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Showing papers on "Magnetoresistance published in 1970"


Journal ArticleDOI
TL;DR: In this article, the Hartree-Fock approximation is used to describe the band overlap or Wilson transition, which occurs when a conduction band overlaps a valence band; this is discussed in § 2 and for noncrystalline systems in § 15.
Abstract: An account is given of some of the mechanisms which can lead to a transition from a metallic to a nonmetallic state, when a parameter such as the interatomic distance or temperature is varied. The simplest of these is the band overlap or Wilson transition, which occurs when a conduction band overlaps a valence band; this is discussed in § 2 and for noncrystalline systems in § 15. These transitions can be described in the Hartree-Fock approximation. If the insulating property is due essentially to the repulsion between electrons (e2/r12), then the nonmetallic state is normally antiferromagnetic. The possibility of describing it by normal band theory with a spin-dependent potential is discussed in § 5. It is emphasized that antiferromagnetism can exist in the metallic state, and that the conditions for the appearance of conductivity and the disappearance of antiferromagnetism are not always the same. The nonmetallic behaviour, that is the existence of a Hubbard gap, normally persists above the Neel temperature (as in NiO), as does the gap in some metals, but not in chromium. Disordered systems, such as doped semiconductors, are discussed; here in the metallic state we suggest that the two Hubbard bands overlap, and that the metal-nonmetal transition can be described as an Anderson transition (§ 16). This model gives a simple explanation of the negative magnetoresistance. In some materials a transition occurs which does not involve magnetic moments or structural change, and for d bands, following Halperin and Rice, and Weger, we introduce the concept of an `orbital orientation wave' in degenerate d bands (§§ 5, 19.3, 19.4). A number of specific materials are discussed.

148 citations


Journal ArticleDOI
TL;DR: In this article, resistivity and magnetoresistance data obtained from 77 to 700 °K were presented, which suggest an interpretation based on a strongly spin-polarized conduction band.
Abstract: Resistivity and magnetoresistance data obtained from 77 to 700 °K are presented. These data suggest an interpretation based on a strongly spin-polarized conduction band. A model is developed based ...

135 citations


Journal ArticleDOI
TL;DR: In this paper, the second derivative of the magnetoresistance of high purity samples of n-type InSb, InAs and GaAs over a wide range of temperatures was observed.
Abstract: Magnetophonon peaks are observed in the second derivative of the magnetoresistance of high purity samples of n-type InSb, InAs and GaAs over a wide range of temperatures. The temperature dependence of the band-edge effective mass in each material is deduced and compared with that predicted from the dilatational component of the change in band gap with temperature. In the case of InSb, the agreement is excellent but, with InAs and GaAs, the observed change is greater than that predicted although still less than that obtained by substitution of the change of optical energy gap with temperature.

71 citations


Journal ArticleDOI
TL;DR: In this article, the relationship between the Hall mobility and the magnetoresistance mobility is determined experimentally for GaAs at room temperature, and the ratio is found to beμm/μH = 1.03±0.07.
Abstract: Geometrical magnetoresistance is developed as a technique for the determination of the Hall mobility of carriers in bulk effect GaAs microwave diodes at low electric fields. Spurious magnetoresistance effects due to inhomogeneities are analyzed and are shown to be negligible to first order for conductivity gradients oriented along the direction of the impressed electric field. For epitaxially grown GaAs, this is the predominant type of inhomogeneity and is due to diffusion of impurities out of the substrate or to a change in the doping during the growing process. The effect of contact resistance on the measurements of mobility is discussed as are a number of other practical aspects of the method, including the effect of misorientation of the magnetic field, the errors caused by finite aspect ratios of the diodes, heating by the measuring current, and the effect of magnetic shielding by parts of some commonly used microwave packages. The relationship between the Hall mobility and the magnetoresistance mobility is determined experimentally for GaAs at room temperature. The ratio is found to beμm/μH = 1.03±0.07.

