Showing papers on "Magnetoresistance published in 1981"

Magnetoresistance in Two-Dimensional Disordered Systems: Effects of Zeeman Splitting and Spin-Orbit Scattering

Abstract: Effects of Zeeman splitting and spin-orbit scattering on the resistance in two-dimensional disordered systems are theoretically studied. The field dependence of the magnetoresistance is shown to have the characteristic anisotropy. The present theory explains the qualitative features of the experimental observations by Komori et al. in Cu granular films.

Synthesis and some properties of black phosphorus single crystals

Abstract: Black phosphorus single crystals were prepared from a solution of white phosphorus in liquid bismuth The temperature dependence of the electrical resistivity and magnetoresistivity, and the reflection spectrum at room temperature were measured The intrinsic band gap energy was estimated to be 031 eV and negative magnetoresistance was observed at 42 K Intercalation of AsF5 to black phosphorus was tried and several-fold increase in the electrical conductivity was observed

Effect of Spin-Orbit Interaction on Magnetoresistance in the Weakly Localized Regime of Three-Dimensional Disordered Systems

Abstract: Effects of Zeeman spin splitting and spin-orbit interaction on magnetoresistance in three-dimensional disordered systems are investigated in the weakly localized regime and the results are compared with recent experiments on InSb by Morita et al.

Effects of Mutual Interactions in Weakly Localized Regime of Disordered Two-Dimensional Systems. I. Magnetoresistance and Spin-Susceptibility

Abstract: Effects of mutual interactions on conductivity, magnetoresistance and spin-susceptibility have been examined in the weakly localized regime of two-dimensional disordered systems. Both conductivity and spin-susceptibility have logarithmic correction with respect to temperature. Field dependence of the magnetoresistance, which can be appreciably different from that due to impurity scattering alone, is shown to be sensitive to temperature.

Low-temperature magnetoresistance of a disordered metal

Abstract: A contribution to the magnetoresistance is observed at temperatures below 100 mK in bulk metallic Si: P that is unanticipated within theoretical analyses of localization. This contribution is positive, approximately independent of sample orientation, and varying roughly as the square root of the applied field. An analysis of Coulomb interactions including spin splitting is presented which, when combined with localization, describes the magnetoresistance.

Magnetic delocalisation of a two-dimensional electron gas and the quantum law of electron-electron scattering

Abstract: Discusses the effect of a magnetic field on the weak localisation of a two-dimensional electron gas. It is shown that due to quantum corrections the electron-electron relaxation time tau ee varies with electron temperature T and tau ee-1=A1T+A2T2, in the temperature range 3K-0.1K. This short tau ee causes a rapid transition between states which are weakly localised and so reduces the logarithmic correction to the conductance. Negative magnetoresistance measurements are reported for (100) silicon MOSFETs in the temperature range 0.1-4K.

Displacement detector having first and second magnetoresistive elements with a bias field at 45° to each element

Abstract: The magnetic field sensing apparatus includes first and second magnetoresistive elements having respective angularly disposed current path portions through which a bias current flows and to which a bias magnetic field is supplied. An external magnetic signal field is supplied from a magnetic source, and the magnetoresistive elements are relatively displaceable with respect to this source. The bias field is supplied at an angle of approximately 45° with respect to the direction in which the bias current flows in each current path; and the source of external magnetic field generates a signal field whose polarity gradually decreases and then changes over to an opposite polarity at a boundary region. This change in the signal field is sensed by the magnetic sensor as it is relatively displaced, thereby producing an output signal that varies substantially linearly with this displacement over a predetermined range on both sides of the boundary region.

Positive Magnetoresistance Induced by Zeeman Splitting in Two-Dimensional Systems

Abstract: It is shown that In T term of the conductivity due to electron-electron interaction, discussed by Altshuler et al. and by Fukuyama, is partly suppressed by Zeeman splitting of the electronic levels. Magnetoconductance of the form ln H appears when the Zeeman energy is much larger than κ T . The magnitude of this term is independent of the direction of the magnetic field and its prefactor is \({-}e^{2}/2 \pi^{2}\hbar \) when the screening length is much smaller than the Fermi wave length.

