the superlattices can be considered as a glassy ferromagnetic insulator. These experimental results are closely related to the interfacial spin reconstruction revealed by the first-principles calculations, and the dependence of the reentrant spin glass behavior on the LSMO layer thickness is in line with the general phase diagram of a spin system derived from the infinite-range SK model. The results of this work underscore the manganite/cuprate superlattices as a versatile platform of creating artificial materials with tailored interfacial spin coupling and physical properties. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Observation of large low-field magnetoresistance in spinel cobaltite: A new half-metal

KAUST Repository

Li, Peng

2015-12-10

Low-field magnetoresistance is an effective and energy-saving way to use half-metallic materials in magnetic reading heads and magnetic random access memory. Common spin-polarized materials with low field magnetoresistance effect are perovskite-type manganese, cobalt, and molybdenum oxides. In this study, we report a new type of spinel cobaltite materials, self-assembled nanocrystalline NiCo2O4, which shows large low field magnetoresistance as large as –19.1% at 0.5 T and –50% at 9 T (2 K). The large low field magnetoresistance is attributed to the fast magnetization rotation of the core nanocrystals. The surface spin-glass is responsible for the observed weak saturation of magnetoresistance under high fields. Our calculation demonstrates that the half-metallicity of NiCo2O4 comes from the hopping eg electrons within the tetrahedral Co-atoms and the octahedral Ni-atoms. The discovery of large low-field magnetoresistance in simple spinel oxide NiCo2O4, a non-perovskite oxide, leads to an extended family of low-field magnetoresistance materials. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Observation of large low-field magnetoresistance in spinel cobaltite: A new half-metal

KAUST Repository

Li, Peng; Xia, Chuan; Zheng, Dongxing; Wang, Ping; Jin, Chao; Bai, Haili

2015-01-01

Low-field magnetoresistance is an effective and energy-saving way to use half-metallic materials in magnetic reading heads and magnetic random access memory. Common spin-polarized materials with low field magnetoresistance effect are perovskite-type manganese, cobalt, and molybdenum oxides. In this study, we report a new type of spinel cobaltite materials, self-assembled nanocrystalline NiCo2O4, which shows large low field magnetoresistance as large as –19.1% at 0.5 T and –50% at 9 T (2 K). The large low field magnetoresistance is attributed to the fast magnetization rotation of the core nanocrystals. The surface spin-glass is responsible for the observed weak saturation of magnetoresistance under high fields. Our calculation demonstrates that the half-metallicity of NiCo2O4 comes from the hopping eg electrons within the tetrahedral Co-atoms and the octahedral Ni-atoms. The discovery of large low-field magnetoresistance in simple spinel oxide NiCo2O4, a non-perovskite oxide, leads to an extended family of low-field magnetoresistance materials. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Study of magnetoresistance in the supercooled state of Dy-Y alloys

Science.gov (United States)

Jena, Rudra Prasad; Lakhani, Archana

2018-02-01

We report the magnetoresistance studies on Dy1-xYx (x ≤ 0.05) alloys across the first order helimagnetic to ferromagnetic phase transition. These alloys exhibit multiple magnetic phases on varying the temperature and magnetic field. The magnetoresistance studies in the hysteresis region shows irreversibility in forward and reverse field cycles. The resistivity values at zero field for these alloys after zero field cooling to the measurement temperatures, are different in both forward and reverse field cycles. The path dependence of magnetoresistance suggests the presence of helimagnetic phase as the supercooled metastable state which transforms to the stable ferromagnetic state on increasing the field. At high magnetic fields negative magnetoresistance following a linear dependence with field is observed which is attributed to the magnon scattering.

Electron magnetic resonance study of monovalent Na doping in Pr0.6Sr0.4−xNaxMnO3 manganites

International Nuclear Information System (INIS)

Thaljaoui, Rachid; Boujelben, Wahiba; Pękała, Marek; Szydłowska, Jadwiga; Cheikhrouhou, Abdelwaheb

2012-01-01

Highlights: ► New monovalent doped manganites Pr 0.6 Sr 0.4−x Na x MnO 3 (x = 0, 0.05). ► Comparison of electron magnetic resonance spectra in ferro- and paramagnetic phases. ► Double exchange interactions weakened by Na doping as indicated by activation energy. ► Magnetic susceptibility derived from resonance intensity obeys Curie–Weiss law. - Abstract: Effect of monovalent Na doping on the magnetic properties is studied in Pr 0.6 Sr 0.4−x Na x MnO 3 system (x = 0, 0.05) using X-band electron magnetic resonance and magnetization measurements. Temperature variation of magnetic resonance spectra of doped and undoped manganites is analyzed for paramagnetic and ferromagnetic states and compared to similar systems. In paramagnetic phase the magnetic susceptibility proportional to resonance signal intensity is found to obey the Curie–Weiss law. The effective magnetic moment becomes smaller in doped manganite. The paramagnetic Curie temperature derived from signal intensity equals to 312 and 306 K for the undoped and doped manganites, respectively, and is close to values obtained from magnetization variation in paramagnetic phase. The activation energy determined using the adiabatic small polaron hopping model is higher for the undoped than the doped manganite, which proves that the Na doping slightly reduces the Mn 3+ /Mn 4+ double exchange interactions.

Magnetoresistance of nanogranular Ni/NiO controlled by exchange anisotropy

International Nuclear Information System (INIS)

Del Bianco, L.; Spizzo, F.; Tamisari, M.; Allia, P.

2013-01-01

A link between exchange anisotropy and magnetoresistance has been found to occur in a Ni/NiO sample consisting of Ni nanocrystallites (mean size ∼13 nm, Ni content ∼33 vol%) dispersed in a NiO matrix. This material shows metallic-type electric conduction and isotropic spin-dependent magnetoresistance as well as exchange bias effect. The latter is the outcome of an exchange anisotropy arising from the contact interaction between the Ni phase and the NiO matrix. Combined analysis of magnetization M(H) and magnetoresistance MR(H) loops measured in the 5–250 K temperature range after zero-field-cooling (ZFC) and after field-cooling (FC) from 300 K reveals that the magnetoresistance is influenced by exchange anisotropy, which is triggered by the FC process and can be modified in strength by varying the temperature. Compared to the ZFC case, the exchange anisotropy produces a horizontal shift of the FC MR(H) loop along with a reduction of the MR response associated to the reorientation of the Ni moments. A strict connection between magnetoresistance and remanent magnetization of FC loops on one side and the exchange field on the other, ruled by exchange anisotropy, is indicated. - Highlights: • Nanogranular Ni/NiO with giant magnetoresistance (MR) and exchange bias effect. • Exchange anisotropy produces a shift of the field-cooled MR(H) loop and reduces MR. • MR, remanence of field-cooled loops and exchange field are three correlated quantities. • It is possible to control MR of nanogranular systems through the exchange anisotropy

Stripe domains and magnetoresistance in thermally deposited nickel films

International Nuclear Information System (INIS)

Sparks, P.D.; Stern, N.P.; Snowden, D.S.; Kappus, B.A.; Checkelsky, J.G.; Harberger, S.S.; Fusello, A.M.; Eckert, J.C.

2004-01-01

We report a study of the domain structure and magnetoresistance of thermally deposited nickel films. For films thicker than 17 nm, we observe striped domains with period varying with film thickness as a power law with exponent 0.21±0.02 up to 120 nm thickness. There is a negative magnetoresistance for fields out of the plane

Stripe domains and magnetoresistance in thermally deposited nickel films

Science.gov (United States)

Sparks, P. D.; Stern, N. P.; Snowden, D. S.; Kappus, B. A.; Checkelsky, J. G.; Harberger, S. S.; Fusello, A. M.; Eckert, J. C.

2004-05-01

We report a study of the domain structure and magnetoresistance of thermally deposited nickel films. For films thicker than 17nm, we observe striped domains with period varying with film thickness as a power law with exponent 0.21+/-0.02 up to 120nm thickness. There is a negative magnetoresistance for fields out of the plane.

Stripe domains and magnetoresistance in thermally deposited nickel films

Energy Technology Data Exchange (ETDEWEB)

Sparks, P.D. E-mail: sparks@hmc.edu; Stern, N.P.; Snowden, D.S.; Kappus, B.A.; Checkelsky, J.G.; Harberger, S.S.; Fusello, A.M.; Eckert, J.C

2004-05-01

We report a study of the domain structure and magnetoresistance of thermally deposited nickel films. For films thicker than 17 nm, we observe striped domains with period varying with film thickness as a power law with exponent 0.21{+-}0.02 up to 120 nm thickness. There is a negative magnetoresistance for fields out of the plane.

Large, Linear, and Tunable Positive Magnetoresistance of Mechanically Stable Graphene Foam-Toward High-Performance Magnetic Field Sensors.

Science.gov (United States)

Sagar, Rizwan Ur Rehman; Galluzzi, Massimiliano; Wan, Caihua; Shehzad, Khurram; Navale, Sachin T; Anwar, Tauseef; Mane, Rajaram S; Piao, Hong-Guang; Ali, Abid; Stadler, Florian J

2017-01-18

Here, we present the first observation of magneto-transport properties of graphene foam (GF) composed of a few layers in a wide temperature range of 2-300 K. Large room-temperature linear positive magnetoresistance (PMR ≈ 171% at B ≈ 9 T) has been detected. The largest PMR (∼213%) has been achieved at 2 K under a magnetic field of 9 T, which can be tuned by the addition of poly(methyl methacrylate) to the porous structure of the foam. This remarkable magnetoresistance may be the result of quadratic magnetoresistance. The excellent magneto-transport properties of GF open a way toward three-dimensional graphene-based magnetoelectronic devices.

Structural domain walls in polar hexagonal manganites

Science.gov (United States)

Kumagai, Yu

2014-03-01

The domain structure in the multiferroic hexagonal manganites is currently intensely investigated, motivated by the observation of intriguing sixfold topological defects at their meeting points [Choi, T. et al,. Nature Mater. 9, 253 (2010).] and nanoscale electrical conductivity at the domain walls [Wu, W. et al., Phys. Rev. Lett. 108, 077203 (2012).; Meier, D. et al., Nature Mater. 11, 284 (2012).], as well as reports of coupling between ferroelectricity, magnetism and structural antiphase domains [Geng, Y. et al., Nano Lett. 12, 6055 (2012).]. The detailed structure of the domain walls, as well as the origin of such couplings, however, was previously not fully understood. In the present study, we have used first-principles density functional theory to calculate the structure and properties of the low-energy structural domain walls in the hexagonal manganites [Kumagai, Y. and Spaldin, N. A., Nature Commun. 4, 1540 (2013).]. We find that the lowest energy domain walls are atomically sharp, with {210}orientation, explaining the orientation of recently observed stripe domains and suggesting their topological protection [Chae, S. C. et al., Phys. Rev. Lett. 108, 167603 (2012).]. We also explain why ferroelectric domain walls are always simultaneously antiphase walls, propose a mechanism for ferroelectric switching through domain-wall motion, and suggest an atomistic structure for the cores of the sixfold topological defects. This work was supported by ETH Zurich, the European Research Council FP7 Advanced Grants program me (grant number 291151), the JSPS Postdoctoral Fellowships for Research Abroad, and the MEXT Elements Strategy Initiative to Form Core Research Center TIES.

Dependence of Fe/Cr superlattice magnetoresistance on orientation of external magnetic field

International Nuclear Information System (INIS)

Ustinov, V.V.; Romashev, L.N.; Minin, V.I.; Semerikov, A.V.; Del', A.R.

1995-01-01

The paper presents the results of investigations into giant magnetoresistance of [Fe/Cr] 30 /MgO superlattices obtained using molecular-beam epitaxy under various orientations of magnetic field relatively to the layers of superlattice and to the direction of current flow. Theory of orientation dependence of superlattice magnetoresistance enabling to describe satisfactorily behaviour of magnetoresistance at arbitrary direction of magnetic field on the ground of results of magnetoresistance measurements in magnetic field parallel and perpendicular to plane of layers, is elaborated. It is pointed out that it is possible to obtain field dependence of superlattice magnetization on the ground of measurement results. 9 refs., 6 figs

Formation of manganite fibers under the directing of cationic surfactant

International Nuclear Information System (INIS)

Sun Xiaodan; Kong Xiangdong; Wang Yude; Ma Chunlai; Cui Fuzhai; Li Hengde

2006-01-01

The effects of organic molecules on the morphology control of inorganic materials in the process of biomineralization have long been realized. Nowadays, these effects have been utilized to prepare inorganic materials with desired morphologies in different systems. In this paper, manganite (MnOOH) fibers are chemically synthesized under extremely low surfactant (cetyltrimethylammonium bromide CTAB) concentrations at basic conditions. Powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) are used to characterize the products. Characterization of samples aged for different time shows that the formation of MnOOH fibers is intimately related to a layered structured manganese oxide. A corresponding transformation mechanism is proposed based on the experiment results, and it could be inferred that CTAB plays an important directing role in this process

On the magnetoresistance of heavy fermion compounds

International Nuclear Information System (INIS)

Lee Chengchung; Chen Chung

1992-09-01

Starting from two-conduction-band Anderson lattice model, the magneto-transport properties of heavy fermion systems are studied in the slave boson mean field theory. The residual magnetoresistivity induced by different kinds of impurities is calculated, and the experimentally detected positive maximum structure in the residual magnetoresistance of heavy fermion systems is reproduced. The transition of field-dependent resistivity from nonmonotonic to monotonic behaviour with increasing temperature can be explained naturally by including the charge fluctuation effect. The influence of applied pressure is also investigated. (author). 22 refs, 5 figs

Giant magnetoresistance and anomalous transport in phosphorene-based multilayers with noncollinear magnetization

Science.gov (United States)

Zare, Moslem; Majidi, Leyla; Asgari, Reza

2017-03-01

We theoretically investigate the unusual features of the magnetotransport in a monolayer phosphorene ferromagnetic/normal/ferromagnetic (F/N/F) hybrid structure. We find that the charge conductance can feature a minimum at parallel (P) configuration and a maximum near the antiparallel (AP) configuration of magnetization in the F/N/F structure with n -doped F and p -doped N regions and also a finite conductance in the AP configuration with the N region of n -type doping. In particular, the proposed structure exhibits giant magnetoresistance, which can be tuned to unity. This perfect switching is found to show strong robustness with respect to increasing the contact length and tuning the chemical potential of the N region with a gate voltage. We also explore the oscillatory behavior of the charge conductance or magnetoresistance in terms of the size of the N region. We further demonstrate the penetration of the spin-transfer torque into the right F region and show that, unlike graphene structure, the spin-transfer torque is very sensitive to the chemical potential of the N region as well as the exchange field of the F region.

Interface-induced spin Hall magnetoresistance enhancement in Pt-based tri-layer structure.

Science.gov (United States)

Huang, Shun-Yu; Li, Hong-Lin; Chong, Cheong-Wei; Chang, Yu-Ying; Lee, Min-Kai; Huang, Jung-Chun-Andrew

2018-01-08

In this study, we integrated bilayer structure of covered Pt on nickel zinc ferrite (NZFO) and CoFe/Pt/NZFO tri-layer structure by pulsed laser deposition system for a spin Hall magnetoresistance (SMR) study. In the bilayer structure, the angular-dependent magnetoresistance (MR) results indicate that Pt/NZFO has a well-defined SMR behavior. Moreover, the spin Hall angle and the spin diffusion length, which were 0.0648 and 1.31 nm, respectively, can be fitted by changing the Pt thickness in the longitudinal SMR function. Particularly, the MR ratio of the bilayer structure (Pt/NZFO) has the highest changing ratio (about 0.135%), compared to the prototype structure Pt/Y 3 Fe 5 O 12 (YIG) because the NZFO has higher magnetization. Meanwhile, the tri-layer samples (CoFe/Pt/NZFO) indicate that the MR behavior is related with CoFe thickness as revealed in angular-dependent MR measurement. Additionally, comparison between the tri-layer structure with Pt/NZFO and CoFe/Pt bilayer systems suggests that the SMR ratio can be enhanced by more than 70%, indicating that additional spin current should be injected into Pt layer.

Effect of uniaxial strain on the tunnel magnetoresistance of T-shaped graphene nanoribbon based spin-valve

Science.gov (United States)

Fouladi, A. Ahmadi

2016-07-01

We theoretically investigated the spin-dependent transport through a T-shaped graphene nanoribbon (TsGNR) based spin-valve consisting of armchair graphene sandwiched between two semi-infinite ferromagnetic armchair graphene nanoribbon leads in the presence of an applied uniaxial strain. Based on a tight-binding model and standard nonequilibrium Green's function technique, it is demonstrated that the tunnel magnetoresistance (TMR) for the system can be increased about 98% by tuning the uniaxial strain. Our results show that the absolute values of TMR around the zero bias voltage for compressive strain are larger than tensile strain. In addition, the TMR of the system can be nicely controlled by GNR width.

Quantum conductance in electrodeposited nanocontacts and magnetoresistance measurements

DEFF Research Database (Denmark)

Elhoussine, F.; Encinas, A.; Mátéfi-Tempfli, Stefan

2003-01-01

The conductance and magnetoresistance measurements in magnetic Ni-Ni and Co-Ni nanocontacts prepared by electrodeposition within the pores of a track of track-etched polymer membrane were discussed. At room temperature, Ni-Ni constrictions were found to show broad quantization plateaus of conduct...... of conductance during their dissolution in units of e/h, as expected for ferromagnetic ballistic nanocontacts. The measurement of the positive and negative magnetoresistance in Co-Ni nanocontacts was also elaborated....

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.

Large linear magnetoresistance from neutral defects in Bi$_2$Se$_3$

OpenAIRE

Kumar, Devendra; Lakhani, Archana

2016-01-01

The chalcogenide Bi$_2$Se$_3$ can attain the three dimensional (3D) Dirac semimetal state under the influence of strain and microstrain. Here we report the presnece of large linear magnetoresistance in such a Bi$_2$Se$_3$ crystal. The magnetoresistance has quadratic form at low fields which crossovers to linear above 4 T. The temperature dependence of magnetoresistance scales with carrier mobility and the crossover field scales with inverse of mobility. Our analysis suggest that the linear ma...

Spin injection and magnetoresistance in MoS2-based tunnel junctions using Fe3Si Heusler alloy electrodes.

Science.gov (United States)

Rotjanapittayakul, Worasak; Pijitrojana, Wanchai; Archer, Thomas; Sanvito, Stefano; Prasongkit, Jariyanee

2018-03-19

Recently magnetic tunnel junctions using two-dimensional MoS 2 as nonmagnetic spacer have been fabricated, although their magnetoresistance has been reported to be quite low. This may be attributed to the use of permalloy electrodes, injecting current with a relatively small spin polarization. Here we evaluate the performance of MoS 2 -based tunnel junctions using Fe 3 Si Heusler alloy electrodes. Density functional theory and the non-equilibrium Green's function method are used to investigate the spin injection efficiency (SIE) and the magnetoresistance (MR) ratio as a function of the MoS 2 thickness. We find a maximum MR of ~300% with a SIE of about 80% for spacers comprising between 3 and 5 MoS 2 monolayers. Most importantly, both the SIE and the MR remain robust at finite bias, namely MR > 100% and SIE > 50% at 0.7 V. Our proposed materials stack thus demonstrates the possibility of developing a new generation of performing magnetic tunnel junctions with layered two-dimensional compounds as spacers.

Large linear magnetoresistance in topological crystalline insulator Pb_0_._6Sn_0_._4Te

International Nuclear Information System (INIS)

Roychowdhury, Subhajit; Ghara, Somnath; Guin, Satya N.; Sundaresan, A.; Biswas, Kanishka

2016-01-01

Classical magnetoresistance generally follows the quadratic dependence of the magnetic field at lower field and finally saturates when field is larger. Here, we report the large positive non-saturating linear magnetoresistance in topological crystalline insulator, Pb_0_._6Sn_0_._4Te, at different temperatures between 3 K and 300 K in magnetic field up to 9 T. Magnetoresistance value as high as ∼200% was achieved at 3 K at magnetic field of 9 T. Linear magnetoresistance observed in Pb_0_._6Sn_0_._4Te is mainly governed by the spatial fluctuation carrier mobility due to distortions in the current paths in inhomogeneous conductor. - Graphical abstract: Large non-saturating linear magnetoresistance has been evidenced in topological crystalline insulator, Pb_0_._6Sn_0_._4Te, at different temperatures between 3 K and 300 K in magnetic field up to 9 T. - Highlights: • Large non-saturating linear magnetoresistance was achieved in the topological crystalline insulator, Pb_0_._6Sn_0_._4Te. • Highest magnetoresistance value as high as ~200% was achieved at 3 K at magnetic field of 9 T. • Linear magnetoresistance in Pb_0_._6Sn_0_._4Te is mainly governed by the spatial fluctuation of the carrier mobility.

Probing electronic phase transitions with phonons via inelastic neutron scattering: superconductivity in borocarbides, charge and magnetic order in manganites

Energy Technology Data Exchange (ETDEWEB)

Weber, F.

2007-11-02

The present thesis concentrates on the signatures of strong electron-phonon coupling in phonon properties measured by inelastic neutron scattering. The inelastic neutron scattering experiments were performed on the triple-axis spectrometers 1T and DAS PUMA at the research reactors in Saclay (France) and Munich (Germany), respectively. The work is subdivided into two separate chapters: In the first part, we report measurements of the lattice dynamical properties, i.e. phonon frequency, linewidth and intensity, of the conventional, i.e. phonon-mediated, superconductor YNi{sub 2}B{sub 2}C of the rare-earth-borocarbide family. The detailed check of theoretical predictions for these properties, which were calculated in the theory group of our institute, was one major goal of this work. We measured phonons in the normal state, i.e. T>T{sub c}, for several high symmetry directions up to 70 meV. We were able to extract the full temperature dependence of the superconducting energy gap 2{delta}(T) from our phonon scans with such accuracy that even deviations from the weak coupling BCS behaviour could be clearly observed. By measuring phonons at different wave vectors we demonstrated that phonons are sensitive to the gap anisotropy under the precondition, that different phonons get their coupling strength from different parts of the Fermi surface. In the second part, we investigated the properties of Mn-O bond-stretching phonons in the bilayer manganite La{sub 2-2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7}. At the doping level x=0.38 this compound has an ferromagnetic groundstate and exhibits the so-called colossal magnetoresistance effect in the vicinity of the Curie temperature T{sub C}. The atomic displacement patterns of the investigated phonons closely resemble possible Jahn-Teller distortions of the MnO{sub 6} octahedra, which are introduced in this compound by the Jahn-Teller active Mn{sup 3+} ions. We observed strong renormalizations of the phonon frequencies and clear peaks of

Probing electronic phase transitions with phonons via inelastic neutron scattering: superconductivity in borocarbides, charge and magnetic order in manganites

International Nuclear Information System (INIS)

Weber, F.

2007-01-01

The present thesis concentrates on the signatures of strong electron-phonon coupling in phonon properties measured by inelastic neutron scattering. The inelastic neutron scattering experiments were performed on the triple-axis spectrometers 1T and DAS PUMA at the research reactors in Saclay (France) and Munich (Germany), respectively. The work is subdivided into two separate chapters: In the first part, we report measurements of the lattice dynamical properties, i.e. phonon frequency, linewidth and intensity, of the conventional, i.e. phonon-mediated, superconductor YNi 2 B 2 C of the rare-earth-borocarbide family. The detailed check of theoretical predictions for these properties, which were calculated in the theory group of our institute, was one major goal of this work. We measured phonons in the normal state, i.e. T>T c , for several high symmetry directions up to 70 meV. We were able to extract the full temperature dependence of the superconducting energy gap 2Δ(T) from our phonon scans with such accuracy that even deviations from the weak coupling BCS behaviour could be clearly observed. By measuring phonons at different wave vectors we demonstrated that phonons are sensitive to the gap anisotropy under the precondition, that different phonons get their coupling strength from different parts of the Fermi surface. In the second part, we investigated the properties of Mn-O bond-stretching phonons in the bilayer manganite La 2-2x Sr 1+2x Mn 2 O 7 . At the doping level x=0.38 this compound has an ferromagnetic groundstate and exhibits the so-called colossal magnetoresistance effect in the vicinity of the Curie temperature T C . The atomic displacement patterns of the investigated phonons closely resemble possible Jahn-Teller distortions of the MnO 6 octahedra, which are introduced in this compound by the Jahn-Teller active Mn 3+ ions. We observed strong renormalizations of the phonon frequencies and clear peaks of the intrinsic phonon linewidth near the order

Magnetoresistance in amorphous NdFeB/FeB compositionally modulated multilayers

International Nuclear Information System (INIS)

Peral, G.; Briones, F.; Vicent, J.L.

1991-01-01

Resistance measurements have been done in amorphous Nd 12 Fe 80 B 8 sputtered films and in amorphous sputtered Nd 26 Fe 68 B 6 /Fe 92 B 8 multilayers between 6 and 150 K with applied magnetic field parallel (LMR) and perpendicular (TMR) up to 7 T. The samples were grown by dc triode sputtering, with nominal unequal (2:1) layer thicknesses. The layered character of the samples have been tested by x-ray diffraction. Longitudinal magnetoresistance (LMR) is positive and transverse magnetoresistance (TMR) is negative. The magnetoresistance values are higher than in amorphous ferromagnets, and multilayering of these alloys produces much larger magnetoresistance values than either alloy alone and there is a strong dependence on the multilayer wavelength. The MR shows a weak temperature dependence in the temperature interval that was investigated

Unidirectional spin Hall magnetoresistance in topological insulator/ferromagnetic layer heterostructures

Science.gov (United States)

Kally, James; Lv, Yang; Zhang, Delin; Lee, Joon Sue; Samarth, Nitin; Wang, Jian-Ping; Department of Electrical; Computer Engineering, University of Minnesota, Minneapolis Collaboration; Department of Physics, Pennsylvania State University Collaboration

The surface states of topological insulators offer a potentially very efficient way to generate spins and spin-orbit torques to magnetic moments in proximity. The switching by spin-orbit torque itself only requires two terminals so that a charge current can be applied. However, a third terminal with additional magnetic tunneling junction structure is needed to sense the magnetization state if such devices are used for memory and logic applications. The recent discovery of unidirectional spin Hall magnetoresistance in heavy metal/ferromagnetic and topological insulator/magnetically doped topological insulator systems offers an alternative way to sense magnetization while still keeping the number of terminals to minimal two. The unidirectional spin Hall magnetoresistance in topological insulator/strong ferromagnetic layer heterostructure system has yet not been reported. In this work, we report our experimental observations of such magnetoresistance. It is found to be present and comparable to the best result of the previous reported Ta/Co systems in terms of magnetoresistance per current density per total resistance.

Large linear magnetoresistivity in strongly inhomogeneous planar and layered systems

International Nuclear Information System (INIS)

Bulgadaev, S.A.; Kusmartsev, F.V.

2005-01-01

Explicit expressions for magnetoresistance R of planar and layered strongly inhomogeneous two-phase systems are obtained, using exact dual transformation, connecting effective conductivities of in-plane isotropic two-phase systems with and without magnetic field. These expressions allow to describe the magnetoresistance of various inhomogeneous media at arbitrary concentrations x and magnetic fields H. All expressions show large linear magnetoresistance effect with different dependencies on the phase concentrations. The corresponding plots of the x- and H-dependencies of R(x,H) are represented for various values, respectively, of magnetic field and concentrations at some values of inhomogeneity parameter. The obtained results show a remarkable similarity with the existing experimental data on linear magnetoresistance in silver chalcogenides Ag 2+δ Se. A possible physical explanation of this similarity is proposed. It is shown that the random, stripe type, structures of inhomogeneities are the most suitable for a fabrication of magnetic sensors and a storage of information at room temperatures

Investigation of structure and magnetoresistance in Co/ZnO films

International Nuclear Information System (INIS)

Quan Zhiyong; Xu Xiaohong; Li Xiaoli; Feng, Q.; Gehring, G. A.

2010-01-01

Co/ZnO films were deposited on glass substrates by magnetron sputtering at room temperature. The structure of the as-deposited films is studied by means of x-ray diffraction, x-ray photoelectron spectroscopy, and the zero-field-cooled and field-cooled magnetization curves. It is shown that the as-deposited samples consist of a mixture of regions of metallic Co and semiconducting ZnO. Large negative magnetoresistance of 26% and 11.9% are observed in the as-deposited Co/ZnO film with Co concentration of 50.7 at. % at 10 K and room temperature, respectively. Structural analysis, the temperature dependence of the conductivity and magnetoresistance reveal that the magnetoresistance is induced by spin-dependent tunneling between regions of conducting magnetic Co through the ZnO semiconducting barriers. The enhanced magnetoresistance in the low temperature regime may be related to the existence of higher-order tunneling processes between large Co regions mediated by small Co particles.

Abnormal magnetization and field-induced transition in (La0.73Bi0.27)0.67Ca0.33MnO3

International Nuclear Information System (INIS)

Li Haina; Wu Yuying; Yu Hongwei; Chen Ziyu; Huang Yan; Wang Shaoliang; Li Liang; Xia Zhengcai

2010-01-01

The magnetic field dependence of magnetization of Bi doped manganites (La 1-x Bi x ) 0.67 Ca 0.33 MnO 3 (x=0.27) was investigated at different temperatures with a pulsed high magnetic field. A metamagnetic transition was observed in the magnetization measurement, which revealed the coexistence of charge ordering (CO) and ferromagnetic (FM) phases. With decreasing magnetic field, the field-induced FM phases remained stable even when the magnetic field decreased to zero. This result suggests that ferromagnetic interactions are enhanced due to the effect of the pulsed high magnetic field, which makes the doped manganites a good system for magnetoresistance materials.

Abnormal magnetization and field-induced transition in (La{sub 0.73}Bi{sub 0.27}){sub 0.67}Ca{sub 0.33}MnO{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Li Haina; Wu Yuying [Department of Physics, Huazhong University of Science and Technology, Wuhan (China); Yu Hongwei [College of Science, Naval University of Engineering, Wuhan (China); Chen Ziyu [Department of Physics, Huazhong University of Science and Technology, Wuhan (China); Huang Yan; Wang Shaoliang; Li Liang [Wuhan Pulsed High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan (China); Xia Zhengcai, E-mail: xia9020@hust.edu.c [Wuhan Pulsed High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan (China)

2010-09-15

The magnetic field dependence of magnetization of Bi doped manganites (La{sub 1-x}Bi{sub x}){sub 0.67}Ca{sub 0.33}MnO{sub 3} (x=0.27) was investigated at different temperatures with a pulsed high magnetic field. A metamagnetic transition was observed in the magnetization measurement, which revealed the coexistence of charge ordering (CO) and ferromagnetic (FM) phases. With decreasing magnetic field, the field-induced FM phases remained stable even when the magnetic field decreased to zero. This result suggests that ferromagnetic interactions are enhanced due to the effect of the pulsed high magnetic field, which makes the doped manganites a good system for magnetoresistance materials.

