Showing papers on "Magnetoresistance published in 1984"
IBM1
TL;DR: The magnetoresistance of sub-0.4-m-diam Au and Au rings was measured in a perpendicular magnetic field at temperatures as low as 5 mK in search of simple, periodic resistance oscillations that would be evidence of flux quantization in normal-metal rings.
Abstract: The magnetoresistance of sub-0.4-\ensuremath{\mu}m-diam Au and ${\mathrm{Au}}_{60}$${\mathrm{Pd}}_{40}$ rings was measured in a perpendicular magnetic field at temperatures as low as 5 mK in search of simple, periodic resistance oscillations that would be evidence of flux quantization in normal-metal rings. However, instead of simple oscillations, a very complex structure developed in the magnetoresistance at low temperatures. Fourier analysis of all the data did not reveal convincing evidence for flux quantization in the rings. Complex structure similar to that observed in the rings was also found in the magnetoresistance of short, narrow, Au and ${\mathrm{Au}}_{60}$${\mathrm{Pd}}_{40}$ lines. This structure appears to be associated with the small size of the devices.
223 citations
TL;DR: CeCu 6 is shown to be a typical substance in the Kondo lattice ground state, having no magnetic ordering, and the anisotropic negative magnetoresistance is found at low temperatures, which probably reflects the orthorhombic crystal structure as mentioned in this paper.
Abstract: CeCu 6 is shown to be a typical substance in the Kondo lattice ground state, having no magnetic ordering. The anisotropic negative magnetoresistance is found at low temperatures, which probably reflects the orthorhombic crystal structure.
136 citations
TL;DR: In this paper, the Schmid model for homopolar optical-phonon scattering can explain the temperature dependence of electron mobility above 40 K and the optical phonon involved in the process is identified as the ${A}_{1}^{\ensuremath{'}}$ phonon with energy 143 meV.
Abstract: Electron scattering mechanisms in $n$-type indium selenide are investigated by means of the temperature dependence (4-500 K) of Hall mobility and the magnetic field dependence of Hall and magnetoresistance coefficients The Schmid model for homopolar optical-phonon scattering can explain the temperature dependence of electron mobility above 40 K The electron-phonon coupling constant is determined, ${g}^{2}=0054$ The optical phonon involved in the process is identified as the ${A}_{1}^{\ensuremath{'}}$ phonon with energy 143 meV The magnetic field dependence of Hall and magnetoresistance coefficients is discussed in terms of the Jones-Zener expansion
128 citations
TL;DR: To obtain a detailed view of the power deposition pattern resulting from time-varying magnetic fields used in hyperthermia, a method of modeling portions of the human body using an impedance network is developed.
Abstract: To obtain a detailed view of the power deposition pattern resulting from time-varying magnetic fields used in hyperthermia, we have developed a method of modeling portions of the human body using an impedance network. The region of interest is subdivided into a number of cells, each of which is then replaced by an equivalent impedance, and the currents induced in the resulting network due to the prescribed magnetic field are found by the application of circuit theory.
122 citations
TL;DR: A theory of coherence relaxation due to electron-electron collisions with small energy transfers in thin wires, films and inversion layers is presented in this article, where a qualitative description of weak localization and anomalous magnetoresistance in normal metals is given.
Abstract: A qualitative description of weak localization and anomalous magnetoresistance in normal metals is given. Such coherent effects as resistance oscillations of a hollow cylinder with magnetic flux and oscillations of current, flowing through a thick SNS-junction, to which a constant voltage is applied, are considered. A theory of coherence relaxation due to electron-electron collisions with small energy transfers in thin wires, films and inversion layers is presented.
60 citations
TL;DR: In this paper, the weak localization theory of magnetoresistance in two-dimensional systems is re-investigated and a formulation is developed which is applicable up to magnetic field much larger than the exsisting theory.
Abstract: Weak localization theory of magnetoresistance in two-dimensional systems is re-investigated. A formulation is developed which is applicable up to magnetic field much larger than the exsisting theory. The result of the calculation is compared with the experiment on GaAs/AlGaAs heterojunction and the agreement between them is satisfactory.
59 citations
TL;DR: In this paper, anomalous magnetoresistance in amorphous CuZr at low temperature has been observed and can be precisely accounted for in theoretical models of localization for 3D metallic systems in the presence of strong spin-orbit interactions.
44 citations
TL;DR: In this paper, the authors measured the temperature dependence of resistivity and found that the material behaves as a classical metallic conductor, with an intrinsic resistivity proportional to temperature and having a room temperature value of ∼11μΩ cm.