The transport properties of Heusler alloys: 'ideal' local moment ferromagnets

Abstract: The authors have made resistivity, magnetoresistance, Hall effect and thermoelectric power measurements on the Heusler alloys Pd2MnSn, Ni2MnSn and Cu2MnAl. Results are characteristic of well-ordered spin-only local-moment ferromagnets. The thermoelectric power curves all show a unique behaviour which the authors suggest is that characteristic of any local-moment ferromagnet.

Low-temperature magnetoresistance of CeAl3

Abstract: A low-temperature magnetoresistance of CeAl3 is discussed using a model in which the potential scattering at Ce sites leads to a virtual bound state beow epsilon F and the scattering on the 4f magnetic fluctuations gives rise to a narrow Kondo resonance at epsilon F. Positive magnetoresistance is predicted in the zero-temperature limit while it decreases with the increase of temperature and changes sign at T approximately=TK/2 pi . The minimum magnetoresistance is reached at about T-TK/2.

Linear Magnetoresistance Caused by Sample Thickness Variations

Abstract: Experiments are presented which show that surface imperfections can give rise to a larger linear magnetoresistance than previously supposed; in fact, large enough to explain many hitherto-unexplained published results. A theoretical model, which takes into account both the finite width of the sample and the Hall fields within it, is shown to describe the experimental results quantitatively, without the use of adjustable parameters.

Self-Consistent Treatment of Two-Dimensional Anderson Localization in Magnetic Fields

Abstract: A self-consistent treatment of the Anderson localization by Vollhardt and Wolfle [Phys. Rev. B22 (1980) 4666] is extended to systems without time reversal symmetry by use of a diagrammatical method. In this paper magnetoresistance in two dimension is calculated for the case where the field effect can be treated quasiclassically. It is found that the magnetic field enhances the conductivity, though the system remains insulator in the absence of inelastic scatterings. The present investigation indicates that the one-parameter scaling theory cannot describe systems without the time reversal symmetry.

Magnetic sensor with two series-connected magnetoresistive elements and a bias magnet for sensing the proximity of a relatively movable magnetically permeable member

Abstract: A magnetic sensor for sensing the proximity of a magnetically permeable member, the sensor and member being relatively movable with respect to each other and having an axis of movement disposed within a fixed plane. The magnetic sensor includes two coplanar magnetoresistive elements, each element having a main current conducting path and possessing anisotropic resistance as a function of the direction of a resultant magnetic field applied thereto. The two magnetoresistive elements are connected in series, and a d.c. current is supplied to the series-connected elements. First and second saturating bias magnetic fields are supplied, as by a bias magnet, to respective ones of the magnetoresistive elements at the same angle θ o to each of the respective main current conducting paths in the absence of the magnetically permeable member. The angle at which each bias field is supplied is changed by substantially equal and opposite small deviation angles ±Δθ in response to the relative movement of the permeable member proximate the magnetic sensor. An output circuit is coupled to the junction defined by the series-connected magnetoresistive elements to produce an output signal which varies as a function of the deviation angles by which the angles of the bias fields change.

The electrical resistivity of potassium at low temperatures

Abstract: Measurements of the electrical resistivity as a function of temperature are described for the temperature interval from 1.1 to 4.2K for potassium samples with resistance ratios varying between 390 and 8200. The measurements show the existence of phonon drag in the resistivity and also a weakly temperature-dependent term Tm (with m close to 2), with a sample-dependent magnitude. The temperature-dependent resistivity rho (T) in this temperature interval can be represented by rho (T)=AT2+BT exp (-20 K/T). The possibility of ascribing the AT2 term to electron-electron scattering is discussed. The possible influence of the dislocation density on the linear magnetoresistance and on the deviations from Matthiessen's rule is discussed briefly.