Flat magnetic exchange springs as mechanism for additional magnetoresistance in magnetic nanoisland arrays

Energy Technology Data Exchange (ETDEWEB)

Boltaev, A.P.; Pudonin, F.A. [P. N. Lebedev Physical Institute of the Russian Academy of Sciences, Leninskiy Prospekt 53, 119991 Moscow (Russian Federation); Sherstnev, I.A., E-mail: sherstnev@lebedev.ru [P. N. Lebedev Physical Institute of the Russian Academy of Sciences, Leninskiy Prospekt 53, 119991 Moscow (Russian Federation); Egorov, D.A. [National Research Nuclear University MEPhI, Kashirskoe shosse 31, 115409 Moscow (Russian Federation); Kozmin, A.M. [National Research University of Electronic Technology, Shokin Square, 1, Zelenograd, 124482 Moscow (Russian Federation)

2017-04-15

Process of magnetization and magnetoresistance have been studied in nanoisland bilayer systems of FeNi-Co. Hysteresis loops show characteristic features (steps) most clearly observed in certain orientations of the sample in a magnetic field. To explain these features the concept of flat magnetic exchange spring has been introduced for nanoisland bilayers. It has been proposed that additional magnetoresistance can be the result of spin-dependent scattering of electrons in the area of flat magnetic exchange spring. Magnetoresistance studies of bilayer systems has shown that additional magnetoresistance occurs at the same magnetic fields as steps on hysteresis loops. - Highlights: • Metallic FeNi-Co bilayers are studied. • FeNi and Co layers magnetize independently. • Concept of flat spin spring is proposed. • Additional magnetoresistance occurs in intermediate magnetic fields.

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).

Flat magnetic exchange springs as mechanism for additional magnetoresistance in magnetic nanoisland arrays

International Nuclear Information System (INIS)

Boltaev, A.P.; Pudonin, F.A.; Sherstnev, I.A.; Egorov, D.A.; Kozmin, A.M.

2017-01-01

Process of magnetization and magnetoresistance have been studied in nanoisland bilayer systems of FeNi-Co. Hysteresis loops show characteristic features (steps) most clearly observed in certain orientations of the sample in a magnetic field. To explain these features the concept of flat magnetic exchange spring has been introduced for nanoisland bilayers. It has been proposed that additional magnetoresistance can be the result of spin-dependent scattering of electrons in the area of flat magnetic exchange spring. Magnetoresistance studies of bilayer systems has shown that additional magnetoresistance occurs at the same magnetic fields as steps on hysteresis loops. - Highlights: • Metallic FeNi-Co bilayers are studied. • FeNi and Co layers magnetize independently. • Concept of flat spin spring is proposed. • Additional magnetoresistance occurs in intermediate magnetic fields.

Tunnel magnetoresistance in alumina, magnesia and composite tunnel barrier magnetic tunnel junctions

International Nuclear Information System (INIS)

Schebaum, Oliver; Drewello, Volker; Auge, Alexander; Reiss, Guenter; Muenzenberg, Markus; Schuhmann, Henning; Seibt, Michael; Thomas, Andy

2011-01-01

Using magnetron sputtering, we have prepared Co-Fe-B/tunnel barrier/Co-Fe-B magnetic tunnel junctions with tunnel barriers consisting of alumina, magnesia, and magnesia-alumina bilayer systems. The highest tunnel magnetoresistance ratios we found were 73% for alumina and 323% for magnesia-based tunnel junctions. Additionally, tunnel junctions with a unified layer stack were prepared for the three different barriers. In these systems, the tunnel magnetoresistance ratios at optimum annealing temperatures were found to be 65% for alumina, 173% for magnesia, and 78% for the composite tunnel barriers. The similar tunnel magnetoresistance ratios of the tunnel junctions containing alumina provide evidence that coherent tunneling is suppressed by the alumina layer in the composite tunnel barrier. - Research highlights: → Transport properties of Co-Fe-B/tunnel barrier/Co-Fe-B magnetic tunnel junctions. → Tunnel barrier consists of MgO, Al-Ox, or MgO/Al-Ox bilayer systems. → Limitation of TMR-ratio in composite barrier tunnel junctions to Al-Ox values. → Limitation indicates that Al-Ox layer is causing incoherent tunneling.

Theory of magnetoresistance of organic molecular tunnel junctions with nonmagnetic electrodes

Science.gov (United States)

Shi, Sha; Xie, Zuoti; Liu, Feilong; Smith, Darryl L.; Frisbie, C. Daniel; Ruden, P. Paul

2017-04-01

Large room-temperature magnetoresistance observed for devices composed of self-assembled monolayers of different oligophenylene thiols sandwiched between gold contacts has recently been reported [Z. Xie, S. Shi, F. Liu, D. L. Smith, P. P. Ruden, and C. D. Frisbie, ACS Nano 10, 8571 (2016), 10.1021/acsnano.6b03853]. The transport mechanism through the organic molecules was determined to be nonresonant tunneling. To explain this kind of magnetoresistance, we develop an analytical model based on the interaction of the tunneling charge carrier with an unpaired charge carrier populating a contact-molecule interface state. The Coulomb interaction between carriers causes the transmission coefficients to depend on their relative spin orientation. Singlet and triplet pairing of the tunneling and the interface carriers thus correspond to separate conduction channels with different transmission probabilities. Spin relaxation enabling transitions between the different channels, and therefore tending to maximize the tunneling current for a given applied bias, can be suppressed by relatively small magnetic fields, leading to large magnetoresistance. Our model elucidates how the Coulomb interaction gives rise to transmission probabilities that depend on spin and how an applied magnetic field can inhibit transitions between different spin configurations.

Anisotropic giant magnetoresistance in NbSb2

Science.gov (United States)

Wang, Kefeng; Graf, D.; Li, Lijun; Wang, Limin; Petrovic, C.

2014-01-01

The magnetic field response of the transport properties of novel materials and then the large magnetoresistance effects are of broad importance in both science and application. We report large transverse magnetoreistance (the magnetoresistant ratio ~ 1.3 × 105% in 2 K and 9 T field, and 4.3 × 106% in 0.4 K and 32 T field, without saturation) and field-induced metal-semiconductor-like transition, in NbSb2 single crystal. Magnetoresistance is significantly suppressed but the metal-semiconductor-like transition persists when the current is along the ac-plane. The sign reversal of the Hall resistivity and Seebeck coefficient in the field, plus the electronic structure reveal the coexistence of a small number of holes with very high mobility and a large number of electrons with low mobility. The large MR is attributed to the change of the Fermi surface induced by the magnetic field which is related to the Dirac-like point, in addition to orbital MR expected for high mobility metals. PMID:25476239

Light-induced magnetoresistance in solution-processed planar hybrid devices measured under ambient conditions.

Science.gov (United States)

Banerjee, Sreetama; Bülz, Daniel; Reuter, Danny; Hiller, Karla; Zahn, Dietrich R T; Salvan, Georgeta

2017-01-01

We report light-induced negative organic magnetoresistance (OMAR) measured in ambient atmosphere in solution-processed 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) planar hybrid devices with two different device architectures. Hybrid electronic devices with trench-isolated electrodes (HED-TIE) having a channel length of ca. 100 nm fabricated in this work and, for comparison, commercially available pre-structured organic field-effect transistor (OFET) substrates with a channel length of 20 µm were used. The magnitude of the photocurrent as well as the magnetoresistance was found to be higher for the HED-TIE devices because of the much smaller channel length of these devices compared to the OFETs. We attribute the observed light-induced negative magnetoresistance in TIPS-pentacene to the presence of electron-hole pairs under illumination as the magnetoresistive effect scales with the photocurrent. The magnetoresistance effect was found to diminish over time under ambient conditions compared to a freshly prepared sample. We propose that the much faster degradation of the magnetoresistance effect as compared to the photocurrent was due to the incorporation of water molecules in the TIPS-pentacene film.

Magnetoresistance and Hall resistivity of semimetal WTe2 ultrathin flakes.

Science.gov (United States)

Luo, Xin; Fang, Chi; Wan, Caihua; Cai, Jialin; Liu, Yong; Han, Xiufeng; Lu, Zhihong; Shi, Wenhua; Xiong, Rui; Zeng, Zhongming

2017-04-07

This article reports the characterization of WTe 2 thin flake magnetoresistance and Hall resistivity. We found it does not exhibit magnetoresistance saturation when subject to high fields, in a manner similar to their bulk characteristics. The linearity of Hall resistivity in our devices confirms the compensation of electrons and holes. By relating experimental results to a classic two-band model, the lower magnetoresistance values in our samples is demonstrated to be caused by decreased carrier mobility. The dependence of mobility on temperature indicates the main role of optical phonon scattering at high temperatures. Our results provide more detailed information on carrier behavior and scattering mechanisms in WTe 2 thin films.

Correlation of thickness and magnetization in LCMO film

Indian Academy of Sciences (India)

Colossal magnetoresistance; manganite; thin film; La0.67Mn0.33MnO3. ... We suggest that the difference in the magnetization under FC and ZFC conditions may be due to strain-induced anisotropy arising from the lattice mismatch between the substrate and the film or due to the shape anisotropy due to epitaxial growth.

Magnetoresistance of amorphous CuZr: weak localization in a three dimensional system

International Nuclear Information System (INIS)

Bieri, J.B.; Fert, A.; Creuzet, G.

1984-01-01

Observations of anomalous magnetoresistance in amorphous CuZr at low temperature are reported. The magnetoresistance can be precisely accounted for in theoretical models of localization for 3-dimensional metallic systems in the presence of strong spin-orbit interactions (with a significant additional contribution from the quenching of superconducting fluctuations at the lowest temperatures). Magnetoresistance measurements on various other systems show that such 3-dimensional localization effects are very generally observed in amorphous alloys. (author)

Improved crystallinity, spatial arrangement and monodispersity of submicron La{sub 0.7}Ba{sub 0.3}MnO{sub 3} powders: A citrate chelation approach

Energy Technology Data Exchange (ETDEWEB)

Rao, Ch. N. [Department of Applied Physics, Defence Institute of Advanced Technology, Girinagar, Pune 411025 (India); Samatham, S. Shanmukharao; Ganesan, V.; Sathe, V.G.; Phase, D.M. [UGC-DAE Consortium for Scientific Research, Khandwa Road, Indore 452 017 (India); Kale, S.N., E-mail: sangeetakale2004@gmail.com [Department of Applied Physics, Defence Institute of Advanced Technology, Girinagar, Pune 411025 (India)

2012-11-15

The perovskite manganite systems have been the materials of tremendous interest due to their strong correlation between structure, transport and magnetism. These materials in their single-crystal form show colossal magneto-resistance (CMR), but the applied fields are very high ({approx}1-5 T). The polycrystalline samples do show high low-field magneto-resistance (LFMR), but good amount of control over particle sizes and grain-boundary distribution is required, which is well known but less realized in practical approaches. In this context, we report on synthesis and manipulation of polycrystalline La{sub 0.7}Ba{sub 0.3}MnO{sub 3} (LBMO) submicron powders using citric acid chelation. The Citrate-gel route is used to synthesize poly-dispersed LBMO powders which are subjected to citrate chelation for a duration of 0 (LB0) to 4 h(LB4) . The samples show improved ordering in X-ray diffraction patterns. Raman spectroscopy scans indicate changed mode signatures due to the probable chelating process, which alters the surface morphology. X-ray photoelectron microscopy shows an evidence of fine citrate layer on the grain boundaries. Low temperature B-H curves exhibit fine hysteresis loops for all samples, while room temperature B-H curves shows paramagnetic response. Scanning electron microscopy images showed the formation of well arranged, connected, mono-dispersed grains of LB4 sample, as against polydispered LB0. The magneto-resistance (at H=100 kOe) is seen to enhance for LB4 at its transition temperature (75%, as compared to LB0, where it is 60%), which can be attributed to the well-controlled inter-grain tunneling phenomenon and thin insulating regions in between, created due to citrate chelation, which probably enhances the scattering phenomenon and its susceptibility to applied fields. As citric acid is known to chelate Mn ions, it probably chelates the smaller LB particulate structure and leaves behind citrate-connected submicron grains of LBMO, which are seen to be

Anomalous electronic structure and magnetoresistance in TaAs2.

Science.gov (United States)

Luo, Yongkang; McDonald, R D; Rosa, P F S; Scott, B; Wakeham, N; Ghimire, N J; Bauer, E D; Thompson, J D; Ronning, F

2016-06-07

The change in resistance of a material in a magnetic field reflects its electronic state. In metals with weakly- or non-interacting electrons, the resistance typically increases upon the application of a magnetic field. In contrast, negative magnetoresistance may appear under some circumstances, e.g., in metals with anisotropic Fermi surfaces or with spin-disorder scattering and semimetals with Dirac or Weyl electronic structures. Here we show that the non-magnetic semimetal TaAs2 possesses a very large negative magnetoresistance, with an unknown scattering mechanism. Density functional calculations find that TaAs2 is a new topological semimetal [ℤ2 invariant (0;111)] without Dirac dispersion, demonstrating that a negative magnetoresistance in non-magnetic semimetals cannot be attributed uniquely to the Adler-Bell-Jackiw chiral anomaly of bulk Dirac/Weyl fermions.

Structural and magnetotransport properties of the Y doped A-site deficient double layered manganites La{sub 1.2−x}□{sub 0.2}Y{sub x}Ca{sub 1.6}Mn{sub 2}O{sub 7}

Energy Technology Data Exchange (ETDEWEB)

Mahamdioua, N., E-mail: mahamdioua.nabil@gmail.com [LEND, Faculty of Science and Technology, Jijel University, Jijel 18000 (Algeria); Amira, A. [LEND, Faculty of Science and Technology, Jijel University, Jijel 18000 (Algeria); Altintas, S.P. [Department of Physics, Faculty of Arts and Sciences, AIB University, Bolu 14280 (Turkey); Koc University, Surface Science and Technology Center (KUYTAM), 34450-Sariyer, Istanbul (Turkey); Varilci, A.; Terzioglu, C. [Department of Physics, Faculty of Arts and Sciences, AIB University, Bolu 14280 (Turkey)

2016-08-15

We present structural, magnetic and electrical properties of the polycrystalline A-site-deficient yttrium doped double layered manganites La{sub 1.2−x}□{sub 0.2}Y{sub x}Ca{sub 1.6}Mn{sub 2}O{sub 7} (x=0.2, 0.3 and 0.4) prepared by a solid state reaction method. The samples crystallize in the tetragonal structure with the space group I4/mmm. Doping with Y decreases the cell parameters and causes a decrease of the metal-insulator transition temperature. The same evolution with doping is also seen for the deduced Curie temperature from susceptibility curves which present a clear paramagnetic-ferromagnetic transition. The significant positive intrinsic magnetoresistance, shown in all samples, reaches 85% at 122 K under 7 T for 0.3 doped sample and can be attributed to the suppression of spin fluctuations via aligning the spins under external magnetic field, while the extrinsic one is attributed to the inter-grain spin-polarized tunneling across the grain boundaries. The simulation of the resistivity curves in the entire temperature range show that the percolation model is suitable to fit our results. The applied magnetic field increases the density of states near the Fermi level, which is in accordance with the observed decrease of resistivity. - Graphical abstract: Resistivity and magnetoresistance of La{sub 1.2−x}□{sub 0.2}Y{sub x}Ca{sub 1.6}Mn{sub 2}O{sub 7} (x=0.2, 0.3, 0.4). Solid lines correspond to the fitting results. Display Omitted.

Extremely large and significantly anisotropic magnetoresistance in ZrSiS single crystals

Energy Technology Data Exchange (ETDEWEB)

Lv, Yang-Yang; Zhang, Bin-Bin; Yao, Shu-Hua, E-mail: shyao@nju.edu.cn, E-mail: ybchen@nju.edu.cn, E-mail: zhoujian@nju.edu.cn; Zhou, Jian, E-mail: shyao@nju.edu.cn, E-mail: ybchen@nju.edu.cn, E-mail: zhoujian@nju.edu.cn; Zhang, Shan-Tao; Lu, Ming-Hui [National Laboratory of Solid State Microstructures and Department of Materials Science and Engineering, Nanjing University, Nanjing 210093 (China); Li, Xiao; Chen, Y. B., E-mail: shyao@nju.edu.cn, E-mail: ybchen@nju.edu.cn, E-mail: zhoujian@nju.edu.cn [National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093 (China); Chen, Yan-Feng [National Laboratory of Solid State Microstructures and Department of Materials Science and Engineering, Nanjing University, Nanjing 210093 (China); Collaborative Innovation Center of Advanced Microstructure, Nanjing University, Nanjing 210093 (China)

2016-06-13

Recently, the extremely large magnetoresistance (MR) observed in transition metal telluride, like WTe{sub 2}, attracted much attention because of the potential applications in magnetic sensor. Here, we report the observation of extremely large magnetoresistance as 3.0 × 10{sup 4}% measured at 2 K and 9 T magnetic field aligned along [001]-ZrSiS. The significant magnetoresistance change (∼1.4 × 10{sup 4}%) can be obtained when the magnetic field is titled from [001] to [011]-ZrSiS. These abnormal magnetoresistance behaviors in ZrSiS can be understood by electron-hole compensation and the open orbital of Fermi surface. Because of these superior MR properties, ZrSiS may be used in the magnetic sensors.

Studies of colossal magnetoresistive oxides with radioactive isotopes

CERN Document Server

CERN. Geneva. ISOLDE and Neutron Time-of-Flight Experiments Committee; Amaral, V S; Araújo, J P; Butz, T; Correia, J G; Dubourdieu, C; Habermeier, H U; Lourenço, A A; Marques, J G; Da Silva, M F A; Senateur, J P; Soares, J C; Sousa, J B; Suryan, R; Tokura, Y; Tavares, P B; Tomioka, Y; Tröger, W; Vantomme, A; Vieira, J M; Wahl, U; Weiss, F P; INTC

2000-01-01

We propose to study Colossal Magnetoresistive (CMR) oxides with several nuclear techniques, which use radioactive elements at ISOLDE. Our aim is to provide local and element selective information on some of the doping mechanisms that rule electronic interactions and magnetoresistance, in a complementary way to the use of conventional characterisation techniques. Three main topics are proposed: \\\\ \\\\ a) Studies of local [charge and] structural modifications in antiferromagnetic LaMnO$_{3+ \\delta}$ and La$_{1-x}$R$_{x}$MnO$_{3}$ with R=Ca and Cd, doped ferromagnetic systems with competing interactions: - research on the lattice site and electronic characterisation of the doping element. \\\\ \\\\ b) Studies of self doped La$_{x}$R$_{1-x}$MnO$_{3+\\delta}$ systems, with oxygen and cation non-stoichiometry: -learning the role of defects in the optimisation of magnetoresistive properties. \\\\ \\\\ c) Probing the disorder and quenched random field effects in the vicinity of the charge or orbital Ordered/Ferromagnetic phase...

Light-induced magnetoresistance in solution-processed planar hybrid devices measured under ambient conditions

Directory of Open Access Journals (Sweden)

Sreetama Banerjee

2017-07-01

Full Text Available We report light-induced negative organic magnetoresistance (OMAR measured in ambient atmosphere in solution-processed 6,13-bis(triisopropylsilylethynylpentacene (TIPS-pentacene planar hybrid devices with two different device architectures. Hybrid electronic devices with trench-isolated electrodes (HED-TIE having a channel length of ca. 100 nm fabricated in this work and, for comparison, commercially available pre-structured organic field-effect transistor (OFET substrates with a channel length of 20 µm were used. The magnitude of the photocurrent as well as the magnetoresistance was found to be higher for the HED-TIE devices because of the much smaller channel length of these devices compared to the OFETs. We attribute the observed light-induced negative magnetoresistance in TIPS-pentacene to the presence of electron–hole pairs under illumination as the magnetoresistive effect scales with the photocurrent. The magnetoresistance effect was found to diminish over time under ambient conditions compared to a freshly prepared sample. We propose that the much faster degradation of the magnetoresistance effect as compared to the photocurrent was due to the incorporation of water molecules in the TIPS-pentacene film.

Magnetoresistance manipulation and sign reversal in Mn-doped ZnO nanowires.

Science.gov (United States)

Sapkota, Keshab R; Chen, Weimin; Maloney, F Scott; Poudyal, Uma; Wang, Wenyong

2016-10-14

We report magnetoresistance (MR) manipulation and sign reversal induced by carrier concentration modulation in Mn-doped ZnO nanowires. At low temperatures positive magnetoresistance was initially observed. When the carrier concentration was increased through the application of a gate voltage, the magnetoresistance also increased and reached a maximum value. However, further increasing the carrier concentration caused the MR to decrease, and eventually an MR sign reversal from positive to negative was observed. An MR change from a maximum positive value of 25% to a minimum negative value of 7% was observed at 5 K and 50 KOe. The observed MR behavior was modeled by considering combined effects of quantum correction to carrier conductivity and bound magnetic polarons. This work could provide important insights into the mechanisms that govern magnetotransport in dilute magnetic oxides, and it also demonstrated an effective approach to manipulating magnetoresistance in these materials that have important spintronic applications.

NbSe3: Fermi surface and magnetoresistance under uniaxial stress

International Nuclear Information System (INIS)

Tessema, G.X.; Gamble, B.K.; Kuh, J.; Skove, M.J.; Lacerda, A.H.; Bennett, M.

1999-01-01

The Fermi surface of NbSe 3 below the two CDW transitions is still not very clear. Large magnetoresistance and giant quantum oscillations have been seen at low temperature below the second CDW transition. The SdH oscillations are attributed to one or several small pieces of electron or hole pockets spared by the two CDW transitions at 145 and 59 K. In a previous low field study (μ 0 H<8 T) of the transverse magnetoresistance (H in the (b,c) plane) we have shown that the extremal area of one of these pockets decreases linearly with strain, ε, vanishing at ε = 2.5%. Here we extend our study into the high magnetic field regime (pulsed 60 T) and investigate the effect of uniaxial stress on the magnetoresistance (I//H). Our high field study is consistent with the fermiology study and shows that uniaxial stress leads to the obliteration of a small closed pocket. Above 1% strain the magnetoresistance is linear with H with no sign of saturation. (orig.)

Effect of pressure on the magnetic properties of lanthanum manganite

International Nuclear Information System (INIS)

Gonchar', L. E.; Leskova, Yu. V.; Nikiforov, A. E.; Kozlenko, D. P.

2010-01-01

The crystalline structure of pure lanthanum manganite under external hydrostatic pressure has been studied. The behavior of magnetic properties and nuclear magnetic resonance (NMR) spectra under these conditions is theoretically predicted. It is shown that an increase in the Neel temperature with pressure is not only caused by the general contraction of the crystal, but is also related to certain peculiarities in the baric behavior of the orbital structure.

Electroresistive and magnetoresistive effects in electron doped manganite La0.7Ce0.3MnO3 thin films

International Nuclear Information System (INIS)

Bajaj, Kavita; Jesudasan, John; Bagwe, Vivas; Raychaudhuri, Pratap

2007-01-01

Full text: The influence of electric current and magnetic field separately and in conjugation on the transport behavior of patterned La 0.7 Ce 0.3 MnO 3 thin films on (001) LaAlO 3 substrate is studied. Measurements were carried out in the regime of low current densities, for dc currents. In absence of magnetic field significant reduction in peak resistance (R p ) was found with increasing bias current. This effect is also present when a magnetic field is applied though the magnitude of the electroresistance (ER=(R(I=0.05μA)-R(I=50μA))/R(I=50μA)) decreases. The metal-insulator transition temperature (T p ) increases both with increasing current and with magnetic field. The current-voltage characteristics at various temperatures above and below T p show nonlinearity for small currents due to electroresistance and large currents due to Joule heating. The behavior of resistance with current is similar at various temperatures decreasing initially with increasing current and then nearly leveling off. We observe an interesting correlation between effect of electric current and magnetic field. The magnetoresistance (MR (R H=0 -R H=1T )/R H=0 ) decreases with increasing bias current, while ER decreases with increasing magnetic field. Both ER and MR show a maximum near T p . This interesting correlation between these two effects suggests that both these effects suggests that both these effects arise from the same origin

Sign change of magnetoresistance in Gd-doped amorphous carbon granular films.

Science.gov (United States)

Ding, Shihao; Jin, Chao; Fan, Ziwei; Li, Peng; Bai, Haili

2015-11-11

Gd/C granular films with 11% Gd were fabricated by facing-target magnetron sputtering at room temperature and then annealed at 300-650 °C for 1.5 h. A magnetoresistance of -82% was obtained in the Gd/C films annealed at 650 °C at 3 K under a magnetic field of 50 kOe. A sign change of the magnetoresistance from negative to positive and then back to negative was observed in all samples as the temperature decreases. Grain boundary scattering effects, wave-function-shrinkage, cotunneling and Gd-Gd interactions account for the mechanisms of the magnetoresistance effects in different temperature regions. The sign of the magnetoresistance also varies as the magnetic field increases. At the transition temperature of 25 K, the wave-function-shrinkage effect competes with cotunneling and Gd-Gd interactions at different magnetic fields. The competition between the wave-function-shrinkage effect and the grain boundary scattering effect is approximately at the transition temperature of 100 K. The temperature range of positive magnetoresistance expands and transition temperatures are changed as the annealing temperature increases. It is related to the expansion of the temperature region for the wave-function-shrinkage effect which occurs in the Mott variable range hopping conduction mechanism.

Tunneling magnetoresistance in junctions composed of ferromagnets and time-reversal invariant topological superconductors

International Nuclear Information System (INIS)

Yan, Zhongbo; Wan, Shaolong

2016-01-01

Tunneling magnetoresistance between two ferrromagnets is an issue of fundamental importance in spintronics. In this work, we show that tunneling magnetoresistance can also emerge in junctions composed of ferromagnets and time-reversal invariant topological superconductors without spin-rotation symmetry. Here the physical origin is that when the spin-polarization direction of an injected electron from the ferromagnet lies in the same plane of the spin-polarization direction of Majorana zero modes, the electron will undergo a perfect spin-equal Andreev reflection, while injected electrons with other spin-polarization directions will be partially Andreev reflected and partially normal reflected, which consequently has a lower conductance, and therefore, the magnetoresistance effect emerges. Compared to conventional magnetic tunnel junctions, an unprecedented advantage of the junctions studied here is that arbitrary high tunneling magnetoresistance can be obtained even when the magnetization of the ferromagnets are weak and the insulating tunneling barriers are featureless. Our findings provide a new fascinating mechanism to obtain high tunneling magnetoresistance. (paper)

Relation of Giant Thermo-EMF, Magnetothermo-EMF, Magnetoresistance, and Magnetization to Magnetic Impurity States in Manganites Nd(1- x)Sr x MnO3 and Sm(1- x)Sr x MnO3

Science.gov (United States)

Koroleva, L. I.; Batashev, I. K.; Morozov, A. S.; Balbashov, A. M.; Szymczak, H.; Slawska-Waniew, A.

2018-02-01

Thermo-EMF, magnetothermo-EMF, magnetoresistance, and magnetization of single-crystal samples of Nd(1- x)Sr x MnO3 and Sm(1- x)Sr x MnO3 with 0 ≤ x ≤ 0.3 have been studied experimentally. A sharp increase in the thermo-EMF and giant magnetothermo-EMF and magnetoresistance has been observed near the Curie point T C in compounds with 0.15 ≤ x ≤ 0.3. At the same time, no peculiarities have been found in compositions with x = 0. Since compounds with x > 0 consist of ferromagnetic clusters of the ferron type that reside in an antiferromagnetic A-type matrix, this means that the sharp increase in the thermo-EMF near T C is caused by ferrons. Indeed, the disappearance of ferrons due to a magnetic field or heating above T C leads to an abrupt decrease in the thermo-EMF. Therefore, thermo-EMF in alloyed magnetic semiconductors has been determined by the impurity concentration and the sample volume.

Tunneling anisotropic magnetoresistance: A spin-valve-like tunnel magnetoresistance using a single magnetic layer

Czech Academy of Sciences Publication Activity Database

Gould, C.; Rüster, C.; Jungwirth, Tomáš; Girgis, E.; Schott, G. M.; Giraud, R.; Brunner, K.; Schmidt, G.; Molenkamp, L. W.

2004-01-01

Roč. 93, č. 11 (2004), 117203/1-117203/4 ISSN 0031-9007 R&D Projects: GA ČR GA202/02/0912 Institutional research plan: CEZ:AV0Z1010914 Keywords : semiconductor spintronics * tunneling anisotropic magnetoresistance Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 7.218, year: 2004

Enhanced magnetoresistance in the binary semimetal NbAs2 due to improved crystal quality

Science.gov (United States)

Yokoi, K.; Murakawa, H.; Komada, M.; Kida, T.; Hagiwara, M.; Sakai, H.; Hanasaki, N.

2018-02-01

We have observed an extremely large magnetoresistance exceeding 1.9 million at 1.7 K at 40 T for a single crystal of the binary semimetal NbAs2. The magnetoresistive behavior for this compound is quantitatively reproduced by a semiclassical two-carrier model in which the significant enhancement of magnetoresistance is attributed to the almost full compensation of the hole and electron densities (0.994 6 ×105cm2 /V .s ). Our results indicate that binary semimetals with higher carrier densities have a great potential for exhibiting a further divergent increase in magnetoresistance merely through an improvement in crystal quality.

Structure and transport properties of La.sub.1-x./sub.Sr.sub.x./sub.MnO.sub.3./sub. granular ceramics

Czech Academy of Sciences Publication Activity Database

Jirák, Zdeněk; Hirschner, Jan; Kaman, Ondřej; Knížek, Karel; Levinský, Petr; Maryško, Miroslav; Hejtmánek, Jiří

2017-01-01

Roč. 50, č. 7 (2017), 1-15, č. článku 075001. ISSN 0022-3727 R&D Projects: GA ČR GA15-10088S Institutional support: RVO:68378271 Keywords : magnetic nanoparticles * perovskite manganite * tunnelling magnetoresistance Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 2.588, year: 2016

Measurement and simulation of anisotropic magnetoresistance in single GaAs/MnAs core/shell nanowires

International Nuclear Information System (INIS)

Liang, J.; Wang, J.; Cooley, B. J.; Rench, D. W.; Samarth, N.; Paul, A.; Dellas, N. S.; Mohney, S. E.; Engel-Herbert, R.

2012-01-01

We report four probe measurements of the low field magnetoresistance (MR) in single core/shell GaAs/MnAs nanowires (NWs) synthesized by molecular beam epitaxy, demonstrating clear signatures of anisotropic magnetoresistance that track the field-dependent magnetization. A comparison with micromagnetic simulations reveals that the principal characteristics of the magnetoresistance data can be unambiguously attributed to the nanowire segments with a zinc blende GaAs core. The direct correlation between magnetoresistance, magnetization, and crystal structure provides a powerful means of characterizing individual hybrid ferromagnet/semiconductor nanostructures.