Abstract: High purity, single‐phase TiSi2 thin films were prepared by deposition of titanium onto polycrystalline silicon layers followed by furnace annealing. Measurements of the temperature dependence of resistivity show that the material behaves as a classical metallic conductor, with an intrinsic resistivity proportional to temperature and having a room temperature value of ∼11μΩ cm. Geometrical magnetoresistance measurements on Corbino disk samples give a ‘‘representative’’mobility value (∼60 cm2/V‐s at room temperature) that mirrors the temperature dependence of resistivity. The very small Hall effect, taken together with a sizeable physical magnetoresistance, indicates the material is predominantly an electron conductor with a spectrum of mobility values for carriers on the Fermi surface because an isotropic, two‐band model cannot quantitatively account for the data.
44 citations
TL;DR: In this paper, the magnetic moment per formula unit of CoPt increases with dilution which is attributed to a platinum moment of ≊ 0.3μB over the entire range of compositions.
Abstract: Crystalline films of CoxPt1−x were prepared over the range of x=0.26 to 0.84 atomic fraction by rf sputtering. Magnetization measurements show a wide range of anisotropy conditions including perpendicular anisotropy at intermediate compositions. The magnetic moment per formula unit of Co‐Pt increases with dilution which we attribute to a platinum moment of ≊0.3 μB over the entire range of compositions. The Hall effect and anisotropic magnetoresistance are both large at x≊0.4.
42 citations
TL;DR: In this article, the uniaxial anisotropy field H a of nominally single acicular particles was measured by three different methods, and the coercivity was also found.
Abstract: The uniaxial anisotropy field H a of nominally single acicular particles was measured by three different methods, and the coercivity was also found. A very dilute suspension was made in a viscous liquid, and a particle observed with the microscope. Various types of magnetic field were then applied, and the particle's change in orientation enabled H_{a}, H_{c} and/or H r to be determined. One method gave anomalously low values for H a , but it was possible to reconcile the results. The larger values lay in a range consistent with the chain-of-spheres and prolate ellipsoid models. There was a linear relationship between H a and H r (or H c ). The results suggested new reversal mechanisms.
38 citations
IBM1
TL;DR: In this paper, the magnetic, transport, and structural properties of RF sputtered Fe-Pt thin films were studied as a function of Pt content from 0 to 75 at.
Abstract: The magnetic, transport, and structural properties of RF sputtered Fe-Pt thin films were studied as a function of Pt content from 0 to 75 at.%. Polycrystalline ferromagnetic films were obtained in the range studied. The properties of the films are very similar to those obtained for bulk alloys. A body-centered-cubic phase is obtained for as-deposited films with less than 25 at.% Pt, and a face-centered-cubic structure is obtained for films with more than 25 at.% Pt. By annealing equiatomic Fe-Pt films, very large coercivities (about 10 kOersteds) can be obtained depending on the thickness, duration and temperature of annealing. The magnetization of Fe-Pt films is sufficiently large such that a moment of approximately 0.4 Bohr magneton must be associated with the Pt if Fe remains at 2.2 Bohr magneton per atom. The magnetostriction, Hall effect, and anisotropic magnetoresistance are all large near the equiatomic range of compositions.
IBM1
TL;DR: In this article, magnetotransport measurements were performed on GaSb-InAs-GaSb heterostructures, down to 0.55 K and up to 28 T. At moderate and high fields, the magnetoresistance vanishes and the Hall resistance shows plateaus at values of h ie 2 when i = 1, 2, 3, 4, 5 2.
TL;DR: In this paper, the temperature dependence of the magnetization, electrical resistivity and magnetoresistance of the stoichiometric Ni 3 Al have been measured, and the experimental results are consistent with the predictions of the self-consistent renormalization (SCR) theory of spin fluctuations.
Abstract: The temperature dependence of the magnetization, electrical resistivity and magnetoresistance of the stoichiometric Ni 3 Al have been measured. The spontaneous magnetization under the zero magnetic field and temperature T , M (0, T ) has a temperature dependence in a form of M (0, T ) 2 ∝ T 4/3 in a wide temperature range. The electrical resistivity shows a T 5/3 -dependence in a temperature range below and above T c . These experimental results are consistent with the predictions of the self-consistent renormalization (SCR) theory of spin fluctuations. The experimental results of the magnetoresistance are also discussed with the SCR theory.
TL;DR: In this article, the authors observed positive, anisotropic, strongly-temperature-dependent magnetoresistance in ultrathin [6-55]-\AA{}] Pd films.