70 citations


Journal ArticleDOI
TL;DR: The magnetic field dependence of the negative magnetoresistance can be described by −Δϱ/ϱ ∼ √ B n with 0.5 < n < 1.
Abstract: The amorphous semiconductors Ge, Si, InSb and GeTe show a completely different magnetoresistance compared from the crystalline phase. The sign of Δϱ/ϱ mainly is negative and its value is independent on the angle between current and magnetic field. The field dependence of the negative magnetoresistance can be described by −Δϱ/ϱ ∼  B n with 0.5 < n < 1. It is supposed that the negative effect is due to a hopping component of the conductivity. The strong decrease of − Δϱ/ϱ at high temperatures is explained by the assumption, that with increasing temperature the conductivity is more and more dominated by carriers in extended states. An ordinary magnetoresistance has been observed in the highly conductive state of an Ovonic memory switch, indicating that this state is due to a partial crystallization of the amorphous sample.

60 citations


Journal ArticleDOI
TL;DR: In this paper, anomalous phonons were measured as a function of temperature between 4°K and 300°C, and it was shown that the influence of the defects on the temperature-dependent part of the electrical resistivity plays an important role mainly at low temperatures.
Abstract: Deviations from Matthiessen's rule (MR) due to phonons inCuAu andCuNi alloys were measured as a function of temperature between 4°K and 300°C. They can amount to 40% of the residual resistivity of the doped samples. A second group of measurements concerns deviations from MR that occur inCuNi during a neutron irradiation at 4.6°K. It turned out that there are two essential reasons for these deviations. The first one is the influence of the defects on the temperature-dependent part of the electrical resistivity. It plays an important role mainly at low temperatures. We found experimentally and theoretically aT5 dependence for this additional resistivity at low temperatures. The second reason is the existence of anisotropies in the Fermi surface of Cu and in the scattering potential of the defects. These deviations can be described, as suggested by J. M. Ziman, by a two-band model for the Fermi surface. Furthermore, we could show that the enhanced resistivity increase in theCuNi alloys during neutron irradiation at 4.6°K, which was generally interpreted as an enhanced defect production, is essentially caused by deviations from MR. Measurements of the longitudinal magnetoresistance of the doped copper at 4.2°K were very useful for discriminating between the different causes of deviations from MR.

57 citations


Journal ArticleDOI
TL;DR: In this article, various types of electron transitions in strong magnetic fields due to qualitative changes of the energy spectrum of electrons (and hence of properties of materials) were predicted and observed at certain critical values of the magnetic field.
Abstract: Various types of electron transitions in strong magnetic fields due to qualitative changes of the energy spectrum of electrons (and hence of properties of materials) were predicted and observed at certain critical values of the magnetic field. Metallic and semiconducting Bi-Sb alloys were investigated in the concentration range of Sb up to 8 at % and from 8 at % to 16 at % correspondingly. The transversal and longitudinal magnetoresistance measurements on Bi-Sb alloy single crystals were performed at various orientations of current and fields relative to the crystalline axes. The measurements were performed in magnetic fields up to 600 kOe.at temperatures from 4.2 to 77°K. The following types of electron transitions were discovered: (a) semiconductor-metal transition; (b) a transition from a semiconducting state into a state with an abnormally small energy gap between the zones referred to as a “quasimetallic”; (c) a transition semiconductor-“quasimetal”-semiconductor; (d) a transition semiconductor-“quasimetal”-semiconductor-metal; and (e) metal-semiconductor transition.

56 citations


Journal ArticleDOI
TL;DR: The magnetoresistance of three samples of high purity n-type insb(nd-na varying from 5*1013 to 5 *1014 cm-3) is studied at lattice temperatures of 11 and 20 k with electric field strengths sufficient (>100 mv cm-1) to heat the electron distribution appreciably above the temperature of the lattice and at magnetic field strengths such that the effect of landau quantization is apparent as mentioned in this paper.
Abstract: The magnetoresistance of three samples of high purity n-type insb(nd-na varying from 5*1013 to 5*1014 cm-3) is studied at lattice temperatures of 11 and 20 k with electric field strengths sufficient (>100 mv cm-1) to heat the electron distribution appreciably above the temperature of the lattice and at magnetic field strengths such that the effect of landau quantization is apparent. Two distinct types of magnetophonon extrema are observed, each having a different dependence on electric field and temperature. The first consists of a series of minima which are only observed when the electron temperature is in excess of about 20 k and which arises from the emission of long wavelength longitudinal optical (lo) phonons.

