Showing papers on "Magnetoresistance published in 1977"

Antiferromagnetic-ferromagnetic exchange bias films

Abstract: In thin film magnetic transducers, e.g., inductive or magnetoresistive recording heads, at least a pair of layers of a ferromagnetic material and an antiferromagnetic material are deposited upon one another and exchange coupled to retain a unidirectional bias in the plane of the ferromagnetic material. When multiple pairs of layers are used, they are separated by layers of nonmagnetic material. In some cases, successive pairs of layers of material with unidirectional bias have their directions of bias pointing in opposite directions. The domain walls in the layers of material are minimized by this technique.

The Electrical Properties of Disordered Metals

Abstract: The theory of how metals conduct electronically had for a long time been confined to metals that are crystalline with the constituent atoms in regular arrays The discovery of how to make solid amorphous alloys led to an explosion of measurements of the electronic properties of these new materials, and the emergence of a range of interesting low temperature phenomena This 1995 book describes in physical terms the theory of the electrical conductivity, Hall coefficient, magnetoresistance and thermopower of disordered metals and alloys The author begins by showing how conventional Boltzmann theory can be extended and modified when the mean free path of the conduction electrons becomes comparable with their wavelength and interionic separation The consequence of this is explored and the theory tested by application to experimental data on metallic glasses Designed as a self-contained review, the book will appeal to non-specialist physicists, metallurgists and chemists with an interest in disordered metals

A model for the anomalous magnetoresistance in amorphous semiconductors

Abstract: A semiclassical random walk hopping model is proposed in order to explain the anomalous magnetoresistance in amorphous germanium and silicon in the hopping regime. A general expression is derived for the magnetoresistance. The magnetoresistance is deduced to be the result of the modification of the spin-flip relaxation time by the external magnetic field. Explicit formulae are derived within the variable range hopping theory of Mott and the spin relaxation model described previously by the present authors. The model can then account for the variety of experimental observations in these materials.

In situ measurement of Hall effect, magnetoresistance, resistivity, and TCR of bismuth films

Abstract: In situ measurements of Hall effect, magnetoresistance, resistivity, and temperature coefficient of resistivity of bismuth films (700–2600 A) were carried out in a specially designed evacuation chamber. The films were deposited on a glass substrate at 150°C and at a pressure of ∼10−6 Torr. The values of the mean free path and specular scattering parameter obtained were 14100 A and 0.5, respectively. The effect of the grain boundary on the electrical resistivity was also accounted for in the light of the Mayadas‐Shatzkes theory.

Magnetotransport and superconductivity in dilute Fe alloys NbSe/sub 2/, TaSe/sub 2/, and TaS/sub 2/. [B up to 220 kG, 0 to 10 at. % Fe]

Abstract: Single crystals of dilute iron alloys of the layer structures NbSe/sub 2/, TaSe/sub 2/, and TaS/sub 2/ have been studied using measurements of magnetoresistance and Hall effect in magnetic fields up to 220 kG. Iron concentrations in the range 0--10 at.% can induce spin-exchange scattering, metal-insulator transitions, or enhanced superconducting anisotropy depending on the phase of the crystal and the type of iron doping. Kondo-like resistance minima accompanied by negative magnetoresistance and anomalous Hall effects are observed in the 2H phase of Fe/sub x/TaSe/sub 2/ and Fe/sub x/NbSe/sub 2/. A ln H behavior at high fields and a ln T behavior at zero field or low fields have been fit to theoretical expressions and antiferromagnetic exchange constants on the order of -0.1 eV are obtained. Excess iron doping of 2H-TaS/sub 2/ produces enhanced superconductivity characterized by parameters similar to those observed for organic intercalation. The interlayer coupling strength is consistent with a tunneling model describing both the iron-doped material and the organic intercalates. Substitutional iron doping of TaS/sub 2/ and TaSe/sub 2/ stabilizes the 1T phase and produces a dramatic rise in resistivity at low temperature following at T/sup -..cap alpha../ power-law behavior.

Magnetotransport properties of noble metals containing rare-earth impurities. I. Quadrupole scattering by rare-earth impurities in gold

Abstract: We report measurements of the magnetoresistance of gold containing rare-earth impurities in longitudinal and transverse magnetic fields. For rare-earths with orbital magnetism the dominant effect is an anisotropic magnetoresistance due to the scattering of the conduction electrons by the electric quadrupole moment of the $4f$ shell. This effect vanishes for gadolinium impurities (no quadrupole moment). We present a model of the anisotropic magnetoresistance induced by quadrupole scattering. From the analysis of the experimental results we derive the strength of the interaction of the conduction electrons with the quadrupole moment of the $4f$ shell.

