Diffusion hall effect in compensated metals

Analytical investigation is made of the electron-hole diffusion in compensated media like semimetals, which takes place under crossed electric and magnetic fields. It is shown that the diffusion of carriers causes a transverse field effect different to the usual Hall one, if the conducting medium is bounded. The transverse voltage due to this effect increases almost linearly with the magnetic field (H), and changes its sign according to the polarity of H. This voltage is observable even for bulk specimens for which the usual size effect is negligible, but its appearance is easily masked in the presence of impurities. A detailed discussion is made for bismuth, considering a non-parabolic model for the electron Fermi surface. The transverse voltage is found to be very sensitive to the surface recombination velocity of the carriers as well as to the impurity concentration.     

On the theory of surface impedance of metals placed in a magnetic field

The smooth non-monotonous dependence of the metal surface impedance upon the magnetic field H is investigated theoretically for the cases of diffuse and specular reflection of electrons from the specimen boundary. The type of the electron-surface interaction has been found to have very little effect on the magnitude of the impedance Z_α(H) in the range of weak magnetic fields [equation (1)]. In a strong field [equation (2)] the surface impedance behaves differently for diffuse and specular reflection. The form of the Z_α(H) function depends essentially on the ratio of the electromagnetic wave frequency ω and the collision frequency of electrons ν. This provides a possibility of establishing experimentally the frequency of electron collisions with volume scatterers.     

The defects influence on domain wall propagation in bistable glass-coated microwires

We studied the domain wall (DW) dynamics of magnetically bistable amorphous glass-coated Fe₇₄B₁₃Si₁₁C₂ microwires. In according to our experimental results magnetic field dependences of DW velocity of studied microwires can be divided into two groups: with uniform or uniformly accelerated DW propagation along the microwire. Strong correlation between the type of the magnetic field dependence of domain wall velocity, v(H), and the distribution of the local nucleation fields has been observed.Moreover, we observed abrupt increasing of DW velocity (jump) on the magnetic field dependences of the domain wall velocity, v(H), for the both types of the v(H) dependences. At the same time usual linear increasing of the domain wall velocity with magnetic field persists below these jumps. It was found that the jump height correlates with the location of nucleation place of the new domain wall. We have measured local nucleation field distribution in all the microwires. From local nucleation field distribution we have obtained the DW nucleation locations and estimated the jump height     

Surface impedance of a superconducting slab in the mixed state: Effect of the surface barrier

The effect of the surface barrier on the surface impedance Z of a type-II superconductor slab with a finite thickness is investigated in dc magnetic fields H ₀, which are aligned parallel or perpendicular to the slab plane. It is demonstrated that, in a perpendicular geometry, the surface resistivity ρ_s=ReZ has a maximum when the depth of penetration of the ac magnetic field is of the order of the slab thickness (size effect). For a parallel orientation of the magnetic field H ₀, the effect of the Bean-Livingston surface barrier manifests itself as a decrease in the dissipative loss and a change in the field dependence of the surface resistivity characterized by a magnetic hysteresis. It is shown for the first time that, under the conditions of persistent trapped magnetic flux, the dependence ρ_s(H ₀) is a decreasing function, which is associated, in particular, with a nontrivial suppression of the size effect.     

Magnetoacoustic effect in non-degenerate semiconductors

The effect of ultrasonic waves propagating at an angle ? relative to the direction of a magnetic field in nondegenerate semiconductors such as n-type InSb has been studied by using a quantum treatment which is valid at high frequencies and in strong magnetic fields. Numerical results show that both the absorption coefficient and the change in the sound velocity depend on the direction of the propagation of ultrasonic waves relative to the magnetic field.     