Thickness Dependent Interlayer Magnetoresistance in Multilayer Graphene Stacks

Directory of Open Access Journals (Sweden)

S. C. Bodepudi

2016-01-01

Full Text Available Chemical Vapor Deposition grown multilayer graphene (MLG exhibits large out-of-plane magnetoresistance due to interlayer magnetoresistance (ILMR effect. It is essential to identify the factors that influence this effect in order to explore its potential in magnetic sensing and data storage applications. It has been demonstrated before that the ILMR effect is sensitive to the interlayer coupling and the orientation of the magnetic field with respect to the out-of-plane (c-axis direction. In this work, we investigate the role of MLG thickness on ILMR effect. Our results show that the magnitude of ILMR effect increases with the number of graphene layers in the MLG stack. Surprisingly, thicker devices exhibit field induced resistance switching by a factor of at least ~107. This effect persists even at room temperature and to our knowledge such large magnetoresistance values have not been reported before in the literature at comparable fields and temperatures. In addition, an oscillatory MR effect is observed at higher field values. A physical explanation of this effect is presented, which is consistent with our experimental scenario.

Open-loop magneto-resistance sensor-based DC current transformer for FAIR

Energy Technology Data Exchange (ETDEWEB)

Soliman, Eman; Hofmann, Klaus [Technical University Darmstadt (Germany); Reeg, Hansjoerg; Schwickert, Marcus [GSI Helmholtzzentrum fuer Schwerionenforschung, Darmstadt (Germany)

2016-07-01

A Novel DC Current Transformer (N-DCCT) is currently under development for FAIR. The N-DCCT is going to be installed inside the SIS100 synchrotron. The proposed system is no longer based on magnetic modulation principle of the conventional DCCT. Instead, a Magneto-resistance sensor is utilized to detect the magnetic field of the ion-beam. For a first prototype the N-DCCT is realized as an open-loop system. It consists of a high permeability slotted ring core and up to two MR sensors. The maximum ion-beam current magnetic field is concentrated inside the ring core air gaps. MR sensors are placed inside the core air gaps. The sensor output voltage is directly proportional to the ion-beam current. The system is implemented using commercial Tunneling MR sensors. Measurements using one single sensor, as well as the application of two sensors are presented in this work. The sensitivity of the proposed N-DCCT is 0.566 [V/A] for one single MR sensor and 1.56 [V/A] when two sensors are implemented.

Magnetoresistance stories of double perovskites

Indian Academy of Sciences (India)

2015-05-28

May 28, 2015 ... Tunnelling magnetoresistance (TMR) in polycrystalline double perovskites has been an important research topic for more than a decade now, where the nature of the insulating tunnel barrier is the core issue of debate. Other than the nonmagnetic grain boundaries as conventional tunnel barriers, intragrain ...

Magnetoresistance Probe of Ultrathin Mn5Ge3 Films with Anderson Weak Localization

International Nuclear Information System (INIS)

Li-Jun, Chen; De-Yong, Wang; Qing-Feng, Zhan; Wei, He; Qing-An, Li

2008-01-01

We present the magnetoresistance measurements of ultrathin Mn 5 Ge 3 films with different thicknesses at low temperatures. Owing to the lattice mismatch between Mn 5 Ge 3 and Ge (111), the thickness of Mn 5 Ge 3 films has a significant effect on the magnetoresistance. When the thickness of Mn is more than 72 monolayers (MLs), the magnetoresistance of the Mn 5 Ge 3 films appears a peak at about 6kOe, which shows that the magnetoresistance results from the Anderson weak localization effect and the variable range hopping in the presence of a magnetic field. The magnetic and semiconducting properties indicate that the Mn 5 Ge 3 film is a potential material for spin injection. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Oscillations in magnetoresistance and interlayer coupling in magnetic sandwich structures

International Nuclear Information System (INIS)

Barnas, J.; Bulka, B.

1997-01-01

Kubo formalism is used to calculate the magnetoresistance due to magnetization rotation in a structure consisting two magnetic films separated by nonmagnetic layer. In the approximation of an uniform relaxation time of each layer, the oscillatory term in magnetoresistance corresponds to the oscillation period which depends on the potential barriers at the interfaces. This period is longer than the oscillation period observed in the coupling parameter. (author)

Spin–orbit coupling induced magnetoresistance oscillation in a dc biased two-dimensional electron system

International Nuclear Information System (INIS)

Wang, C M; Lei, X L

2014-01-01

We study dc-current effects on the magnetoresistance oscillation in a two-dimensional electron gas with Rashba spin-orbit coupling, using the balance-equation approach to nonlinear magnetotransport. In the weak current limit the magnetoresistance exhibits periodical Shubnikov-de Haas oscillation with changing Rashba coupling strength for a fixed magnetic field. At finite dc bias, the period of the oscillation halves when the interbranch contribution to resistivity dominates. With further increasing current density, the oscillatory resistivity exhibits phase inversion, i.e., magnetoresistivity minima (maxima) invert to maxima (minima) at certain values of the dc bias, which is due to the current-induced magnetoresistance oscillation. (paper)

Quasi-linear magnetoresistance and the violation of Kohler's rule in the quasi-one-dimensional Ta₄Pd₃Te₁₆ superconductor.

Science.gov (United States)

Xu, Xiaofeng; Jiao, W H; Zhou, N; Guo, Y; Li, Y K; Dai, Jianhui; Lin, Z Q; Liu, Y J; Zhu, Zengwei; Lu, Xin; Yuan, H Q; Cao, Guanghan

2015-08-26

We report on the quasi-linear in field intrachain magnetoresistance in the normal state of a quasi-one-dimensional superconductor Ta4Pd3Te16 (Tc ~ 4.6 K). Both the longitudinal and transverse in-chain magnetoresistance shows a power-law dependence, Δρ∝B(α) with the exponent α close to 1 over a wide temperature and field range. The magnetoresistance shows no sign of saturation up to 50 T studied. The linear magnetoresistance observed in Ta4Pd3Te16 is found to be overall inconsistent with the interpretations based on the Dirac fermions in the quantum limit, charge conductivity fluctuations as well as quantum electron-electron interference. Moreover, it is observed that the Kohler's rule, regardless of the field orientations, is violated in its normal state. This result suggests the loss of charge carriers in the normal state of this chain-containing compound, due presumably to the charge-density-wave fluctuations.

Domain wall magnetoresistance in BiFeO3 thin films measured by scanning probe microscopy.

Science.gov (United States)

Domingo, N; Farokhipoor, S; Santiso, J; Noheda, B; Catalan, G

2017-08-23

We measure the magnetotransport properties of individual 71° domain walls in multiferroic BiFeO 3 by means of conductive-atomic force microscopy (C-AFM) in the presence of magnetic fields up to one Tesla. The results suggest anisotropic magnetoresistance at room temperature, with the sign of the magnetoresistance depending on the relative orientation between the magnetic field and the domain wall plane. A consequence of this finding is that macroscopically averaged magnetoresistance measurements for domain wall bunches are likely to underestimate the magnetoresistance of each individual domain wall.

Magnonic Crystal Theory of the Spin-Wave Frequency Gap in Low-Doped $La_{1-x}Ca_{x}MnO_{3}$ Manganites

OpenAIRE

Krawczyk, M.; Puszkarski, H.

2005-01-01

A theory of three-dimensional (3D) hypothetical magnonic crystal (conceived as the magnetic counterpart of the well-known photonic crystal) is developed and applied to explain the existence of a spin-wave frequency gap recently revealed in low-doped manganites $La_{1-x}Ca_{x}MnO_{3}$ by neutron scattering. A successful confrontation with the experimental results allows us to formulate a working hypothesis that certain manganites could be regarded as 3D magnonic crystals existing in nature.

Temperature dependence of non-Debye disorder in doped manganites

International Nuclear Information System (INIS)

Meneghini, C.; Cimino, R.; Pascarelli, S.; Mobilio, S.; Raghu, C.; Sarma, D.D.

1997-01-01

Ca-doped manganite La 1-x Ca x MnO 3 samples with x=0.2 and 0.4 were investigated by extended x-ray absorption fine structure (EXAFS) as a function of temperature and preparation method. The samples exhibit characteristic resistivity change across the metal-insulator (MI) transition temperature whose shape and position depend on Ca-doping concentration and sample thermal treatment. EXAFS results evidenced an increase of nonthermal disorder at the MI transition temperature which is significantly correlated with the resistivity behavior. copyright 1997 The American Physical Society

Contribution of Jahn-Teller and charge transfer excitations to the photovoltaic effect of manganite/titanite heterojunctions

Science.gov (United States)

Ifland, Benedikt; Hoffmann, Joerg; Kressdorf, Birte; Roddatis, Vladimir; Seibt, Michael; Jooss, Christian

2017-06-01

The effect of correlation effects on photovoltaic energy conversion at manganite/titanite heterojunctions is investigated. As a model system we choose a heterostructure consisting of the small polaron absorber Pr0.66Ca0.34MnO3 (PCMO) epitaxially grown on single-crystalline Nb-doped SrTi0.998Nb0.002O3 (STNO) substrates. The high structural and chemical quality of the interfaces is proved by detailed characterization using high-resolution transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) studies. Spectrally resolved and temperature-dependent photovoltaic measurements show pronounced contributions of both the Jahn-Teller (JT) excitations and the charge transfer (CT) transitions to the photovoltaic effect at different photon energies. A linear temperature dependence of the open-circuit voltage for an excitation in the PCMO manganite is only observed below the charge-ordering temperature, indicating that the diffusion length of the photocarrier exceeds the size of the space charge region. The photovoltaic response is compared to that of a heterojunction of lightly doped Pr0.05Ca0.95MnO3 (CMO)/STNO, where the JT transition is absent. Here, significant contributions of the CT transition to the photovoltaic effect set in below the Neel temperature. We conclude that polaronic correlations and ordering effects are essentials for photovoltaic energy conversion in manganites.

Magnetoresistance of tungsten thin wafer at the multichannel surface scattering of conduction electrons

International Nuclear Information System (INIS)

Lutsishin, P.P.; Nakhodkin, T.N.

1982-01-01

The magnetoresistance of tungsten thin wafer with the (110) surface was studied at the adsorption of tungsten dioxide. The method of low-energy electron diffraction was used to study the symmetry of ordered surface structures. Using the method of the magnetoresistance measurement the character of the scattering of conduction electrons was investigated. THe dependence of magnetoresistance on the surface concentration of tungsten dioxide correlated w1th the structure of the surface layer of atoms, what was explained with allowance for diffraction of conduction electrons at the metal boundary. The magnetoresistance maximum for the (2x2) structure, which characterised decrease in surface conduction under the conditions of static skin effect, was explained by multichannel mirror reflection with the recombinations of electron and ho.le sections of Fermi Surface

Morphology evolution in spinel manganite films deposited from an aqueous solution

International Nuclear Information System (INIS)

Ko, Song Won; Li, Jing; Trolier-McKinstry, Susan

2012-01-01

Spinel manganite films were deposited by the spin spray technique at low deposition temperatures ( 1000, agglomeration of small particles was dominant, which suggests that homogeneous nucleation is dominant during deposition. Heterogeneous nucleation was critical to obtain dense films. - Highlights: ► Film microstructure depends on supersaturation. ► Heterogeneous nucleation induces dense and continuous films. ► The spin spray technique enables use of a variety of substrates.

Observation of magnetic polarons in the magnetoresistive pyrochlore Lu2V2O7

International Nuclear Information System (INIS)

Storchak, Vyacheslav G; Brewer, Jess H; Eshchenko, Dmitry G; Mengyan, Patrick W; Zhou Haidong; Wiebe, Christopher R

2013-01-01

Materials that exhibit colossal magnetoresistance (CMR) have attracted much attention due to their potential technological applications. One particularly interesting model for the magnetoresistance of low-carrier-density ferromagnets involves mediation by magnetic polarons (MP)—electrons localized in nanoscale ferromagnetic ‘droplets’ by their exchange interaction. However, MP have not previously been directly detected and their size has been difficult to determine from macroscopic measurements. In order to provide this crucial information, we have carried out muon spin rotation measurements on the magnetoresistive semiconductor Lu 2 V 2 O 7 in the temperature range from 2 to 300 K and in magnetic fields up to 7 T. Magnetic polarons with characteristic radius R ≈ 0.4 nm are detected below about 100 K, where Lu 2 V 2 O 7 exhibits CMR; at higher temperature, where the magnetoresistance vanishes, these MP also disappear. This observation confirms the MP-mediated model of CMR and reveals the microscopic size of the MP in magnetoresistive pyrochlores. (paper)

Tunneling Spectroscopy Study of Spin-Polarized Quasiparticle Injection Effects in Cuparate/Manganite Heterostructures

Science.gov (United States)

Wei, J. Y. T.; Yeh, N. C.; Vasquez, R. P.

1998-01-01

Scanning tunneling spectroscopy was performed at 4.2K on epitaxial thin-film heterostructures comprising YBa2Cu3O7 and La0.7Ca0.3MnO3, to study the microscopic effects of spin-polarized quasiparticle injection from the half-metallic ferromagnetic manganite on the high-Tc cuprate superconductor.

Magnetic Field Sensors Based on Giant Magnetoresistance (GMR Technology: Applications in Electrical Current Sensing

Directory of Open Access Journals (Sweden)

Càndid Reig

2009-10-01

Full Text Available The 2007 Nobel Prize in Physics can be understood as a global recognition to the rapid development of the Giant Magnetoresistance (GMR, from both the physics and engineering points of view. Behind the utilization of GMR structures as read heads for massive storage magnetic hard disks, important applications as solid state magnetic sensors have emerged. Low cost, compatibility with standard CMOS technologies and high sensitivity are common advantages of these sensors. This way, they have been successfully applied in a lot different environments. In this work, we are trying to collect the Spanish contributions to the progress of the research related to the GMR based sensors covering, among other subjects, the applications, the sensor design, the modelling and the electronic interfaces, focusing on electrical current sensing applications.

The Control of Anisotropic Transport in Manganites by Stripy Domains

Science.gov (United States)

Ju, Changcheng; Lu, Xiaomei; Chu, Yinghao

2014-03-01

Epitaxial thin film acts as a significant tool to investigate novel phenomena of complex oxide systems. Extrinsic constraint1 of uniform or certain designed buffer layer strain could be easily implanted to these materials. However, the strain distribution might be quite complicated by involving micro- or nano-lattice distortions which could partially relax the strain and determine the complex phase diagrams of thin film, meanwhile introducing structural and physical inhomogeneities. In this work , we report 71° striped ferroelectric domains created in BFO can also epitaxially lock the perovskite manganites leading to the emerge of ordered structural domain. LSMO/BFO hetero-epitaxial samples are deposited by PLD. The 71° periodic striped domains and coherent growth are demonstrated by PFM and X-ray analysis. Plan-view TEM and X-ray RSM have been used to confirm the epitaxial relationships of the functional layers and IP lattice constant. Both the simulation and structural analysis demonstrate we can create a periodic ordered stripe structural domain in LSMO. And this will leave an anisotropic distribution of structural domain walls which makes it possible to capture the anisotropic tunneling for strong electron-lattice coupling in manganites. Temperature-dependent resistivity measurements reveal a substantial anisotropic resistivities and a remarkable shift of the MI transition between the perpendicular and parallel to the stripe domain directions.

On the role of minority carriers in the frequency dependence of organic magnetoresistance

NARCIS (Netherlands)

Janssen, Paul; Wagemans, W.; Verhoeven, Wouter; van der Heijden, E.H.M.; Kemerink, M.; Koopmans, B.

2011-01-01

In this work we investigate the frequency dependence of organic magnetoresistance (OMAR) both in small molecule-based (Alq3) and polymer (PPV derivative) materials, and investigate its thickness dependence. For all devices, we observed a strong decrease in magnetoconductance (MC) with increasing

Isothermal anisotropic magnetoresistance in antiferromagnetic metallic IrMn.

Science.gov (United States)

Galceran, R; Fina, I; Cisneros-Fernández, J; Bozzo, B; Frontera, C; López-Mir, L; Deniz, H; Park, K-W; Park, B-G; Balcells, Ll; Martí, X; Jungwirth, T; Martínez, B

2016-10-20

Antiferromagnetic spintronics is an emerging field; antiferromagnets can improve the functionalities of ferromagnets with higher response times, and having the information shielded against external magnetic field. Moreover, a large list of aniferromagnetic semiconductors and metals with Néel temperatures above room temperature exists. In the present manuscript, we persevere in the quest for the limits of how large can anisotropic magnetoresistance be in antiferromagnetic materials with very large spin-orbit coupling. We selected IrMn as a prime example of first-class moment (Mn) and spin-orbit (Ir) combination. Isothermal magnetotransport measurements in an antiferromagnetic-metal(IrMn)/ferromagnetic-insulator thin film bilayer have been performed. The metal/insulator structure with magnetic coupling between both layers allows the measurement of the modulation of the transport properties exclusively in the antiferromagnetic layer. Anisotropic magnetoresistance as large as 0.15% has been found, which is much larger than that for a bare IrMn layer. Interestingly, it has been observed that anisotropic magnetoresistance is strongly influenced by the field cooling conditions, signaling the dependence of the found response on the formation of domains at the magnetic ordering temperature.

The study of the sample size on the transverse magnetoresistance of bismuth nanowires

International Nuclear Information System (INIS)

Zare, M.; Layeghnejad, R.; Sadeghi, E.

2012-01-01

The effects of sample size on the galvanomagnetice properties of semimetal nanowires are theoretically investigated. Transverse magnetoresistance (TMR) ratios have been calculated within a Boltzmann Transport Equation (BTE) approach by specular reflection approximation. Temperature and radius dependence of the transverse magnetoresistance of cylindrical Bismuth nanowires are given. The obtained values are in good agreement with the experimental results, reported by Heremans et al. - Highlights: ► In this study effects of sample size on the galvanomagnetic properties of Bi. ► Nanowires were explained by Parrott theorem by solving the Boltzmann Transport Equation. ► Transverse magnetoresistance (TMR) ratios have been measured by specular reflection approximation. ► Temperature and radius dependence of the transverse magnetoresistance of cylindrical Bismuth nanowires are given. ► The obtained values are in good agreement with the experimental results, reported by Heremans et al.

Crystal structure of (110) oriented La0.7Sr0.3MnO3 grown on (001) silicon

International Nuclear Information System (INIS)

Sinha, Umesh Kumar; Sahoo, Antarjami; Padhan, Prahallad

2016-01-01

The mixed valance perovskite manganites have attracted a considerable attention due to their colossal magnetoresistance behavior. In particular, La 0.7 Sr 0.3 MnO 3 (LSMO) show half metallicity and possess Curie temperature (T C ) above room temperature, which makes this material an attractive candidate for spintronic device application. Thin films of LSMO were grown on (001) oriented Silicon (Si) using sputtering technique

Tuning the magnetoresistance of ultrathin WTe2 sheets by electrostatic gating.

Science.gov (United States)

Na, Junhong; Hoyer, Alexander; Schoop, Leslie; Weber, Daniel; Lotsch, Bettina V; Burghard, Marko; Kern, Klaus

2016-11-10

The semimetallic, two-dimensional layered transition metal dichalcogenide WTe 2 has raised considerable interest due to its huge, non-saturating magnetoresistance. While for the origin of this effect, a close-to-ideal balance of electrons and holes has been put forward, the carrier concentration dependence of the magnetoresistance remains to be clarified. Here, we present a detailed study of the magnetotransport behaviour of ultrathin, mechanically exfoliated WTe 2 sheets as a function of electrostatic back gating. The carrier concentration and mobility, determined using the two band model and analysis of the Shubnikov-de Haas oscillations, indicate enhanced surface scattering for the thinnest sheets. By the back gate action, the magnetoresistance could be tuned by up to ∼100% for a ∼13 nm-thick WTe 2 sheet.

Resistance and magnetoresistance of annealed amorphous carbon films containing Fe3C nanograins

International Nuclear Information System (INIS)

Lee Yuhua; Han Taichun; Wur, C.-S.

2004-01-01

The temperature-dependent resistance and the field-dependent magnetoresistance were measured for films annealed at temperatures from 250 deg. C to 550 deg. C for a period of 60 min. Results of temperature-dependent resistance show electrical tunneling conductance in the films annealed at T a =250 deg. C and 350 deg. C only. The largest magnetoresistance ratio (MR) of 23% at temperature T=2 K was observed for T a =350 deg. C. The variations of both the temperature dependence of resistance and the magnetoresistance with the annealing temperature are discussed

Study of the temperature dependence of giant magnetoresistance in metallic granular composite

International Nuclear Information System (INIS)

Ju Sheng; Li, Z.-Y.

2002-01-01

The temperature dependence of the giant magnetoresistance of metallic granular composite is studied. It is considered that the composite contains both large magnetic grains with surface spin S' and small magnetic impurities. It is found that the decrease of surface spin S' of grain is the main cause of an almost linear decrease of giant magnetoresistance with the increase of temperature in high temperature range. The magnetic impurities, composed of several atoms, lead to an almost linear increase of the giant magnetoresistance with the decrease of temperature in low temperature range. Our calculations are in good agreement with recent experimental data for metallic nanogranular composites

Tailoring anisotropic magnetoresistance and giant magnetoresistance hysteresis loops with spin-polarized current injection

International Nuclear Information System (INIS)

Wegrowe, J.-E.; Kelly, D.; Hoffer, X.; Guittienne, Ph.; Ansermet, J.-Ph.

2001-01-01

Current pulses were injected into magnetic nanowires. Their effect on the magnetoresistance hysteresis loops was studied for three morphologies: homogeneous Ni wires, copper wires containing five cobalt/copper bilayers, and hybrid structures composed of a homogeneous Ni half wire and a multilayered Co/Cu half wire. The characteristic features of the action of the current on the magnetization are shown and discussed. [copyright] 2001 American Institute of Physics

Oxygen and disorder effect in the magnetic properties of manganite films

Energy Technology Data Exchange (ETDEWEB)

Sirena, M. E-mail: sirenam@ib.cnea.gov.ar; Haberkorn, N.; Granada, M.; Steren, L.B.; Guimpel, J

2004-05-01

We have made a systematic study of the magnetic properties of low doped manganite films submitted to different oxygenation treatments. We have found that oxygenation dynamics depends critically of the strain field in the sample. The T{sub C} and the Mr increase as the oxygen content is increased. A decrease of the coercive field of the LSMO-STO films was observed, indicating that annealing treatments increase the oxygen content reducing oxygen vacancies.

Oxygen and disorder effect in the magnetic properties of manganite films

International Nuclear Information System (INIS)

Sirena, M.; Haberkorn, N.; Granada, M.; Steren, L.B.; Guimpel, J.

2004-01-01

We have made a systematic study of the magnetic properties of low doped manganite films submitted to different oxygenation treatments. We have found that oxygenation dynamics depends critically of the strain field in the sample. The T C and the Mr increase as the oxygen content is increased. A decrease of the coercive field of the LSMO-STO films was observed, indicating that annealing treatments increase the oxygen content reducing oxygen vacancies

Anisotropic magnetoresistance and tunneling magnetoresistance of conducting filaments in NiO with different resistance states

Science.gov (United States)

Zhao, Diyang; Qiao, Shuang; Luo, Yuxiang; Chen, Aitian; Zhang, Pengfei; Zheng, Ping; Sun, Zhong; Guo, Minghua; Chiang, F.-K.; Wu, Jian; Luo, Jianlin; Li, Jianqi; Wang, Yayu; Zhao, Yonggang; Tsinghua University Team; Chinese Academy of Sciences Collaboration

Resistive switching (RS) effect in conductor/insulator/conductor thin-film stacks has attracted much attention due to its interesting physics and potentials for applications. NiO is one of the most representative systems and its RS effect has been generally explained by the formation and rupture of Ni related conducting filaments, which are very unique since they are formed by electric forming process. We study the MR behaviors in NiO RS films with different resistance states. Rich and interesting MR behaviors were observed, including the normal and anomalous anisotropic magnetoresistance (AMR) and tunneling magnetoresistance (TMR), etc., which provide new insights into the nature of the filaments and their evolution in the resistive switching process. First-principles calculation reveals the essential role of oxygen migration into the filaments during the RESET process and can account for the experimental results. Our work provides a new avenue for the exploration of the conducting filaments in RS materials, and is significant for understanding the RS mechanism as well as multifunctional device design.

Negative and positive magnetoresistance in bilayer graphene: Effects of weak localization and charge inhomogeneity

International Nuclear Information System (INIS)

Chen Yungfu; Bae, Myung-Ho; Chialvo, Cesar; Dirks, Travis; Bezryadin, Alexey; Mason, Nadya

2011-01-01

We report measurements of magnetoresistance in bilayer graphene as a function of gate voltage (carrier density) and temperature. We examine multiple contributions to the magnetoresistance, including those of weak localization (WL), universal conductance fluctuations (UCF), and inhomogeneous charge transport. A clear WL signal is evident at all measured gate voltages (in the hole doped regime) and temperature ranges (from 0.25 to 4.3 K), and the phase coherence length extracted from the WL data does not saturate at low temperatures. The WL data is fit to demonstrate that the electron-electron Nyquist scattering is the major source of phase decoherence. A decrease in UCF amplitude with increase in gate voltage and temperature is shown to be consistent with a corresponding decrease in the phase coherence length. In addition, a weak positive magnetoresistance at higher magnetic fields is observed, and attributed to inhomogeneous charge transport. -- Research highlights: → Weak localization theory describes low-field magnetoresistance in bilayer graphene. → Electron-electron Nyquist scattering limits phase coherence in bilayer graphene. → Positive magnetoresistance reveals charge inhomogeneity in bilayer graphene.

Anomalies of magnetoresistance of compounds with atomic clusters RB12 (R = Ho, Er, Tm, Lu)

International Nuclear Information System (INIS)

Sluchanko, N. E.; Bogach, A. V.; Glushkov, V. V.; Demishev, S. V.; Samarin, N. A.; Sluchanko, D. N.; Dukhnenko, A. V.; Levchenko, A. V.

2009-01-01

The magnetoresistance and magnetization of single-crystal samples of rare-earth dodecaborides RB 12 (R = Ho, Er, Tm, Lu) have been measured at low temperatures (1.8-35 K) in a magnetic field of up to 70 kOe. The effect of positive magnetoresistance that obeys the Kohler's rule Δρ/ρ = f(ρ(0, 300 K)H/ρ(0, T)) is observed for the nonmagnetic metal LuB 12 . In the magnetic dodecaborides HoB 12 , ErB 12 , and TmB 12 , three characteristic regimes of the magnetoresistance behavior have been revealed: the positive magnetoresistance effect similar to the case of LuB 12 is observed at T > 25 K; in the range T N ≤ T ≤ 15 K, the magnetoresistance becomes negative and depends quadratically on the external magnetic field; and, finally, upon the transition to the antiferromagnetic phase (T N ), the positive magnetoresistance is again observed and its amplitude reaches 150% for HoB 12 . It has been shown that the observed anomalies of negative magnetoresistance in the paramagnetic phase can be explained within the Yosida model of conduction electron scattering by localized magnetic moments. The performed analysis confirms the formation of spin-polaron states in the 5d band in the vicinity of rare-earth ions in paramagnetic and magnetically ordered phases of RB 12 and makes it possible to reveal a number of specific features in the transformation of the magnetic structure of the compounds under investigation

Investigation of the tunnel magnetoresistance in junctions with a strontium stannate barrier

Science.gov (United States)

Althammer, Matthias; Mishra, Rohan; Borisevich, Albina J.; Singh, Amit Vikam; Keshavarz, Sahar; Yurtisigi, Mehmet Kenan; Leclair, Patrick; Gupta, Arunava

We experimentally investigate the structural, magnetic and electrical transport properties of La0.67Sr0.33MnO3 based magnetic tunnel junctions with a SrSnO3 barrier. Our results show that despite the high density of defects in the strontium stannate barrier the observed tunnel magnetoresistance is comparable to tunnel junctions with a better lattice matched SrTiO3 barrier, reaching values of up to 350 % at T = 5 K . Further analysis of the current-voltage characteristics of the junction and the bias voltage dependence of the observed tunnel magnetoresistance show a decrease of the TMR with increasing bias voltage. Our results suggest that by reducing the structural defects in the strontium stannate barrier, even larger TMR ratios might be possible in the future. We gratefully acknowledge financial support via NSF-ECCS Grant No. 1509875.

Magnetoresistance and magnetic breakdown phenomenon in amorphous magnetic alloys

International Nuclear Information System (INIS)

Chen Hui-yu; Gong Xiao-yu

1988-01-01

Transverse magnetoresistance in amorphous magnetic alloys (Fe/sub 1-//sub x/CO/sub x/) 82 Cu/sub 0.4/Si/sub 4.4/B/sub 13.2/ were measured at room temperature and in the magnetic field range 0--15 kOe. For large magnetic field, three different functional dependences of magnetoresistance on magnetic field strength have been found as follows: (1) Δrho/rho approaches saturation. (2) Δrho/rho increases proportionally to H 2 . (3) For x = 0.15, a sharp Δrho/rho peak appears at a certain magnetic field strength in spatial angular orientation of both magnetic field and electric currents. Case (3) is a magnetic breakdown phenomenon. Magnetic breakdown occurs at the gap between the spin-up and spin-down sheets of the Fermi surface. This gap is the spin-orbit gap and its magnitude is a sensitive function of magnetization. Hence the magnitude and width of the magnetoresistance peak and the magnetic field strength at the peak point are functions of angular orientation of both magnetic field and electric current

Topological dynamics of vortex-line networks in hexagonal manganites

Science.gov (United States)

Xue, Fei; Wang, Nan; Wang, Xueyun; Ji, Yanzhou; Cheong, Sang-Wook; Chen, Long-Qing

2018-01-01

The two-dimensional X Y model is the first well-studied system with topological point defects. On the other hand, although topological line defects are common in three-dimensional systems, the evolution mechanism of line defects is not fully understood. The six domains in hexagonal manganites converge to vortex lines in three dimensions. Using phase-field simulations, we predicted that during the domain coarsening process, the vortex-line network undergoes three types of basic topological changes, i.e., vortex-line loop shrinking, coalescence, and splitting. It is shown that the vortex-antivortex annihilation controls the scaling dynamics.

Domain wall magnetoresistance in nanowires: Dependence on geometrical factors and material parameters

International Nuclear Information System (INIS)

Allende, S.; Retamal, J.C.; Altbir, D.; D'Albuquerque e Castro, J.

