Showing papers on "Magnetoresistance published in 1987"
TL;DR: In this paper, a current transfer model is proposed in which weak conduction along the c axis plays a role in limiting critical-current density at grain boundaries, and the effect of intrinsic conduction anisotropy is discussed.
Abstract: Measurements of the transport critical‐current density (Jc), magnetization Jc, and magnetoresistance in a number of bulk sintered samples of Y1Ba2Cu3Ox from several different laboratories indicate that the transport Jc is limited by weak‐link regions between high Jc regions. The weak‐link Jc has a Josephson character, decreasing by two orders of magnitude as the magnetic field is increased from 0.1 to 10 mT at 77 K. An examination of the grain‐boundary region in Y1Ba2Cu3Ox shows no observable impurities or second phases to the scale of the [001] lattice planes (∼12 A). The effect of intrinsic conduction anisotropy is discussed. A current‐transfer model is proposed in which weak conduction along the c axis plays a role in limiting Jc at grain boundaries. Orienting the grains in the powder state during processing may result in enhanced transport Jc in bulk conductors.
283 citations
TL;DR: In this paper, specific heat, magnetization, and transport properties (resistivity, thermoelectric power, and thermal conductivity) of single-crystal CeCu6 are reported with special emphasis on the effect of magnetic field.
Abstract: Measurements of the specific heat, magnetization, and transport properties (resistivity, thermoelectric power, and thermal conductivity) of single-crystal CeCu6 are reported with special emphasis on the effect of magnetic field. The relative field variations of the differential susceptibility, the coefficients of the linear temperature term of the specific heat, and theT
2 resistivity term are presented. They are directly related to the field curvature of the magnetization, indicating the itinerant nature of thef electrons. The Wilson ratio reaches a maximum atH=H*, which may correspond to a crossover from a low-field phase in which antiferromagnetic correlations dominate, to a highly polarized phase. Intersite coupling seems to play an important role in heavy-fermion compounds. Another interesting result is the occurrence of residual positive magnetoresistivity, which also appears to be a general feature of heavy-fermion compounds. The properties of CeCu6 are compared to those of otherf instability compounds and to present theories.
146 citations
TL;DR: In this article, the magnetic properties of the heavy fermion state of CeCu 6 were investigated and the Hall coefficient was found to be almost independent of the cerium concentration.
130 citations
TL;DR: In this paper, magnetic moments of about 3μB/U at high temperature and U-U distances from 3.51 to 4.68 A were measured for several equiatomic ternary intermetallic compounds of formula RTX with R = U, Th, Hf and Ti, T a transition metal (Co, Ni, Ru, Rh, Pd, Ir, Pt and Au), and X = Al, Ga, Sn and Sb).
107 citations
TL;DR: In this paper, the magnetic properties of the heavy-fermion superconductors CeCu2Si2, UBe13, UPt3 and URuSi2 were investigated.
Abstract: Experimental results are presented on the magnetic properties of the heavy-fermion superconductors CeCu2Si2, UBe13, UPt3 and URu2Si2, both in the normal state (susceptibility and magnetoresistance) and in the superconducting state (Meissner effect, upper and lower critical field). At elevated temperatures, not only CeCu2Si2 and the non-superconducting reference compound CeAl3, but also UBe13 behave like a dense array of independent Kondo impurities. At lower temperatures (T ⩽ 1 K) the onset of coherent scattering leads to new phenomena which are characteristic for the Kondo lattice. These concern e.g. a sign change of the magnetoresistance and a maximum in the upper critical field of CeCu2Si2. In all investigated heavy-fermion superconductors a superconducting order parameter is at Tc only formed on part of the Fermi-surface. In pure UBe13, as well as in Th-doped samples, the rest of the Fermi-surfaces becomes superconducting at about 0.5Tc, while in CeCu2Si2 parts of the Fermi-surface with “light” electrons stay normal down to very low temperatures. Though very anisotropic, the superconducting state of CeCu2Si2 appears to be a conventional one. In UPt3, on the other hand, evidence for a nonconventional order parameter is found. No conclusion can be drawn regarding the nature of the superconducting state of UBe13.