45 citations


Journal ArticleDOI
TL;DR: The electrical resistivity, Hall effect, and magnetoresistance of β'-phase NiAl (45 ~ 60) at% Ni, CsCl-type structure) have been measured on about ten specimens of different compositions as discussed by the authors.

36 citations


Journal ArticleDOI
TL;DR: In this paper, the transverse magnetoresistance, pxx, of an aluminium single crystal has been measured at 4·2°K in fields in the direction up to 60 koe, and it is observed to undergo large oscillations, periodic in reciprocal field, with a frequency of 4·59 × 105 oe. The oscillations are superimposed on a background whose slope increases with field.
Abstract: The transverse magnetoresistance, pxx, of an aluminium single crystal has been measured at 4·2°K in fields in the [001] direction up to 60 koe. Above 20 koe it is observed to undergo large oscillations, periodic in reciprocal field, with a frequency of 4·59 × 105 oe. The oscillations are superimposed on a background whose slope increases with field. The Hall component of resistance, pyx, is found to be proportional to field and not to oscillate, and the longitudinal magnetoresistance, pzz, does not saturate and undergoes small oscillations. The cause of the behaviour of pxx and pyx is shown to be magnetic breakdown, which allows holes to change from one orbit to another in an adjacent Brillouin zone using a third zone part of the Fermi surface as a bridge. This mechanism alters the effective paths of the electrons and leads to a higher resistance than would obtain if only simply closed orbits were possible. The resistance oscillations are a consequence of the field dependence of the probability o...

34 citations


Journal ArticleDOI
01 Jun 1970-Carbon
TL;DR: In this paper, the magnetoresistance and its field dependence (down to 20G) were investigated at temperatures of 1.6, 4.2, 77 and 300°K for soft carbons heattreated in the range 1000-3200°C.

Journal ArticleDOI
TL;DR: In this article, a two-band model with a sharp mobility edge is presented, which produces a negative magnetoresistance varying linearly with magnetic field, and does not require the existence of localized magnetic states.

Journal ArticleDOI
TL;DR: In this paper, the linear magnetoresistance effect in pure potassium was measured using two independent methods: four-terminal measurements on straight narrow samples showed transverse and longitudinal effects of the same magnitude and an induced torque method was then used on large good single crystals.
Abstract: Measurements of the linear magnetoresistance effect in pure potassium were made using two independent methods. Four-terminal measurements on straight narrow samples showed transverse and longitudinal effects of the same magnitude. An induced torque method was then used on large good single crystals. In these the magnetoresistance was of the same order of magnitude as in the narrow samples and it was isotropic. The presence of the linear variation of resistivity with field in this case of a probeless method, where no obvious boundary value problems occur, adds to the existing evidence that the effect is not a result of sample shape or contact configuration.

Journal ArticleDOI
TL;DR: In this article, the Hall coefficient and magnetoresistance in a weak magnetic field are investigated for the impurity conduction processes based on a simplified model where the impure potential is short-ranged.
Abstract: The Hall coefficient and the magnetoresistance in a weak magnetic field are investigated for the impurity conduction processes based on a simplified model where the impurity potential is short-ranged. The formation of the impurity band and the modification of the intrinsic band are treated on the same footing by the Green function method. It is shown that the sign of the Hall coefficient is always electronic for n -type semiconductors irrespective of the degree of compensation. Two origins of the magneto-resistance, the Zeeman spin splitting and the Landau orbital motion, are separately calculated and both longitudinal and transverse magnetoresistances are shown to be of the same order of magnitude in the impurity band region. Numerical calculations of these transport coefficients are carried out as functions of the impurity concentration and of the degree of compensation. Intuitive discussion is made on the intrinsic nature of the impurity conduction processes. Further, the relation between the Hall coef...

