Showing papers on "Magnetoresistance published in 1992"
TL;DR: Giant magnetoresistance in heterogeneous thin film Cu-Co alloys consisting of ultrafine Co-rich precipitate particles in a Cu-rich matrix is observed, modeled by including spin-dependent scattering at the interfaces between the particles and the matrix, as well as the spin- dependent scattering in the Co- rich particles.
Abstract: We have observed giant magnetoresistance in heterogeneous thin film Cu-Co alloys consisting of ultrafine Co-rich precipitate particles in a Cu-rich matrix. The magnetoresistance scales inversely with the average particle diameter. This behavior is modeled by including spin-dependent scattering at the interfaces between the particles and the matrix, as well as the spin-dependent scattering in the Co-rich particles.
1,566 citations
TL;DR: The coexistence of remanent magnetization and unsaturated spins as well as the large negative magnetoresistance at low temperatures is explained by the formation of large bound magnetic polarons.
Abstract: Magnetotransport properties of p-type (In,Mn)As, a new diluted magnetic semiconductor based on a III-V semiconductor, are studied. The interaction between the holes and the Mn 3d spins is manifested in the anomalous Hall effect, which dominates the Hall resistivity from low temperature (0.4 K) to nearly room temperature, and in the formation of partial ferromagnetic order below 7.5 K, which is a cooperative phenomenon related to carrier localization. The coexistence of remanent magnetization and unsaturated spins as well as the large negative magnetoresistance at low temperatures is explained by the formation of large bound magnetic polarons.
964 citations
TL;DR: The results clearly show that the giant magnetoresistance is enhanced by the presence of roughness, indicating that interfacial roughness should be explicitly included in theoretical calculations and experimental characterization of superlattices exhibiting giant Magnetoresistance.
Abstract: We have performed detailed studies of the structure, magnetotransport, and magnetization of Fe/Cr superlattices as a function of systematic changes in interfacial roughness. The results clearly show that the giant magnetoresistance is enhanced by the presence of roughness. This fact indicates that interfacial roughness should be explicitly included in theoretical calculations and experimental characterization of superlattices exhibiting giant magnetoresistance.
329 citations
TL;DR: Magnetoresistive random-access memory (MRAM) is an integrated combination of nonvolatile thin film magnetic storage and semiconductor support circuits as mentioned in this paper, which can offer improvements of 100 in read time and substantial simplification in circuitry.
255 citations
TL;DR: It is shown that chaos and nonlinear resonances are clearly reflected in the magnetotransport in lateral surface superlattices and thereby explain a series of magnetoresistance peaks observed recently in ``antidot'' arrays on semiconductor heterojunctions.
Abstract: We show that chaos and nonlinear resonances are clearly reflected in the magnetotransport in lateral surface superlattices and thereby explain a series of magnetoresistance peaks observed recently in ``antidot'' arrays on semiconductor heterojunctions. We find a mechanism of cyclotron-orbit pinning in an electric field resulting from Kolmogorov-Arnol'd-Moser tori. An experimental verification is suggested in terms of an enhanced cyclotron frequency associated with an anomalously reduced cyclotron radius.
222 citations
TL;DR: In this paper, the authors reported giant magnetoresistance in [Ni81Fe19/Cu]N multilayers at 4.2 K, with an oscillation period and phase similar to that in Co/Cu multilayer.
Abstract: We report giant magnetoresistance in [Ni81Fe19/Cu]N multilayers. Saturation magnetoresistance values exceeding 16% for saturation fields of only 600 Oe are found at 300 K. In addition, we show evidence for well‐defined oscillations in saturation magnetoresistance as a function of Cu spacer layer thickness at 4.2 K, with an oscillation period and phase similar to that in Co/Cu multilayers. However, the temperature dependence of the magnetoresistance, while weak for thin Cu layers, is much stronger for thicker Cu layers. Consequently at 300 K only a single oscillation in magnetoresistance for thin Cu layers is found. We show that the properties of the Ni81Fe19/Cu multilayers are very sensitive to annealing at moderate temperatures, which may limit the possible technological applications of such structures.
197 citations
TL;DR: In this paper, a spin-dependent scattering model was proposed to explain various features of the magnetoresistance and to predict new features, and the model was further extended to include the temperature dependence.
Abstract: It has been recently found that giant magnetoresistance can also be obtained in metallic films containing magnetic particles. Based on spin‐dependent scattering, we propose a model that allows us to explain various features of the magnetoresistance and to predict new features. The model is further extended to include the temperature dependence of the magnetoresistance.