80 citations
TL;DR: In this article, the effect of temperature on the exchange coupling at the interface of three different bilayered materials was studied with the objective of developing temperature-stable single-domain materials for magnetoresistive readback heads.
Abstract: The effect of temperature on the exchange coupling at the interface of three different bilayered materials was studied with the objective of developing temperature‐stable single‐domain materials for magnetoresistive readback heads. Exchange field (HE) was measured from room temperature to 245 °C for NiFe films coupled to FeMn, αFe2O3, and TbCo. In the permalloy‐FeMn system, the exchange field decreases linearly, and reaches zero at about 150 °C, which is close to the Neel temperature of the antiferromagnet. These results agree well with previous work [C. Tsang and Kenneth Lee, J. Appl. Phys. 53, 2605 (1982)]. HE also decreases linearly in the αFe2O3 system, from 6.8 Oe at room temperature to 1.8 Oe at 245 °C. While the αFe2O3 system offers greater temperature stability, the exchange field produced is not very large, and the coercivity is somewhat high. Changes in HE with variations in the thickness of the αFe2O3 layer were also noted. Results for permalloy coupled to ferrimagnetic amorphous TbCo indicate ...
51 citations
TL;DR: Mesures de la diffusion magnetique d'atomes de Fe dans Au en fonction de the temperature dans le domaine entre 0,08 et 4 K.
Abstract: Mesures de la diffusion magnetique d'atomes de Fe dans Au en fonction de la temperature dans le domaine entre 0,08 et 4 K
46 citations
TL;DR: It is concluded that there exists grains in the sample with superconducting transition temperatures at least as high as 160 K, and the field dependence of the effect strongly supports this interpretation.
Abstract: We have observed anomalous voltage excursions as a function of temperature and magnetic field in samples of Y-Ba-Cu-O above 100 K. These transient voltages are attributed to flux jumps which are characteristic of granular superconductors. The field dependence of the effect strongly supports this interpretation. We conclude that there exists grains in the sample with superconducting transition temperatures at least as high as 160 K.
40 citations
TL;DR: In this article, high-field magnetoresistivity and magnetization experiments have been performed on a monocrystalline sample of the antiferromagnetic superconductor URu2Si2, for a field direction along the tetragonal axis.
38 citations
TL;DR: In this article, a single crystal of TmBa2Cu3O7−δ with a superconducting critical temperature of 86 K has been measured at nitrogen temperature with the magnetic field applied perpendicular and parallel to the (a,b) plane.
35 citations
IBM1
TL;DR: The traversal time for diffusion is used to calculate the mean square area enclosed between two randomly selected paths in a disordered conductor.
Abstract: Classical diffusion through a disordered region, connected to leads with unscattered carrier motion, can be characterized by reflection and transmission probabilities and by the time it takes a carrier to diffuse through the sample. This traversal time is found, following a suggestion by Pippard, by letting carriers be absorbed along the way and calculating the resulting reduction in transmission. The traversal time for diffusion is used to calculate the mean square area enclosed between two randomly selected paths in a disordered conductor. In the presence of a magnetic field, this area determines the field scale over which the magnetoresistance exhibits uncorrelated random fluctuations.
TL;DR: In the temperature regime above T/sub c/, the Kosterlitz-Thouless vortex unbinding temperature, the resistance was found to obey universal magnetic field scaling and the magnetoresistance displayed an activated temperature dependence characteristic of vortex pinning.