2014-01-01

The magnetoresistance associated with the presence of domain walls in metallic nanowires is investigated as a function of geometrical parameters, corresponding to the wall thickness and the nanowire width, as well as of material parameters, such as the band filling and the exchange interaction. Transport across the structure is described within Landauer formalism. Both cases of saturated and non-saturated ferromagnets are considered, and in all of them the contributions from spin-flip and non-spin-flip are separately analyzed. It has been found that for certain range of parameters deviations in the normalized magnetoresistance as high as 20% may be achieved. In addition, it has been shown that the spin-flip process is dependent on the wall thickness. - Highlights: • We identify thickness regions within which transport across the wall is dominated by either spin-flip or non-spin-flip process. • We analyze the dependence of the magnetoresistance on both the material's band filling and strength of the exchange interaction. • We identify parameter ranges within which magnetoresistance ratios as high as 20% or even more might be achieved

Domain wall magnetoresistance in nanowires: Dependence on geometrical factors and material parameters

Energy Technology Data Exchange (ETDEWEB)

Allende, S.; Retamal, J.C. [Departamento de Física, CEDENNA, Universidad de Santiago de Chile, USACH, Avenida Ecuador 3493, 917-0124 Santiago (Chile); Altbir, D., E-mail: dora.altbir@usach.cl [Departamento de Física, CEDENNA, Universidad de Santiago de Chile, USACH, Avenida Ecuador 3493, 917-0124 Santiago (Chile); D' Albuquerque e Castro, J. [Instituto de Física, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, Rio de Janeiro 21941-972 (Brazil)

2014-04-15

The magnetoresistance associated with the presence of domain walls in metallic nanowires is investigated as a function of geometrical parameters, corresponding to the wall thickness and the nanowire width, as well as of material parameters, such as the band filling and the exchange interaction. Transport across the structure is described within Landauer formalism. Both cases of saturated and non-saturated ferromagnets are considered, and in all of them the contributions from spin-flip and non-spin-flip are separately analyzed. It has been found that for certain range of parameters deviations in the normalized magnetoresistance as high as 20% may be achieved. In addition, it has been shown that the spin-flip process is dependent on the wall thickness. - Highlights: • We identify thickness regions within which transport across the wall is dominated by either spin-flip or non-spin-flip process. • We analyze the dependence of the magnetoresistance on both the material's band filling and strength of the exchange interaction. • We identify parameter ranges within which magnetoresistance ratios as high as 20% or even more might be achieved.

Drastic Pressure Effect on the Extremely Large Magnetoresistance in WTe2: Quantum Oscillation Study.

Science.gov (United States)

Cai, P L; Hu, J; He, L P; Pan, J; Hong, X C; Zhang, Z; Zhang, J; Wei, J; Mao, Z Q; Li, S Y

2015-07-31

The quantum oscillations of the magnetoresistance under ambient and high pressure have been studied for WTe2 single crystals, in which extremely large magnetoresistance was discovered recently. By analyzing the Shubnikov-de Haas oscillations, four Fermi surfaces are identified, and two of them are found to persist to high pressure. The sizes of these two pockets are comparable, but show increasing difference with pressure. At 0.3 K and in 14.5 T, the magnetoresistance decreases drastically from 1.25×10(5)% under ambient pressure to 7.47×10(3)% under 23.6 kbar, which is likely caused by the relative change of Fermi surfaces. These results support the scenario that the perfect balance between the electron and hole populations is the origin of the extremely large magnetoresistance in WTe2.

Interface-engineered oxygen octahedral coupling in manganite heterostructures

Science.gov (United States)

Huijben, M.; Koster, G.; Liao, Z. L.; Rijnders, G.

2017-12-01

Control of the oxygen octahedral coupling (OOC) provides a large degree of freedom to manipulate physical phenomena in complex oxide heterostructures. Recently, local tuning of the tilt angle has been found to control the magnetic anisotropy in ultrathin films of manganites and ruthenates, while symmetry control can manipulate the metal insulator transition in nickelate thin films. The required connectivity of the octahedra across the heterostructure interface enforces a geometric constraint to the 3-dimensional octahedral network in epitaxial films. Such geometric constraint will either change the tilt angle to retain the connectivity of the corner shared oxygen octahedral network or guide the formation of a specific symmetry throughout the epitaxial film. Here, we will discuss the control of OOC in manganite heterostructures by interface-engineering. OOC driven magnetic and transport anisotropies have been realized in LSMO/NGO heterostructures. Competition between the interfacial OOC and the strain further away from the interface leads to a thickness driven sharp transition of the anisotropic properties. Furthermore, octahedral relaxation leading to a change of p-d hybridization driven by interfacial OOC appears to be the strongest factor in thickness related variations of magnetic and transport properties in epitaxial LSMO films on NGO substrates. The results unequivocally link the atomic structure near the interfaces to the macroscopic properties. The strong correlation between a controllable oxygen network and the functionalities will have significant impact on both fundamental research and technological application of correlated perovskite heterostructures. By controlling the interfacial OOC, it is possible to pattern in 3 dimensions the magnetization to achieve non-collinear magnetization in both in-plane and out of plane directions, thus making the heterostructures promising for application in orthogonal spin transfer devices, spin oscillators, and low

Magnetic after-effect in manganite films

International Nuclear Information System (INIS)

Sirena, M.; Steren, L.B.; Guimpel, J.

2001-01-01

The time dependence of the magnetic and transport properties on La 0.6 Sr 0.4 MnO 3 films and bulk samples has been studied through magnetization and resistivity measurements. A magnetic after-effect has been observed in all samples. At low temperatures, the low-field magnetization, can be described by the function M(t)=M c +M d exp(-t/τ)+S(H,T)ln(t). The resistivity increases logarithmically in the same temperature range, indicating the evolution of the sample to a more disordered state. Above a characteristic temperature, this behaviour is reversed and an increase of the magnetization with time is observed. The relaxation parameters depend on the bulk or films character of the samples. In the latter case, a dependence on the film thickness was found. A direct correlation between the time dependence of the resistivity and magnetization curves in manganite compounds was found

Magnetoresistance effect in perovskite-like RCu3Mn4O12 (R - rare earth ion, Th)

International Nuclear Information System (INIS)

Lobanovskij, L.S.; Troyanchuk, I.O.; Trukhanov, S.V.; Pastushonok, S.N.; Pavlov, V.I.

2003-01-01

The study on the electric properties and magnetoresistance effect in the RCu 3 Mn 4 O 12 (where R is the rare-earth ion, Th) is carried out. It is established that all the compositions of the given series demonstrate the magnetoresistive effect, the value whereof at the liquid nitrogen temperature reaches 20% in the field 0.9 T. The increase in the magnetoresistance with the temperature decrease and high sensitivity to the weak magnetic fields at low temperatures indicate that this effect is intergranular. The peak of the magnetoresistance is identified near the Curie temperature (T C ). It is supposed that the degree of the magnetoresistance near the temperature of the magnetic ordering depends on the conditions of the samples synthesis and the effect of the intergranular interlayer on the transport properties of these compositions [ru

Ballistic magnetoresistance of electrodeposited nanocontacts in thin film and micrometer wire gaps

International Nuclear Information System (INIS)

Garcia, N.; Cheng, H.; Wang, H.; Nikolic, N.D.; Guerrero, C.A.; Papageorgopoulos, A.C.

2004-01-01

In this paper, we review the recent advances and progress in ballistic magnetoresistance (BMR) in magnetic nanocontacts electrodeposited in thin films and micrometer gaps. We report the influence of magnetostriction in the measurements under different configurations and substrates, as well as the contribution of the magnetic material forming the contacts. To avoid the magnetostriction effect, we have fabricated magnetic nanocontacts in Cu wires and Cu films. Similar BMR results can be observed in these systems. Our results show that the BMR effect should depend on the microproperties of the nanocontacts and should not be related with the macroproperties of the electrodes. The magnetostriction results, measured by an atomic force microscopy system with a built-in electromagnet, clearly show that there is no direct relationship between the displacement (caused by the magnetostriction effect) and the value of BMR. In fact, we present large magnetoresistance values for permalloy, coinciding with displacements in the latter's structure less than 1 nm, which is the smallest clearly observable shift allowed by our atomic force microscope. Repetitions of hundreds of R(H) curves are presented for different materials with different coercive fields. The interpretation of the results is based on the formation of an interfacial transparent layer (non-stoichiometric oxide, sulfur, etc.) at the nanocontact where the theory can explain large magnetoresistance values

Magnetoresistance of Mn-decorated topological line defects in graphene

KAUST Repository

Obodo, Tobechukwu Joshua

2015-01-13

We study the spin polarized transport through Mn-decorated 8-5-5-8 topological line defects in graphene using the nonequilibrium Green\\'s function formalism. Strong preferential bonding overcomes the high mobility of transition metal atoms on graphene and results in stable structures. Despite a large distance between the magnetic centers, we find a high magnetoresistance and attribute this unexpected property to very strong induced π magnetism, in particular for full coverage of all octagonal hollow sites by Mn atoms. In contrast to the magnetoresistance of graphene nanoribbon edges, the proposed system is well controlled and therefore suitable for applications.

Single nucleotide polymorphism (SNP) detection on a magnetoresistive sensor

DEFF Research Database (Denmark)

Rizzi, Giovanni; Østerberg, Frederik Westergaard; Dufva, Martin

2013-01-01

We present a magnetoresistive sensor platform for hybridization assays and demonstrate its applicability on single nucleotide polymorphism (SNP) genotyping. The sensor relies on anisotropic magnetoresistance in a new geometry with a local negative reference and uses the magnetic field from...... the sensor bias current to magnetize magnetic beads in the vicinity of the sensor. The method allows for real-time measurements of the specific bead binding to the sensor surface during DNA hybridization and washing. Compared to other magnetic biosensing platforms, our approach eliminates the need...... for external electromagnets and thus allows for miniaturization of the sensor platform....

Magnetoresistance of Mn-decorated topological line defects in graphene

KAUST Repository

Obodo, Tobechukwu Joshua; Kahaly, M. Upadhyay; Schwingenschlö gl, Udo

2015-01-01

We study the spin polarized transport through Mn-decorated 8-5-5-8 topological line defects in graphene using the nonequilibrium Green's function formalism. Strong preferential bonding overcomes the high mobility of transition metal atoms on graphene and results in stable structures. Despite a large distance between the magnetic centers, we find a high magnetoresistance and attribute this unexpected property to very strong induced π magnetism, in particular for full coverage of all octagonal hollow sites by Mn atoms. In contrast to the magnetoresistance of graphene nanoribbon edges, the proposed system is well controlled and therefore suitable for applications.

Interlayer magnetoresistance in multilayer Dirac electron systems: motion and merging of Dirac cones

International Nuclear Information System (INIS)

Assili, M; Haddad, S

2013-01-01

We theoretically study the effect of the motion and the merging of Dirac cones on the interlayer magnetoresistance in multilayer graphene-like systems. This merging, which can be induced by a uniaxial strain, gives rise in a monolayer Dirac electron system to a topological transition from a semi-metallic phase to an insulating phase whereby Dirac points disappear. Based on a universal Hamiltonian, proposed to describe the motion and the merging of Dirac points in two-dimensional Dirac electron crystals, we calculate the interlayer conductivity of a stack of deformed graphene-like layers using the Kubo formula in the quantum limit where only the contribution of the n = 0 Landau level is relevant. A crossover from a negative to a positive interlayer magnetoresistance is found to take place as the merging is approached. This sign change of the magnetoresistance can also result from a coupling between the Dirac valleys, which is enhanced as the magnetic field amplitude increases. Our results describe the behavior of the magnetotransport in the organic conductor α-(BEDT) 2 I 3 and in a stack of deformed graphene-like systems. The latter can be simulated by optical lattices or microwave experiments in which the merging of Dirac cones can be observed. (paper)

Interlayer magnetoresistance in multilayer Dirac electron systems: motion and merging of Dirac cones

Science.gov (United States)

Assili, M.; Haddad, S.

2013-09-01

We theoretically study the effect of the motion and the merging of Dirac cones on the interlayer magnetoresistance in multilayer graphene-like systems. This merging, which can be induced by a uniaxial strain, gives rise in a monolayer Dirac electron system to a topological transition from a semi-metallic phase to an insulating phase whereby Dirac points disappear. Based on a universal Hamiltonian, proposed to describe the motion and the merging of Dirac points in two-dimensional Dirac electron crystals, we calculate the interlayer conductivity of a stack of deformed graphene-like layers using the Kubo formula in the quantum limit where only the contribution of the n = 0 Landau level is relevant. A crossover from a negative to a positive interlayer magnetoresistance is found to take place as the merging is approached. This sign change of the magnetoresistance can also result from a coupling between the Dirac valleys, which is enhanced as the magnetic field amplitude increases. Our results describe the behavior of the magnetotransport in the organic conductor α-(BEDT)2I3 and in a stack of deformed graphene-like systems. The latter can be simulated by optical lattices or microwave experiments in which the merging of Dirac cones can be observed.

Interlayer magnetoresistance in multilayer Dirac electron systems: motion and merging of Dirac cones.

Science.gov (United States)

Assili, M; Haddad, S

2013-09-11

We theoretically study the effect of the motion and the merging of Dirac cones on the interlayer magnetoresistance in multilayer graphene-like systems. This merging, which can be induced by a uniaxial strain, gives rise in a monolayer Dirac electron system to a topological transition from a semi-metallic phase to an insulating phase whereby Dirac points disappear. Based on a universal Hamiltonian, proposed to describe the motion and the merging of Dirac points in two-dimensional Dirac electron crystals, we calculate the interlayer conductivity of a stack of deformed graphene-like layers using the Kubo formula in the quantum limit where only the contribution of the n = 0 Landau level is relevant. A crossover from a negative to a positive interlayer magnetoresistance is found to take place as the merging is approached. This sign change of the magnetoresistance can also result from a coupling between the Dirac valleys, which is enhanced as the magnetic field amplitude increases. Our results describe the behavior of the magnetotransport in the organic conductor α-(BEDT)2I3 and in a stack of deformed graphene-like systems. The latter can be simulated by optical lattices or microwave experiments in which the merging of Dirac cones can be observed.

Magnetoresistive ceramics. Recent progress: from basic understanding to applications

Directory of Open Access Journals (Sweden)

Fontcuberta, J.

2004-06-01

Full Text Available Magnetoresistive ceramics, based on half-metallic ferromagnetic oxides have received renewed attention in the last few years because of their possible applications. Here, we review some recent progress on the development of magnetoresistive ceramic materials such as La2/3Sr1/ 3MnO3 and Sr2FeMoO6 ceramic materials. We shall revisit their basic properties, the strategies that have been employed to understand and to improve their intrinsic properties, pushing the limits of their operation at temperatures well above room-temperature, and the development of some applications. This effort has required the contribution of a number of actors. Starting from research laboratories, it has progressively involved industries that nowadays are able to supply high quality raw-materials or to manufacture magnetoresistive components at large scale.

Las cerámicas magnetorresistivas, basadas en óxidos semi-metálicos ferromagnéticos han recibido una renovada atención en los últimos años debido a sus posibles aplicaciones. Se revisan aquí algunos de los recientes progresos en el desarrollo de materiales cerámicos magnetorresistivos como La2/3Sr1/3MnO3 y Sr2FeMoO6. Se revisitan sus propiedades básicas, las estrategias empleadas para entender y mejorar sus propiedades intrínsecas, llevando sus límites de operación a temperaturas muy por encima de temperatura ambiente, y el desarrollo de algunas aplicaciones. Este esfuerzo ha requerido al contribución de un gran número de actores. Comenzando por laboratorios de investigación, se ha implicado progresivamente a industrias que hoy en día están capacitadas para suministrar materias primas de alta calidad o para fabricar componentes magnetorresistivos a gran escala.

Enhanced magnetotransport in nanopatterned manganite nanowires.

Science.gov (United States)

Marín, Lorena; Morellón, Luis; Algarabel, Pedro A; Rodríguez, Luis A; Magén, César; De Teresa, José M; Ibarra, Manuel R

2014-02-12

We have combined optical and focused ion beam lithographies to produce large aspect-ratio (length-to-width >300) single-crystal nanowires of La2/3Ca1/3MnO3 that preserve their functional properties. Remarkably, an enhanced magnetoresistance value of 34% in an applied magnetic field of 0.1 T in the narrowest 150 nm nanowire is obtained. The strain release at the edges together with a destabilization of the insulating regions is proposed to account for this behavior. This opens new strategies to implement these structures in functional spintronic devices.

Resistance switching induced by electric fields in manganite thin films

International Nuclear Information System (INIS)

Villafuerte, M; Juarez, G; Duhalde, S; Golmar, F; Degreef, C L; Heluani, S P

2007-01-01

In this work, we investigate the polarity-dependent Electric Pulses Induced Resistive (EPIR) switching phenomenon in thin films driven by electric pulses. Thin films of 0.5 Ca 0.5 MnO 3 (manganite) were deposited by PLD on Si substrate. The transport properties at the interface between the film and metallic electrode are characterized in order to study the resistance switching. Sample thermal treatment and electrical field history are important to be considered for get reproducible EPIR effect. Carriers trapping at the interfaces are considered as a possible explanation of our results

Suppression of Magnetoresistance in Thin WTe2 Flakes by Surface Oxidation.

Science.gov (United States)

Woods, John M; Shen, Jie; Kumaravadivel, Piranavan; Pang, Yuan; Xie, Yujun; Pan, Grace A; Li, Min; Altman, Eric I; Lu, Li; Cha, Judy J

2017-07-12

Recent renewed interest in layered transition metal dichalcogenides stems from the exotic electronic phases predicted and observed in the single- and few-layer limit. Realizing these electronic phases requires preserving the desired transport properties down to a monolayer, which is challenging. Surface oxides are known to impart Fermi level pinning or degrade the mobility on a number of different systems, including transition metal dichalcogenides and black phosphorus. Semimetallic WTe 2 exhibits large magnetoresistance due to electron-hole compensation; thus, Fermi level pinning in thin WTe 2 flakes could break the electron-hole balance and suppress the large magnetoresistance. We show that WTe 2 develops an ∼2 nm thick amorphous surface oxide, which shifts the Fermi level by ∼300 meV at the WTe 2 surface. We also observe a dramatic suppression of the magnetoresistance for thin flakes. However, due to the semimetallic nature of WTe 2 , the effects of Fermi level pinning are well screened and are not the dominant cause for the suppression of magnetoresistance, supported by fitting a two-band model to the transport data, which showed the electron and hole carrier densities are balanced down to ∼13 nm. However, the fitting shows a significant decrease of the mobilities of both electrons and holes. We attribute this to the disorder introduced by the amorphous surface oxide layer. Thus, the decrease of mobility is the dominant factor in the suppression of magnetoresistance for thin WTe 2 flakes. Our study highlights the critical need to investigate often unanticipated and sometimes unavoidable extrinsic surface effects on the transport properties of layered dichalcogenides and other 2D materials.

Electric-field driven insulator-metal transition and tunable magnetoresistance in ZnO thin film

Science.gov (United States)

Zhang, Le; Chen, Shanshan; Chen, Xiangyang; Ye, Zhizhen; Zhu, Liping

2018-04-01

Electrical control of the multistate phase in semiconductors offers the promise of nonvolatile functionality in the future semiconductor spintronics. Here, by applying an external electric field, we have observed a gate-induced insulator-metal transition (MIT) with the temperature dependence of resistivity in ZnO thin films. Due to a high-density carrier accumulation, we have shown the ability to inverse change magnetoresistance in ZnO by ionic liquid gating from 10% to -2.5%. The evolution of photoluminescence under gate voltage was also consistent with the MIT, which is due to the reduction of dislocation. Our in-situ gate-controlled photoluminescence, insulator-metal transition, and the conversion of magnetoresistance open up opportunities in searching for quantum materials and ZnO based photoelectric devices.

Nonmonotonic magnetoresistance of a two-dimensional viscous electron-hole fluid in a confined geometry

Science.gov (United States)

Alekseev, P. S.; Dmitriev, A. P.; Gornyi, I. V.; Kachorovskii, V. Yu.; Narozhny, B. N.; Titov, M.

2018-02-01

Ultrapure conductors may exhibit hydrodynamic transport where the collective motion of charge carriers resembles the flow of a viscous fluid. In a confined geometry (e.g., in ultra-high-quality nanostructures), the electronic fluid assumes a Poiseuille-type flow. Applying an external magnetic field tends to diminish viscous effects leading to large negative magnetoresistance. In two-component systems near charge neutrality, the hydrodynamic flow of charge carriers is strongly affected by the mutual friction between the two constituents. At low fields, the magnetoresistance is negative, however, at high fields the interplay between electron-hole scattering, recombination, and viscosity results in a dramatic change of the flow profile: the magnetoresistance changes its sign and eventually becomes linear in very high fields. This nonmonotonic magnetoresistance can be used as a fingerprint to detect viscous flow in two-component conducting systems.

Misfit dislocations of anisotropic magnetoresistant Nd0.45Sr0.55MnO3 thin films grown on SrTiO3 (1 1 0) substrates

International Nuclear Information System (INIS)

Tang, Y.L.; Zhu, Y.L.; Meng, H.; Zhang, Y.Q.; Ma, X.L.

2012-01-01

Nd 0.45 Sr 0.55 MnO 3 is an A-type antiferromagnetic manganite showing obvious angular-dependent magnetoresistance, which can be tuned by misfit strain. The misfit strain relaxation of Nd 0.45 Sr 0.55 MnO 3 thin films is of both fundamental and technical importance. In this paper, microstructures of epitaxial Nd 0.45 Sr 0.55 MnO 3 thin films grown on SrTiO 3 (1 1 0) substrates by pulsed laser deposition were investigated by means of (scanning) transmission electron microscopy. The Nd 0.45 Sr 0.55 MnO 3 thin films exhibit a two-layered structure: a continuous perovskite layer epitaxial grown on the substrate followed by epitaxially grown columnar nanostructures. An approximately periodic array of misfit dislocations is found along the interface with line directions of both 〈1 1 1〉 and [0 0 1]. High-resolution (scanning) transmission electron microscopy reveals that all the misfit dislocations possess a〈1 1 0〉-type Burgers vectors. A formation mechanism based on gliding or climbing of the dislocations is proposed to elucidate this novel misfit dislocation configuration. These misfit dislocations have complex effects on the strain relaxation and microstructure of the films, and thus their influence needs further consideration for heteroepitaxial perovskite thin film systems, especially for films grown on substrates with low-symmetry surfaces such as SrTiO 3 (1 1 0) and (1 1 1), which are attracting attention for their potentially new functions.

Oscillating Magnetoresistance in Graphene p-n Junctions at Intermediate Magnetic Fields.

Science.gov (United States)

Overweg, Hiske; Eggimann, Hannah; Liu, Ming-Hao; Varlet, Anastasia; Eich, Marius; Simonet, Pauline; Lee, Yongjin; Watanabe, Kenji; Taniguchi, Takashi; Richter, Klaus; Fal'ko, Vladimir I; Ensslin, Klaus; Ihn, Thomas

2017-05-10

We report on the observation of magnetoresistance oscillations in graphene p-n junctions. The oscillations have been observed for six samples, consisting of single-layer and bilayer graphene, and persist up to temperatures of 30 K, where standard Shubnikov-de Haas oscillations are no longer discernible. The oscillatory magnetoresistance can be reproduced by tight-binding simulations. We attribute this phenomenon to the modulated densities of states in the n- and p-regions.

Strain driven anisotropic magnetoresistance in antiferromagnetic La$_{0.4}$Sr$_{0.6}$MnO$_{3}$

OpenAIRE

Wong, A. T.; Beekman, C.; Guo, H.; Siemons, W.; Gai, Z.; Arenholz, E.; Takamura, Y.; Ward, T. Z.

2014-01-01

We investigate the effects of strain on antiferromagnetic (AFM) single crystal thin films of La 1-x Sr x MnO 3 (x = 0.6). Nominally unstrained samples have strong magnetoresistance with anisotropic magnetoresistances (AMR) of up to 8%. Compressive strain suppresses magnetoresistance but generates AMR values of up to 63%. Tensile strain presents the only case of a metal-insulator transition and demonstrates a previously unreported AMR behavior. In all three cases, we find evidence of magnetic...

Peculiarities of magnetoresistance in InSb whiskers at cryogenic temperatures

Energy Technology Data Exchange (ETDEWEB)

Druzhinin, A., E-mail: druzh@polynet.lviv.ua [Lviv Polytechnic National University, Bandera Str., 12, 79013 Lviv (Ukraine); International Laboratory of High Magnetic Fields and Low Temperatures, Gajowicka 95, Wroclaw (Poland); Ostrovskii, I.; Khoverko, Yu. [Lviv Polytechnic National University, Bandera Str., 12, 79013 Lviv (Ukraine); International Laboratory of High Magnetic Fields and Low Temperatures, Gajowicka 95, Wroclaw (Poland); Liakh-Kaguy, N.; Khytruk, I. [Lviv Polytechnic National University, Bandera Str., 12, 79013 Lviv (Ukraine); Rogacki, K. [International Laboratory of High Magnetic Fields and Low Temperatures, Gajowicka 95, Wroclaw (Poland)

2015-12-15

Highlights: • Magnetoresistance in InSb whiskers with impurity concentration near MIT is studied. • SdH oscillations of transverse and longitudinal magnetoresistance are examined. • Mechanisms of electron scattering are determined • Main crystal parameters of InSb whiskers are determined. - Abstract: The study of the magnetoresistance in InSb whiskers with an impurity concentration in the vicinity to the metal-insulator phase transition, at low temperature range 4.2–77 K, and in fields, with induction up to 14 T, was conducted. The presence of Shubnikov-de Haas oscillations in both transverse and longitudinal magnetoresistance was observed. The following parameters of InSb whiskers were defined: period of oscillations 0.1 T{sup −1}, cyclotron effective mass of electrons m{sub c} ≈ 0.14m{sub o,} concentration of charge carriers 2.3 × 10{sup 17} cm{sup −3}, g-factor g{sup *} ≈ 30 and Dingle temperature T{sub D} = 14.5 K. To determine the nature of crystal defects, the electron scattering processes on the short-range potential, caused by interaction with polar and nonpolar optical phonons, piezoelectric and acoustic phonons, static strain centers and ionized impurities in n-InSb whiskers, with defect concentration 2.9 × 10{sup 17} cm{sup −3}, are considered. The temperature dependences of electron mobility in the range 4.2–500 K were calculated.

Magnetoresistance anomalies in ultra-thin granular YBa2Cu3O7−δ bridges

International Nuclear Information System (INIS)

Levi, D.; Shaulov, A.; Koren, G.; Yeshurun, Y.

2013-01-01

Highlights: •Negative magnetoresistance slope in the Tesla regime is observed at low temperatures. •Phase slips explains the observed magnetoresistance at high temperatures. •Quasiparticles tunneling explains the negative slope. -- Abstract: We report on magnetoresistance measurements in 10 nm thick and submicron-wide granular YBa 2 Cu 3 O 7−δ bridges. The results show a strong dependence of the resistance on the magnetic field at low fields crossing over to a relatively weak field dependence at high fields. The field derivative of the resistance at high fields decreases as the temperature is lowered and eventually changes sign, exhibiting a negative slope in a wide field range in the Tesla regime. This negative slope is sensitive to the bias current, turning to be positive as the bias current increases. This complex magnetoresistance behavior is attributed to both phase slips in a distribution of strongly and weakly linked superconducting grains, and tunneling of quasiparticles between grains. The latter dominates at low temperatures and high fields, giving rise to the negative magnetoresistance slope

Negative magnetoresistance in Dirac semimetal Cd3As2.

Science.gov (United States)

Li, Hui; He, Hongtao; Lu, Hai-Zhou; Zhang, Huachen; Liu, Hongchao; Ma, Rong; Fan, Zhiyong; Shen, Shun-Qing; Wang, Jiannong

2016-01-08

A large negative magnetoresistance (NMR) is anticipated in topological semimetals in parallel magnetic fields, demonstrating the chiral anomaly, a long-sought high-energy-physics effect, in solid-state systems. Recent experiments reveal that the Dirac semimetal Cd3As2 has the record-high mobility and positive linear magnetoresistance in perpendicular magnetic fields. However, the NMR has not yet been unveiled. Here we report the observation of NMR in Cd3As2 microribbons in parallel magnetic fields up to 66% at 50 K and visible at room temperatures. The NMR is sensitive to the angle between magnetic and electrical fields, robust against temperature and dependent on the carrier density. The large NMR results from low carrier densities in our Cd3As2 samples, ranging from 3.0 × 10(17) cm(-3) at 300 K to 2.2 × 10(16) cm(-3) below 50 K. We therefore attribute the observed NMR to the chiral anomaly. In perpendicular magnetic fields, a positive linear magnetoresistance up to 1,670% at 14 T and 2 K is also observed.

Invariant exchange perturbation theory for multicenter systems and its application to the calculation of magnetic chains in manganites

International Nuclear Information System (INIS)

Orlenko, E. V.; Ershova, E. V.; Orlenko, F. E.

2013-01-01

The formalism of exchange perturbation theory is presented with regard to the general principles of constructing an antisymmetric vector with the use of the Young diagrams and tableaux in which the coordinate and spin parts are not separated. The form of the energy and wave function corrections coincides with earlier obtained expressions, which are reduced in the present paper to a simpler form of a symmetry-adapted perturbation operator, which preserves all intercenter exchange contributions. The exchange perturbation theory (EPT) formalism itself is presented in the standard form of invariant perturbation theory that takes into account intercenter electron permutations between overlapping nonorthogonal states. As an example of application of the formalism of invariant perturbation theory, we consider the magnetic properties of perovskite manganites La 1/3 Ca 2/3 MnO 3 that are associated with the charge and spin ordering in magnetic chains of manganese. We try to interpret the experimental results obtained from the study of the effect of doping the above alloys by the model of superexchange interaction in manganite chains that is constructed on the basis of the exchange perturbation theory (EPT) formalism. The model proposed makes it possible to carry out a quantitative analysis of the effect of substitution of manganese atoms by doping elements with different electron configurations on the electronic structure and short-range order in a magnetic chain of manganites

Magnetoresistance of samarium in the 4.2-300 K range

International Nuclear Information System (INIS)

Trubitsyn, V.A.; Shalashov, V.F.

1980-01-01

Electric conductivity, transverse and longitudinal magnetoresistance of polycrystalline samarium with the purity of 99.9% in the 4.2-300 K temperature range and in magnetic fields up to 50 ke, are measured. The constituent of specific electric conductivity caused by spin disorder is 30.7 μOhmxcm, m*/m=2.6, the exchange parameter is G=3.1 eVxA 3 . Both transverse and longitudinal magnetoresistance are positive at 4.2 K; and the increase of temperature reveals a number of anomalies, evidently conditioned by the alteration of samarium magnetic structure

Magnetic after-effect in manganite films

Energy Technology Data Exchange (ETDEWEB)

Sirena, M. E-mail: sirenam@ib.cnea.gov.ar; Steren, L.B.; Guimpel, J

2001-05-01

The time dependence of the magnetic and transport properties on La{sub 0.6}Sr{sub 0.4}MnO{sub 3} films and bulk samples has been studied through magnetization and resistivity measurements. A magnetic after-effect has been observed in all samples. At low temperatures, the low-field magnetization, can be described by the function M(t)=M{sub c}+M{sub d} exp(-t/{tau})+S(H,T)ln(t). The resistivity increases logarithmically in the same temperature range, indicating the evolution of the sample to a more disordered state. Above a characteristic temperature, this behaviour is reversed and an increase of the magnetization with time is observed. The relaxation parameters depend on the bulk or films character of the samples. In the latter case, a dependence on the film thickness was found. A direct correlation between the time dependence of the resistivity and magnetization curves in manganite compounds was found.