Journal ArticleDOI
TL;DR: In this paper, a two-band model for the conduction electrons was proposed to describe the deviations that were measured in the deformed and irradiated copper samples and in Cu alloys in a consistent way, using the same parameters (ratio τ N /τ B of the relaxation times for the neck and belly of the Fermi surface).
Abstract: Deviations from Matthiessen's rule (MR) in cold-worked Cu samples have been measured as a function of temperature between 4°K and room temperature. They can amount up to 100% of the residual resistivity. A second group of measurements concerns deviation from the additivity of the residual resistivities that arise in the deformed specimens when point defects are added at 4.6° K during a neutron irradiation. In a third group of experiments we investigated deviations from MR as a function of temperature in undeformed Cu samples that have been neutron irradiated at 4.6°K and annealed at different temperatures. There are two essential reasons for these deviations: (1) Defects can change the vibrational behavior of the lattice and so alter the temperature-dependent part of the electrical resistivity. The additional resistivity is found experimentally and theoretically to depend asT 5 on temperature at low temperatures. (2) Anisotropies in the Fermi surface of Cu and in the scattering potentials of the defects give rise to deviations from MR. These deviations can be described by a two-band model for the conduction electrons. Within the framework of this model we were able to describe the deviations that were measured in the deformed Cu samples and in Cu alloys (earlier experiments) in a consistent way, using the same parameters (ratio τ N /τ B of the relaxation times for the neck and belly of the Fermi surface) for the two-band model. Furthermore we could show that the enhanced resistivity increase during neutron irradiation observed in deformed Cu samples is not the consequence of an enhanced defect production rate but that it is a result of deviations from MR due to the different scattering behavior of the defects induced by irradiation and cold work. Measurements of the longitudinal magnetoresistance of the deformed and irradiated copper samples give additional information about the scattering anisotropy of the defects and therefore allow for separating the contributions of the two types of defects the combination of which causes deviations from MR.

Journal ArticleDOI
TL;DR: In this article, the Bruggeman-Odelevsky method has been applied to polycrystalline metals in a magnetic field and the influence of three different factors on the galvanomagnetic properties of a polycrystal has been investigated.

Journal ArticleDOI
TL;DR: In this article, electrical resistivity and magnetoresistance evidence for the occurrence of conduction electron scattering from giant polarization clouds in paramagnetic Ni-Cu alloys was found for the first time.

Journal ArticleDOI
TL;DR: In this article, the magnetic properties and the electrical resistivity, the Hall effect, the thermoelectric power, and the magnetoresistance were carried out on polycrystalline rhombohedral Cr2S3.

Journal ArticleDOI
TL;DR: In this article, the magnetic-field dependence of the ground state of the singlet collective bound state was investigated and it was shown that the z-component of the spin correlation which sticks around the impurity remains unchanged even in the limit of increasing field.
Abstract: Recent two publications by Y osida and Y oshimori have clarified the detailed electronic structure of the singlet collective bound state developed so far by them and by Okiji. In this paper, by means of their method, the magnetic-field dependence of the local electronic struc­ ture of the ground state is investigated. In particular, it is shown that the z-component of the spin correlation which sticks around the impurity remains unchanged even in the limit of increasing field. From this calculation, an expression for the magnetoresistance is inferred with the aid of the Friedel sum rule : 1t .d R(.d)=Rocos22- (Eo2+.J2)t/2 ' where E0 denotes the binding energy of the singlet state and .J the Zeeman energy of the free spin. It is to be noticed that this has no logarithmic field dependence. It is further shown that the relation

Journal ArticleDOI
TL;DR: Magnetic and transport measurements in ferromagnetic EuB6 show evidence for a Fisher-Langer-type resistance anomaly near Tc, and they may not be a simple ferromagnet, and the magnetic coupling might be influenced by a temperaturedependent conduction electron concentration as mentioned in this paper.
Abstract: Magnetic and transport measurements in ferromagnetic EuB6 show (a) evidence for a Fisher‐Langer‐type resistance anomaly near Tc, (b) that EuB6 may not be a simple ferromagnet, and (c) that the magnetic coupling might be influenced by a temperature‐dependent conduction electron concentration.

Journal ArticleDOI
TL;DR: In this article, the transverse magneto-resistance of n -Si in different crystallographic directions at 77°K and at field strengths up to 5 kV/cm was measured.

Journal ArticleDOI
TL;DR: In this article, the longitudinal and transverse magnetoresistance and Hall coefficient of indium antimonide in the magnetic freeze-out range were measured, assuming conduction is only due to electrons remaining in the conduction band.
Abstract: Measurements of the longitudinal and transverse magnetoresistance and Hall coefficient of indium antimonide in the magnetic freeze-out range are described. For magnetic fields greater than 5 kG, the longitudinal magnetoresistance can be readily interpreted, assuming conduction is only due to electrons remaining in the conduction band. This is considered to be more plausible than the interpretation of the Hall coefficient used by previous authors, in which it is assumed that a two-band model can be used up to quite high fields. On the basis of conduction by a single band, values of the donor ionization energy as a function of magnetic field are calculated, with no adjustable parameters, and compared with the theory of Yafet, Keyes, and Adams.