Abstract: We observe positive, anisotropic, strongly-temperature-dependent magnetoresistance in ultrathin [(6-55)-\AA{}] Pd films. Interpreted in the light of recent theory, we find that localization effects dominate, but that electron-interaction effects are present as well. A strong spin-orbit scattering (symplectic limit) causes the localization-induced magnetoresistance to be positive. The inelastic scattering rate varies as ${T}^{2}$, although its magnitude is considerably larger than expected for electron-electron scattering. In some films we find a low-temperature drooping of the magnetoresistance which cannot be explained in the conventional localization---plus---electron-interaction theory.
TL;DR: In this article, the transport properties of very thin (2.5 monolayer) films of Ag epitaxially grown on clean Ge (001) substrates are reported, and the films consist of a monoline coverage plus isolated three dimensional islands.
TL;DR: In this paper, a model is presented in which the magnetic field induces a transition from transport in a conduction band to an impurity band, in which activation energy appears due to the separation of the two Hubbard bands.
Abstract: The metal-insulator transition in n-type InP doped in excess of the Mott criterion has been induced by the application of a magnetic field. In the metallic regime the authors have investigated the corrections due to quantum interference and the electron-electron interaction. The interaction effect increases with decreasing temperature with a consequent reduction in the negative magnetoresistance. In the absence of the magnetic field the correction due to localisation dominates above 2.0K and that due to interactions below. Fields greater than 10T induce a metal-insulator transition which has been investigated down to 30 mK. A minimum metallic conductivity is found, in agreement with previous work at higher temperatures, and the activation energy varies linearly with magnetic field. A model is presented in which the magnetic field induces a transition from transport in a conduction band to an impurity band, in the impurity band the activation energy appears due to the separation of the two Hubbard bands.
TL;DR: In this article, the transmission coefficient between two terminals of an effectively one-dimensional (1D) ring with arbitrary scatterers is calculated exactly as a function of enclosed magnetic flux, φ.
TL;DR: In this paper, the transport properties of chain-like compounds M2Mo6X6 with M=In or Tl and X=Se or Te were investigated, and only one of them was found to be superconducting, with a critical temperature between 5.5 and 6.6 K.
Abstract: We report on transport properties of chain-like compounds M2Mo6X6 with M=In or Tl and X=Se or Te. Only Tl2Mo6Se6 is found to be superconducting, with a critical temperature between 5.5 and 6.6 K. The superconducting properties are extremely dependent on the sample preparation. We have determined large azimuthal and polar anisotropies by magnetoresistance measurements. Properties of rare-earth-substituted samples, such as Eu2−x
Tl
x
Mo
6
Se
6
, are also reported.
TL;DR: In this article, the magnetoresistive switching behavior of small permalloy/silicon monoxide/permalloy sandwich elements is investigated and compared with single layer elements.
Abstract: The magnetoresistive (MR) switching behavior of small permalloy/silicon monoxide/permalloy sandwich elements is investigated. A comparison with single layer elements shows that the best MR‐switching results are found for the sandwich structures with the smallest dimensions (10×100 μm). A theoretical calculation based on the magnetostatic coupling between the two permalloy layers of the sandwich and on inhomogeneous demagnetizing fields shows good agreement with the experimental results. The formation of magnetic domain configurations other than those found in small single layer elements is illustrated using a ferrofluid observation technique.
TL;DR: In this paper, a negative photoresistance effect at Al0.3Ga0.7As/GaAs interface in the presence of a magnetic field B is discovered and explained, and the observed behavior of the resistance is associated with photoexcitation of electrons from donor vacancy (DX) centers in the highly doped AlGaAs region.
Abstract: A novel negative photoresistance effect at Al0.3Ga0.7As/GaAs interface in the presence of a magnetic field B is discovered and explained. At low temperatures (T=4.2 K) illumination of the sample leads to a persistent electron accumulation in the GaAs channel (the well‐known persistent photoconductivity effect). In the presence of B≳0.3 T the dependence of the longitudinal resistance (as measured by the four‐probe method) shows an anomalous behavior in that the resistance increases sharply with the increasing concentration n of carriers provided by light. In the same range of concentrations the longitudinal resistance at fixed n is proportional to B2. It is shown that the observed behavior of the resistance is associated with photoexcitation of electrons from donor vacancy (DX) centers in the highly doped AlGaAs region resulting in the creation of a second conducting layer of high charge density and low mobility.
TL;DR: The longitudinal and transverse magnetoresistances of disordered NiMn alloys with about 21, 26, 28, and 30 at.m.n have been measured in magnetic fields up to ∼75 kG and in the temperature range 1.2-80 K as discussed by the authors.