Enhanced temperature-independent magnetoresistance below the ...

Indian Academy of Sciences (India)

The film exhibits a large nearly temperature-independent magnetoresistance around 99% in the temperature regime below p. The zero field-cooled (ZFC) and field-cooled (FC) magnetization data at 50 Oe shows irreversibility between the ZFC and FC close to the ferromagnetic transition temperature c = 250 K. The ZFC ...

Evolution and control of the phase competition morphology in a manganite film

OpenAIRE

Zhou, Haibiao; Wang, Lingfei; Hou, Yubin; Huang, Zhen; Lu, Qingyou; Wu, Wenbin

2015-01-01

The competition among different phases in perovskite manganites is pronounced since their energies are very close under the interplay of charge, spin, orbital and lattice degrees of freedom. To reveal the roles of underlying interactions, many efforts have been devoted towards directly imaging phase transitions at microscopic scales. Here we show images of the charge-ordered insulator (COI) phase transition from a pure ferromagnetic metal with reducing field or increasing temperature in a str...

Titania-coated manganite nanoparticles: synthesis of the shell, characterization and MRI properties

Czech Academy of Sciences Publication Activity Database

Jirák, Zdeněk; Kuličková, Jarmila; Herynek, Vít; Maryško, Miroslav; Koktan, Jakub; Kaman, Ondřej

2017-01-01

Roč. 427, Apr (2017), s. 245-250 ISSN 0304-8853 R&D Projects: GA ČR GA15-10088S; GA ČR GA16-04340S Institutional support: RVO:68378271 ; RVO:68378041 Keywords : magnetic nanoparticles * core-shell nanoparticles * titania coating * perovskite manganite * magnetic resonance imaging * transverse relaxivity Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 2.630, year: 2016

Detection of magnetic resonance signals using a magnetoresistive sensor

Science.gov (United States)

Budker, Dmitry; Pines, Alexander; Xu, Shoujun; Hilty, Christian; Ledbetter, Micah P; Bouchard, Louis S

2013-10-01

A method and apparatus are described wherein a micro sample of a fluidic material may be assayed without sample contamination using NMR techniques, in combination with magnetoresistive sensors. The fluidic material to be assayed is first subject to pre-polarization, in one embodiment, by passage through a magnetic field. The magnetization of the fluidic material is then subject to an encoding process, in one embodiment an rf-induced inversion by passage through an adiabatic fast-passage module. Thereafter, the changes in magnetization are detected by a pair of solid-state magnetoresistive sensors arranged in gradiometer mode. Miniaturization is afforded by the close spacing of the various modules.

Magnetoresistance of microstructured permalloy ellipses having multi-domain configurations

International Nuclear Information System (INIS)

Kuo, C.Y.; Chung, W.S.; Wu, J.C.; Horng, Lance; Wei, Z.-H.; Lai, M.-F.; Chang, C.-R.

2007-01-01

Mirostructured permalloy ellipses having purposely designed multi-domain configurations were investigated. The samples were fabricated using e-beam lithography through a lift-off process. The magnetoresistance measurements were carried out with a constant dc sensing current under the external magnetic field applied along the short axis. The magnetoresistance curves manifest characteristic features in accordance with the specific domain configurations. Step-like/kink features were observed on the ellipses with cross-tie wall/two-vortex configuration and step-like plus kink magnetorsistance curve was found on the ellipse with cross-tie wall combining with two-vortex structure. A magnetic force microscopy and a micromagnetic simulation were employed to support these results

Anomalous rf magnetoresistance in copper at 4/degree/K

International Nuclear Information System (INIS)

Halama, H.J.; Prodell, A.G.; Rogers, J.T.

1988-03-01

We have measured the effect of a magnetic field on the surface resistance of polycrystalline Cu at f = 1.2 GHz and at 4.4/degree/K; under these conditions the surface resistance is well into the anomalous skin effect regime but has not reached its limiting value. We find that the transverse and longitudinal magnetoresistance are an order of magnitude smaller than the DC magnetoresistance and depend quadratically on the field. At low fields we observe a decrease in surface resistance with increasing field which can be interpreted as a size effect of the TF surface current. 17 refs., 4 figs., 1 tab

Electrical control of memristance and magnetoresistance in oxide magnetic tunnel junctions

KAUST Repository

Zhang, Kun

2015-01-01

Electric-field control of magnetic and transport properties of magnetic tunnel junctions has promising applications in spintronics. Here, we experimentally demonstrate a reversible electrical manipulation of memristance, magnetoresistance, and exchange bias in Co/CoO–ZnO/Co magnetic tunnel junctions, which enables the realization of four nonvolatile resistance states. Moreover, greatly enhanced tunneling magnetoresistance of 68% was observed due to the enhanced spin polarization of the bottom Co/CoO interface. The ab initio calculations further indicate that the spin polarization of the Co/CoO interface is as high as 73% near the Fermi level and plenty of oxygen vacancies can induce metal–insulator transition of the CoO1−v layer. Thus, the electrical manipulation mechanism on the memristance, magnetoresistance and exchange bias can be attributed to the electric-field-driven migration of oxygen ions/vacancies between very thin CoO and ZnO layers.

Giant anisotropic magnetoresistance and planar Hall effect in the Dirac semimetal Cd3As2

Science.gov (United States)

Li, Hui; Wang, Huan-Wen; He, Hongtao; Wang, Jiannong; Shen, Shun-Qing

2018-05-01

Anisotropic magnetoresistance is the change tendency of resistance of a material on the mutual orientation of the electric current and the external magnetic field. Here, we report experimental observations in the Dirac semimetal Cd3As2 of giant anisotropic magnetoresistance and its transverse version, called the planar Hall effect. The relative anisotropic magnetoresistance is negative and up to -68% at 2 K and 10 T. The high anisotropy and the minus sign in this isotropic and nonmagnetic material are attributed to a field-dependent current along the magnetic field, which may be induced by the Berry curvature of the band structure. This observation not only reveals unusual physical phenomena in Weyl and Dirac semimetals, but also finds additional transport signatures of Weyl and Dirac fermions other than negative magnetoresistance.

Robust giant magnetoresistive effect type multilayer sensor

NARCIS (Netherlands)

Lenssen, K.M.H.; Kuiper, A.E.T.; Roozeboom, F.

2002-01-01

A robust Giant Magneto Resistive effect type multilayer sensor comprising a free and a pinned ferromagnetic layer, which can withstand high temperatures and strong magnetic fields as required in automotive applications. The GMR multi-layer has an asymmetric magneto-resistive curve and enables

Anomalous magnetisation process in UFe4Al8 probed by magnetisation and magnetoresistance

International Nuclear Information System (INIS)

Godinho, M.; Estrela, P.; Goncalves, A.P.; Almeida, M.; Spirlet, J.C.; Bonfait, G.

1996-01-01

A strong anisotropic magnetoresistance has been measured in a single crystal of UFe 4 Al 8 and has been used to prove the ferromagnetic order of the U lattice. The giant anomaly detected in the magnetoresistance curves is interpreted as two 90 rotations of the magnetisation. This interpretation has been confirmed by magnetisation measurements. (orig.)

Giant magnetoresistance, three-dimensional Fermi surface and origin of resistivity plateau in YSb semimetal.

Science.gov (United States)

Pavlosiuk, Orest; Swatek, Przemysław; Wiśniewski, Piotr

2016-12-09

Very strong magnetoresistance and a resistivity plateau impeding low temperature divergence due to insulating bulk are hallmarks of topological insulators and are also present in topological semimetals where the plateau is induced by magnetic field, when time-reversal symmetry (protecting surface states in topological insulators) is broken. Similar features were observed in a simple rock-salt-structure LaSb, leading to a suggestion of the possible non-trivial topology of 2D states in this compound. We show that its sister compound YSb is also characterized by giant magnetoresistance exceeding one thousand percent and low-temperature plateau of resistivity. We thus performed in-depth analysis of YSb Fermi surface by band calculations, magnetoresistance, and Shubnikov-de Haas effect measurements, which reveals only three-dimensional Fermi sheets. Kohler scaling applied to magnetoresistance data accounts very well for its low-temperature upturn behavior. The field-angle-dependent magnetoresistance demonstrates a 3D-scaling yielding effective mass anisotropy perfectly agreeing with electronic structure and quantum oscillations analysis, thus providing further support for 3D-Fermi surface scenario of magnetotransport, without necessity of invoking topologically non-trivial 2D states. We discuss data implying that analogous field-induced properties of LaSb can also be well understood in the framework of 3D multiband model.

Asymmetric electroresistance of cluster glass state in manganites

KAUST Repository

Lourembam, James

2014-03-31

We report the electrostatic modulation of transport in strained Pr0.65(Ca0.75Sr0.25)0.35MnO3 thin films grown on SrTiO3 by gating with ionic liquid in electric double layer transistors (EDLT). In such manganite films with strong phase separation, a cluster glass magnetic state emerges at low temperatures with a spin freezing temperature of about 99 K, which is accompanied by the reentrant insulating state with high resistance below 30 K. In the EDLT, we observe bipolar and asymmetric modulation of the channel resistance, as well as an enhanced electroresistance up to 200% at positive gate bias. Our results provide insights on the carrier-density-dependent correlated electron physics of cluster glass systems.

Magnetism and magnetoresistance from different origins in Co/ZnO:Al granular films

Energy Technology Data Exchange (ETDEWEB)

Quan, Zhiyong, E-mail: quanzy@sxnu.edu.cn; Liu, Xia; Song, Zhilin; Xu, Xiaohong, E-mail: xuxh@dns.sxnu.edu.cn

2016-12-01

Co/ZnO:Al granular films were made on glass substrates by sequential magnetron sputter deposition of ultrathin Co layer and ZnO:Al layer at room temperature. The as-deposited films consist of superparamagnetic Co particles dispersed in ZnO:Al (~2% Al) semiconductor matrix. Distinguished magnetoresistance effect at room temperature was obtained in the as-deposited films, which obviously reduced after annealing due to the growth of Co particles. The size of important magnetic particles was analyzed by Langevin function for hysteresis loops and magnetoresistance curves at room temperature. It was found that small magnetic particle contribute to magnetoresistance behavior and large particles dominate the room temperature magnetism in Co/ZnO:Al granular films.

Giant magnetoresistive properties of FexAu100-x alloys produced by mechanical alloying

International Nuclear Information System (INIS)

Socolovsky, L.M.; Sanchez, F.H.; Shingu, P.H.

2001-01-01

The Fe x Au 100- x alloys were produced for the first time by mechanical alloying. Resistance of samples with iron concentrations of x=15, 20, 25, and 30 at% were measured at 77 K under an applied field of 14 kOe. A maximum in magnetoresistive ratio (Δρ/ρ) of 3.5% was obtained for Fe 25 Au 75 . Samples were annealed in order to enhance magnetoresistive properties. These samples exhibit larger ratios, primarily due to the elimination of defects. X-ray diffraction Moessbauer spectroscopy and magnetoresistance measurements were performed, in order to correlate bulk and hyperfine magnetic properties with crystalline structure. X-ray diffractograms show an FCC structure, with no evidence for a BCC one

Large magnetoresistance in (AA')2FeReO6 double perovskites

International Nuclear Information System (INIS)

Teresa, J.M. de; Serrate, D.; Blasco, J.; Ibarra, M.R.; Morellon, L.

2005-01-01

We review the main structural, magnetic and magnetotransport properties of the intriguing (AA') 2 FeReO 6 magnetic double perovskites. As the average cation size decreases, the crystallographic structure at room temperature evolves from cubic [(AA') 2 =Ba 2 , Ba 1.5 Sr 0.5 , BaSr, Ba 0.5 Sr 1.5 ] to tetragonal [(AA') 2 =Sr 2 ] and monoclinic [(AA') 2 =Ca 0.5 Sr 1.5 , CaSr, Ca 1.5 Sr 0.5 , Ca 2 ]. The Curie temperature increases anomalously from ∼303K for Ba 2 to ∼522K for Ca 2 in sharp contrast with the observed behaviour in the isostructural compounds (AA') 2 FeMoO 6 . Other anomalous features in the (AA') 2 FeReO 6 series are: the large magnetic anisotropy, the large magnetoelastic coupling and the semiconducting behaviour of the monoclinic compounds. The monoclinic compounds undergo a structural/magnetic transition at T S below 125K. Three different magnetoresistance mechanisms have been identified: the intergrain negative magnetoresistance effect, which is present across the whole series of compounds, and in the case of the monoclinic compounds below T S a negative magnetoresistance effect associated to the melting of the low-temperature phase and a positive magnetoresistance effect only present in (AA') 2 =Ca 2 below T∼50K

Magnetoresistance and Curie temperature of GaAs semiconductor doped with Mn ions

International Nuclear Information System (INIS)

Yalishev, V.Sh.

2006-02-01

Key words: diluted magnetic semiconductors, magnetoresistance, ferromagnetism, ionic implantation, molecular-beam epitaxy, magnetic clusters, Curie temperature. Subjects of the inquiry: Diluted magnetic semiconductor GaAs:Mn. Aim of the inquiry: determination of the possibility of the increase of Curie temperature in diluted magnetic semiconductors based on GaAs doped with Mn magnetic impurity. Method of inquiry: superconducting quantum interference device (SQUID), Hall effect, magnetoresistance, atomic and magnetic force microscopes. The results achieved and their novelty: 1. The effect of the additional doping of Ga 0,965 Mn 0,035 As magnetic epitaxial layers by nonmagnetic impurity of Be on on the Curie temperature was revealed. 2. The exchange interaction energy in the investigated Ga 0,965 Mn 0,035 As materials was determined by the means of the magnetic impurity dispersion model from the temperature dependence of the resistivity measurements. 3. The effect of magnetic clusters dimensions and illumination on the magnetoresistance of GaAs materials containing nano-dimensional magnetic clusters was studied for the first time. Practical value: Calculated energy of the exchange interaction between local electrons of magnetic ions and free holes in Ga 1-x Mn x As magnetic semiconductors permitted to evaluate the theoretical meaning of Curie temperature depending on concentration of free holes and to compare it with experimental data. Sphere of usage: micro- and nano-electronics, solid state physics, physics of semiconductors, magnetic materials physics, spin-polarized current sources. (author)

The tunneling magnetoresistance and spin-polarized optoelectronic properties of graphyne-based molecular magnetic tunnel junctions

International Nuclear Information System (INIS)

Yang, Zhi; Ouyang, Bin; Lan, Guoqing; Xu, Li-Chun; Liu, Ruiping; Liu, Xuguang

2017-01-01

Using density functional theory and the non-equilibrium Green’s function method, we investigate the spin-dependent transport and optoelectronic properties of the graphyne-based molecular magnetic tunnel junctions (MMTJs). We find that these MMTJs exhibit an outstanding tunneling magnetoresistance (TMR) effect. The TMR value is as high as 10 6 %. When the magnetization directions of two electrodes are antiparallel under positive or negative bias voltages, two kinds of pure spin currents can be obtained in the systems. Furthermore, under the irradiation of infrared, visible or ultraviolet light, spin-polarized photocurrents can be generated in the MMTJs, but the corresponding microscopic mechanisms are different. More importantly, if the magnetization directions of two electrodes are antiparallel, the photocurrents with different spins are spatially separated, appearing at different electrodes. This phenomenon provides a new way to simultaneously generate two spin currents. (paper)

Effects of magnetic and structural properties on magnetoresistance in amorphous TbFeCo

International Nuclear Information System (INIS)

Yumoto, S.; Hidaka, Y.; Okada, O.

1990-01-01

An extraordinary magnetoresistance effect, linearly dependent on the external magnetic field, is observed in amorphous TbFeCo films. The electrical resistance jumps by δρ at magnetization reversal. δρ depends on Tb concentration and it becomes nearly zero at about Tb 26 at. % concentration. To clarify the Tb concentration dependence of δρ, the magnetic properties and the heat treatment effect are examined. It is found that the magnetic anisotropy field (H k ) is maximum at about Tb 26 at. % and the gradient of linear magnetoresistance, δρ/(ρ 0 H c ), is proportional to the -H k + const, where ρ 0 is the electric resistance in zero field, H c is the coercive force, and the constant is about 100 kOe. The structural relaxation, a coercive force change by the heat treatment up to 200 degree C, is examined. It is found that as δρ/(ρ 0 H c ) in the as-sputtered state decreases, the coercive force change by the heat treatment decreases. The coercive force change is minimum at about Tb 26 at. %, where δρ/(ρ 0 H c ) becomes zero. These results mean that linear magnetoresistance is related to structure relaxation by heat treatment. The δρ disappearance at about Tb 26 at. % is based on the stable structure against heat treatment and the largest magnetic anisotropy field

The effect of magnetic ordering on the giant magnetoresistance of Cr-Fe-V and Cr-Fe-Mn

International Nuclear Information System (INIS)

Somsen, Ch.; Acet, M.; Nepecks, G.; Wassermann, E.F.

2000-01-01

Cr-rich Cr 1-x Fe x alloys with compositions in the vicinity of mixed ferromagnetic and antiferromagnetic exchange (x=0.18) exhibit giant magnetoresistance. In order to understand the influence of the antiferromagnetism of Cr on the giant magnetoresistance one can manipulate the antiferromagnetic exchange either by adding vanadium, which destroys the antiferromagnetism of Cr, or by adding manganese, which enhances it. Cr-Fe-V and Cr-Fe-Mn alloys also have Curie temperatures that lie between low temperatures and room temperature in the concentration region where giant magnetoresistance is observed. Therefore, they are also used as samples to study the magnetoresistance as a function of the strength of FM exchange. We discuss these points in the light of temperature and concentration-dependent magnetoresistance experiments on Cr 0.99-x Fe x V 0.01 , Cr 0.96-x Fe x V 0.04 , Cr 0.90-x Fe x Mn 0.10 and Cr 0.55 Fe x Mn 0.45-x alloys. Results indicate that the most favorable condition for a large magnetoresistance in these alloys occurs at temperatures near the Curie temperature

Tuning spin transport properties and molecular magnetoresistance through contact geometry

Science.gov (United States)

Ulman, Kanchan; Narasimhan, Shobhana; Delin, Anna

2014-01-01

Molecular spintronics seeks to unite the advantages of using organic molecules as nanoelectronic components, with the benefits of using spin as an additional degree of freedom. For technological applications, an important quantity is the molecular magnetoresistance. In this work, we show that this parameter is very sensitive to the contact geometry. To demonstrate this, we perform ab initio calculations, combining the non-equilibrium Green's function method with density functional theory, on a dithienylethene molecule placed between spin-polarized nickel leads of varying geometries. We find that, in general, the magnetoresistance is significantly higher when the contact is made to sharp tips than to flat surfaces. Interestingly, this holds true for both resonant and tunneling conduction regimes, i.e., when the molecule is in its "closed" and "open" conformations, respectively. We find that changing the lead geometry can increase the magnetoresistance by up to a factor of ˜5. We also introduce a simple model that, despite requiring minimal computational time, can recapture our ab initio results for the behavior of magnetoresistance as a function of bias voltage. This model requires as its input only the density of states on the anchoring atoms, at zero bias voltage. We also find that the non-resonant conductance in the open conformation of the molecule is significantly impacted by the lead geometry. As a result, the ratio of the current in the closed and open conformations can also be tuned by varying the geometry of the leads, and increased by ˜400%.

Tuning spin transport properties and molecular magnetoresistance through contact geometry

International Nuclear Information System (INIS)

Ulman, Kanchan; Narasimhan, Shobhana; Delin, Anna

2014-01-01

Molecular spintronics seeks to unite the advantages of using organic molecules as nanoelectronic components, with the benefits of using spin as an additional degree of freedom. For technological applications, an important quantity is the molecular magnetoresistance. In this work, we show that this parameter is very sensitive to the contact geometry. To demonstrate this, we perform ab initio calculations, combining the non-equilibrium Green's function method with density functional theory, on a dithienylethene molecule placed between spin-polarized nickel leads of varying geometries. We find that, in general, the magnetoresistance is significantly higher when the contact is made to sharp tips than to flat surfaces. Interestingly, this holds true for both resonant and tunneling conduction regimes, i.e., when the molecule is in its “closed” and “open” conformations, respectively. We find that changing the lead geometry can increase the magnetoresistance by up to a factor of ∼5. We also introduce a simple model that, despite requiring minimal computational time, can recapture our ab initio results for the behavior of magnetoresistance as a function of bias voltage. This model requires as its input only the density of states on the anchoring atoms, at zero bias voltage. We also find that the non-resonant conductance in the open conformation of the molecule is significantly impacted by the lead geometry. As a result, the ratio of the current in the closed and open conformations can also be tuned by varying the geometry of the leads, and increased by ∼400%

Tuning spin transport properties and molecular magnetoresistance through contact geometry.

Science.gov (United States)

Ulman, Kanchan; Narasimhan, Shobhana; Delin, Anna

2014-01-28

Molecular spintronics seeks to unite the advantages of using organic molecules as nanoelectronic components, with the benefits of using spin as an additional degree of freedom. For technological applications, an important quantity is the molecular magnetoresistance. In this work, we show that this parameter is very sensitive to the contact geometry. To demonstrate this, we perform ab initio calculations, combining the non-equilibrium Green's function method with density functional theory, on a dithienylethene molecule placed between spin-polarized nickel leads of varying geometries. We find that, in general, the magnetoresistance is significantly higher when the contact is made to sharp tips than to flat surfaces. Interestingly, this holds true for both resonant and tunneling conduction regimes, i.e., when the molecule is in its "closed" and "open" conformations, respectively. We find that changing the lead geometry can increase the magnetoresistance by up to a factor of ∼5. We also introduce a simple model that, despite requiring minimal computational time, can recapture our ab initio results for the behavior of magnetoresistance as a function of bias voltage. This model requires as its input only the density of states on the anchoring atoms, at zero bias voltage. We also find that the non-resonant conductance in the open conformation of the molecule is significantly impacted by the lead geometry. As a result, the ratio of the current in the closed and open conformations can also be tuned by varying the geometry of the leads, and increased by ∼400%.

Anomalous magnetoresistance in the spinel superconductor LiTi2O4.

Science.gov (United States)

Jin, K; He, G; Zhang, X; Maruyama, S; Yasui, S; Suchoski, R; Shin, J; Jiang, Y; Yu, H S; Yuan, J; Shan, L; Kusmartsev, F V; Greene, R L; Takeuchi, I

2015-05-20

LiTi2O4 is a unique compound in that it is the only known spinel oxide superconductor. The lack of high quality single crystals has thus far prevented systematic investigations of its transport properties. Here we report a careful study of transport and tunnelling spectroscopy in epitaxial LiTi2O4 thin films. An unusual magnetoresistance is observed which changes from nearly isotropic negative to prominently anisotropic positive as the temperature is decreased. We present evidence that shows that the negative magnetoresistance likely stems from the suppression of local spin fluctuations or spin-orbit scattering centres. The positive magnetoresistance suggests the presence of an orbital-related state, also supported by the fact that the superconducting energy gap decreases as a quadratic function of magnetic field. These observations indicate that the spin-orbital fluctuations play an important role in LiTi2O4 in a manner similar to high-temperature superconductors.

Strain effects on anisotropic magnetoresistance in a nanowire spin valve

Science.gov (United States)

Hossain, Md I.; Maksud, M.; Subramanian, A.; Atulasimha, J.; Bandyopadhyay, S.

2016-11-01

The longitudinal magnetoresistance of a copper nanowire contacted by two cobalt contacts shows broad spin-valve peaks at room temperature. However, when the contacts are slightly heated, the peaks change into troughs which are signature of anisotropic magnetoresistance (AMR). Under heating, the differential thermal expansion of the contacts and the substrate generates a small strain in the cobalt contacts which enhances the AMR effect sufficiently to change the peak into a trough. This shows the extreme sensitivity of AMR to strain. The change in the AMR resistivity coefficient due to strain is estimated to be a few m Ω -m/microstrain.

Extremely large magnetoresistance and Kohler's rule in PdSn4: A complete study of thermodynamic, transport, and band-structure properties

Science.gov (United States)

Jo, Na Hyun; Wu, Yun; Wang, Lin-Lin; Orth, Peter P.; Downing, Savannah S.; Manni, Soham; Mou, Dixiang; Johnson, Duane D.; Kaminski, Adam; Bud'ko, Sergey L.; Canfield, Paul C.

2017-10-01

The recently discovered material PtSn4 is known to exhibit extremely large magnetoresistance (XMR) that also manifests Dirac arc nodes on the surface. PdSn4 is isostructural to PtSn4 with the same electron count. We report on the physical properties of high-quality single crystals of PdSn4 including specific heat, temperature- and magnetic-field-dependent resistivity and magnetization, and electronic band-structure properties obtained from angle-resolved photoemission spectroscopy (ARPES). We observe that PdSn4 has physical properties that are qualitatively similar to those of PtSn4, but find also pronounced differences. Importantly, the Dirac arc node surface state of PtSn4 is gapped out for PdSn4. By comparing these similar compounds, we address the origin of the extremely large magnetoresistance in PdSn4 and PtSn4; based on detailed analysis of the magnetoresistivity ρ (H ,T ) , we conclude that neither the carrier compensation nor the Dirac arc node surface state are the primary reason for the extremely large magnetoresistance. On the other hand, we find that, surprisingly, Kohler's rule scaling of the magnetoresistance, which describes a self-similarity of the field-induced orbital electronic motion across different length scales and is derived for a simple electronic response of metals to an applied magnetic field is obeyed over the full range of temperatures and field strengths that we explore.

Tunneling magnetoresistance dependence on the temperature in a ferromagnetic Zener diode

Energy Technology Data Exchange (ETDEWEB)

Comesana, E; Aldegunde, M; GarcIa-Loureiro, A, E-mail: enrique.comesana@usc.e [Departamento de Electronica e Computacion, Universidade de Santiago de Compostela, 15782 Santiago de Compostela (Spain)

2009-11-15

In the present work we focus on the study of the temperature dependence of the tunnelling current in a ferromagnetic Zener diode. We predict the tunneling magnetoresistance dependence on the temperature. Large doping concentrations lead to magnetic semiconductors with Curie temperature T{sub C} near or over room temperature and this will facilitate the introduction of new devices that make use of the ferromagnetism effects. According to our calculations the tunneling magnetoresistance has the form TMR {proportional_to} (T{sup n}{sub C}-T{sup n}).

Magnetoresistance in hybrid organic spin valves at the onset of multiple-step tunneling.

Science.gov (United States)

Schoonus, J J H M; Lumens, P G E; Wagemans, W; Kohlhepp, J T; Bobbert, P A; Swagten, H J M; Koopmans, B

2009-10-02

By combining experiments with simple model calculations, we obtain new insight in spin transport through hybrid, CoFeB/Al2O3(1.5 nm)/tris(8-hydroxyquinoline)aluminium (Alq3)/Co spin valves. We have measured the characteristic changes in the I-V behavior as well as the intrinsic loss of magnetoresistance at the onset of multiple-step tunneling. In the regime of multiple-step tunneling, under the condition of low hopping rates, spin precession in the presence of hyperfine coupling is conjectured to be the relevant source of spin relaxation. A quantitative analysis leads to the prediction of a symmetric magnetoresistance around zero magnetic field in addition to the hysteretic magnetoresistance curves, which are indeed observed in our experiments.

Efficient spin injection and giant magnetoresistance in Fe / MoS 2 / Fe junctions

KAUST Repository

Dolui, Kapildeb

2014-07-02

We demonstrate giant magnetoresistance in Fe/MoS2/Fe junctions by means of ab initio transport calculations. We show that junctions incorporating either a monolayer or a bilayer of MoS2 are metallic and that Fe acts as an efficient spin injector into MoS2 with an efficiency of about 45%. This is the result of the strong coupling between the Fe and S atoms at the interface. For junctions of greater thickness, a maximum magnetoresistance of ∼300% is obtained, which remains robust with the applied bias as long as transport is in the tunneling limit. A general recipe for improving the magnetoresistance in spin valves incorporating layered transition metal dichalcogenides is proposed. © 2014 American Physical Society.

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.

Unsaturated magnetoconductance of epitaxial La0.7Sr0.3MnO3 thin films in pulsed magnetic fields up to 60 T

Directory of Open Access Journals (Sweden)

Wei Niu

2017-05-01

Full Text Available We report on the temperature and field dependence of resistance of La0.7Sr0.3MnO3 thin films over a wide temperature range and in pulsed magnetic fields up to 60 T. The epitaxial La0.7Sr0.3MnO3 thin films were deposited by laser molecular beam epitaxy. High magnetic field magnetoresistance curves were fitted by the Brillouin function, which indicated the existence of magnetically polarized regions and the underlying hopping mechanism. The unsaturated magnetoconductance was the most striking finding observed in pulsed magnetic fields up to 60 T. These observations can deepen the fundamental understanding of the colossal magnetoresistance in manganites with strong correlation of transport properties and magnetic ordering.

Physical and chemical properties of calcium doped neodymium manganite

International Nuclear Information System (INIS)

Tikhonova, L.A.; Zhuk, P.P.; Tonoyan, A.A.; Vecher, A.A.

1991-01-01

Physical and chemical properties of calcium doped neodymium manganite were investigated. It was shown that structure of perovskite with O'-orthorhombic distortion was characteristic for solid solutions of Nd 1-x Ca x MnO 3 (x=0-0.5). Maximum of conductivity for samples with x=0.2 was determined. Inversion of conductivity from p- (x=0) to n-type (x=0.5) was observed in increase of concentration of calcium doped addition. Values of thermal expansion coefficient of studied solid solutions of Nd 1-x Ca x MnO 3 didn't depend on concentration of doped addition within the range 700 to 1200 K and were (9.9-11.3)·10 -6 K -1

Structure and giant magnetoresistance of carbon-based amorphous films prepared by magnetron sputtering

International Nuclear Information System (INIS)

Ma, L.; He, M.F.; Liu, Z.W.; Zeng, D.C.; Gu, Z.F.; Cheng, G.