Abstract: This paper reports an experimental study of the influence of a magnetic field on the phase transition and low-temperature dynamical properties of two-dimensional superconducting films. Five samples of granular indium/indium oxide composite films were studied, with sheet resistances varying from 945 to 3150 ..cap omega../D'Alembertian, and thicknesses from 100 to 250 A. Measurements were made of the resistance R(T,H) and of the current-voltage characteristics in perpendicular magnetic fields of maximum value 30 G. The temperature range investigated ranged from 0.7T/sub c//sub 0/ to 1.5T/sub c//sub 0/, where T/sub c//sub 0/ is the Bardeen-Cooper-Schrieffer mean-field transition temperature. In the temperature regime above T/sub c/, the Kosterlitz-Thouless vortex unbinding temperature, the resistance was found to obey universal magnetic field scaling. Below T/sub c/, the magnetoresistance displayed an activated temperature dependence characteristic of vortex pinning. The pinning activation energy U(H,T) increased with a Ginzburg-Landau temperature dependence below T/sub c/ and displayed an unusual magnetic field dependence, varying inversely with magnetic field below 1 G, but becoming independent of field in stronger fields. As T/sub c/ was approached from below, all signs of vortex pinning disappeared, with U(H,T/sub c/) = 0 and the magnetoresistance exhibiting linear Bardeen-Stephen behavior. These results are interpreted in themore » context of other work on two-dimensional superconductors.« less
TL;DR: In this article, the Shubnikov-de Haas oscillations are studied, and clear evidence is presented for magnetic depopulation of 1-dimensional subbands of GaAs.
TL;DR: In this article, a theoretical analysis of weak localization in inhomogeneous magnetic fields is presented, showing that the weak localization correction to the classical conductivity is the result of interference effects characteristic of quantum-mechanical motion in a disordered conductor.
Abstract: A theoretical analysis of weak localization in inhomogeneous magnetic fields is presented. The weak-localization correction to the classical conductivity is the result of interference effects characteristic of quantum-mechanical motion in a disordered conductor. The phase-coherence length, set by inelastic collisions, describes the spatial limit to single-particle quantum-mechanical interference. When this length exceeds the length scale over which the magnetic field is uniform the standard theory of the weak-localization magnetoresistance in a uniform magnetic field is no longer applicable. The coherent quantum-mechanical motion probes the inhomogeneity of the magnetic field, and the conductivity thus exhibits its nonlocal dependence on the magnetic field. The inhomogeneity of the magnetic field is shown to lead to observable changes in macroscopic quantities; one possible experimental method of testing the effects of weak localization in inhomogeneous magnetic fields is presented.
TL;DR: The magnetoresistance Δϱ(B ) of CeCu 2 Si 2 samples with different stoichiometry and of a CeAl 3 polycrystal has been measured at low temperatures and high magnetic fields as discussed by the authors.
Patent•
04 Nov 1987
TL;DR: In this article, a magnetic rotary encoder system is described, which includes a magnetoresistive sensor having a magnetorsistive element array which is selectively connected to accommodate a number of different diameter encoder wheels each wheel of which contains a different number of pieces of magnetic information recorded at corresponding different wavelengths.
Abstract: A magnetic rotary encoder system includes a magnetoresistive sensor having a magnetoresistive element array which is selectively connected to accommodate a number of different diameter encoder wheels each wheel of which contains a different number of pieces of magnetic information recorded at corresponding different wavelengths. A sensing and conditioning circuit is coupled to the magnetoresistive sensor and detects changes in resistance of the magnetoresistive elements when a magnetic field produced by a magnetic pole causes the magnetoresistive resistance to drop. Output signals are provided in quadrature to increase the resolution of the system.
TL;DR: In this article, the authors describe experimental results of the low-temperature magnetoresistance measurement in a nanometer-structure doped GaAs wire with the thickness of 200A, the width of 0.3 μm and the length of 2 μm.
TL;DR: In this article, the transverse magnetoresistance has been measured on the single-crystal samples at 4.2 K in magnetic fields up to 17.5 T. The experiment indicates the possibility that there may exist an open sheet of the Fermi surface which supports open orbits in the (110) direction on the plane.