Magnetotransport properties of noble metals containing rare-earth impurities. II. Theory

Abstract: Rare-earth impurities in noble metals induce an anisotropic magnetoresistance and a skew scattering contribution to the Hall resistivity. These effects are due to anisotropic terms of the $4f$---conduction-electron interaction, but an estimate of these terms based on conduction electrons in plane-wave states gives values too small to explain the experimental data. We have taken into account the admixture of $5d$ screening electrons into the conduction band, and we obtain a $4f$---conduction-electron interaction which has large anisotropic terms in addition to the conventional spin interaction. We have used in this calculation atomic $4f\ensuremath{-}5d$ Slater integrals, and we also had to estimate the width of the $5d$ virtual bound state. When we assume that the $5d$ electrons are in ${t}_{2g}$ states, we find that our estimate of the anisotropy of the magnetoresistance and of the skew scattering effect are in fair agreement with the experimental data. However, we find too large a negative isotropic magnetoresistance.

Field effect and magnetoresistance in small bismuth wires

Abstract: The change in the electrical resistance as a function of applied electrostatic charge, known as the field effect, has been measured in Bi wires ranging in size from 2.6 to 29 \ensuremath{\mu}m. These measurements were made at 4.2 K in the presence of applied magnetic fields of varying strengths and directions. The changes in resistance of the samples as a function of applied parallel magnetic field, in fields up to 7 \ifmmode\times\else\texttimes\fi{} ${10}^{5}$ A/m, have been analyzed as a combination of the bulk longitudinal magnetoresistance and a decrease in the amount of surface scattering. Simultaneous measurements of the field effect in these magnetic fields show, in general, a decrease in the field effect as the surface scattering decreases. When the applied magnetic fields are not parallel to the sample axis the magnetoresistance data indicate increased surface scattering, and an increase in the size of the field effect is also seen. These results are interpreted as suggesting that a major contribution to the field effect in our samples is due to changes in the surface scattering of the intrinsic carriers caused by the added charge. The magnetoresistance data allow us to estimate the specularity coefficient $p$ for two samples to be 0.33 and 0.41, and the change in $p$ with added charge to be 0.1 ${(\mathrm{C}/{\mathrm{m}}^{2})}^{\ensuremath{-}1}$ and 0.3 ${(\mathrm{C}/{\mathrm{m}}^{2})}^{\ensuremath{-}1}$.

Formation and properties of the impurity band in n‐ZnSe

Abstract: The Hall effect, conductivity, mobility, and magnetoresistance of low-resistivity n-ZnSe crystals in the temperature range from 4.2 to 300 K are investigated. At room temperature, the electron concentration of the samples investigated is 2 × 1016 to 5 × 1017 cm―3. The maximum electron mobility observed at 60 K is equal to U = 2200 cm2/Vs. Following experimental results are obtained: a maximum on the temperature dependence of Hall cofficient, the negative magneto-resistance in the helium temperatures range described by Toyozawa's theory and discussed assuming the existence of an impurity band in the samples investigated. A model of the impurity band formation in n-ZnSe is proposed and its basic parameters are determined. Russian Text Ignored

Galvanomagnetic effects in amorphous film alloys

Abstract: Measurements of the spontaneous Hall effect and magnetization of a series of rare earth-transition metal amorphous film alloys fit a model that the Hall asymmetric scattering is simply the sum of the Hall angles of the alloy components. Alloys of the form Gd .2 (TM) .8 where TM is Mn, Fe, Co or Ni show a maximum of \rho_{H}/\rho the Hall angle, (where ρ H is the Hall resistivity and ρ the sample resistivity) for Gd .2 (TM) .8 of 6%. We find that other rare earth elements have lower \rho_{H}/\rho ratios than Gd and that Nd-Fe alloys exhibit a smaller \rho_{H}/\rho than Gd-Fe because the Nd moments are in an disordered state. Of the alloys studied Gd .2 (TM) .8 is suitable for a Hall sensor because R s the spontaneous Hall coefficient ( \rho_{H} = R_{s}4\piM ) is also large, approximately 10-2μΩcm/G. This is because Gd .2 Fe .8 is a nearly compensated ferrimagnet and 4\piM is low. The anisotropic magnetoresistance in rare earth-transition metal alloys is about 0.1 to 0.2% and does not scale with ρ. The Corbino disc type magnetoresistance is found to be smaller than expected because in the demagnetized state magnetic domains remain effective Hall scatterers.