2014-01-01

Pure amorphous carbon (a-C) and Co-doped Co x C 1−x films were prepared on n-Si(100) substrates by dc magnetron sputtering. In Co–C films, the nano-sized amorphous Co particles were homogeneously dispersed in the amorphous cross-linked carbon matrix. The structures of a-C and Co x C 1−x films were investigated by X-ray photoelectron spectroscopy and Raman spectroscopy. The results showed that the a-C films were diamond-like carbon (DLC) films. After doping cobalt into DLC film, the sp 3 -hybridized carbon content in DLC composite films almost had no change. The as-deposited Co x C 1−x granular films had larger value of magnetoresistance (MR) than the amorphous carbon film. A very high positive MR, up to 15.5% at magnetic field B = 0.8 T and x = 2.5 at.% was observed in a Co x C 1−x granular film with thickness of 80 nm at room temperature when the external magnetic field was perpendicular to the electric current and the film surface. With increase of the film thickness and Co-doped content, the MR decreased gradually. It remains a challenge to well explain the observed MR effect in the Co x C 1−x granular films. - Highlights: • The amorphous carbon films were diamond-like carbon films. • No carbide appearing, the Co–C composite films form a good metal/insulator system. • A high positive magnetoresistance, up to 15.5% at B = 0.8 T was observed in Co–C films

Impact of Annealing Temperature on the Physical Properties of the Lanthanum Deficiency Manganites

Directory of Open Access Journals (Sweden)

Skini Ridha

2017-10-01

Full Text Available The lanthanum deficiency manganites La0.8-x□xCa0.2MnO3 (x = 0, 0.1 and 0.2, where □ is a lanthanum vacancy, were prepared using the classic ceramic methods with different thermal treatments (1373 K and 973 K. The structural, magnetic, and magnetocaloric properties of these compounds were studied as a function of annealing temperature. It was noted that the annealing temperature did not affect the crystal structure of our samples (orthorhombic structure with Pnma space group. Nevertheless, a change in the variation of the unit cell volume V, the average bond length dMn–O, and the average bond angles θMn–O–Mn were observed. Magnetization versus temperature study has shown that all samples exhibited a magnetic transition from ferromagnetic (FM to paramagnetic (PM phase with increasing temperature. However, it can be clearly seen that the annealing at 973 K induced an increase of the magnetization. In addition, the magnetocaloric effect (MCE as well as the relative cooling power (RCP were estimated. As an important result, the values of MCE and RCP in our Lanthanum-deficiency manganites are reported to be near to those found in gadolinium, considered as magnetocaloric reference material.

A study of inelastic electron-phonon interactions on tunneling magnetoresistance of a nano-scale device

International Nuclear Information System (INIS)

Modarresi, M.; Roknabadi, M.R.; Shahtahmasbi, N.; Vahedi Fakhrabad, D.; Arabshahi, H.

2011-01-01

In this research, we have studied the effect of inelastic electron-phonon interactions on current-voltage characteristic and tunneling magnetoresistance of a polythiophene molecule that is sandwiched between two cobalt electrodes using modified Green's function method as proposed by Walczak. The molecule is described with a modified Su-Schrieffer-Heeger Hamiltonian. The ground state of the molecule is obtained by Hellman-Feynman theorem. Electrodes are described in the wide-band approximation and spin-flip is neglected during conduction. Our calculation results show that with increase in voltage the currents increase and tunneling magnetoresistance decreases. Change in tunneling magnetoresistance due to inelastic interactions is limited in a small bias voltage interval and can be neglected in the other bias voltages. -- Research Highlights: →We investigate the effect of inelastic interaction on transport properties. →Due to inelastic interactions tunneling magnetoresistance decreases. →Decrease in TMR is restricted in a small voltage interval.

Superconducting transition and low-field magnetoresistance of a niobium single crystal at 4.2 deg. K; Transition supraconductrice et magnetoresistance en champ faible d'un echantillon monocristallin de niobium a 4.2 deg. K

Energy Technology Data Exchange (ETDEWEB)

Perriot, G [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires. Service de physique du solide et de resonnance magnetique

1967-01-01

We report the study of the electrical resistance of a niobium single crystal, at 4.2 deg. K, from the beginning of the superconductive transition to 80 kilo oersteds. Critical fieldsH{sub c2} and H{sub c3} have been determined. Influences on superconductive transition of current density, field-current angle, crystal orientation and magnetoresistance have been studied. Variation laws of low-field transverse and longitudinal magneto-resistances have been determined. (author) [French] La variation de la resistance electrique d'un monocristal cylindrique de niobium a ete etudiee, a 4,2 deg. K, depuis le debut de la transition supraconductrice jusqu'a 80 kilooersteds. Les champs critiques H{sub c2} et H{sub c3} ont ete determines. On a etudie l'influence de la densite de courant, de l'angle champ-courant, de l'anisotropie cristalline et de la magnetoresistance sur la transition supraconductrice. Les lois de variation des magnetoresistances transversale et longitudinale ont ete determinees dans le domaine des champs faibles. (auteur)

Features of magnetic susceptibility and inhomogeneous magnetic state in La-Sr manganites

International Nuclear Information System (INIS)

Dovgij, V.T.; Linnik, A.I.; Kamenev, V.I.; Prokopenko, V.K.; Mikhajlov, V.I.; Khokhlov, V.A.; Kadontseva, A.M.; Linnik, T.A.; Davydejko, N.V.; Turchenko, V.A.

2007-01-01

Anomalous magnetic susceptibility has been observed in mono- and polycrystalline (ceramic) samples of La-Sr manganites. The oscillations of the magnetic susceptibility observed for monocrystal samples in the vicinity of the Curie temperature (and in the paramagnetic region) are explained by the existence of magnetic clusters. The appearance of susceptibility oscillations in ceramic samples is attributed to the formation of magnetic clusters, which may occur both in grains (at the interface between ferro- and antiferromagnetic phases) and at the grain boundaries [ru

Magnetoresistance based determination of basic parameters of minority charge carriers in solid matter

Directory of Open Access Journals (Sweden)

Y.O. Uhryn

2017-12-01

Full Text Available Magnetoresistance as a tool of basic parameters determination of minority charge carriers and the ratio of minority charge carriers conductivity to majority ones in solid matter has been considered within the framework of the phenomenological two-band model. The criterion of the application of this model has been found. As examples of these equations usage the conductor, semiconductor and superconductor have been introduced. From the obtained temperature dependences of the aforementioned values in superconductor, a supposition of a deciding role of minority charge carriers in the emergence of superconductivity state has been made.

A Magnetoresistive Tactile Sensor for Harsh Environment Applications

KAUST Repository

Alfadhel, Ahmed; Khan, Mohammed Zahed Mustafa; Cardoso, Susana; Leitao, Diana; Kosel, Jü rgen

2016-01-01

A magnetoresistive tactile sensor is reported, which is capable of working in high temperatures up to 140 °C. Hair-like bioinspired structures, known as cilia, made out of permanent magnetic nanocomposite material on top of spin-valve giant magnetoresistive (GMR) sensors are used for tactile sensing at high temperatures. The magnetic nanocomposite, consisting of iron nanowires incorporated into the polymer polydimethylsiloxane (PDMS), is very flexible, biocompatible, has high remanence, and is also resilient to antagonistic sensing ambient. When the cilia come in contact with a surface, they deflect in compliance with the surface topology. This yields a change of the GMR sensor signal, enabling the detection of extremely fine features. The spin-valve is covered with a passivation layer, which enables adequate performance in spite of harsh environmental conditions, as demonstrated in this paper for high temperature.

A Magnetoresistive Tactile Sensor for Harsh Environment Applications

KAUST Repository

Alfadhel, Ahmed

2016-05-07

A magnetoresistive tactile sensor is reported, which is capable of working in high temperatures up to 140 °C. Hair-like bioinspired structures, known as cilia, made out of permanent magnetic nanocomposite material on top of spin-valve giant magnetoresistive (GMR) sensors are used for tactile sensing at high temperatures. The magnetic nanocomposite, consisting of iron nanowires incorporated into the polymer polydimethylsiloxane (PDMS), is very flexible, biocompatible, has high remanence, and is also resilient to antagonistic sensing ambient. When the cilia come in contact with a surface, they deflect in compliance with the surface topology. This yields a change of the GMR sensor signal, enabling the detection of extremely fine features. The spin-valve is covered with a passivation layer, which enables adequate performance in spite of harsh environmental conditions, as demonstrated in this paper for high temperature.

A Magnetoresistive Tactile Sensor for Harsh Environment Applications

Directory of Open Access Journals (Sweden)

Ahmed Alfadhel

2016-05-01

Full Text Available A magnetoresistive tactile sensor is reported, which is capable of working in high temperatures up to 140 °C. Hair-like bioinspired structures, known as cilia, made out of permanent magnetic nanocomposite material on top of spin-valve giant magnetoresistive (GMR sensors are used for tactile sensing at high temperatures. The magnetic nanocomposite, consisting of iron nanowires incorporated into the polymer polydimethylsiloxane (PDMS, is very flexible, biocompatible, has high remanence, and is also resilient to antagonistic sensing ambient. When the cilia come in contact with a surface, they deflect in compliance with the surface topology. This yields a change of the GMR sensor signal, enabling the detection of extremely fine features. The spin-valve is covered with a passivation layer, which enables adequate performance in spite of harsh environmental conditions, as demonstrated in this paper for high temperature.

Extraordinary magnetoresistance in semiconductor/metal hybrids: A review

KAUST Repository

Sun, J.; Kosel, Jü rgen

2013-01-01

The Extraordinary Magnetoresistance (EMR) effect is a change in the resistance of a device upon the application of a magnetic field in hybrid structures, consisting of a semiconductor and a metal. The underlying principle of this phenomenon is a

Temperature dependence of magnetoresistance in neutron-irradiated and unirradiated high resistivity p-type silicon

International Nuclear Information System (INIS)

Yildirim, M.; Efeoglu, H.; Abay, B.; Yogurtcu, Y.K.

1996-01-01

The temperature dependence of the transverse magnetoresistance in irradiated and unirradiated p-type Si is studied in the range from 120 to 290 K. The magnetoresistance coefficients for the unirradiated left angle 001 right angle and left angle 1 anti 10 right angle samples increases with decreasing sample temperature in the range from 160 to 290 K, however, this behavior is reversed below 160 K. It is proposed that this reversal is due to the double injection effect. The magnetoresistance coefficient for the irradiated left angle 001 right angle sample increases with decreasing sample temperature in the range of 120 to 290 K and is greater than that for the unirradiated left angle 001 right angle sample. This result can be explained by increased scattering due to the increased number of defects produced by irradiation. On the other hand, the magnetoresistance coefficient for the unirradiated left angle 1 anti 10 right angle sample is found to be greater than that of the unirradiated left angle 001 right angle sample. (orig.)

Negative magnetoresistance without well-defined chirality in the Weyl semimetal TaP.

Science.gov (United States)

Arnold, Frank; Shekhar, Chandra; Wu, Shu-Chun; Sun, Yan; Dos Reis, Ricardo Donizeth; Kumar, Nitesh; Naumann, Marcel; Ajeesh, Mukkattu O; Schmidt, Marcus; Grushin, Adolfo G; Bardarson, Jens H; Baenitz, Michael; Sokolov, Dmitry; Borrmann, Horst; Nicklas, Michael; Felser, Claudia; Hassinger, Elena; Yan, Binghai

2016-05-17

Weyl semimetals (WSMs) are topological quantum states wherein the electronic bands disperse linearly around pairs of nodes with fixed chirality, the Weyl points. In WSMs, nonorthogonal electric and magnetic fields induce an exotic phenomenon known as the chiral anomaly, resulting in an unconventional negative longitudinal magnetoresistance, the chiral-magnetic effect. However, it remains an open question to which extent this effect survives when chirality is not well-defined. Here, we establish the detailed Fermi-surface topology of the recently identified WSM TaP via combined angle-resolved quantum-oscillation spectra and band-structure calculations. The Fermi surface forms banana-shaped electron and hole pockets surrounding pairs of Weyl points. Although this means that chirality is ill-defined in TaP, we observe a large negative longitudinal magnetoresistance. We show that the magnetoresistance can be affected by a magnetic field-induced inhomogeneous current distribution inside the sample.

Linear magnetoresistance and surface to bulk coupling in topological insulator thin films.

Science.gov (United States)

Singh, Sourabh; Gopal, R K; Sarkar, Jit; Pandey, Atul; Patel, Bhavesh G; Mitra, Chiranjib

2017-12-20

We explore the temperature dependent magnetoresistance of bulk insulating topological insulator thin films. Thin films of Bi 2 Se 2 Te and BiSbTeSe 1.6 were grown using the pulsed laser deposition technique and subjected to transport measurements. Magnetotransport measurements indicate a non-saturating linear magnetoresistance (LMR) behavior at high magnetic field values. We present a careful analysis to explain the origin of LMR taking into consideration all the existing models of LMR. Here we consider that the bulk insulating states and the metallic surface states constitute two parallel conduction channels. Invoking this, we were able to explain linear magnetoresistance behavior as a competition between these parallel channels. We observe that the cross-over field, where LMR sets in, decreases with increasing temperature. We propose that this cross-over field can be used phenomenologically to estimate the strength of surface to bulk coupling.

Superconducting spin-triplet-MRAM with infinite magnetoresistance ratio

Energy Technology Data Exchange (ETDEWEB)

Lenk, Daniel; Ullrich, Aladin; Obermeier, Guenter; Mueller, Claus; Krug von Nidda, Hans-Albrecht; Horn, Siegfried; Tidecks, Reinhard [Institut fuer Physik, Universitaet Augsburg, D-86159 Augsburg (Germany); Morari, Roman [Institut fuer Physik, Universitaet Augsburg, D-86159 Augsburg (Germany); D. Ghitsu Institute of Electronic Engineering and Nanotechnologies ASM, Academiei Str. 3/3, MD2028 Kishinev (Moldova, Republic of); Solid State Physics Department, Kazan Federal University, 420008 Kazan (Russian Federation); Zdravkov, Vladimir I. [Institut fuer Physik, Universitaet Augsburg, D-86159 Augsburg (Germany); D. Ghitsu Institute of Electronic Engineering and Nanotechnologies ASM, Academiei Str. 3/3, MD2028 Kishinev (Moldova, Republic of); Institute of Applied Physics and Interdisciplinary Nanoscience Center, Universitaet Hamburg, Jungiusstrasse 9A, D-20355 Hamburg (Germany); Sidorenko, Anatoli S. [D. Ghitsu Institute of Electronic Engineering and Nanotechnologies ASM, Academiei Str. 3/3, MD2028 Kishinev (Moldova, Republic of); Tagirov, Lenar R. [Institut fuer Physik, Universitaet Augsburg, D-86159 Augsburg (Germany); Solid State Physics Department, Kazan Federal University, 420008 Kazan (Russian Federation)

2016-07-01

We fabricated a nanolayered hybrid superconductor-ferromagnet spin-valve structure, i.e. the superconducting transition temperature of this structure depends on its magnetic history. The observed spin-valve effect is based on the generation of the long range odd in frequency triplet component, arising from a non-collinear relative orientation of the constituent ferromagnetic layers. We investigated the effect both as a function of the sweep amplitude of the magnetic field, determining the magnetic history, and the applied transport current. Moreover, we demonstrate the possibility of switching the system from the normal o the superconducting state by applying field pulses, yielding an infinite magnetoresistance ratio.

Power law field dependence of the 2D magnetoresistance in (TMTSF)2PF6

International Nuclear Information System (INIS)

Kriza, G.; Szeghy, G.; Kezsmarki, I.; Mihaly, G.

1999-01-01

The magnetoresistance of the quasi-one-dimensional organic conductor (TMTSF) 2 PF 6 is studied for currents flowing parallel to the best conducting a and second best conducting b directions in magnetic fields perpendicular to the a-b plane under a hydrostatic pressure of 0.8 GPa. As a function of the magnetic field, the magnetoresistance follows a power law ΔR/R = (B/B 0 ) 3/2 both in the a and b directions. The a-b plane conductivity anisotropy is field independent. The scaling field B 0 , characterizing the strength of the magnetoresistance, follows an exponential temperature dependence B 0 ∝exp(T/T 0 ) with a field-independent characteristic temperature T 0 = 10 K. (orig.)

Magnetoresistance in organic semiconductors: Including pair correlations in the kinetic equations for hopping transport

Science.gov (United States)

Shumilin, A. V.; Kabanov, V. V.; Dediu, V. I.

2018-03-01

We derive kinetic equations for polaron hopping in organic materials that explicitly take into account the double occupation possibility and pair intersite correlations. The equations include simplified phenomenological spin dynamics and provide a self-consistent framework for the description of the bipolaron mechanism of the organic magnetoresistance. At low applied voltages, the equations can be reduced to those for an effective resistor network that generalizes the Miller-Abrahams network and includes the effect of spin relaxation on the system resistivity. Our theory discloses the close relationship between the organic magnetoresistance and the intersite correlations. Moreover, in the absence of correlations, as in an ordered system with zero Hubbard energy, the magnetoresistance vanishes.

Resistive switching and voltage induced modulation of tunneling magnetoresistance in nanosized perpendicular organic spin valves

Directory of Open Access Journals (Sweden)

Robert Göckeritz

2016-04-01

Full Text Available Nanoscale multifunctional perpendicular organic spin valves have been fabricated. The devices based on an La0.7Sr0.3MnO3/Alq3/Co trilayer show resistive switching of up to 4-5 orders of magnitude and magnetoresistance as high as -70% the latter even changing sign when voltage pulses are applied. This combination of phenomena is typically observed in multiferroic tunnel junctions where it is attributed to magnetoelectric coupling between a ferromagnet and a ferroelectric material. Modeling indicates that here the switching originates from a modification of the La0.7Sr0.3MnO3 surface. This modification influences the tunneling of charge carriers and thus both the electrical resistance and the tunneling magnetoresistance which occurs at pinholes in the organic layer.

Effects of disorder on the out-of-plane magnetoresistance in the high-Tc BISCCO compound

International Nuclear Information System (INIS)

Khalil, A.E.

1997-01-01

An explanation is proposed to account for the observed anisotropic out-of-plane magnetoresistivity of the single crystal high temperature superconductor BISCCO compound. The explanation is based on a dynamic scaling model for conductivity fluctuations in the superconducting matrix. In this model, it is assumed that the c-axis conduction in an applied field parallel to the c-direction occurs through defect-mediated interplanar ''weak links'' which behave as an array of parallel, independently fluctuating, superconducting channels. The model also takes into account the possibility of thermally induced dimensional crossover above which the superconducting layers are effectively decoupled and behave as a quasi two-dimensional system. The predictions of the model are consistent with the magnetoresistance measurements reported for two separate experiments on Bi 2 Sr 2 CaCu 2 O 8 single crystals. (orig.)

Magnetoresistance of films and strips with the diffuse surface scattering

International Nuclear Information System (INIS)

Aronov, A.G.

1993-08-01

Magnetoresistance of films in a parallel magnetic field and strips in a perpendicular field is considered. The temperature and magnetic field dependencies of magnetoconductance depend on the time evolution of the correlator of phases. This correlator has different behavior as the function of time: the ergodic behavior at small magnetic fields is changed on the nonergodic one at large magnetic fields in spite of the diffusion electron motion due to a diffuse scattering on boundaries. This leads to unusual temperature and magnetic field dependencies of magnetoresistance. The ergodic hypothesis is not applicable to mesoscopical fluctuations at such a large quasiclassical field. (author). 6 refs, 5 figs

Magnetoresistance measurements of different geometries on epitaxial InP and GaInAs/InP layers

Energy Technology Data Exchange (ETDEWEB)

Somogyi, K. [Hungarian Academy of Sciences, Budapest (Hungary). Research Inst. for Technical Physics

1996-12-31

Hall effect measurement is the main method of the determination of the charge carrier mobility in semiconductors. Magnetoresistance measurements are much less used for the same purpose, perhaps because of the influence of the sample geometry or of the scattering factor differing from the Hall factor. On the other hand, in the case of the epitaxial layers, all these measurements require semi-insulating substrate. In this work two aspects of the magnetoresistance measurements and use of them is demonstrated. First classical geometrical magnetoresistance measurements on InP are studied. On the other hand, a method is presented and applied to sandwich structures in order to measure the geometrical magnetoresistance on epitaxial layers grown on conducting substrates. Resistance of structures metal-epitaxial layer-substrate-metal is measured in the dependence on the angle between the current and magnetic field vectors.

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

Terahertz–infrared electrodynamics of overdoped manganites La.sub.1-x./sub.Ca.sub.x./sub.MnO.sub.3./sub

Czech Academy of Sciences Publication Activity Database

Kadyrov, L.S.; Gorshunov, B.P.; Zhukova, E.S.; Torgashev, V. I.; Prokhorov, A. S.; Motovilova, E.A.; Fischgrabe, F.; Moshnyaga, V.T.; Zhang, T.; Kremer, R. K.; Pracht, U.; Zapf, S.; Pokorný, Jan; Untereiner, G.; Kamba, Stanislav; Dressel, M.

2014-01-01

Roč. 87, 10-11 (2014), s. 1050-1059 ISSN 0141-1594 Institutional support: RVO:68378271 Keywords : manganites * terahertz Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.954, year: 2014

Tuning the magnetocaloric properties of La0.7Ca0.3MnO3 manganites through Ni-doping

Science.gov (United States)

Gómez, A.; Chavarriaga, E.; Supelano, I.; Parra, C. A.; Morán, O.

2018-04-01

The effect of Ni2+ doping on the magnetic and magnetocaloric properties of La0.7Ca0.3MnO3 manganites synthesized via the auto-combustion method is reported. The aim of studying Ni2+-substituted La0.7Ca0.3Mn1 - xNixO3 (x = 0 , 0.02 , 0.07, and 0.1) manganites was to explore the possibility of increasing the operating temperature range for the magnetocaloric effect through tuning of the magnetic transition temperature. X-ray diffraction analysis confirmed the phase purity of the synthesized samples. The substitution of Mn3+ ions by Ni2+ ions in the La0.7Ca0.3MnO3 lattice was also corroborated through this technique. The dependence of the magnetization on the temperature reveals that all the compositions exhibit a well-defined ferromagnetic to paramagnetic transition near the Curie temperature. A systematic decrease in the values of the Curie temperature is clearly observed upon Ni2+ doping. Probably the replacement of Mn3+ by Ni2+ ions in the La0.7Ca0.3MnO3 lattice weakens the Mn3+-O-Mn4+ double exchange interaction, which leads to a decrease in the transition temperature and the magnetic moment in the samples. By using Arrott plots, it was found that the phase transition from ferromagnetic to paramagnetic is second order. The maximum magnetic entropy changes observed for the x = 0 , 0.02 , 0.07, and 0.1 composites was 0.85, 0.77, 0.63, and 0.59 J/kg K, respectively, under a magnetic field of 1.5 T. In general, it was verified that the magnetic entropy change achieved for La0.7Ca0.3Mn1 - xNixO3 manganites synthesized via the auto-combustion method is higher than those reported for other manganites with comparable Ni2+-doping levels synthesized via standard solid state reaction. The addition of Ni2+ increases the value of the relative cooling power as compared to that of the parent compound. The highest value of this parameter (∼60 J/kg) is found for a Ni-doping level of 2% around 230 K in a field of 1.5 T.

Wheatstone bridge-giant magnetoresistance (GMR) sensors based on Co/Cu multilayers for bio-detection applications

Science.gov (United States)

Antarnusa, G.; Elda Swastika, P.; Suharyadi, E.

2018-04-01

A Wheatstone bridge-giant magnetoresistance (GMR) sensor was successfully developed for a potential biomaterial detection. In order to achieve this, a giant magnetoresistive [Co(1.5nm/Cu(1.0nm)]20 multilayer structures have been fabricated by DC magnetron sputtering method, showing a magnetoresistance (MR) of 2.7%. The X-Ray diffraction (XRD) patterns showed that Co/Cu film multilayer has a high degree of crystallinity with a single peak corresponding to face-centered cubic (111) structure at 2θ = 44.1°. Co/Cu multilayers exhibit a soft magnetic behavior with the saturation magnetization (Ms) of 1489 emu/cc and the coercivity (Hc) of 11.2 Oe. The magnetite Fe3O4 nanoparticles used as a bimolecular labels (nanotags) were synthesized via co-precipitation method, exhibiting a soft magnetic behavior with Ms of 77.16 emu/g and Hc of 49 Oe. XRD patterns and transmission electron microscopy (TEM) images showed that Fe3O4 was well crystallized and it grew in their inverse spinel structure with an average size of around 10 nm. The GMR sensor design was used to detect a biomolecules of streptavidin magnetic particles with concentration 10, 20, 30, and 40 μl/ml and α-amylase enzyme with consentration 10, 20, 30, and 40 μl/ml captured using polyethylene glycol (PEG)/Fe3O4 nanoparticles. Various applied magnetic fields of 0-650 Gauss have been performed using electromagnetic with the various currents of 0-5 A. Here, the final value of the output voltage signals for the streptavidin magnetic particles concentration is 1.2 mV (10 μl/ml). The output voltage changes with the increase of concentration. It was reported that the output voltage signal of the Wheatstone bridge exhibits log-linear function in real time measurement of the concentration of streptavidin magnetic particles and α-amylase enzyme respectively, making the sensor suitable for use as a biomolecule concentration detector. Thus, the combination of Co/Cu multilayer, Wheatstone bridge, magnetite and PEG polymer

The effect of MgO doping on the structure, magnetic and magnetotransport properties of La0.8Sr0.2MnO3 composite

International Nuclear Information System (INIS)

Aezami, A.; Eshraghi, M.; Kameli, P.; Salamati, H.

2007-01-01

Full text: The recent observation of anomalously Colossal Magnetoresistance (CMR) in the La 1-x A x MnO 3 (A = Sr, Ca, Ba or vacancies) system, has spurred renewed interest in studying these doped perovskite manganites. The properties of these materials are explained by double exchange theory of Zener and electron lattice interaction. However, the intrinsic CMR effect in the perovskite manganites is found on a magnetic field scale of several teslas and a narrow temperature range. It was found that, the presence of grain boundaries in polycrystalline samples leads to a large Low Field Magnetoresistance (LFMR) effect over a wide temperature range below the Curie temperature Tc. To achieve LFMR, different properties are considered. One of them is mixing of these CMR materials with secondary insulator phases. In this work, La 0.8 Sr 0.2 MnO 3 (LSMO) was selected as matrix material and MgO as a dopant. The La 0.8 Sr 0.2 MnO 3/x MgO samples with x= 0, 1, 2, 3, 5 and 7.5 Wt.% were prepared by Solid State Reaction method. Studies show that most part of the MgO goes into the perovskite lattice and Mg substituted Mn in LSMO and remainder segregates as a separate phase at the grain boundaries. Results also show that the value of MR decreases for all the doping levels. It seems that, due to the almost same ionic radii of Mg2+ and Mn2+, and at the higher sintering temperature, Mg2+ mostly replaced Mn3+ and weakens double exchange interaction. This speculation has been confirmed by XRD, SEM, susceptibility, resistivity and magnetoresistance analysis and measurements. (authors)

Surface spin glass and exchange bias effect in Sm0.5Ca0.5MnO3 manganites nano particles

Directory of Open Access Journals (Sweden)

S. K. Giri

2011-09-01

Full Text Available In this letter, we report that the charge/orbital order state of bulk antiferromagnetic Sm0.5Ca0.5MnO3 is suppressed and confirms the appearance of weak ferromagnetism below 65 K followed by a low temperature spin glass like transition at 41 K in its nano metric counterpart. Exchange anisotropy effect has been observed in the nano manganites and can be tuned by the strength of the cooling magnetic field (Hcool. The values of exchange fields (HE, coercivity (HC, remanence asymmetry (ME and magnetic coercivity (MC are found to strongly depend on cooling magnetic field and temperature. HE increases with increasing Hcool but for larger Hcool, HE tends to decrease due to the growth of ferromagnetic cluster size. Magnetic training effect has also been observed and it has been analyzed thoroughly using spin relaxation model. A proposed phenomenological core-shell type model is attributed to an exchange coupling between the spin-glass like shell (surrounding and antiferromagnetic core of Sm0.5Ca0.5MnO3 nano manganites mainly on the basis of uncompensated surface spins. Results suggest that the intrinsic phase inhomogeneity due to the surface effects of the nanostructured manganites may cause exchange anisotropy, which is of special interests for potential application in multifunctional spintronic devices.

Large magnetization and frustration switching of magnetoresistance in the double-perovskite ferrimagnet Mn2FeReO6.

Science.gov (United States)

Arévalo-López, Angel M; McNally, Graham M; Attfield, J Paul

2015-10-05

Ferrimagnetic A2 BB'O6 double perovskites, such as Sr2 FeMoO6 , are important spin-polarized conductors. Introducing transition metals at the A-sites offers new possibilities to increase magnetization and tune magnetoresistance. Herein we report a ferrimagnetic double perovskite, Mn2 FeReO6 , synthesized at high pressure which has a high Curie temperature of 520 K and magnetizations of up to 5.0 μB which greatly exceed those for other double perovskite ferrimagnets. A novel switching transition is discovered at 75 K where magnetoresistance changes from conventional negative tunneling behavior to large positive values, up to 265 % at 7 T and 20 K. Neutron diffraction shows that the switch is driven by magnetic frustration from antiferromagnetic Mn(2+) spin ordering which cants Fe(3+) and Re(5+) spins and reduces spin-polarization. Ferrimagnetic double perovskites based on A-site Mn(2+) thus offer new opportunities to enhance magnetization and control magnetoresistance in spintronic materials. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Tunnelling anisotropic magnetoresistance due to antiferromagnetic CoO tunnel barriers

Science.gov (United States)

Wang, K.; Sanderink, J. G. M.; Bolhuis, T.; van der Wiel, W. G.; de Jong, M. P.

2015-01-01

A new approach in spintronics is based on spin-polarized charge transport phenomena governed by antiferromagnetic (AFM) materials. Recent studies have demonstrated the feasibility of this approach for AFM metals and semiconductors. We report tunneling anisotropic magnetoresistance (TAMR) due to the rotation of antiferromagnetic moments of an insulating CoO layer, incorporated into a tunnel junction consisting of sapphire(substrate)/fcc-Co/CoO/AlOx/Al. The ferromagnetic Co layer is exchange coupled to the AFM CoO layer and drives rotation of the AFM moments in an external magnetic field. The results may help pave the way towards the development of spintronic devices based on AFM insulators. PMID:26486931

Magnon Broadening Effects in Double Layered Manganite La_1.2 Sr_1.8 Mn_2 O_7

OpenAIRE

Furukawa, Nobuo; Hirota, Kazuma

1999-01-01

Magnon linewidth of La_1.2 Sr_1.8 Mn_2 O_7 near the Brillouin zone boundary is investigated from both theoretical and experimental points of view. Abrupt magnon broadening is ascribed to a strong magnon-phonon coupling. Magnon broadening observed in cubic perovskite manganites is also discussed.

Progress towards vertical transport study of proton-irradiated InAs/GaSb type-II strained-layer superlattice materials for space-based infrared detectors using magnetoresistance measurements

Science.gov (United States)

Malone, Mitchell C.; Morath, Christian P.; Fahey, Stephen; Klein, Brianna; Cowan, Vincent M.; Krishna, Sanjay

2015-09-01

InAs/GaSb type-II strained-layer superlattice (T2SLS) materials are being considered for space-based infrared detector applications. However, an inadequate understanding of the role of carrier transport, specifically the vertical mobility, in the radiation tolerance of T2SLS detectors remains. Here, progress towards a vertical transport study of proton-irradiated, p-type InAs/GaSb T2SLS materials using magnetoresistance measurements is reported. Measurements in the growth direction of square mesas formed from InAs/GaSb superlattice material were performed using two distinct contact geometries in a Kelvin mode setup at variable magnetic fields, ranging from -9 T to 9 T, and temperatures, ranging from 5 K and 300 K. The results here suggested multi-carrier conduction and a field-dependent series resistance from the contact layer were present. The implications of these results and the plans for future magnetoresistance measurements on proton-irradiated T2SLS materials are discussed.