Abstract: To investigate topological properties of the Fermi surface of the intermetallic compound LaIn3, which attracts interest because of its magnetic and superconducting properties, the transverse magnetoresistance has been measured on the single-crystal samples at 4.2 K in magnetic fields up to 17.5 T. The experiment indicates the possibility that there may exist an open sheet of the Fermi surface which supports open orbits in the (110) direction on the (110) plane. The APW energy band-structure calculation predicts that LaIn3 may have a multiply connected open Fermi surface, whose topology is consistent with the experimental results.
TL;DR: In this paper, a selectively doped GaAs-AlGaAs submicron ring with a width of 0.35μm and a diameter of 1μm was fabricated from a MBE grown film making use of electron beam lithography and dry etching methods.
TL;DR: Magnetization, Hall effect and magnetoresistivity measurements down to 380 mk up to 23 T and down to 50 mK up to 12.5 T on the antiferromagnetic compound CePb3 are described as mentioned in this paper.
TL;DR: In this paper, the Yosida theory was adopted to calculate the resistivities and magnetoresistances of the dense Kondo Ce compounds quantitatively, and the wave number integration numerically was carried out.
Abstract: In order to calculate magnetoresistances due to the Ce impurities coupled with conduction electrons by the s - f exchange interaction, conditions for determining the number of local conduction electrons around Ce are given, which are valid for arbitrary spin-orbit and crystal-field splittings of Ce ion. General arguments for resistivity and magnetoresistance are given. In order to discuss the resistivities and magnetoresistances of the dense Kondo Ce compounds quantitatively, we adopt the Yosida theory and carry out the wave number integration numerically. It is shown that the resistivity along the crystal c -axis becomes small for crystalline fields with tetragonal or hexagonal symmetry and that a peak of magnetoresistance is expected due to the Kondo effect re-enhancement.
TL;DR: The luminescence of wide-modulation n-doped multiple quantum wells under high magnetic fields (up to 23) shows the recombination of the electrons and the holes in the lowest Landau level of the three electronic subbands occupied as mentioned in this paper.
Abstract: The luminescence of wide-modulation (500 A\r{}) n-doped multiple quantum wells under high magnetic fields (up to 23) shows the recombination of the electrons and the holes in the lowest Landau level of the three electronic subbands occupied. The luminescence intensity shows an oscillatory behavior with magnetic field corresponding to the depopulation of successive subbands. At a fixed luminescence frequency, the intensity shows a synchronical behavior with magnetoresistance oscillations when the luminescence energy corresponds to deexcitation of electrons with the the Fermi energy.
Patent•
20 Apr 1987TL;DR: In this paper, a magnetoresistance type magnetic head is proposed, in which a magnetoreduction film is disposed through an insulating film between two soft magnetic bodies, and a signal leadout conductor for the magnetoreductor is disposed in the film so that its surface is at the same level as that of the insulating material.
Abstract: A magnetoresistance type magnetic head, in which a magnetoresistance film is disposed through an insulating film between two soft magnetic bodies, and a signal leadout conductor for the magnetoresistance film is disposed in the insulating film so that its surface is at the same level as that of the insulating film, thereby providing a high-performance magnetoresistance type magnetic head, in which the gap length is small and the resistance of the signal leadout conductor portion is small.
TL;DR: Magnetoresistivity and Hall effect measurements on the antiferromagnetic compound CeAl 2, up to 20 T for T > 1.4 K and up to 10 T down to 50 mK, are described in this article.
TL;DR: In this paper, the upper critical fields of high-Tc superconducting oxides, La1.85Sr0.15CuO4-δ, Y0.4Ba0.6CuOy and YBa2Cu3O7-´, were measured by magnetoresistance method under a pulsed magnetic field up to 60 T in a temperature region 4.2 K to Tc.