Magnetic recorded information reproducing apparatus

Abstract: A magnetic head in which two magnetoresistive elements are disposed in parallel to patterns recorded on a magnetic recording medium and spaced apart from each other by a distance shorter than a minimum interval of the recorded patterns, the magnetoresistive elements being each disposed between adjacent ones of magnetic shields through an insulator. A magnetic recorded data readout device employs the magnetic head and generates an output proportional to a composite difference resistance obtained by differentially combining resistance variations of the two magnetoresistive elements. A device is provided for detecting the position of magnetization transition of the recorded pattern and the direction of relative movement of the magnetic head to the magnetic recording medium from the zero cross point, and the direction of inclination of the waveform of the output generated by the magnetic recorded data readout device.

Critical resistance and magnetoresistance in magnetic materials

Abstract: Recent developments in the understanding of the critical behaviour of the resistance in magnetic materials are reviewed. This behaviour is determined by the electronic structure and the magnetic energy of the system. The calculated temperature and magnetic field dependences in the vicinity of the critical temperature, T c , are found to be the same as those of the magnetic energy for ferromagnets, but are more complicated for antiferromagnets. The relevant experimental data are compared with the theoretical predictions and suggestions are made for improvement of the data analysis, in order to derive from it critical exponents and critical ratios.

Transport in magnetic alloys: Scattering asymmetries (anisotropic scattering, skew scattering, side-jump)

Abstract: The scattering of conduction electrons by magnetic impurities depends on the current direction with respect to the impurity moments (anisotropic scattering effect) and is different to the left and to the right (skew scattering and side-jump effects). The scattering asymmetries show up in magnetoresistance and Hall effect experiments and have been mainly studied for rare-earth impurities. They are of interest for determining the anisotropic terms of the conduction electron-impurity interaction, such as quadrupolar Coulomb terms or orbital exchange terms. In alloys with transition metal impurities they can reveal the unquenced orbital part of the magnetic moment.

Oscillatory magnetotransport in the layer compounds 4Hb-TaS/sub 2/ and 2H-TaSe/sub 2/

Abstract: Quantum oscillations have been observed in the magnetoresistance and Hall effect of 4Hb-TaS/sub 2/ and 2H-TaSe/sub 2/ in fields up to 230 kG. For magnetic fields perpendicular to the layers at least twelve frequencies in the range 0.044 to 8.2 MG have been observed in 4Hb-TaS/sub 2/. Eleven frequencies in the range 1.6 to 44.6 MG have been observed in 2H-TaSe/sub 2/. The angular dependence of the frequencies generally follows functions of the form ..omega../sub perpendicular//sintheta, where ..omega../sub perpendicular/ is the frequency observed for field perpendicular to the layers and theta is the angle between the field and the layers. The angular dependence is consistent with that expected for a nearly-two-dimensional cylindrical Fermi surface, and the small cross sections corresponding to the observed frequencies indicate that the Fermi-surface sections result from the 3a/sub 0/ x 3a/sub 0/ x c/sub 0/ charge-density-wave superlattice. Maxima in the magnetoresistance rotation diagrams indicate the presence of open orbits along the c axis in both materials. Features in the field dependence of the magnetoresistance and Hall effect of 4Hb-TaS/sub 2/ suggest the presence of magnetic breakdown while the field dependence observed in 2H-TaSe/sub 2/ is well behaved, although magnetic breakdown may play a role inmore » the orbits associated with the highest frequencies.« less

Magnetic field modulation technique for the study of hot carrier oscillatory magnetoresistance phenomena

Abstract: A new experimental technique is reported which allows the detection of the oscillatory components of the magnetoresistance of semiconductors subject to high electric fields, where the pulse length must be in the submicrosecond region in order to avoid lattice heating. It uses a combination of sampling and magnetic field modulation techniques. Its capability of resolving hot‐electron magnetophonon structure in n–InSb at 77 and 4.2 K for up to N=10 Landau level spacings is demonstrated.