Antisite disorder-induced low-field magnetoresistance in some frustrated Sr2FeMoO6

International Nuclear Information System (INIS)

Cai Tianyi; Ju Sheng; Li Zhenya

2006-01-01

Considering the existence of antiferromagnetic patches induced by the antisite disorder in ferrimagnetic Sr 2 FeMoO 6 , we have developed a resistor network model to account for the effects of the antisite disorder on the magnetoresistance in this material. It is proposed that the magnetic disorder resulting from the existence of frustration around the antiferromagnetic patches will be suppressed under the applied magnetic field and low-field magnetoresistance will be observed. For samples with low levels of antisite defects, the magnetoresistive behaviour may be strongly affected by the different degrees of magnetic inhomogeneity. Our calculated results are in agreement with experimental observations

Angular Magnetoresistance and Hall Measurements in New Dirac Material, ZrSiS

Science.gov (United States)

Ali, Mazhar; Schoop, Leslie; Lotsch, Bettina; Parkin, Stuart

Dirac and Weyl materials have shot to the forefront of condensed matter research in the last few years. Recently, the square-net material, ZrSiS, was theorized and experimentally shown (via ARPES) to host several highly dispersive Dirac cones, including the first Dirac cone demanded by non-symmorphic symmetry in a Si square net. Here we report the magnetoresistance and Hall Effect measurements in this compound. ZrSiS samples with RRR = 40 were found to have MR values up to 6000% at 2 K, be predominantly p-type with a carrier concentration of ~8 x 1019 cm-3 and mobility ~8500 cm2/Vs. Angular magnetoresistance measurements reveal a peculiar behavior with multiple local maxima, depending on field strength, indicating of a sensitive and sensitive Fermi surface. SdH oscillations analysis confirms Hall and angular magnetoresistance measurements. These results, in the context of the theoretical and ARPES results, will be discussed.

Mobility controlled linear magnetoresistance with 3D anisotropy in a layered graphene pallet

KAUST Repository

Zhang, Qiang

2016-09-27

A bulk sample of pressed graphene sheets was prepared under hydraulic pressure (similar to 150 MPa). The cross-section of the sample demonstrates a layered structure, which leads to 3D electrical transport properties with anisotropic mobility. The electrical transport properties of the sample were measured over a wide temperature (2-400 K) and magnetic field (-140 kOe <= H <= 140 kOe) range. The magnetoresistance measured at a fixed temperature can be described by R(H, theta) = R(epsilon H-theta, 0) with epsilon(theta) =(cos(2)theta + gamma(-2) sin(2)theta)(1/2), where gamma is the mobility anisotropy constant and theta is the angle between the normal of the sample plane and the magnetic field. The large linear magnetoresistance (up to 36.9% at 400 K and 140 kOe) observed at high fields is ascribed to a classical magnetoresistance caused by mobility fluctuation (Delta mu). The magnetoresistance value at 140 kOe was related to the average mobility () because of the condition Delta mu < . The carrier concentration remained constant and the temperature-dependent resistivity was proportional to the average mobility, as verified by Kohler\\'s rule. Anisotropic dephasing length was deduced from weak localization observed at low temperatures.

Magnetic detection of mercuric ion using giant magnetoresistance-based biosensing system.

Science.gov (United States)

Wang, Wei; Wang, Yi; Tu, Liang; Klein, Todd; Feng, Yinglong; Li, Qin; Wang, Jian-Ping

2014-04-15

We have demonstrated a novel sensing strategy employing a giant magnetoresistance (GMR) biosensor and DNA chemistry for the detection of mercuric ion (Hg(2+)). This assay takes advantages of high sensitivity and real-time signal readout of GMR biosensor and high selectivity of thymine-thymine (T-T) pair for Hg(2+). The assay has a detection limit of 10 nM in both buffer and natural water, which is the maximum mercury level in drinking water regulated by U.S. Environmental Protection Agency (EPA). The magnitude of the dynamic range for Hg(2+) detection is up to three orders (10 nM to 10 μM). Herein, GMR sensing technology is first introduced into a pollutant monitoring area. It can be foreseen that the GMR biosensor could become a robust contender in the areas of environmental monitoring and food safety testing.

Anomalous Hall effect and magnetoresistance behavior in Co/Pd1−xAgx multilayers

KAUST Repository

Guo, Z. B.

2013-02-13

In this paper, we report anomalous Hall effect (AHE) correlated with the magnetoresistance behavior in [Co/Pd1-xAg x]n multilayers. For the multilayers with n = 6, the increase in Ag content from x = 0 to 0.52 induces the change in AHE sign from negative surface scattering-dominated AHE to positive interface scattering-dominated AHE, which is accompanied with the transition from anisotropy magnetoresistance (AMR) dominated transport to giant magnetoresistance (GMR) dominated transport. For n = 80, scaling analysis with Rs ∝ρ xx γ yields γ ∼ 3.44 for x = 0.52 which presents GMR-type transport, in contrast to γ ∼ 5.7 for x = 0 which presents AMR-type transport. © 2013 American Institute of Physics.

Electric field-induced magnetoresistance in spin-valve/piezoelectric multiferroic laminates for low-power spintronics

International Nuclear Information System (INIS)

Huong Giang, D.T.; Thuc, V.N.; Duc, N.H.

2012-01-01

Electric field-induced magnetic anisotropy has been realized in the spin-valve-based {Ni 80 Fe 20 /Cu/Fe 50 Co 50 /IrMn}/piezoelectric multiferroic laminates. In this system, electric-field control of magnetization is accomplished by strain mediated magnetoelectric coupling. Practically, the magnetization in the magnetostrictive FeCo layer of the spin-valve structure rotates under an effective compressive stress caused by the inverse piezoelectric effect in external electrical fields. This phenomenon is evidenced by the magnetization and magnetoresistance changes under the electrical field applied across the piezoelectric layer. The result shows great potential for advanced low-power spintronic devices. - Highlights: ► Investigate electric field-induced magnetic anisotropy in spin-valve/piezoelectric. ► Magnetization, magnetoresistance changes under electric field across piezoelectric. ► Magnetization in magnetostrictive FeCo-layer rotates under a compressive stress. ► This advance shows great implications for low-power electronics and spintronics.

Apparent negative magnetoresistance without independent Weyl pockets in the Weyl semimetal TaP

Energy Technology Data Exchange (ETDEWEB)

Hassinger, Elena; Arnold, Frank; Naumann, Marcel; Wu, Shu-Chun; Sun, Yan; Donizeth dos Reis, Ricardo; Ajeesh, Mukkattu O.; Shekhar, Chandra; Kumar, Nitesh; Schmidt, Marcus; Baenitz, Michael; Borrmann, Horst; Nicklas, Michael; Felser, Claudia [Max Planck Institute for Chemical Physics of Solids, Dresden (Germany); Grushin, Adolfo; Bardarson, Jens [Max Planck Institute for Physics of Complex Systems, Dresden (Germany); Yan, Binghai [Max Planck Institute for Chemical Physics of Solids, Dresden (Germany); Max Planck Institute for Physics of Complex Systems, Dresden (Germany)

2016-07-01

In the recently discovered Weyl semimetals, an unconventional negative longitudinal magnetoresistance is expected due to a phenomenon called chiral anomaly. An open question is, how close the Fermi energy needs to be to the Weyl nodes, in order to detect this phenomenon. This question can only be addressed by knowing the electronic bandstructure, i.e. the position of the Fermi energy, and the intrinsic longitudinal magnetoresistance precisely. Here, we report the detailed Fermi surface topology of the Weyl semimetal TaP determined via angle-resolved quantum oscillation spectra combined with band-structure calculations. The Fermi surface consists of an electron and a hole banana without independent pockets around the Weyl points. Although the absence of independent Fermi surface pockets around the Weyl points means that no chiral anomaly is expected, we detect a negative longitudinal magnetoresistance. We discuss possible origins.

Piecewise parabolic negative magnetoresistance of two-dimensional electron gas with triangular antidot lattice

International Nuclear Information System (INIS)

Budantsev, M. V.; Lavrov, R. A.; Pogosov, A. G.; Zhdanov, E. Yu.; Pokhabov, D. A.

2011-01-01

Extraordinary piecewise parabolic behavior of the magnetoresistance has been experimentally detected in the two-dimensional electron gas with a dense triangular lattice of antidots, where commensurability magnetoresistance oscillations are suppressed. The magnetic field range of 0–0.6 T can be divided into three wide regions, in each of which the magnetoresistance is described by parabolic dependences with high accuracy (comparable to the experimental accuracy) and the transition regions between adjacent regions are much narrower than the regions themselves. In the region corresponding to the weakest magnetic fields, the parabolic behavior becomes almost linear. The observed behavior is reproducible as the electron gas density changes, which results in a change in the resistance by more than an order of magnitude. Possible physical mechanisms responsible for the observed behavior, including so-called “memory effects,” are discussed.

Giant magnetoresistance in melt spun Cu85Co10Ni5

DEFF Research Database (Denmark)

Curiotto, Stefano; Johnson, Erik; Celegato, Federica

2009-01-01

CuCoNi rapidly solidified alloys are interesting because they display giant magnetoresistance (GMR). In the present work a Cu85Co10Ni5 alloy has been synthesized by melt spinning and analysed for GMR. The ribbons obtained have been annealed at different temperatures and the evolution of the crystal...... structure with annealing has been studied by X-ray diffraction. The. ne microstructure has been observed by TEM and related to the magnetic properties, investigated in a vibrating sample magnetometer. In the studied composition the magnetoresistance was found to be lower than in binary CuCo alloys without...

Giant negative magnetoresistance in Ni(quinoline-8-selenoate)2.

Science.gov (United States)

Black, Nicholas; Daiki, Tonouchi; Matsushita, Michio M; Woollins, J Derek; Awaga, Kunio; Robertson, Neil

2017-12-20

The magnetic, structural, conductivity and magnetoresistance properties of [Ni(quinoline-8-selenoate) 2 ] ([Ni(qs) 2 ]) have been studied. Despite the insolubility of the material necessitating its study as a powdered sample, a remarkably high conductivity has been measured. The conductivity is an order of magnitude greater than the thin-film processable thiol analogue previously reported and has been interpreted through the same space-charge limited conduction mechanism with charges injected from the electrodes. The introduction of selenium, results in a material with conductivity approaching metallic due to the enhanced interaction between adjacent molecules. Additionally, under an applied magnetic field, the material displays a negative magnetoresistance effect above 35% at 2 K. The effect can still be observed at 200 K and is interpreted in terms of a double-exchange mechanism.

Magnetoresistive biosensors for quantitative proteomics

Science.gov (United States)

Zhou, Xiahan; Huang, Chih-Cheng; Hall, Drew A.

2017-08-01

Quantitative proteomics, as a developing method for study of proteins and identification of diseases, reveals more comprehensive and accurate information of an organism than traditional genomics. A variety of platforms, such as mass spectrometry, optical sensors, electrochemical sensors, magnetic sensors, etc., have been developed for detecting proteins quantitatively. The sandwich immunoassay is widely used as a labeled detection method due to its high specificity and flexibility allowing multiple different types of labels. While optical sensors use enzyme and fluorophore labels to detect proteins with high sensitivity, they often suffer from high background signal and challenges in miniaturization. Magnetic biosensors, including nuclear magnetic resonance sensors, oscillator-based sensors, Hall-effect sensors, and magnetoresistive sensors, use the specific binding events between magnetic nanoparticles (MNPs) and target proteins to measure the analyte concentration. Compared with other biosensing techniques, magnetic sensors take advantage of the intrinsic lack of magnetic signatures in biological samples to achieve high sensitivity and high specificity, and are compatible with semiconductor-based fabrication process to have low-cost and small-size for point-of-care (POC) applications. Although still in the development stage, magnetic biosensing is a promising technique for in-home testing and portable disease monitoring.

Magnetoresistance effect of heat generation in a single-molecular spin-valve

International Nuclear Information System (INIS)

Jiang, Feng; Yan, Yonghong; Wang, Shikuan; Yan, Yijing

2016-01-01

Based on non-equilibrium Green's functions' theory and small polaron transformation's technology, we study the heat generation by current through a single-molecular spin-valve. Numerical results indicate that the variation of spin polarization degree can change heat generation effectively, the spin-valve effect happens not only in electrical current but also in heat generation when Coulomb repulsion in quantum dot is smaller than phonon frequency and interestingly, when Coulomb repulsion is larger than phonon frequency, the inverse spin-valve effect appears by sweeping gate voltage and is enlarged with bias increasing. The inverse spin-valve effect will induce the unique heat magnetoresistance effect, which can be modulated from heat-resistance to heat-gain by gate voltage easily. - Highlights: • Spin-valve effect of heat generation happens when Coulomb repulsion in quantum dot is less than phonon frequency. • When Coulomb repulsion is larger than phonon frequency, inverse spin-valve effect appears and is enlarged with bias increasing. • The variation of spin polarization degree can change heat generation effectively. • The heat magnetoresistance can be modulated from heat-resistance to heat-gain by gate voltage easily.

Study of magnetoresistance and conductance of bicrystal grain ...

Indian Academy of Sciences (India)

Presence of grain boundary exhibits substantial magnetoresistance ratio (MRR) in the low field and low temperature region. Bicrystal grain boundary contribution in MRR disappears at temperature > 175 K. At low temperature, - characteristic of the microbridge across bicrystal grain boundary is nonlinear. Analysis of ...

Resistance transition assisted geometry enhanced magnetoresistance in semiconductors

International Nuclear Information System (INIS)

Luo, Zhaochu; Zhang, Xiaozhong

2015-01-01

Magnetoresistance (MR) reported in some non-magnetic semiconductors (particularly silicon) has triggered considerable interest owing to the large magnitude of the effect. Here, we showed that MR in lightly doped n-Si can be significantly enhanced by introducing two diodes and proper design of the carrier path [Wan, Nature 477, 304 (2011)]. We designed a geometrical enhanced magnetoresistance (GEMR) device whose room-temperature MR ratio reaching 30% at 0.065 T and 20 000% at 1.2 T, respectively, approaching the performance of commercial MR devices. The mechanism of this GEMR is: the diodes help to define a high resistive state (HRS) and a low resistive state (LRS) in device by their openness and closeness, respectively. The ratio of apparent resistance between HRS and LRS is determined by geometry of silicon wafer and electrodes. Magnetic field could induce a transition from LRS to HRS by reshaping potential and current distribution among silicon wafer, resulting in a giant enhancement of intrinsic MR. We expect that this GEMR could be also realized in other semiconductors. The combination of high sensitivity to low magnetic fields and large high-field response should make this device concept attractive to the magnetic field sensing industry. Moreover, because this MR device is based on a conventional silicon/semiconductor platform, it should be possible to integrate this MR device with existing silicon/semiconductor devices and so aid the development of silicon/semiconductor-based magnetoelectronics. Also combining MR devices and semiconducting devices in a single Si/semiconductor chip may lead to some novel devices with hybrid function, such as electric-magnetic-photonic properties. Our work demonstrates that the charge property of semiconductor can be used in the magnetic sensing industry, where the spin properties of magnetic materials play a role traditionally

Extremely large magnetoresistance and Kohler's rule in PdSn4 : A complete study of thermodynamic, transport, and band-structure properties

International Nuclear Information System (INIS)

Jo, Na Hyun; Wu, Yun; Wang, Lin-Lin; Orth, Peter P.; Downing, Savannah S.

2017-01-01

The recently discovered material PtSn 4 is known to exhibit extremely large magnetoresistance (XMR) that also manifests Dirac arc nodes on the surface. PdSn 4 is isostructural to PtSn 4 with the same electron count. Here, we report on the physical properties of high-quality single crystals of PdSn 4 including specific heat, temperature- and magnetic-field-dependent resistivity and magnetization, and electronic band-structure properties obtained from angle-resolved photoemission spectroscopy (ARPES). We observe that PdSn 4 has physical properties that are qualitatively similar to those of PtSn 4 , but find also pronounced differences. Importantly, the Dirac arc node surface state of PtSn 4 is gapped out for PdSn 4 . By comparing these similar compounds, we address the origin of the extremely large magnetoresistance in PdSn 4 and PtSn 4 ; based on detailed analysis of the magnetoresistivity ρ (H , T) , we conclude that neither the carrier compensation nor the Dirac arc node surface state are the primary reason for the extremely large magnetoresistance. On the other hand, we also find that, surprisingly, Kohler's rule scaling of the magnetoresistance, which describes a self-similarity of the field-induced orbital electronic motion across different length scales and is derived for a simple electronic response of metals to an applied magnetic field is obeyed over the full range of temperatures and field strengths that we explore.

Probing the ground state and zero-field cooled exchange bias by magnetoresistance measurement in Mn{sub 50}Ni{sub 41}Sn{sub 9} ribbon

Energy Technology Data Exchange (ETDEWEB)

Chen, Jiyun [Jiangsu Laboratory of Advanced Functional Materials, Department of Physics, Changshu Institute of Technology, Changshu 215500 (China); School of Materials Science and Engineering, China University of Mining & Technology, Xuzhou 221116 (China); Tu, Ruikang [Jiangsu Laboratory of Advanced Functional Materials, Department of Physics, Changshu Institute of Technology, Changshu 215500 (China); School of Materials Science and Engineering, Soochow University, Suzhou 215000 (China); Fang, Xiaoting [Jiangsu Laboratory of Advanced Functional Materials, Department of Physics, Changshu Institute of Technology, Changshu 215500 (China); Gu, Quanchao [Jiangsu Laboratory of Advanced Functional Materials, Department of Physics, Changshu Institute of Technology, Changshu 215500 (China); School of Materials Science and Engineering, Soochow University, Suzhou 215000 (China); Zhou, Yanying [Jiangsu Laboratory of Advanced Functional Materials, Department of Physics, Changshu Institute of Technology, Changshu 215500 (China); Cui, Rongjing [Department of Chemistry, Changshu Institute of Technology, Changshu 215500 (China); Han, Zhida, E-mail: han@cslg.edu.cn [Jiangsu Laboratory of Advanced Functional Materials, Department of Physics, Changshu Institute of Technology, Changshu 215500 (China); Zhang, Lei; Fang, Yong [Jiangsu Laboratory of Advanced Functional Materials, Department of Physics, Changshu Institute of Technology, Changshu 215500 (China); Qian, Bin, E-mail: njqb@cslg.edu.cn [Jiangsu Laboratory of Advanced Functional Materials, Department of Physics, Changshu Institute of Technology, Changshu 215500 (China); Zhang, Chengliang [School of Science, Jiangnan University, Wuxi 214122 (China); Jiang, Xuefan [Jiangsu Laboratory of Advanced Functional Materials, Department of Physics, Changshu Institute of Technology, Changshu 215500 (China)

2017-03-15

Recently, a new type of exchange bias (EB) after zero-field cooling has attracted considerable interest mainly in bulk magnetic competing systems. Here, we use a detailed magnetotransport investigation to probe the ground state and zero-field cooled EB (ZEB) in Mn{sub 50}Ni{sub 41}Sn{sub 9} ribbon. Both ZEB and field cooled EB were detected in magnetoresistance results consistent with magnetic measurement. A pure spin-glass ground state is proposed based on parabolic shape of low-field magnetoresistance combined with AC magnetization, memory effect. The appearance of ZEB is attributed to the field-induced nucleation and growth of ferromagnetic domains in the spin glass matrix forming unidirectional anisotropy at the interface. - Highlights: • Magnetoresistance was first used to probe the ground state and ZEB in Ni-Mn-based alloys. • A pure spin-glass ground state is proposed in Mn{sub 50}Ni{sub 41}Sn{sub 9} ribbon. • Field-induced nucleation and growth of ferromagnetic domains in SG results in ZEB.

Large intragrain magnetoresistance above room temperature in the double perovskite Ba2FeMoO6

International Nuclear Information System (INIS)

Maignan, A.; Raveau, B.; Martin, C.; Hervieu, M.

1999-01-01

Large intragrain magnetoresistance (MR) in the ordered double perovskite, Ba 2 FeMo 6 , is shown for the first time. The latter appears near T c (340 K), i.e., above room temperature. This effect originates from a double-exchange-like mechanism, based on antiferromagnetic coupling of localized high spin 3d 5 Fe 3+ , and itinerant 4d 1 Mo 5+ species. Besides this bulk MR, low field tunneling MR at lower temperatures (T 2 FeMoO 6 . Such a coexistence of both effects, intragrain and intergrain magnetoresistance, might extend to all members of this double perovskite family, suggesting the possibility of optimizing the MR for working at room temperature in a low magnetic field, by tuning the T c of solid solutions of such perovskites

Thermal transport in cuprates, cobaltates, and manganites

International Nuclear Information System (INIS)

Berggold, K.

2006-09-01

The subject of this thesis is the investigation of the thermal transport properties of three classes of transition-metal oxides: Cuprates, cobaltates, and manganites. The layered cuprates R 2 CuO 4 with R=La, Pr, Nd, Sm, Eu, and Gd show an anomalous thermal conductivity κ. Two maxima of κ are observed as a function of temperature for a heat current within the CuO 2 planes, whereas for a heat current perpendicular to the CuO 2 planes only a conventional phononic low-temperature maximum of κ is present. Evidence is provided that the high-temperature maximum is caused by heat-carrying excitations on the CuO 2 square lattice. Moreover, it is shown that the complex low-temperature and magnetic-field behavior of κ in Nd 2 CuO 4 is most likely caused by additional phonon scattering rather than by heat-carrying Nd magnons, as it was proposed in the literature. In the cobaltates RCoO 3 with R=La, Pr, Nd, and Eu, a temperature-induced spin-state transition of the Co 3+ ions occurs. It is shown that the additional lattice disorder caused by the random distribution of populated higher spin states causes a large suppression of the thermal conductivity of LaCoO 3 for T>25 K. The effect is much weaker in PrCoO 3 and NdCoO 3 due to the increased spin gap. A quantitative analysis of the responsible mechanisms based on EuCoO 3 as a reference compound is provided. A main result is that the static disorder is sufficient to explain the suppression of κ. No dynamical Jahn-Teller distortion, as proposed in the literature, is necessary to enhance the scattering strength. Below 25 K, k is mainly determined by resonant phonon scattering on paramagnetic impurity levels, e.g. caused by oxygen non-stoichiometry. Such a suppression of the thermal conductivity by resonant scattering processes is e.g. known from Holmium ethylsulfate. This effect is most pronounced in LaCoO 3 , presumably due to magnetic polaron formation. In the doped compounds La 1-x Sr x CoO 3 with 0≤x≤0.25, a large

Grain boundary structures in La2/3Ca1/3MnO3 thin films

International Nuclear Information System (INIS)

Miller, D. J.; Lin, Y.-K.; Vlasko-Vlasov, V.; Welp, U.

1999-01-01

As with many other oxide-based compounds that exhibit electronic behavior, structural defects have a strong influence on the electronic properties of the CMR manganites. In this work, the authors have studied the effect of grain boundaries on the transport properties and on the local orientation of magnetization. Thin films of the perovskite-related La 2/3 Ca 1/3 MnO 3 compound were deposited onto bicrystal substrates using pulsed laser deposition. Transport measurements showed some enhancement of magnetoresistance across the grain boundary. The structure of the boundary was evaluated by electron microscopy. In contrast with the highly meandering boundaries typically observed in bicrystals of high temperature superconductors, the boundaries in these films are relatively straight and well defined. However, magneto-optical imaging showed that the local magnetization was oriented out of the plane at the grain boundary while it was oriented within the plane in the grains on either side. This coordinated reorientation of local magnetization near the grain boundary leads to enhanced magnetoresistance across the boundary in low fields

Temperature dependence of magnetoresistance in copper single crystals

Science.gov (United States)

Bian, Q.; Niewczas, M.

2018-03-01

Transverse magnetoresistance of copper single crystals has been measured in the orientation of open-orbit from 2 K to 20 K for fields up to 9 T. The experimental Kohler's plots display deviation between individual curves below 16 K and overlap in the range of 16 K-20 K. The violation of the Kohler's rule below 16 K indicates that the magnetotransport can not be described by the classical theory of electron transport on spherical Fermi surface with a single relaxation time. A theoretical model incorporating two energy bands, spherical and cylindrical, with different relaxation times has been developed to describe the magnetoresistance data. The calculations show that the electron-phonon scattering rates at belly and neck regions of the Fermi surface have different temperature dependencies, and in general, they do not follow T3 law. The ratio of the relaxation times in belly and neck regions decreases parabolically with temperature as A - CT2 , with A and C being constants.

A novel approach for simultaneous measurements of Hall effect and magnetoresistance effect in solid and liquid state of gallium and mercury metals

International Nuclear Information System (INIS)

Ogita, M.; Nakao, M.; Singh, C.D.; Mogi, I.; Awaji, S.

2004-01-01

An AC-DC method has been proposed for simultaneous measurements of Hall effect and magnetoresistance effect in solid and liquid state of Ga and Hg metals. In low magnetic field Hall signal in solid state is proportional to magnetic field B, while in liquid state Hall signal is affected by magnetoresistance effect. It has been found that magnetoresistance has a B 2 dependence on magnetic field and affects the Hall signal. In high magnetic field, the Hall effect in liquid state is affected by a very large magnetoresistance effect compared in solid state. The magnetoresistance effect in liquid state is higher than solid state

A top-contacted extraordinary magnetoresistance sensor fabricated with an unpatterned semiconductor epilayer

KAUST Repository

Sun, Jian

2013-04-01

An extraordinary magnetoresistance device is developed from an unpatterned semiconductor epilayer onto which the metal contacts are fabricated. Compared with conventionally fabricated devices, for which semiconductor patterning and precise alignment are required, this design is not only easier from a technological point of view, but it also has the potential to reduce damage introduced to the semiconductor during fabrication. The device shows a similar magnetoresistance ratio as a conventional one but it has a lower sensitivity. Because of the reduced resistance, and hence less noise, high magnetic field resolution is maintained. © 1980-2012 IEEE.

Resonant tunnel magnetoresistance in a double magnetic tunnel junction

KAUST Repository

Useinov, Arthur; Useinov, Niazbeck Kh H; Tagirov, Lenar R.; Kosel, Jü rgen

2011-01-01

We present quasi-classical approach to calculate a spin-dependent current and tunnel magnetoresistance (TMR) in double magnetic tunnel junctions (DMTJ) FML/I/FMW/I/FMR, where the magnetization of the middle ferromagnetic metal layer FMW can

Superconducting transition and low-field magnetoresistance of a niobium single crystal at 4.2 deg. K; Transition supraconductrice et magnetoresistance en champ faible d'un echantillon monocristallin de niobium a 4.2 deg. K

Energy Technology Data Exchange (ETDEWEB)

Perriot, G. [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires. Service de physique du solide et de resonnance magnetique

1967-01-01

We report the study of the electrical resistance of a niobium single crystal, at 4.2 deg. K, from the beginning of the superconductive transition to 80 kilo oersteds. Critical fieldsH{sub c2} and H{sub c3} have been determined. Influences on superconductive transition of current density, field-current angle, crystal orientation and magnetoresistance have been studied. Variation laws of low-field transverse and longitudinal magneto-resistances have been determined. (author) [French] La variation de la resistance electrique d'un monocristal cylindrique de niobium a ete etudiee, a 4,2 deg. K, depuis le debut de la transition supraconductrice jusqu'a 80 kilooersteds. Les champs critiques H{sub c2} et H{sub c3} ont ete determines. On a etudie l'influence de la densite de courant, de l'angle champ-courant, de l'anisotropie cristalline et de la magnetoresistance sur la transition supraconductrice. Les lois de variation des magnetoresistances transversale et longitudinale ont ete determinees dans le domaine des champs faibles. (auteur)

Monte Carlo simulations of magnetic order in Fe-doped manganites

International Nuclear Information System (INIS)

Alonso, J.; Gutierrez, J.; Barandiaran, J.M.; Bermejo, F.J.; Brey, L.

2008-01-01

The effect of Fe doping on the magnetic properties of La 0.7 Pb 0.3 Mn 1-x Fe x O 3 (x=0, 0.05, 0.1, 0.15 and 0.2) manganites is studied by the Monte Carlo simulation technique. As a first approximation, by means of a simple Heisenberg Hamiltonian, experimental normalized magnetizations at low temperatures have been reproduced for concentrations of Fe (x<0.2), but the calculated order temperatures show a large deviation from the measured ones. This shortcoming can be corrected by using a one electron effective hopping semi-classical Hamiltonian, with a simplified expression for the kinetic energy of the free electrons, which also avoids time-consuming diagonalizations

Elastically strained and relaxed La0.67Ca0.33MnO3 films grown on lanthanum aluminate substrates with different orientations

Science.gov (United States)

Boikov, Yu. A.; Serenkov, I. T.; Sakharov, V. I.; Claeson, T.

2016-12-01

Structure of 40-nm thick La0.67Ca0.33MnO3 (LCMO) films grown by laser evaporation on (001) and (110) LaAlO3 (LAO) substrates has been investigated using the methods of medium-energy ion scattering and X-ray diffraction. The grown manganite layers are under lateral biaxial compressive mechanical stresses. When (110)LAO wafers are used as the substrates, stresses relax to a great extent; the relaxation is accompanied by the formation of defects in a (3-4)-nm thick manganite-film interlayer adjacent to the LCMO-(110)LAO interface. When studying the structure of the grown layers, their electro- and magnetotransport parameters have been measured. The electroresistance of the LCMO films grown on the substrates of both types reached a maximum at temperature T M of about 250 K. At temperatures close to T M magnetoresistance of the LCMO/(110)LAO films exceeds that of the LCMO/(001)LAO films by 20-30%; however, the situation is inverse at low temperatures ( T < 150 K). At T < T M , the magnetotransport in the grown manganite films significantly depends on the spin ordering in ferromagnetic domains, which increase with a decrease in temperature.

Anisotropic Magnetoresistance in Antiferromagnetic Sr_{2}IrO_{4}

Directory of Open Access Journals (Sweden)

C. Wang

2014-11-01

Full Text Available We report point-contact measurements of anisotropic magnetoresistance (AMR in a single crystal of antiferromagnetic Mott insulator Sr_{2}IrO_{4}. The point-contact technique is used here as a local probe of magnetotransport properties on the nanoscale. The measurements at liquid nitrogen temperature reveal negative magnetoresistances (up to 28% for modest magnetic fields (250 mT applied within the IrO_{2} a-b plane and electric currents flowing perpendicular to the plane. The angular dependence of magnetoresistance shows a crossover from fourfold to twofold symmetry in response to an increasing magnetic field with angular variations in resistance from 1% to 14%. We tentatively attribute the fourfold symmetry to the crystalline component of AMR and the field-induced transition to the effects of applied field on the canting of antiferromagnetic-coupled moments in Sr_{2}IrO_{4}. The observed AMR is very large compared to the crystalline AMRs in 3d transition metal alloys or oxides (0.1%–0.5% and can be associated with the large spin-orbit interactions in this 5d oxide while the transition provides evidence of correlations between electronic transport, magnetic order, and orbital states. The finding of this work opens an entirely new avenue to not only gain a new insight into physics associated with spin-orbit coupling but also to better harness the power of spintronics in a more technically favorable fashion.