162 citations
TL;DR: The Boltzmann equation is solved for a system consisting of a ferromagnetic--normal-metal--ferromagnetic metallic trilayer and it is found that a large negative magnetoresistance requires, in general, considerable asymmetry in the interface scattering for the two spin orientation.
Abstract: The Boltzmann equation is solved for a system consisting of a ferromagnetic--normal-metal--ferromagnetic metallic trilayer. The in-plane conductance of the film is calculated for two configurations: the ferromagnetic layers aligned (i) parallel and (ii) antiparallel to each other. The results explain the giant negative magnetoresistance encountered in these systems when an initial antiparallel arrangement is changed into a parallel configuration by application of an external magnetic field. The calculation depends on (a) geometric parameters (the thicknesses of the layers), (b) intrinsic metal parameters (number of conduction electrons, magnetization, and effective masses in the layers), (c) bulk sample properties (conductivity relaxation times), (d) interface scattering properties (diffuse scattering versus potential scattering at the interfaces), and (e) outer surface scattering properties (specular versus diffuse surface scattering). For perfect specular scattering at the surfaces the problem becomes identical to an infinite multilayer, periodic system. It is found that a large negative magnetoresistance requires, in general, considerable asymmetry in the interface scattering for the two spin orientations. All qualitative features of the experiments are reproduced. Quantitative agreement can be achieved with sensible values of the parameters. The effect can be conceptually explained based on considerations of phase-space availability for an electron of a given spinmore » orientation as it travels through the multilayer sample in the various configurations.« less
159 citations
TL;DR: The giant magnetoresistance (MR) of Ni81Fe19/Cu multilayers is dramatically enhanced by inserting thin Co layers at each interface as mentioned in this paper, unambiguously demonstrating the predominant interfacial origin of the giant MR effect.
Abstract: The giant magnetoresistance (MR) of Ni81Fe19/Cu multilayers is dramatically enhanced by inserting thin Co layers at each Ni81Fe19/Cu interface, unambiguously demonstrating the predominant interfacial origin of the giant MR effect. Similarly the long‐range oscillatory MR and interlayer exchange coupling only present in magnetron sputtered Ni81Fe19/Cu multilayers at low temperatures is restored at higher temperatures by the addition of thin Co interface layers. Multilayered structures comprised of Co/Ni81Fe19/Co/Cu exhibit MR of more than 17% for field changes of ±100 Oe at room temperature.
152 citations
TL;DR: Analytical results on the magnetoresistance in limiting cases where either the mean free path is much greater or less than the layer thickness, as well as numerical results for the realistic situation found in Fe/Cr superlattices when they are comparable.
Abstract: We consider multilayered structures consisting of magnetic and nonmagnetic metals. We derive analytic expressions for the conductivities by treating the scattering at the interfaces between layers in the same way as that throughout the layers (bulk). The application of an external magnetic field reorients the magnetization in the magnetic layers, which in turn alter the mean free path of the conduction electrons. This is the origin of the giant magnetoresistance seen in iron-chromium (Fe/Cr) superlattices. We present analytic results on the magnetoresistance in limiting cases where either the mean free path is much greater or less than the layer thickness, as well as numerical results for the realistic situation found in Fe/Cr superlattices when they are comparable.
130 citations
Patent•
22 Oct 1992TL;DR: A magnetoresistance effect element which comprises a substrate and at least two layers of magnetic thin films formed on the substrate via non-magnetic thin film layers is characterized in this article.
Abstract: A magnetoresistance effect element which comprises a substrate and at least two layers of magnetic thin films formed on the substrate via non-magnetic thin film layers The element is characterized in that the coercive forces of the magnetic thin films adjoining each other via the non-magnetic thin film layer are different and the thicknesses of the magnetic and non-magnetic thin film layers are 200 angstroms or less respectively The element exhibits a large rate of resistance change of several to several tens % in a small external magnetic field of about several to several tens Oe Therefore, a highly sensitive magnetic sensor of magnetoresistance type and a magnetic head of magnetoresistance type capable of high-density magnetic recording can be provided
TL;DR: The low-temperature transport properties of amorphous indium oxide films are studied as a function of disorder near the metal-insulator transition to show simple variable-range hopping that turns into an Arrhenius activation as the transition is approached.
Abstract: We study the low-temperature transport properties of amorphous indium oxide films as a function of disorder near the metal-insulator transition. Deep in the insulating regime, the conductivity shows simple variable-range hopping that turns into an Arrhenius activation as the transition is approached. With further decrease in static disorder, superconductivity sets in and the transition temperature increases towards a value of ≃3.3 K. The transition between a superconducting phase and an insulating one is also accompanied by a sign and anisotropy change in the magnetoresistance of the films
TL;DR: In this paper, the magnetotransport phenomenon in α-type crystals of (BEDT-TTF) 2 I 3 which are metallized by applying quasi-hydrostatic pressures is investigated.