Abstract: Upper critical fields of high-Tc superconducting oxides, La1.85Sr0.15CuO4-δ, Y0.4Ba0.6CuOy and YBa2Cu3O7-δ, were measured by magnetoresistance method under a pulsed magnetic field up to 60 T in a temperature region 4.2 K to Tc. The Hc2 (0) defined by the midpoint of the resistive transition are estimated to be 40, 90 and 148 tesla, for La1.85Sr0.15CuO4-δ, Y0.4Ba0.6CuOy and YBa2Cu3O7-δ, respectively.
TL;DR: It is shown that both hole-hole and hole-phonon scattering determine the inelastic lifetime of the conduction carriers.
Abstract: The magnetic field and temperature dependence of the resistance of low-stage acceptor graphite fiber intercalation compounds have been investigated at low temperature. The magnetoresistance curves are well described by the weak-localization theory in two-dimensional disordered systems. From the temperature and field dependence of the magnetoresistance, values of the temperature-dependent inelastic scattering time are obtained. It is shown that both hole-hole and hole-phonon scattering determine the inelastic lifetime of the conduction carriers. The contributions from the weak localization and Coulomb interaction effects to the logarithmic temperature dependence of the resistance have been separated.
TL;DR: By fitting the magnetoresistance measurements to these theories, the resistivity is determined in a way which is independent of the sample geometry, and it is found that it shows a remarkably strong dependence on the alloy composition.
Abstract: The temperature and magnetic field dependence of the electrical resistivity has been measured on single-phase icosahedral ${\mathrm{Mg}}_{32}$(${\mathrm{Al}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Zn}}_{\mathrm{x}}$${)}_{49}$ at x=05 and x=069 For temperatures between 4 and 20 K the observed behavior is found to agree quantitatively with the theories of quantum corrections to electron transport in disordered conductors By fitting the magnetoresistance measurements to these theories, we can determine the resistivity in a way which is independent of the sample geometry, and we find that it shows a remarkably strong dependence on the alloy composition
TL;DR: In this article, the scaling theory of the low-magnetic field Hall effect in a metal-non-metal mixture near its percolation threshold is reviewed and extended to discuss the magnetoresistance in low fields.
Abstract: The scaling theory of the low-magnetic-field Hall effect in a metal-non-metal mixture near its percolation threshold is reviewed and extended to discuss the magnetoresistance in low fields. It is shown that different types of critical behaviour are possible for the Hall coefficient and for the relative magnetoresistance of the mixture, depending upon the physical parameters of the mixture. A pair of new exponents are introduced to describe the critical behaviour of the second-order Hall contribution to the magnetoresistance of the mixture, and upper and lower bounds are suggested for their values.
TL;DR: In this paper, the authors measured the ferromagnetic resistance anisotropy Δρ/ρ0=(ρ∥−ρ⊥)/ ρ0 of Co91Fe09 films with thickness t between 5 and 113 nm.
Abstract: The ferromagnetic resistance anisotropy Δρ/ρ0=(ρ∥−ρ⊥)/ ρ0 of Co91Fe09 films with thickness t between 5 and 113 nm has been measured at 4.2 and 295 K. Here, ρ∥ and ρ⊥ are the resistivities when the magnetization is parallel and perpendicular to the current, and ρ0 is the zero‐field resistivity. Δρ/ρ0 is equal to 2.7% for t>40 nm at 4.2 K, but decreases fast for thinner films. This decrease is associated with an increase of surface scattering and grain‐boundary scattering. We plot Δρ/ρ0 vs ρB/ ρ0 where ρB is the resistivity of a bulk sample. This is the appropriate version for thin films of the ‘‘Parker plot,’’ based on Matthiessen’s rule. Our data form a straight line on this plot, in accordance with theory. Films of thickness ≂80 nm have been annealed at 300 °C, causing a reduction of lattice defects and an increase of Δρ/ρ0. The Parker plot shows that different scattering centers are important in annealed and unannealed samples. We also measured the compositional dependence of Δρ/ρ0 in thick CoxFe100−x f...