Spin-filtering and giant magnetoresistance effects in polyacetylene-based molecular devices

Science.gov (United States)

Chen, Tong; Yan, Shenlang; Xu, Liang; Liu, Desheng; Li, Quan; Wang, Lingling; Long, Mengqiu

2017-07-01

Using the non-equilibrium Green's function formalism in combination with density functional theory, we performed ab initio calculations of spin-dependent electron transport in molecular devices consisting of a polyacetylene (CnHn+1) chain vertically attached to a carbon chain sandwiched between two semi-infinite zigzag-edged graphene nanoribbon electrodes. Spin-charge transport in the device could be modulated to different magnetic configurations by an external magnetic field. The results showed that single spin conduction could be obtained. Specifically, the proposed CnHn+1 devices exhibited several interesting effects, including (dual) spin filtering, spin negative differential resistance, odd-even oscillation, and magnetoresistance (MR). Marked spin polarization with a filtering efficiency of up to 100% over a large bias range was found, and the highest MR ratio for the CnHn+1 junctions reached 4.6 × 104. In addition, the physical mechanisms for these phenomena were also revealed.

Cr doping induced negative transverse magnetoresistance in C d3A s2 thin films

Science.gov (United States)

Liu, Yanwen; Tiwari, Rajarshi; Narayan, Awadhesh; Jin, Zhao; Yuan, Xiang; Zhang, Cheng; Chen, Feng; Li, Liang; Xia, Zhengcai; Sanvito, Stefano; Zhou, Peng; Xiu, Faxian

2018-02-01

The magnetoresistance of a material conveys various dynamic information about charge and spin carriers, inspiring both fundamental studies in physics and practical applications such as magnetic sensors, data storage, and spintronic devices. Magnetic impurities play a crucial role in the magnetoresistance as they induce exotic states of matter such as the quantum anomalous Hall effect in topological insulators and tunable ferromagnetic phases in dilute magnetic semiconductors. However, magnetically doped topological Dirac semimetals are hitherto lacking. Here, we report a systematic study of Cr-doped C d3A s2 thin films grown by molecular-beam epitaxy. With the Cr doping, C d3A s2 thin films exhibit unexpected negative transverse magnetoresistance and strong quantum oscillations, bearing a trivial Berry's phase and an enhanced effective mass. More importantly, with ionic gating the magnetoresistance of Cr-doped C d3A s2 thin films can be drastically tuned from negative to positive, demonstrating the strong correlation between electrons and the localized spins of the Cr impurities, which we interpret through the formation of magnetic polarons. Such a negative magnetoresistance under perpendicular magnetic field and its gate tunability have not been observed previously in the Dirac semimetal C d3A s2 . The Cr-induced topological phase transition and the formation of magnetic polarons in C d3A s2 provide insights into the magnetic interaction in Dirac semimetals as well as their potential applications in spintronics.

Comparative Study of Magnetic Ordering and Electrical Transport in Bulk and Nano-Grained Nd{sub 0.67}Sr{sub 0.33}MnO{sub 3} Manganites

Energy Technology Data Exchange (ETDEWEB)

Arun, B. [Materials Science and Technology Division, CSIR-National Institute for Interdisciplinary Science and Technology, Trivandrum (India); Academy of Scientific and Innovative Research (AcSIR), CSIR, Trivandrum (India); Suneesh, M.V. [Materials Science and Technology Division, CSIR-National Institute for Interdisciplinary Science and Technology, Trivandrum (India); Vasundhara, M., E-mail: vasu.mutta@gmail.com [Materials Science and Technology Division, CSIR-National Institute for Interdisciplinary Science and Technology, Trivandrum (India)

2016-11-15

We have prepared bulk and nano-sized Nd{sub 0.67}Sr{sub 0.33}MnO{sub 3} manganites by solid state and low-temperature mild solgel methods respectively. Both the compounds crystallized into an orthorhombic structure with Pbnm space group confirmed from Rietveld refinement of X-ray powder diffraction patterns. Nano-grained compound shows an average particle size of 22 nm with broad grain size distribution revealed from the Transmission electron micrographs. It appeared that the long range ferromagnetic order becomes unstable upon the reduction of the samples dimension down to nano meter scale. DC magnetization and AC susceptibility results showed frustration of spins in nano-grained compound and thereby it could lead to a cluster glass-like behaviour. Temperature dependence of electrical resistivity under different magnetic fields shows the broad maxima at higher temperatures and a low temperature upturn in both the compounds, however, the latter is more prominent in the nano grained compound. Combination of Kondo effect with electron and phonon interactions govern the low temperature resistivity and a small polaron hopping mechanism dominates at high temperatures for both the compounds. The magnetoresistance is understood by the effect of spin polarized tunneling through the grain boundary. The experimental results revealed that the reduction in particle size influences severely on the magnetic, electrical and magneto transport properties. - Highlights: • Long range ferromagnetic ordered state become unstable in case of nano compound. • It shows broad magnetic transition and cluster glass nature. • Kondo effect with electron-phonon interactions dominate the resistivity at low temperature.

Crystal structure and magnetic properties of La2−x(Sr0.5Ca0.5)1+xMn2O7 (x=0.6, 0.8 and 1.0) Ruddlesden–Popper manganites

International Nuclear Information System (INIS)

Raju, K.; Song, M.S.; Lee, J.Y.

2014-01-01

Double layer perovskite (Ruddlesden–Popper) manganites with the nominal composition of La 2−x (Sr 0.5 Ca 0.5 ) 1+x Mn 2 O 7 (x=0.6, 0.8 and 1.0) were synthesized via a solid state reaction route. X-ray and neutron diffraction were performed at room temperature and the crystal structure was refined using the Rietveld method based on the space group, I4/mmm. The temperature variation of the susceptibility revealed a spin glass transition at 28 K for x=0.6, a charge ordering transition at 245 K and a Neel transition at 170 K for x=1.0. - Highlights: • Lanthanum based double layered manganites were prepared by doping with the same amounts of Sr and Ca. • X-ray and neutron diffraction were performed and the crystal structure was refined using the Rietveld method. • Different magnetic transitions were observed depending upon the doping concentration. • Qualitative explanation for the various observed phenomena was given

Spin polarization at the interface and tunnel magnetoresistance

International Nuclear Information System (INIS)

Itoh, H.; Inoue, J.

2001-01-01

We propose that interfacial states of imperfectly oxidized Al ions may exist in ferromagnetic tunnel junctions with Al-O barrier and govern both the spin polarization and tunnel conductance. It is shown that the spin polarization is positive independent of materials and correlates well with the tunnel magnetoresistance

Spin polarized electron tunneling and magnetoresistance in molecular junctions.

Science.gov (United States)

Szulczewski, Greg

2012-01-01

This chapter reviews tunneling of spin-polarized electrons through molecules positioned between ferromagnetic electrodes, which gives rise to tunneling magnetoresistance. Such measurements yield important insight into the factors governing spin-polarized electron injection into organic semiconductors, thereby offering the possibility to manipulate the quantum-mechanical spin degrees of freedom for charge carriers in optical/electrical devices. In the first section of the chapter a brief description of the Jullière model of spin-dependent electron tunneling is reviewed. Next, a brief description of device fabrication and characterization is presented. The bulk of the review highlights experimental studies on spin-polarized electron tunneling and magnetoresistance in molecular junctions. In addition, some experiments describing spin-polarized scanning tunneling microscopy/spectroscopy on single molecules are mentioned. Finally, some general conclusions and prospectus on the impact of spin-polarized tunneling in molecular junctions are offered.

Magnetoresistive phenomena in an Fe-filled carbon nanotube/elastomer composite

International Nuclear Information System (INIS)

Hudziak, S; Baxendale, M; Darfeuille, A; Zhang, R; Peijs, T; Mountjoy, G; Bertoni, G

2010-01-01

DC magnetoresistive effects were observed in above-percolation-threshold loaded Fe-filled carbon nanotube/polyurethane-urea composite samples. A phenomenological model is derived from interpretation of resistance relaxation for a range of axial strains. The large instantaneous magnetoresistance of + 90% observed at low axial strain was a result of conduction pathway breaking caused by preferential orientation of the conducting nanotubes perpendicular to the axial current flow: a result of the magnetic torque experienced by the ferromagnetic nanotube core. At large strain the observed large instantaneous change in resistance of - 90% resulted from voltage-driven relaxation in the conducting nanotube network. At high axial strain the competition between voltage-driven relaxation and a magnetic torque gave rise to an oscillatory component of resistance relaxation.

Magnetoresistive phenomena in an Fe-filled carbon nanotube/elastomer composite.

Science.gov (United States)

Hudziak, S; Darfeuille, A; Zhang, R; Peijs, T; Mountjoy, G; Bertoni, G; Baxendale, M

2010-03-26

DC magnetoresistive effects were observed in above-percolation-threshold loaded Fe-filled carbon nanotube/polyurethane-urea composite samples. A phenomenological model is derived from interpretation of resistance relaxation for a range of axial strains. The large instantaneous magnetoresistance of + 90% observed at low axial strain was a result of conduction pathway breaking caused by preferential orientation of the conducting nanotubes perpendicular to the axial current flow: a result of the magnetic torque experienced by the ferromagnetic nanotube core. At large strain the observed large instantaneous change in resistance of - 90% resulted from voltage-driven relaxation in the conducting nanotube network. At high axial strain the competition between voltage-driven relaxation and a magnetic torque gave rise to an oscillatory component of resistance relaxation.

Magnetoresistance of drop-cast film of cobalt-substituted magnetite nanocrystals.

Science.gov (United States)

Kohiki, Shigemi; Nara, Koichiro; Mitome, Masanori; Tsuya, Daiju

2014-10-22

An oleic acid-coated Fe2.7Co0.3O4 nanocrystal (NC) self-assembled film was fabricated via drop casting of colloidal particles onto a three-terminal electrode/MgO substrate. The film exhibited a large coercivity (1620 Oe) and bifurcation of the zero-field-cooled and field-cooled magnetizations at 300 K. At 10 K, the film exhibited both a Coulomb blockade due to single electron charging as well as a magnetoresistance of ∼-80% due to spin-dependent electron tunneling. At 300 K, the film also showed a magnetoresistance of ∼-80% due to hopping of spin-polarized electrons. Enhanced magnetic coupling between adjacent NCs and the large coercivity resulted in a large spin-polarized current flow even at 300 K.

Artifacts that mimic ballistic magnetoresistance

International Nuclear Information System (INIS)

Egelhoff, W.F. . E-mail : egelhoff@nist.gov; Gan, L.; Ettedgui, H.; Kadmon, Y.; Powell, C.J.; Chen, P.J.; Shapiro, A.J.; McMichael, R.D.; Mallett, J.J.; Moffat, T.P.; Stiles, M.D.; Svedberg, E.B.

2005-01-01

We have investigated the circumstances underlying recent reports of very large values of ballistic magnetoresistance (BMR) in nanocontacts between magnetic wires. We find that the geometries used are subject to artifacts due to motion of the wires that distort the nanocontact thereby changing its electrical resistance. Since these nanocontacts are often of atomic scale, reliable experiments would require stability on the atomic scale. No method for achieving such stability in macroscopic wires is apparent. We conclude that macroscopic magnetic wires cannot be used to establish the validity of the BMR effect

Ternary NiFeX as soft biasing film in a magnetoresistive sensor

Science.gov (United States)

Chen, Mao-Min; Gharsallah, Neila; Gorman, Grace L.; Latimer, Jacquie

1991-04-01

The properties of NiFeX ternary films (X being Al, Au, Nb, Pd, Pt, Si, and Zr) have been studied for soft-film biasing of the magnetoresistive (MR) trilayer sensor. In general, the addition of the element X into the NiFe alloy film decreases the saturation magnetization Bs and magnetoresistance coefficient of the film, while increasing the film's electrical resistivity ρ. One of the desirable properties of a soft film for biasing is high sheet resistance for minimum current flow. A figure of merit Bsρ that takes into account both the rate of increase in Bs and the rate of decrease in ρ when adding X element was derived to compare the effectiveness of various X elements in reducing the current shunting through the soft-film layer. Using this criterion, NiFeNb and NiFeZr emerge as good soft-film materials having a maximum sheet resistance relative to the MR layer. Other critical properties such as magnetoresistance coefficient, magnetostriction, coercivity, and anisotropy field were also examined and are discussed in this paper.

Experimental Discovery of Magnetoresistance and Its Memory Effect in Methylimidazolium-Type Iron-Containing Ionic Liquids

KAUST Repository

Zhang, Haitao

2016-11-29

The ordering and interactions of charge carriers play a critical role in many physicochemical properties. It is, therefore, interesting to study how a magnetic field affects these physicochemical processes and the consequent behavior of the charge carriers. Here, we report the observation of positive magnetoresistance and its memory effect in methylimidazolium-type iron-containing ionic liquids (ILs). Both the electrical transport and magnetic properties of ILs were measured to understand the mechanism of magnetoresistance behavior and its memory effect. The magnetoresistance effect of [BMIM][FeCl] was found to increase with increasing applied currents. This observed memory effect can be ascribed to the slow order and disorder processes in these ILs due to the large viscosity caused by the interactions among ions.

Structural studies of spinel manganite ceramics with positron annihilation lifetime spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Klym, H; Shpotyuk, O; Hadzaman, I [Institute of Materials of SRC ' Carat' , 202 Stryjska str., Lviv, 79031 (Ukraine); Ingram, A [Opole University of Technology, 75 Ozimska str., Opole, 45370 (Poland); Filipecki, J, E-mail: shpotyuk@novas.lviv.ua, E-mail: klymha@yahoo.com [Institute of Physics of Jan Dlugosz University, 13/15 Armii Krajowei, 42201, Czestochowa (Poland)

2011-04-01

The new transition-metal manganite Cu{sub 0.1}Ni{sub 0.8}Co{sub 0.2}Mn{sub 1.9}O{sub 4} ceramics for temperature sensors with improved functional reliability are first proposed. It is established that the amount of additional NiO phase in these ceramics extracted during sintering play a decisive role. This effect is well revealed only in ceramics having a character fine-grain microstructure, while the monolithization of ceramics caused by great amount of transferred thermal energy reveals an opposite influence. The process of monolitization from the position of evolution of grain-pore structure was studied in these ceramics using positron annihilation lifetime spectroscopy.

Structural studies of spinel manganite ceramics with positron annihilation lifetime spectroscopy

International Nuclear Information System (INIS)

Klym, H; Shpotyuk, O; Hadzaman, I; Ingram, A; Filipecki, J

2011-01-01

The new transition-metal manganite Cu 0.1 Ni 0.8 Co 0.2 Mn 1.9 O 4 ceramics for temperature sensors with improved functional reliability are first proposed. It is established that the amount of additional NiO phase in these ceramics extracted during sintering play a decisive role. This effect is well revealed only in ceramics having a character fine-grain microstructure, while the monolithization of ceramics caused by great amount of transferred thermal energy reveals an opposite influence. The process of monolitization from the position of evolution of grain-pore structure was studied in these ceramics using positron annihilation lifetime spectroscopy.

Normal state resistance and low temperature magnetoresistance of superconducting cables for accelerator magnets

International Nuclear Information System (INIS)

Sampson, W.B.; Garber, M.; Ghosh, A.K.

1988-01-01

The normal state resistivity of the superconducting NbTi cable used in accelerator magnets is usually specified by the resistance per unit length at room temperature (295 K) and the residual resistance ratio (RRR). Using these resistance parameters, the amount of copper in the multifilamentary wire can be calculated. This method is consistent with the traditional etch and weigh technique, and as such is a alternative and convenient way of specifying the copper to superconductor ratio. In principle the magnetoresistance can be calculated from the RRR and the ''Kohler Plot'', for copper. In practice however, measurements of magnetoresistance for a wide variety of SSC inner cables show considerable disagreement with calculation. In this paper the magnetoresistance data on cables with RRR ranging from 50 to 175 are analyzed taking into account the conductor geometry and the effect of the small interfilamentary spacing on the resistivity of copper. 8 refs., 5 figs., 1 tab

Anisotropic Magnetoresistance and Anisotropic Tunneling Magnetoresistance due to Quantum Interference in Ferromagnetic Metal Break Junctions

DEFF Research Database (Denmark)

Bolotin, Kirill; Kuemmeth, Ferdinand; Ralph, D

2006-01-01

We measure the low-temperature resistance of permalloy break junctions as a function of contact size and the magnetic field angle in applied fields large enough to saturate the magnetization. For both nanometer-scale metallic contacts and tunneling devices we observe large changes in resistance w...... with the angle, as large as 25% in the tunneling regime. The pattern of magnetoresistance is sensitive to changes in bias on a scale of a few mV. We interpret the effect as a consequence of conductance fluctuations due to quantum interference....

Heteroepitaxy of Nd{sub 0.67}Sr{sub 0.33}MnO{sub 3} on silicon for bolometric x-ray detector application

Energy Technology Data Exchange (ETDEWEB)

Yong, G. J.; Kolagani, Rajeswari M.; Adhikari, S. [Department of Physics, Astronomy and Geosciences, Towson University, Towson, Maryland 21252 (United States); Drury, O. B.; Gardner, C.; Bionta, R. M.; Friedrich, S. [Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, California 94550 (United States)

2010-11-15

We have recently reported the design concept and sensor fabrication for a novel bolometric x-ray detector based on a rare earth manganite material for application as a total energy monitor for the Linac Coherent Light Source (LCLS) free electron laser at the Stanford Linear Accelerator Center (SLAC). The detector employs epitaxial thin films of Nd{sub 0.67}Sr{sub 0.33}MnO{sub 3} grown on Si by pulsed laser deposition. In this paper we report details of the fabrication of the actual detector, its response characteristics under photon illumination from LCLS, and improvements in the growth scheme of the sensor material on Si using a buffer/template layer scheme that employs yttria-stabilized zirconia, cerium oxide (CeO{sub 2}), and bismuth titanate (Bi{sub 4}Ti{sub 3}O{sub 12}). The thermal sensor response changes linearly with the energy of an optical calibration laser as expected, and the signals from optical and x-ray pulses at LCLS are very similar, thereby validating the design concept. To the best of our knowledge, the LCLS detector application reported here is the first practical use of colossal magnetoresistive manganite bolometers.

Tunable electron heating induced giant magnetoresistance in the high mobility GaAs/AlGaAs 2D electron system.

Science.gov (United States)

Wang, Zhuo; Samaraweera, R L; Reichl, C; Wegscheider, W; Mani, R G

2016-12-07

Electron-heating induced by a tunable, supplementary dc-current (I dc ) helps to vary the observed magnetoresistance in the high mobility GaAs/AlGaAs 2D electron system. The magnetoresistance at B = 0.3 T is shown to progressively change from positive to negative with increasing I dc , yielding negative giant-magnetoresistance at the lowest temperature and highest I dc . A two-term Drude model successfully fits the data at all I dc and T. The results indicate that carrier heating modifies a conductivity correction σ 1 , which undergoes sign reversal from positive to negative with increasing I dc , and this is responsible for the observed crossover from positive- to negative- magnetoresistance, respectively, at the highest B.

Self-consistent study of local and nonlocal magnetoresistance in a YIG/Pt bilayer

Science.gov (United States)

Wang, Xi-guang; Zhou, Zhen-wei; Nie, Yao-zhuang; Xia, Qing-lin; Guo, Guang-hua

2018-03-01

We present a self-consistent study of the local spin Hall magnetoresistance (SMR) and nonlocal magnon-mediated magnetoresistance (MMR) in a heavy-metal/magnetic-insulator heterostructure at finite temperature. We find that the thermal fluctuation of magnetization significantly affects the SMR. It appears unidirectional with respect to the direction of electrical current (or magnetization). The unidirectionality of SMR originates from the asymmetry of creation or annihilation of thermal magnons induced by the spin Hall torque. Also, a self-consistent model can well describe the features of MMR.

Magnetoresistant Co/Cu multilayers: effect of crystallographic orientation of the layers

International Nuclear Information System (INIS)

Boher, P.; Giron, F.; Houdy, P.; Beauvillain, P.; Chappert, C.; Veillet, P.

1992-01-01

In the last few years ferromagnetic/non-ferromagnetic multilayers have received considerable attention due to their great interest formagnetoresistive applications. Giant magnetoresistance has been observed in the Cu/Co system but with quite high saturation field (>>1 kOe). In this paper we report on an original way to enhance this characterisitc, using unusual fcc left angle 100 right angle cristallographic orientation. Special preparation of the right angle 100 right angle silicon substrates is investigated using in-situ kinetic ellipsometry, RHEED, grazing X-ray reflection and X-ray diffraction. We show that good quality fcc right angle 100 right angle pseudo-epitaxial copper surface can be obtained only when two conditions are fulfilled: first the silicon surface must be completely free of native oxide and second the copper buffer layer must be annealed under ultrahigh vacuum. Perfectly clean silicon surfaces are obtained by chemical etching followed by flash heating under ultrahigh vacuum. The copper buffer layer reacts with silicon and gives a textured fcc right angle 100 right angle Cu phase with a 45 rotation of the Cu left angle 100 right angle lattice with regards to the Si right angle 100 right angle one. Additional annealing leads to an homogencous interface silicide layer and improves the cristallinity of the Cu buffer layer. Cu/Co multilayers deposited on this kind of substrate show a well-defined fcc right angle 100 right angle texture for a large range of layer thickness. Oscillation of magnetoresistance with the copper thickness is observed with a period of about 10 A. The maximum of magnetoresistance is found for 20.9 A of Cu (ΔR/R∼6%), and the differential magnetoresistance is very high (ΔR/RΔH = 1.4 kOe -1 ). Combination of antiferromagnetic coupling and quadratic in-plane anisotropy of this special cristallographic orientation is responsible for this improvement. (orig.)

Magnetoresistance in La0.7Ca0.3MnO3-YBa2Cu3O7 F/S/F trilayers

International Nuclear Information System (INIS)

Pena, V.; Visani, C.; Bruno, F.; Garcia-Barriocanal, J.; Arias, D.; Rivera, A.; Sefrioui, Z.; Leon, C.; Te Velthuis, S.G.E.; Hoffmann, A.; Nemes, N.; Garcia-Hernandez, M.; Martinez, J.L.; Santamaria, J.

2007-01-01

We report large magnetoresistance in ferromagnet/superconductor/ferromagnet structures made of La 0.7 Ca 0.3 MnO 3 and YBa 2 Cu 3 O 7 at temperatures along the resistive transition. We find that the magnetoresistance phenomenon is independent on the orientation of electric current versus field. Furthermore, the effect is also independent on the sweep rate of the magnetic field. This excludes interpretations in terms of spontaneous vortices or anisotropic magnetoresistance of the ferromagnetic layers and supports the view that the magnetoresistance phenomenon originates at the spin-dependent transport of quasiparticles transmitted from the ferromagnetic electrodes into the superconductor

High density submicron magnetoresistive random access memory (invited)

Science.gov (United States)

Tehrani, S.; Chen, E.; Durlam, M.; DeHerrera, M.; Slaughter, J. M.; Shi, J.; Kerszykowski, G.

1999-04-01

Various giant magnetoresistance material structures were patterned and studied for their potential as memory elements. The preferred memory element, based on pseudo-spin valve structures, was designed with two magnetic stacks (NiFeCo/CoFe) of different thickness with Cu as an interlayer. The difference in thickness results in dissimilar switching fields due to the shape anisotropy at deep submicron dimensions. It was found that a lower switching current can be achieved when the bits have a word line that wraps around the bit 1.5 times. Submicron memory elements integrated with complementary metal-oxide-semiconductor (CMOS) transistors maintained their characteristics and no degradation to the CMOS devices was observed. Selectivity between memory elements in high-density arrays was demonstrated.

Structural and electronic transformations in substituted La-Sr manganites depending on cations and oxygen content

Science.gov (United States)

Karpasyuk, Vladimir; Badelin, Alexey; Merkulov, Denis; Derzhavin, Igor; Estemirova, Svetlana

2018-05-01

In the present research experimental data are obtained for the Jahn-Teller O‧ phase formation, phase transformation "orthorhombic-rhombohedral structure" and the change of the conductance type in the systems of manganites La3+1-c+xSr2+c-xMn3+1-c-x-2γMn4+c+2γZn2+xO3+γ, La3+1-c-xSr2+c+xMn3+1-c-x-2γMn4+c+2γGe4+xO3+γ, La3+1-cSr2+cMn3+1-x-c-2γMn4+c+2γ(Zn2+0.5Ge4+0.5)xO3+γ, where Mn4+ ions concentration is independent of "x". Ceramic samples were sintered in air at 1473 K. As-sintered samples had an excess of oxygen content. In order to provide stoichiometric oxygen content, the samples were annealed at 1223 K and partial pressure of oxygen PO2 = 10-1 Pа. Structural characteristics of the O‧ phase were obtained. The position of the phase boundary "orthorhombic-rhombohedral structure" and the temperature of the conductance type change depending on the cation composition of manganites and oxygen content were determined. Possible approaches to the interpretation of experimental results were suggested.

Specific features of magnetoresistance during the antiferromagnet—paramagnet transition in Tm1−xYbxB12

International Nuclear Information System (INIS)

Sluchanko, N. E.; Azarevich, A. N.; Bogach, A. V.; Glushkov, V. V.; Demishev, S. V.; Levchenko, A. V.; Filippov, V. B.; Shitsevalova, N. Yu.

2013-01-01

The transverse magnetoresistance Δρ/ρ(H, T) of Tm 1−x Yb x B 12 single crystals is studied in the ytterbium concentration range corresponding to the antiferromagnet-paramagnet transition in a magnetic field up to 80 kOe at low temperatures. A magnetic H-T phase diagram is constructed for the antiferromagnetic state of substitutional Tm 1−x Yb x B 12 solid solutions with x ≤ 0.1. The contributions to the magnetoresistance in the antiferromagnetic and paramagnetic phases of the dodecaborides under study are separated. Along with negative quadratic magnetoresistance -Δρ/ρ ∝ H 2 , the magnetically ordered phase of these compounds is found to have component Δρ/ρ ∝ H that linearly changes in a magnetic field. The negative contribution to the magnetoresistance of Tm 1−x Yb x B 12 is analyzed in terms of the Yosida model for a local magnetic susceptibility.

On-line irradiation testing of a Giant Magneto-Resistive (GMR) sensor

Energy Technology Data Exchange (ETDEWEB)

Olfert, J.; Luloff, B.; MacDonald, D.; Lumsden, R., E-mail: jeff.olfert@cnl.ca [Canadian Nuclear Laboratories, Chalk River, Ontario (Canada)

2016-06-15

Magneto-resistive sensors are rapidly gaining favour for magnetic field sensing applications owing to their high sensitivity, small size, and low cost. Their metallic, nonsemiconductor construction makes them excellent candidates for use in the harsh environments present in nuclear and space applications. In this work, a commercially available magneto-resistive sensor was irradiated up to a total gamma dose of 2 MGy (200 Mrad), and online testing was performed to monitor the sensor throughout the irradiation to detect any degradation. No significant evidence of degradation of the sensor characteristics was observed. A very small (< 1%) change in the bridge balance of the sensor as a function of accumulated dose was detected. (author)

Synthesis and structural properties of n = 1 Ruddlesden-Popper manganites Nd1-xCa1+xMnO4

International Nuclear Information System (INIS)

Nagai, T.; Yamazaki, A.; Kimoto, K.; Matsui, Y.

2008-01-01

Polycrystalline samples of n = 1 Ruddlesden-Popper manganites Nd 1-x Ca 1+x MnO 4 (0.55 ≤ x ≤ 1.00) were synthesized by a solid-state reaction. X-ray diffraction (XRD) and electron diffraction (ED) measurements confirmed that the fundamental crystal structure at room temperature consists of three distorted K 2 NiF 4 -types: orthorhombic Bmab (64) phase in 0.55 ≤ x 1 /acd (142) phase in 0.85 ≤ x ≤ 1.00. Furthermore, in a whole range of 0.55 ≤ x ≤ 0.75, low-temperature magnetic and ED measurements revealed charge-orbital ordering (COO) states, which are accompanied by suppression of magnetization and structural modulations with q = (1 - x)a*. The COO transition temperatures are high with a maximum of ∼330 K at x = 0.67, and then higher than those in non-distorted n = 1 Ruddlesden-Popper manganites. The observations suggest that COO states are much stabilized by the distortion in the fundamental structures

Temperature dependence of the resistivity and tunneling magnetoresistance of sputtered FeHf(Si)O cermet films

NARCIS (Netherlands)

Strijkers, G.J.; Swagten, H.J.M.; Rulkens, B.; Bitter, R.H.J.N.; Jonge, de W.J.M.; Bloemen, P.J.H.; Schep, K.M.

1998-01-01

We have studied the tunneling resistivity and magnetoresistance of reactive sputter deposited FeHfO and FeHfSiO thin granular films. Maximum magnetoresistance ratios at room temperature of 2% and 3.2% were observed for films with compositions of Fe47Hf10O43 and Fe40Hf6Si6O48, respectively. The

Temperature-Dependent Three-Dimensional Anisotropy of the Magnetoresistance in WTe_{2}.

Science.gov (United States)

Thoutam, L R; Wang, Y L; Xiao, Z L; Das, S; Luican-Mayer, A; Divan, R; Crabtree, G W; Kwok, W K

2015-07-24

Extremely large magnetoresistance (XMR) was recently discovered in WTe_{2}, triggering extensive research on this material regarding the XMR origin. Since WTe_{2} is a layered compound with metal layers sandwiched between adjacent insulating chalcogenide layers, this material has been considered to be electronically two-dimensional (2D). Here we report two new findings on WTe_{2}: (1) WTe_{2} is electronically 3D with a mass anisotropy as low as 2, as revealed by the 3D scaling behavior of the resistance R(H,θ)=R(ϵ_{θ}H) with ϵ_{θ}=(cos^{2}θ+γ^{-2}sin^{2}θ)^{1/2}, θ being the magnetic field angle with respect to the c axis of the crystal and γ being the mass anisotropy and (2) the mass anisotropy γ varies with temperature and follows the magnetoresistance behavior of the Fermi liquid state. Our results not only provide a general scaling approach for the anisotropic magnetoresistance but also are crucial for correctly understanding the electronic properties of WTe_{2}, including the origin of the remarkable "turn-on" behavior in the resistance versus temperature curve, which has been widely observed in many materials and assumed to be a metal-insulator transition.

Magnetoresistance in spin glass alloys: Theory and experiment

International Nuclear Information System (INIS)

Mookerjee, A.; Chowdhury, D.

1984-11-01

The magnetoresistance of spin glass alloys is examined within the percolation model of Mookerjee and Chowdhury (1983), the mode freezing model of Hertz (1983) and the constrained relaxation model of Palmer et al. (1984). All three models yield qualitatively similar results in excellent agreement with the experiments of Majumdar (1983, 1984) on AgMn. (author)