The resistivity of weak itinerant-electron ferromagnet

Abstract: The electrical resistivity and magnetoresistance of the weak itinerant-electron ZrZn2 were measured. The resistivity varies with temperature as T2 below the Curie temperature Tc with a large coefficient 4.7 × 10 -8 Ω cm K -2 and changes its slope very slightly at Tc. A negative magnetoresistance was observed above about 10 K. It shows a maximum at Tc. This behaviour is suggested as characteristic of weak itinerant-electron ferromagnets.

Magnetoresistance of UIr3 and UGe3 to 220 kG

Abstract: Topological properties of the Fermi surfaces of UIr3 and UGe3 were investigated. UIr3 is an uncompensated metal with open orbits along 〈110〉. This is in agreement with a proposed model of Arko and Koelling, based on augmented-plane-wave (APW) calculations. UGe3 is a compensated metal, which showed nearly quadratic magnetoresistance behavior for all field directions studied. The results are compared with the APW model of Arko and Koelling, which contains a multiply connected sheet of Fermi surface. The model, or slight variations thereof, is consistent with the available data.

Ferromagnetic Ordering in Mn-doped SnTe Crystals

Abstract: Using a superconducting solenoid attainable up to 40 kG, measurements have been made of the transverse magnetoresistance and Hall voltages in the Mn-doped (0.88 and 2.2 at.%) SnTe crystals at liquid helium temperatures. The magnetic impurity spins align ferromagnetically below certain temperature T m , around which the magnetoresistance becomes negative. The observed Hall effect consists of the normal temperature-independent component R 0 and the extraordinary component R 1 which appears only below T m . A graphically estimated saturation magnetization obeys approximately the Bloch T 3/2 law, which clearly shows the presence of ferromagmetism in this Mn-doped degenerate semiconductor.

Magnetoresistance in Antiferromagnetic α-Mn Metal

Abstract: The temperature dependence and the magnetic field dependence of the resistivity of polycrystalline α-Mn metal were measured between 1.3 and 20 K in external transverse and longitudinal magnetic fields of up to 100 kOe. The anomalously large coefficient of the T 2 term in the low-temperature resistivity of α-Mn was found to decrease appreciably for increase in the applied magnetic fields. These results are interpreted in terms of the suppression of spin fluctuations in the antiferromagnetic α-Mn by the high applied fields. The magnetic field dependence of the resistivity, which was corrected for the effect of cyclotron orbital motion, is shown to be a linear function of the applied fields.

Spin-flip electron scattering in the zero-gap semiconductor Hg 0.86 Cd 0.14 Te

Abstract: A ${0}^{\ensuremath{-}}$ maximum in the longitudinal magnetoresistance of ${\mathrm{Hg}}_{0.86}$${\mathrm{Cd}}_{0.14}$Te has been observed at 10\ifmmode^\circ\else\textdegree\fi{}K, providing evidence for spin-flip electron scattering in the material. Theoretical analysis indicates that the spin-flip processes are caused by acoustic phonons through the deformation-potential interaction.

Anomalous Magnetization and Magnetoresistance of Fe-Ni Invar under High Magnetic Fields

Abstract: Magnetization measurements have been made for Fe–Ni Invar alloys in high magnetic fields up to 180 kOe at high temperatures up to 850 K. In contrast to the case of pure Fe and pure Ni, M 2 - H / M curves for Invar alloys are hardly described by Landau's phenomenological equation in a high field region above 100 kOe. Namely, the M 2 - H / M curves are bent upward in high fields. Furthermore, it was observed that the magnetization curve is deviated upward from linearity by applying high fields in a higher temperature region. This additional magnetization over the usual one was reconfirmed by means of the transversal magnetoresistance effect measured with a pulse high field up to 300 kOe. This anomalous magnetization induced by a high field is considered to be due to re-polarization of low spin states of constituent Fe atoms.

Low‐temperature electron mobility in InSb

Abstract: Available experimental values of electron mobility in InSb samples with known impurity concentration are compared with the theoretical values obtained by an iteration technique including the effects of band nonparabolicity, wave‐function admixture, electron screening, and all scattering mechanisms. Experimental values for the temperature range 20–77 K are found to agree to within 10% with the theoretical values. Values for conductivity mobility, the Hall ratio, and magnetoresistance are also given for different impurity concentrations and compensation ratios. These values should be useful for obtaining the impurity concentration from the knowledge of the experimental values of these transport coefficients.