Abstract: The magnetotransport phenomenon is investigated in α-type crystals of (BEDT-TTF) 2 I 3 which are metallized by applying quasi-hydrostatic pressures. At liquid helium temperatures, a fairly large magnetoresistance which rises in very low field and saturates above 0.5 T is observed. The effect of the magnetic field of 1.2 T is found to be recognizable at temperatures above 50 K. Our interpretation of the phenomenon is that the metal-insulator transition which has been suppressed by the pressure arises again, aided by the magnetic field.
TL;DR: In this paper, the magnetoresistance ratio of single-layer Co-Ag alloy thin films sputtered from a composite target was measured at room temperature in as-deposited, single layer CoAg Alloy thin films.
TL;DR: The magnetoresistance of Si:B is positive for all temperatures and magnetic fields studied, and is attributed to the strong spin-orbit scattering in {ital p}-type silicon associated with the degenerate valence bands.
Abstract: The conductivity has been measured between 55 mK and 4.2 K in zero field and in magnetic fields up to 7.5 T of a series of uncompensated {ital p}-type Si:B samples with dopant concentrations near the critical concentration for the metal-insulator transition. Acceptor wave functions, which are derived in silicon from the degenerate light- and heavy-hole {ital J}=3/2 valence-band maxima at {ital k}=0 and a spin-orbit-split {ital J}=1/2 band, are quite different from donor wave functions associated with the six degenerate conduction-band minima at different equivalent points in the Brillouin zone. Despite this, the conductivity of Si:B is found to be quite similar in many ways to that of Si:P. The critical conductivity exponent for Si:B is close to 1/2 as in Si:P and Si:As, rather than having the expected value of 1. The correction to the zero-temperature conductivity arising from electron-electron interactions is comparable in size, and the temperature dependence of the conductivity in various fixed magnetic fields is also found to be quite similar. For the range of dopant concentrations and experimental parameters of these investigations, the only important experimental difference between the two materials is the sign and size of the magnetoresistance. In contrast with Si:P, whichmore » has both positive and negative components, the magnetoresistance of Si:B is positive for all temperatures and magnetic fields studied. We attribute this to the strong spin-orbit scattering in {ital p}-type silicon associated with the degenerate valence bands.« less
13 Apr 1992
TL;DR: The giant magnetoresistance effect appears in a number of ultrathin multilayer systems in which thin magnetic films, a few tens of AA thick, are separated by nonmagnetic metal films, also on the order of tens to 1000 AA thick.
Abstract: An introduction to the phenomenon of giant magnetoresistance is presented. It is pointed out that the giant magnetoresistance effect appears in a number of ultrathin multilayer systems in which thin magnetic films, a few tens of AA thick, are separated by nonmagnetic metal films, also on the order of tens of AA thick. For the effect to appear, the primary requirement is that the relative orientation of successive magnetic layers must be susceptible to change by the application of a magnetic field. The basic physical origin of the effect is the differential scattering of electrons parallel to and antiparallel to the local magnetization. This differential scattering arises either from the character of the scattering centers or in the different density of states functions for the two spin species. The giant magnetoresistive effect is of interest because of its potential utility in magnetoresistive read heads in the information storage industry. >
TL;DR: A Fermi-surface topological effect is proposed to describe the magnetotransport anisotropy of a quasi-one-dimensional electron system, where the electrons can drift in the field direction with an open-orbit trajectory, causing a resonant increase of the longitudinal conduction.
Abstract: We propose a Fermi-surface topological effect to describe the magnetotransport anisotropy of a quasi-one-dimensional electron system. When the magnetic field is parallel to one of the interchain lattice vectors having finite effective transfer integrals, the electrons can drift in the field direction with an open-orbit trajectory, causing a resonant increase of the longitudinal conduction. This model is applied to the magnetoresistance anisotropy of the quasi-one-dimensional organic superconductor (tetramethyltetraselenafulvalene${)}_{2}$X.
Patent•
IBM1
TL;DR: In this article, the spin valve effect was applied to a magnetoresistive read sensor, where a component of the read element resistance varies as the cosine of the angle between the magnetization directions in two adjacent magnetic layers is described.
