Metals In High Magnetic Fields Research Articles

Grain boundary dynamics and selective grain growth in non-ferromagnetic metals in high magnetic fields

Abstract Grain boundary motion can be affected by a magnetic field if the anisotropy of the magnetic susceptibility generates a gradient of the magnetic free-energy density across the boundary. Due to this magnetic driving force, annealing of locally deformed single crystals in high magnetic fields results in growth selection. The character distribution of the boundaries connected to growth selection is found to be far from random. If a magnetic energy density gradient as a driving force is superimposed to a curvature driving force during grain growth, this biases the microstructure evolution with regard to grain size and crystallographic texture, as it is demonstrated on polycrystalline zinc and titanium. Analysis of individual orientation data reveals that the observed asymmetrical texture stems to a large extent from a difference in grain numbers of the individual texture components.

Electromagnetic quantum waves and their effect on the low temperature magnetoacousticresponse of a quasi-two-dimensional metal

We theoretically analyze weakly attenuated electromagnetic waves in quasi-two-dimensional(Q2D) metals in high magnetic fields. Within the chosen geometry, the magnetic field isdirected perpendicular to the conducting layers of a Q2D conductor. We haveshown that longitudinal collective modes could propagate along the magnetic fieldprovided that the Fermi surface is moderately corrugated. The considered wavespeeds strongly depend on the magnetic field magnitude. Also, we have analyzedinteractions of these quantum waves with sound waves of suitable polarization andpropagation direction, and we have shown that such interaction may bring significantchanges to the low temperature magnetoacoustic response of Q2D conductors.

Grain boundary dynamics and selective grain growth in non-ferromagnetic metals in high magnetic fields

Abstract Grain boundary motion can be affected by a magnetic field if the anisotropy of the magnetic susceptibility generates a gradient of the magnetic free-energy density across the boundary. Due to this magnetic driving force, annealing of locally deformed single crystals in high magnetic fields results in growth selection. The character distribution of the boundaries connected to growth selection is found to be far from random. If a magnetic energy density gradient as a driving force is superimposed to a curvature driving force during grain growth, this biases the microstructure evolution with regard to grain size and crystallographic texture, as it is demonstrated on polycrystalline zinc and titanium. Analysis of individual orientation data reveals that the observed asymmetrical texture stems to a large extent from a difference in grain numbers of the individual texture components.

Size Effect in the High-Field Magnetoconductivity of Pure Metal Single Crystals

The magnetoresistivity of tungsten single crystals with a residual resistivity ratio of up to 70,000 was measured in the temperature range from 4.2 to 55 K in a magnetic field of 10 T. The size effect, i.e., the linear dependence of the magnetoconductivity on the inverse sample dimensions, has been observed in the high-field magnetoconductivity. The experiments show that this phenomenon can be used to separate and study the surface and volume contributions to the magnetoresistivity of pure single crystals of compensated metals from liquid helium temperature up to approximately 25 K. It is shown that the specular reflection coefficient of the conduction electrons for pure metals in high magnetic fields can be determined in this way.

Millimeter-wave spectroscopy of low-dimensional molecular metals in high magnetic fields

We have used a cavity perturbation technique to probe the electrodynamic response of various low-dimensional molecular metals in high magnetic fields. We discuss some of the technical aspects of these measurements and go on to present recent experimental data obtained in magnetic fields of up to 33 T. In addition to providing finite frequency information in this frequency range, which is highly relevant to narrow bandwidth conducting systems, we show how the extreme flexibility and sensitivity of this technique offers great potential for probing the properties of novel materials in high magnetic fields.

Numerical model of quantum oscillations in quasi-two-dimensional organic metals in high magnetic fields.

Departures from standard Lifshitz-Kosevich behavior observed in the oscillatory magnetization and magnetoresistance of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) charge-transfer salts in high magnetic fields are investigated using a numerical model of the Landau levels in a quasi-two-dimensional metal. The numerical model enables oscillations in the chemical potential to be treated, as well as the effects of finite temperature, Landau level broadening, and the presence of additional quasi-one-dimensional Fermi surface sheets. The numerical calculations reproduce experimental magnetization data successfully, and allow several phenomena observed in the experiments to be investigated. It is found that pinning of the chemical potential to the Landau levels is responsible for the apparent anomalously low effective masses of the higher harmonics of the de Haas--van Alphen oscillations observed in recent experiments. In addition, the quasi-one-dimensional components of the Fermi surface are found to have a pronounced influence on the wave form of the oscillations in the model, providing a means by which their density of states can be estimated from experimental results. Whilst the magnetization is a thermodynamic function of state, calculations of the behavior of the magnetoresistance are much more model dependent. In this paper, recent theoretical models for the longitudinal magnetoresistance in semiconductor superlattices have been modified for use with the BEDT-TTF salts and are shown to successfully reproduce the form of the experimental data. The strongly peaked structure of the magnetoresistance, which comes about when the chemical potential is situated in or close to the gap between adjacent Landau levels, is found to be responsible for the apparent strong increase of the effective mass which has recently been reported in high field transport measurements. \textcopyright{} 1996 The American Physical Society.