Low-field peak effect in type II superconductors

The combined effect of a surface (edge) barrier and volume pinning on the dependence of critical current I _c on the magnetic field (I⊥H ₀) in bulk type II superconductors is investigated. In low magnetic fields, there is a portion of the curve I _c(H ₀) where I _c grows with H ₀, causing a nontrivial peak effect in this field range. Such behavior is explained by the combined effect of a surface (edge) barrier and volume pinning, the latter being rather sensitive to the transport current density distribution in a superconductor.     

Induced magnetic phase transitions in GdCo/Co-type multilayer films

The magnetic structure transformation of the layered ferrimagnet [Co/Gd₃₆Co₆₄]₄/Co in an external magnetic field was comprehensively studied. Using magnetometrical, magnetooptical, and magnetoresistive techniques, it is established that, when magnetized in fields exceeding a threshold value H _cr, the collinear magnetic structure formed by the magnetic moments of the Co and GdCo layers is distorted. The value H _cr varies nonmonotonically with temperature T and reaches a minimum at the temperature of magnetic compensation of the layered ferrimagnet. The H _cr(T) dependence is well described in terms of the homogeneous ferrimagnet model with an adequately chosen phenomenological intersublattice interaction constant taking into account the weakened coupling of the surface Co layers with the internal part of the actual layer structure.     

Anomalous plasma diffusion transverse to high magnetic fields in InSb

Investigations on the ambipolar diffusion of an electron-hole plasma transverse to a magnetic field have been carried out in InSb. A plasma layer, produced at the surface of the sample by a short laser pulse, was moved through the sample in crossed electric and magnetic fields by the Lorentz force. From the broadening of the plasma layer we found at 80K an enhanced diffusion coefficient which decreased proportional to 1/B for magnetic fields higher than 1T, constrary to the expected classical 1/B ² dependence. Furthermore, the diffusion coefficient was strongly dependent on the electric field. The ambipolar drift velocity, measured simultaneously showed a classical behaviour. Together with the enhanced diffusion we observed instabilites in the electric potential. The instability threshold decreased towards the cathode.     

Infrared emission and lasing due to magnetoelectric-photo effect in InSb: Spectroscopy

Spectroscopic investigations have been carried out on IR emission (and induced absorption) of bulky InSb subjected to a magnetic field H across a current density J passing through it at 80–300 K. Significant contribution of deep-level acceptors, such as Cu⁻ and Cu⁻⁻, to the radiative recombination has been observed at low excitations by J × H force at 80 and 300 K. While at high excitations the emission due to band-to-band recombination dominates even at low temperatures, and at further high excitations notable line narrowing in the spectral line has been disclosed at 80 K, demonstrating occurrence of lasing mostly in a form of multi-mode oscillations but occasionally with single-mode oscillation.     

Response of the electrical resistance of La0.67Ca0.33MnO3(40 nm) films mechanically compressed by the substrate in the course of their formation to electric and magnetic fields

The structure and electrical resistance of La_0.67Ca_0.33MnO₃(40 nm) epitaxial films grown quasicoherently on the surface of LaAlO₃(001) substrates are investigated. Compressive mechanical stresses that are active in the substrate plane during nucleation and growth encourage a decrease in the effective unit cell volume and an increase in the relative concentration of tetravalent manganese ions in the manganite layers. This leads to a decrease in the temperature of the maximum in the temperature dependence of the electrical resistivity of the films by approximately 90 K compared to the Curie temperature for the corresponding stoichiometric bulk crystals. It is found that, at T < 120 K and μ₀ H = 0 (where H is the magnetic field strength), the measuring current depends nonlinearly on the voltage V _b applied to the contacts. An increase in the applied voltage V _b and in the magnetic field strength H favors linearization of the current-voltage characteristics of the films.     

Influence of magnetic field on exciton luminescence

The magnetic field dependence of the exciton emission intensity I_ex(H) has been investigated in Ge crystals stressed along the direction near 〈100〉. In the low field limit the magnetic field correction has been evaluated to the wave functions of the ground and some excited states of an isotropic exciton. The calculated dependence I_ex(H) in the case of Ge is in a good agreement with the experimental one at H ? 0.5 T.     