Abstract: A magnetoresistive read sensor based on the spin valve effect in which a component of the read element resistance varies as the cosine of the angle between the magnetization directions in two adjacent magnetic layers is described. The sensor read element includes two adjacent ferromagnetic layers separated by a non-magnetic metallic layer, the magnetic easy axis of each of the ferromagnetic layers being aligned along the longitudinal axis of the ferromagnetic layers and perpendicular to the trackwidth of an adjacent magnetic storage medium. The sense current flowing in the sensor element generates a bias field which sets the direction of magnetization in each ferromagnetic layer at an equal, but opposite, angle θ with respect to the magnetic easy axis thus providing an angular separation of 2θ in the absence of an applied magnetic signal. The magnetizations of both ferromagnetic layers are responsive to an applied magnetic field to change their angular separation by an amount 2δθ.
TL;DR: In this paper, the magnetotransport properties of spin-valve multilayers were studied theoretically using the same approach as Camley and Barnas, and the absolute change in sheet conductance between parallel and antiparallel alignment of the magnetizations of successive ferromagnetic layers is the most relevant macroscopic quantity to represent and compare the magnetoresistance in these structures.
Abstract: Using the same approach as Camley and Barnas, the author studies theoretically the magnetotransport properties of spin-valve multilayers. He emphasizes that the absolute change in sheet conductance ( Delta G) between parallel and antiparallel alignment of the magnetizations of successive ferromagnetic layers is the most relevant macroscopic quantity to represent and compare the magnetoresistance in these structures. He presents results on the influence of the thicknesses of the ferromagnetic and nonmagnetic layers on the magnetoresistance for the two cases most studied experimentally: sandwiches and multilayers with a large number of periods. He also investigates the influence of the number of periods on the magnetoresistance and discusses the similarities and differences obtained in the respective cases of bulk or interfacial spin-dependent scattering.
TL;DR: In this article, the low-temperature magnetotransport properties of a series of spin-valve structures of composition NiFe t A/Cu 22 A/NiFe 50 A/FeMn 80 A/Cr 15 A. This anisotropy is ascribed to grain boundaries scattering in these sputtered polycrystalline samples.
Abstract: We analyse quantitatively the low-temperature magnetotransport properties of a series of spin-valve structures of composition NiFe t A/Cu 22 A/NiFe 50 A/FeMn 80 A/Cu 15 A. We adopt the approach of Camley and Barnas which is based on the classical Boltzmann equation and assume spin-dependent scattering in the bulk of the ferromagnetic layers. We show that by introducing an anisotropy in the mean-free paths of conduction electrons (of the order of 30%) we can fit with the same set of parameters the variation of the sheet conductance and magnetoresistance with the thicknesses of the Cu and NiFe layers. This anisotropy is ascribed to grain boundaries scattering in these sputtered polycrystalline samples. We also compare our results with others obtained on (Fe/Cr)-type spin-valve multilayers. We emphasise the very important role of the number of periods of the multilayered structure on the magnetotransport properties of these systems.
TL;DR: The contributions of contact potential, interface roughness, and bulk impurity scattering to the spin-selective transmission or spin-valve effect are described by a simple closed formula which, in the absence of spin-flip scattering, unites previous approaches.
Abstract: A theory of the perpendicular transport of electrons through metallic multilayers based on the Landauer-B\"uttiker formalism is presented and applied to the magnetoresistance of antiferromagnetically coupled magnetic multilayers. The contributions of contact potential, interface roughness, and bulk impurity scattering to the spin-selective transmission or spin-valve effect are described by a simple closed formula which, in the absence of spin-flip scattering, unites previous approaches.
Patent•
23 Oct 1992TL;DR: A magnetoresistance effect element includes a multilayer (4) obtained by stacking magnetic and non-magnetic layers (2 and 3) to exhibit a magnetoreduction effect, and a reversal assist layer on formed in contact with the multi-layer (4), to assist reversal of a magnetic moment of the magnetic layer.
Abstract: A magnetoresistance effect element includes a multilayer (4) obtained by stacking magnetic and nonmagnetic layers (2 and 3) to exhibit a magnetoresistance effect, and a reversal assist layer on formed in contact with the multilayer (4) to assist reversal of a magnetic moment of the magnetic layer.
IBM1
TL;DR: The presence of large oscillatory antiferromagnetic interlayer coupling and «giant» magnetoresistance in crystalline (111)-oriented Co/Cu superlattices grown on Pt buffer layers on sapphire substrates is demonstrated.