Journal ArticleDOI
TL;DR: In this article, a memory-type chalcogenide glass, of composition Te81Ge15As4.5, was used for transport measurements and the results of these studies, taken in conjunction with the X-ray and NMR data, can be used to suggest a plausible model for memory behavior.
Abstract: Transport measurements have been performed on the conducting state of a memory-type chalcogenide glass, of composition Te81Ge15As4. DC resistivity was measured from 4°K to 300°K and indicates no carrier freeze-out occurs down to 4°K. The resistance ratio, ϱ(300°K)/ϱ(4°K), was found to be 2.5. AC conductivity measurements at room temperature showed only an 18% increase in σ(ω) up to 150 khz. Hall effect experiments at 100 Hz show no dependence of carrier concentration on temperature from 77°K to 300°K, and indicate a room temperature mobility of 85 cm2/V-sec. The sign of the Hall constant implies that the carriers are holes. Resistance was measured as a function of magnetic field from 0 to 140 kOe, at 1.6°K. The magnetoresistance was positive and proportional to H2 at low fields, with saturation beginning to set in above about 80 kOe. The results of these studies, taken in conjunction with the X-ray and NMR data, can be used to suggest a plausible model for memory behavior in chalcogenide glasses.

Journal ArticleDOI
TL;DR: In this paper, a detailed measurement of the temperature dependence of the longitudinal magnetoresistance of single-crystal Bi-Sb alloys has been made, with static magnetic fields in the range 0-100 kG oriented parallel to the trigonal axis.
Abstract: Accurate and detailed measurements of the temperature dependence of the longitudinal magnetoresistance of single-crystal Bi-Sb alloys have been made, with static magnetic fields in the range 0–100 kG oriented parallel to the trigonal axis. Alloy concentrations were in the range 8–12 at.% Sb, and temperatures in the range 1–35 K. At very high fields the resistance increases with increasing temperature in a metallic manner with “ideal” and “residual” components, in contrast to the semiconductor behavior observed at zero field or low fields. For the high-field semimetal regime the electrical resistance behaves in a simple manner similar to a metal in zero field, in contrast to the complicated magnetoresistance phenomena for metals in low fields. This behavior can be understood in terms of a simple quasi-one-dimensional extreme-quantum-limit regime. The magnetic-field-induced semiconductor-semimetal transition is associated with an energy gap and changes of the energy-band structure which are of order 1 meV. Thermal activation energies for electrical conduction manifest this gap only at temperatures below approximately 20 K. Activation energies an order of magnitude larger which have been measured at considerably higher temperatures are apparently the direct gap at theL-point in the Brillouin zone and are not directly connected with the semiconductor-semimetal transition. Our results indicate that the zero-field indirectL-T energy gap increases from zero somewhere near 7–8 at. % Sb to values only as large as approximately 1.5 meV at 12 at. % Sb. At the magnetic-field induced transition there occurs evidence of an intermediate “excitonic insulator” phase, a resistance minimum below 10 K reminiscent of the Kondo alloy behavior. This anomalous regime is a property of the semiconductor-to-semimetal transition and cannot be associated with the well-known temperature and magnetic-field “freeze-out” of charge carriers in extrinsic semiconductors, or with magnetic ordering of the Kondo type.

Journal ArticleDOI
TL;DR: In this article, a spherical sample is rotated in a transverse magnetic field while measurements are made of the torque produced by currents induced in the sample, and exact expressions for the torque in terms of the magnetoconductivity tensor are derived for a sphere and for an ellipsoid.
Abstract: A method is described in which a spherical sample is rotated in a transverse magnetic field while measurements are made of the torque produced by currents induced in the sample. Exact expressions are derived for the torque in terms of the magnetoconductivity tensor, both for a sphere and for an ellipsoid. The method has been used on large strain-free crystals of potassium, and an example of the results obtained is given.