System for measuring electrical output or energy

Abstract: In an apparatus for the measurement of electrical power, including a multiplier which receives on an input thereof an electrical signal proportional to the voltage component of the electrical power, and which is subjected to an external magnetic field proportional to the current component of the electrical power, an auxiliary magnetic field is applied to the multiplier. The multiplier is a Wheatstone bridge including four ferromagnetic and magnetoresistive thin films, and the magnetic fields have a direction along the direction of the hard magnetic axes of each of the thin films. The thin films are so positioned that the magnetization of two electrically oppositely disposed thin films resulting from the application of the external magnetic field thereto is rotated in a direction opposite to that of the correspondingly resulting magnetization of the remaining thin films, following application of the auxiliary magnetic field to the films.

Magnetoresistance and Hall effect in tetramethyl-tetraselenafulvalene-phosphorus hexafloride [ ( TMTSF ) 2 P F 6 ]

Abstract: We have measured the magnetoresistance and Hall effect of tetramethyl-tetraselena-fulvalene-phosphorus hexafloride as a function of temperature, magnetic field for several orientations, and electric field. For temperatures well below the metal-insulator transition we find a large positive Hall coefficient and positive magnetoresistance, indicating carrier mobilities greater than ${10}^{5}$ ${\mathrm{cm}}^{2}$/V sec at 4.2 K. The magnetoresistance is highly anisotropic for field orientations in theplane perpendicular to the highly conducting axis, indicating a quasi-two-dimensional band structure. The nonlinear conductivity seen with small electric fields below the metal-insulator transition has approximately the same magnetic-field behavior as does the Ohmic conductivity at the same temperature.

Magnetic and transport properties of Fe‐Au and Co‐Au films

Abstract: Thin film cobalt‐gold and iron‐gold alloys have been prepared by sputtering onto water cooled substrates. These alloys are crystalline with residual electrical resistivity (ρ) a factor of five greater than bulk alloys. For FexAu100−x the X‐ray diffraction patterns are characteristic of fcc structures (high Au content) and bcc structures (low Au content); CoxAu100−x shows mixed fcc and hexagonal diffraction patterns. Fe‐Au exhibits a constant magnetic moment per Fe of μB = 2.2 over the range 26 to 92% Fe. The resistivity of Fe‐Au at 4.2°K is about 40μΩcm and is independent of composition. The Hall effect expressed as Rs/ρ2 where Rs is the spontaneous Hall coefficient increases with Fe dilution. Co‐Au shows a concentration dependent magnetic moment which decreases with increasing Au and a Hall effect as given by Rs/ρ2 which increases in magnitude as the Co moment decreases. In addition the resistivity at 4.2 °K of Co‐Au is composition dependent increasing with decreasing Co content. The anisotropic magneto‐resistance in both Fe‐Au and Co‐Au behave similarly with the interesting feature that Δρ(Δρ = ρ∥−ρ⊥) has a maximum at about the same average magnetization as found for other alloys such as Ni‐Fe and Ni‐Co2. At the same composition of maximum Δρ the saturation magnetostriction becomes almost zero.

Magnetoresistance of Two-Dimensional Anderson Localized System in Self-Consistent Treatment

Abstract: Effects of magnetic field on the Anderson localization in two dimension have been investigated by extending the self-consistent treatment by Vollhardt and Wolfle to systems without time reversal symmetry. The magnetic field is found to enhance the conductivity, though the static conductivity at absolute zero of temperature vanishes always within the present formulation which treats the field effect quasiclassically.

Galvanomagnetic properties of 1T-VSe2

Abstract: Galvanomagnetic properties of 1T-VSe2 were investigated. At the normal-incommensurate charge density wave transition temperature a sharp kink in the resistivity and an abrupt slope change in the Hall coefficient were observed. At low temperature the behaviors of resistivity and the Hall coefficient can be well explained by the two-carrier model with temperature dependent mobility ratio. In addition, the angular dependence of magnetoresistance is different from that of ordinary transition metal dichalcogenides.