Theory of Fermi-liquid effects in high-field tunneling.

Fermi-liquid effects are incorporated into the quasiclassical theory of superconductivity to give a quantitative theory for understanding tunneling experiments on real metals in high magnetic fields. The theory is formulated for arbitrary impurity scattering and anisotropy. Numerical calculations are done for the dirty, isotropic limit. The calculations for low spin-orbit scattering show that the energy difference in a magnetic field between spin-up and spin-down electrons is proportional to the l=0 antisymmetric Fermi-liquid parameter as confirmed by recent experiments. Furthermore, this same Fermi-liquid parameter is shown to renormalize the Pauli-limiting field in the calculation of the upper critical field. Recent experiments on thin films of Al are compared with the theoretical calculations.

Pulse technique for measuring magnetoresistance of metals in high magnetic fields

A method for measuring magnetoresistance of metals and metallic alloys in a pulse magnetic field of high intensity is presented. The accuracy of the sample magnetoresistance Δ ρ/ρ0 is ±12% and ±5% for Δ ρ/ρ0 values of 10−3 and 10−1, respectively. This accuracy can be achieved for sample resistances of the order of 10−1–102 Ω.

New Nuclear Spin Relaxation Process in Two Dimensional Metals in High Magnetic Fields

Abstract An unusual linear dependence of the nuclear relaxation rate upon the magnetic field is observed in the incommensurate linear chain compound Hg3-δAsF6. It is shown that the unique two-dimensional character of the conduction electrons motion in this metal enhances the relaxation rate in strong magnetic fields. The incommensurate lattice structure gives rise to very high cyclotron frequency in these fields and makes it possible to observe the enhancement.

Galvano and thermomagnetic measurements using a squid system

We have adapted a SQUID system for measuring transport properties of metals in high magnetic fields, and have used the system to determine the transport coefficients of bismuth at high fields and low temperatures, with special emphasis on quantum oscillations.

Electromagnetically excited acoustic standing-wave resonances in metals in high magnetic fields : R.A. Gordon and G. Seidel, Department of Physics, Brown University, Providence, Rhode Island 02912, U.S.A.

Electromagnetically excited acoustic standing-wave resonances in metals in high magnetic fields : R.A. Gordon and G. Seidel, Department of Physics, Brown University, Providence, Rhode Island 02912, U.S.A.

Effective electric conductivity tensor of polycrystalline metals in high magnetic fields

General equations with unknown parameters are obtained for the effective electric conductivity tensor of polycrystalline mixtures. Different methods of obtaining the unknown parameters are discussed. One of these methods, called in the paper the Bruggeman-Odelevsky method, has been applied to polycrystalline metals in a magnetic field. The influence of three different factors 1) fluctuations of the electron density 2) open orbits, 3) extended orbits, on the galvanomagnetic properties of a polycrystal has been investigated. In the first case agreement is found with Herrng's results, although it is shown that the range of applicability of his method is very restrained. The second case has not been considered by other authors. In the third case it is shown that the averaging method used by earlier authors needs very strong assumptions and this makes their explanation of the linear growth of the magnetoresistance doubtful.

Metals in high magnetic fields

This is a survey paper in which the author discusses the energy level structure of metals in high magnetic fields and the nature of the eigen functions, and relates the various phenomena to one another within the one conceptual framework of the quantum mechanics of electrons moving in a lattice.

The thermal conductivity of metals in high magnetic fields at low temperatures

In heat conductivity measurements between 2 and 4·5° K twenty-seven pure metals have been subjected to a magnetic field of 4 kOe. Of these, Cd, Sn, Pb, Zn, Ga, Ag, Tl and In show appreciable magneto-resistance effects. Single crystals of Cd, Sn and Pb were investigated and of Zn and Ga, single crystals of different orientations. Ag, Tl and In were polycrystalline specimens. Transverse and longitudinal fields were applied, the effect being always greater in the transverse case. Single crystals of Zn, Sn, Cd and a specimen of Tl were investigated in transverse fields up to 18·5 kOe. The thermal resistance of the cadmium crystal was increased by a factor of 1000 at 2·3° K, and the use of this effect in a thermal switch has been suggested. In transverse fields the thermal resistance of all metals was found to rise linearly except for very small fields. Indications of saturation effects were only obtained in longitudinal fields. The results have been discussed on the basis of existing theory.