Journal ArticleDOI
TL;DR: The magnetoresistance of many polycrystalline samples of nickel alloyed with small concentrations of iron, cobalt, manganese, chromium, and carbon has been measured.
Abstract: The magnetoresistance of many polycrystalline samples of nickel alloyed with small concentrations of iron, cobalt, manganese, chromium, and carbon has been measured. An analysis of the data gave the result that all those specimens in which the conduction-electron scattering was dominated by one particular scattering center were found to obey Kohler's rule. However, the details of the magnetoresistance were different in each case, with the exception of the iron, cobalt, and manganese impurities, which formed one group. In addition, the thermal-scattering magnetoresistance and that due to deformation were different again. These observations confirm previous conclusions concerning the validity of Kohler's rule. Extremely large magnetoresistance was found for the iron, cobalt, and manganese group of impurities as scattering centers, which apparently is much larger than observed in any other system. This can be correlated with other electronic properties of the impurities, such as the resistivity and magnetic moment per unit concentration. In particular, the high magnetoresistance appears associated with the presence of large local moments. The zero-field anisotropy in the resistance is also correlated with these same properties. In spite of this correlation, we have no clear interpretation of the extreme magnetoresistance.

Journal ArticleDOI
TL;DR: In this article, the experimental values of the planar Hall constant for monocrystalline InSb with electron concentration(10 16 −10 18 )cm −3 at 4·2°K up to 50 kG are presented.
Abstract: In the article the experimental values of the planar Hall constant for monocrystalline InSb with electron concentration(10 16 –10 18 )cm −3 at 4·2°K up to 50 kG are presented. The relation between the transversal magnetoresistance and planar Hall effect is experimentally verified. The geometrical parametesr of Hall generators affecting the magnitude of the planar Hall voltage are discussed. Using the obtained results the measuring accuracy of an Hall generator in field having all three components is investigated. We show that the planar Hall voltage must be taken in account expecially, when the perpendicular component of the measured field is small relating to planar field components.

Journal ArticleDOI
TL;DR: In this article, a method for growing single-crystal Mg2Pb ingots using a Bridgman method is described. But the method is not congruently melting but forms from a peritectic reaction.
Abstract: A method for growing single‐crystal Mg2Pb is described. A Bridgman method is used, starting with a nonstoichiometric melt (<31.3 at.% Pb). This requirement follows from the recent discovery that Mg2Pb is not congruently melting but forms from a peritectic reaction. The usefulness of an x‐ray microprobe for the analysis of crystal growing problems is demonstrated by a study of eutectic inclusions observed in some Mg2Pb ingots. Measurements are reported of the angular dependence of the magnetoresistance and the magnetic field dependence of the Hall coefficient in fields up to 5200 G and at temperatures of 4.2° and 77°K. The phenomenological coefficients, b, c, and d, determined from the angular dependence of the magnetoresistance show strong field dependence at 4.2°K and obey the symmetry condition for [100] oriented many valley ellipsoids at all fields and temperatures. The Hall coefficient exhibits a strong field dependence, similar to p‐type Ge, which has been fitted by a simple model consisting of two s...

Journal ArticleDOI
TL;DR: Magneto-Seebeck and magnetoresistance measurements were performed on polycrystalline samples of Cd3As2 at 80 °K and at 300 °K.
Abstract: Magneto-Seebeck and magnetoresistance measurements were performed on polycrystalline samples of Cd3As2 at 80 °K and at 300 °K. The result gives an effective mass of m*(0) = 0.012m at the bottom of ...

Journal ArticleDOI
TL;DR: In this article, the transverse thermal magnetoresistance of single-crystal plates of pure aluminum has been measured at liquid helium temperatures, and the high field Lorentz ratio is practically independent of field in agreement with theoretical predictions.
Abstract: The transverse thermal magnetoresistance of single-crystal plates of pure aluminum has been measured at liquid helium temperatures It is shown that the high field Lorentz ratio is practically independent of field in agreement with theoretical predictions, and the value of the Lorentz ratio in high fields is discussed in terms of thermal and electrical relaxation times It is also shown that the previously observed linear increase of the electrical resistivity in high fields is reflected in the thermal resistivity, and the origin of this effect is discussed It is believed that the linear behavior is not caused by a magnetic breakdown effect in this case, but is due to other intrinsic or nonintrinsic effects