Abstract: The longitudinal and the transverse magnetoresistances of disordered NiMn alloys with about 21, 26, 28, and 30 at. % Mn have been measured in magnetic fields up to ∼75 kG and in the temperature range 1.2–80 K. For the 21 at. % Mn alloy the magnetoresistance is anisotropic (Δ ρ∥>0, Δ ρ⊥<0) at the lowest fields and temperatures. No detectable anisotropy is seen in the more concentrated sepcimens. In the critical concentration region (∼25 at. % Mn) the competition between ferromagnetic and spin glass effects is very severe and the magnetoresistance is marked by strong and unusual hysteresis effects in the Δ ρ/ρ0 vs H curves. When the sample is prepared with a remanent magnetization both Δ ρ/ρ0 and its field derivative undergo a discontinuity at H∼−1 kG and T=1.2 K.
TL;DR: In this article, the experimental τ e -1 in the dirty limit is smaller than the theoretical one by a factor of 1.5 ∼2.3, and the temperature dependence of τ e is analyzed by a theory developed recently by Fukuyama and Abrahams.
Abstract: Angular dependence and temperature dependence of negative magnetoresistance in two-dimensional electron gas in GaAs/Al x Ga 1- x As ( x ≃0.3) heterostructure are measured at temperatures between 4.2 K and 1.1 K. The temperature dependence of τ e is analysed by a theory developed recently by Fukuyama and Abrahams. The experimental τ e -1 in the dirty limit is smaller than the theoretical one by a factor of 1.5 ∼2.3.
TL;DR: In this paper, compositionally modulated structures (CMS) of PbTe-Bi with wavelengths between 38-140 A were prepared by thermal evaporation on muscovite mica substrates.
Abstract: Compositionally modulated structures (CMS) of PbTe–Bi with wavelengths between 38–140 A were prepared by thermal evaporation on muscovite mica substrates. There was a well defined epitaxy with the (111) plane and the [110] axis of the CMS parallel to (001) and [100] of the mica. The dc resistivity, Hall coefficient, and magnetoresistance were measured in the temperature range of 1.8 to 300 K and for magnetic fields up to 50 kG. All samples displayed an anomalous logarithmic increase in the resistance at low temperature. The magnetoresistance increased logarithmically with magnetic field H in large fields for the samples with thick PbTe layers (≳45 A), while it went as H1/2 for the samples with thin PbTe layers (≲30 A). The sign of the Hall coefficient changed from negative to positive with increasing Bi layer thickness and the positive Hall coefficient could be changed in sign by increasing the PbTe layer thickness.
TL;DR: In this article, the anomalous resistivity in the order of J 3, which is in proportion to T d /2-2 in the absence of magnetic fields, is seen to be suppressed, once the Zeeman energy exceeds the thermal energy.
Abstract: Magnetoresistance through an interplay between the Kondo effect and the Anderson localization is investigated in the weakly localized regime. The anomalous resistivity in the order of J 3 , which is in proportion to T d /2-2 in the absence of magnetic fields, is seen to be suppressed, once the Zeeman energy exceeds the thermal energy; J , T and d are an exchange interaction constant, temperature and dimensionality, respectively.
TL;DR: In this paper, the Shubnikov-de Haas oscillations of various GaAs/GaAlAs quantum well structures are studied at 4.2 K by applying the strong magnetic field parallel to the layers.
TL;DR: In this article, the authors analyzed magnetoresistance measurements in 2-mu..m-diam hollow Al cylinders within the framework of two-dimensional weak electron localization theories and showed that the observed resistance oscillations, due to the normal quantum interference of electrons enhanced by superconducting fluctuations, are well described by the combined theories of Altshuler and co-workers and Larkin.
Abstract: Magnetoresistance measurements in 2-..mu..m-diam hollow Al cylinders are analyzed within the framework of two-dimensional weak electron localization theories. The observed resistance oscillations, due to the normal quantum interference of electrons enhanced by superconducting fluctuations, are well described by the combined theories of Altshuler and co-workers and Larkin. Values for the different electron interaction times are comparable to the values obtained in plane Al films.
TL;DR: In this article, the weak localization theory of magnetoresistance (incorporating both Zeeman splitting and spin-orbit interaction) predicts values which are lower (up to a factor of ∼ 3) than the experimental values in these high-resistivity alloys.
TL;DR: The transverse magnetoresistance of (TMTSF)2 ClO4 has been investigated in magnetic fields up to 32 T at several temperatures down to 42 K and different angles between B and the crystalline axis as discussed by the authors.