Abstract: We demonstrate the presence of large oscillatory antiferromagnetic (AF) interlayer coupling and ``giant'' magnetoresistance in crystalline (111)-oriented Co/Cu superlattices grown on Pt buffer layers on (0001) sapphire substrates. The AF coupling strength is \ensuremath{\approxeq}4--5 times larger than previously reported for sputtered polycrystalline Co/Cu multilayers. However, a significant fraction of the superlattice (\ensuremath{\approxeq}70%) remains ferromagnetically coupled. This may account for the comparatively low giant magnetoresistance values observed of \ensuremath{\approxeq}40% at 3.5 K and \ensuremath{\approxeq}26% at 295 K compared to values of g120% at 4.2 K and g65% at 295 K, respectively in sputtered structures. Similar crystalline (111) Co/Cu structures grown on Cu buffer layers on GaAs(110) show no evidence for antiferromagnetic coupling, although they are of nearly comparable structural perfection. The presence or absence of antiferromagnetic coupling in (111) Co/Cu superlattices appears to be a result of subtle structural imperfections giving rise to direct ferromagnetic coupling of neighboring Co layers.
TL;DR: In this paper, the authors report and discuss experimental data on the thermoelectric power of magnetic multilayers and ascribe the high temperature part of the MTEP to spin-dependent electron-magnon scattering.
TL;DR: Giant magnetoresistance in heterogeneous, sputtered AgCo thin films is reported in this paper, which consists of Co-rich precipitates in an Ag-rich matrix. But, the magnetoreduction properties depend on the Co concentration as well as the particle size.
Abstract: Giant magnetoresistance in heterogeneous, sputtered AgCo thin films is reported. The films consist of Co‐rich precipitates in an Ag‐rich matrix. Δρ/ρ values as high as 55% at 4.2 K and 20% at room temperature are observed. The magnetoresistance is shown to depend on the Co concentration as well as the particle size. Upon annealing, Δρ/ρ first increases, then decreases. Δρ, however, decreases monotonically with annealing.
TL;DR: In this paper, the shape of the Fermi surface transverse cross-section has been reconstructed using the obtained data and the angular dependence of the slow Shubnikov-de Haas oscillations frequency and some fine features of angular magnetoresistance oscillations have been discussed.
Abstract: Angular magnetoresistance oscillations have been studied systematically for fl(ET)2 IBr2 in the magnetic field rotating in a series of planes perpendicular to the conducting (a, b)plane. The oscillations have been found in all studied planes. The shape of the Fermi surface transverse cross-section has been reconstructed using the obtained data. Angular dependence of the slow Shubnikov-de Haas oscillations frequency and some fine features of angular magnetoresistance oscillations permit to discuss also the structure of the Fermi surface longitudinal cross-section. The Fermi surface consists most likely of main cylinders with inclined warping planes and small pockets or necks between them.
TL;DR: In this article, the first results of magnetic properties and giant magnetoresistance of granular permalloy in a metallic matrix were reported, showing that these new materials have resistivities comparable to those of the ferromagnetic alloys currently used in magnetoresistive devices.
Abstract: We report the first results of magnetic properties and giant magnetoresistance of granular permalloy in a metallic matrix. These new materials have resistivities comparable to those of the ferromagnetic alloys currently used in magnetoresistive devices, but yield significantly larger magnetoresistance effects that are nearly isotropic.
TL;DR: In this paper, the effect of various types of coupling on magnetic domains has been studied in the Fe/Cr system and it was shown that the magnetic domain magnetoresistance is due to spindependent electron scattering at the FeCr interfaces.
TL;DR: Giant magnetoresistance (GMR) has been observed in thin films of Fe and Co in Ag as mentioned in this paper, with a maximum value of 25% in Co20Ag80 at 30 K. Magnetic data show a magnetic transition below room temperature which may be due to spin-glass type of behavior.
Abstract: Giant magnetoresistance (GMR) has been observed in thin films of Fe and Co in Ag. The best results were obtained in the Ag‐rich samples with a maximum value of 25% in Co20Ag80 at 30 K. The GMR values are slightly increased upon annealing. Magnetic data show a magnetic transition below room temperature which may be due to spin‐glass type of behavior. These results are consistent with the microstructure studies which showed a single face centered cubic phase, with very fine grains. Upon annealing separation of the two components is achieved with substantial grain growth.
Patent•
16 Dec 1992
TL;DR: In this article, a sensor of weak magnetic fields with magnetoresistive effect features a metallic multilayer formed by alternating magnetic and non-magnetic metals, where the first and third magnetic layers are blocked by their strong coercive field.
Abstract: A sensor of weak magnetic fields with magnetoresistive effect features a metallic multilayer formed by alternating magnetic and non-magnetic metals. In order to detect weak fields, a sensor is described wherein a magnetic field is coupled by an anti-ferromagnetic type coupling with a first neighboring magnetic layer and by a ferromagnetic type coupling with a third neighboring magnetic layer, so that there is frustration of coupling. The first and third magnetic layers are blocked by their strong coercive field. The sensor finds particular application to detection on magnetic media.