Hall Effect and Magnetoresistance of Co(S x Se 1− x ) 2 , 0≤ x ≤1

Abstract: The Hall effect and the transverse magnetoresistance of Co(S x Se 1- x ) 2 for 0 ≤ x ≤1 were observed in the field strength up to 90 kOe in the temperature ranges 4.2 K to 300 K. The ordinary and extraordinary Hall coefficients were determined. The negative ordinary coefficient gave about one electron in the dγ band for 0 ≤ x ≤1. The extraordinary coefficient was positive in the metamagnetic and ferromagnetic states except for a negative coefficient of CoS 2 . The magnetoresistance of the metamagnetic phase changed remarkably by a magnetic saturation. The increase of the resistivity in the magnetized state was about 60 µΩcm as compared with the non-magnetized state.

Applicability of the planar Hall effect

Abstract: The planar Hall effect in ferromagnetic films has been investigated. Particularly the response to inhomogeneous fields has been studied in view of the method of detection of the Hall voltage (’’one‐sided’’ or traditional). It is concluded that ’’one‐sided’’ detection may be of advantage. The Hall response around the theoretical singularity of the transverse susceptibility has been studied. It is found that a very sensitive device can be designed, based on this effect.

Electronic transport properties in 1T-TaS2

Abstract: The temperature dependences of the Seebeck effect and transverse magnetoresistance are systematically observed on 1T-TaS 2 with various qualities. The Seebeck coefficient is positive in commensurate CDW state and its temperature dependence in 20 K ⪅ T ⪅ 60 K seems to indicate that the samples are classified into two groups: one is metallic and the other is non-metallic although they show all non-metallic behaviors in conductivity. In the non-metallic crystals we found a new anomaly at 20 K, as yet unknown. In the metallic crystals we observed small but negative magnetoresistance at 14.1 K, which suggests the variation of electronic states around this temperature. We discuss the sample dependence in relation to electronic localization and dimensionality.

Jumps and induced anisotropy in the magnetoresistance of CuMn

Abstract: 2014 Magnetoresistances, 039403C1/03C1o, of CuMn 4.7 % and 1.35 % have been measured in fields ranging between + and 2014 35 kG and in the range of liquid helium temperatures. When the remanent magnetization mr is saturated and parallel to the field H, 039403C1/03C10 varies linearly with H for low fields and exhibits jumps. When the field is perpendicular to the initial remanence mr, 039403C1/03C10 is quadratic in H but considerably enhanced with respect to the reversible magnetoresistance for which mr ~ 0. It is found that the magnetoresistance depends only on the vector sum ~H + mr of the macroscopic reversible and irreversible magnetizations. J. Physique LETTRES 42 (1981) L-35 L-39 Classification Physics Abstracts 75.40 15 JANVIER 1981,

Shielded magnetoresistance transducer high data density applications

Abstract: A magnetoresistance transducer for reading data from the tracks of a record carrier comprises at least one magnetoresistance perpendicular to the direction of travel of the data of each track P. First and second plane magnetic means are situated at either side of the magnetoresistance in such manner as to intercept and deflect the magnetic field lines transmitted by the immediate surroundings of the track P and by the data items adjacent to the data item which has the magnetoresistance positioned opposite to it.

Magnetic properties and relaxation processes of magnetic anisotropy in amorphous magnetic ribbons due to heat treatment

Abstract: Thermally activated processes for as-quenched samples of amorphous ribbons of five kinds in which the sample possessing the negative λ is included are studied. It has been shown that the processes depend on the number and species of transition elements included in ribbons. Ribbons including plural transition elements have respectively different values of ΔE at each stage of activated process. The brittle ribbon in the as-quenched state has larger time constants and higher activation energies than the others. The estimated values of activation energies were ranging from 0.7 eV to 1.8 eV. They are regarded as the energies which correspond with the stress relief. No. influence of the sign of λ on the processes has been observed. Only the FeNiPB ribbon has shown the complex variation of magnetic properties with annealing.