Electron distribution function and recombination coefficient in ultracold plasma in a magnetic field

The electron distribution function and diffusion coefficient in energy space have been calculated for the first time for a weakly coupled ultracold plasma in a magnetic field in the range of magnetic fields B = 100?50000 G for various temperatures. The dependence of these characteristics on the magnetic field is analyzed and the distribution function is shown to depend on the electron energy shift in a magnetic field. The position of the “bottleneck” of the distribution function has been found to be shifted toward negative energies with increasing magnetic field. The electron velocity autocorrelators as a function of the magnetic field have been calculated; their behavior suggests that the frequency of collisions between charged particles decreases significantly with increasing magnetic field. The collisional recombination coefficient α _B has been calculated in the diffusion approximation for a weakly coupled ultracold plasma in a magnetic field. An increase in magnetic field is shown to lead to a decrease in α _B and this decrease can be several orders of magnitude.     

Magnetostriction of Hexagonal HoMnO<Subscript>3</Subscript> and YMnO<Subscript>3</Subscript> Single Crystals

We report on the magnetostriction of hexagonal HoMnO₃ and YMnO₃ single crystals in a wide range of applied magnetic fields (up to H = 14 T) at all possible combinations of the mutual orientations of magnetic field H and magnetostriction ΔL/L. The measured ΔL/L(H, T) data agree well with the magnetic phase diagram of the HoMnO₃ single crystal reported previously by other authors. It is shown that the nonmonotonic behavior of magnetostriction of the HoMnO₃ crystal is caused by the Ho³⁺ ion; the magnetic moment of the Mn³⁺ ion parallel to the hexagonal crystal axis. The anomalies established from the magnetostriction measurements of HoMnO₃ are consistent with the phase diagram of these compounds. For the isostructural YMnO₃ single crystal with a nonmagnetic rare-earth ion, the ΔL/L(H, T) dependences are described well by a conventional quadratic law in a wide temperature range (4–100 K). In addition, the magnetostriction effect is qualitatively estimated with regard to the effect of the crystal electric field on the holmium ion.     

The magnetization of PrFeAsO0.60F0.12 superconductor

The magnetization of the PrFeAsO_0.60F_0.12 polycrystalline sample has been measured as functions of temperature and magnetic field (H). The observed total magnetization is the sum of a superconducting irreversible magnetization and a paramagnetic magnetization. Analysis of dc susceptibility χ(T) in the normal state shows that the paramagnetic component of magnetization comes from the Pr³⁺ magnetic moments. The intragrain critical current density (J_L) derived from the magnetization data is large. The J_L(H) curve displays a second peak which shifts towards the high-field region with decreasing temperature. In the low-field region, a plateau up to a field H^* followed by a power law H^?5/8 behavior of J_L(H) is the characteristic of the strong pinning. A vortex phase diagram for the present superconductor has been obtained from the magnetization and resistivity data.     

Magnetic phase diagram of Ni(NO3)2 6NH3

The magnetic phase diagram of Ni(NO₃)₂6NH₃ was determined from the field and temperature dependence of the magnetic susceptibility. The zero temperature exchange and anisotropy fields were determined to be H_E(0) ≈ 26 kOe and H_A(0) ≈ 0.7 kOe respectively.     

The linear dispersion coefficient of surface magnetoplasmons

The dispersion of surface magnetoplasmons supported on a semiconductor-vacuum interface which is normal to an applied magnetic field is investigated. It is assumed that the surface possesses a depletion layer and that the dispersion is of hydrodynamic origin. Dimensionless numerical results are obtained for the magnetic field dependence of the linear dispersion coefficient with special reference being given to n-type InSb.     

The voigt-type microwave Kerr effect in semiconductors with spherical constant energy surfaces1

A plane wave analysis is given for the free-carrier, microwave magneto-Kerr effect in semiconductors having spherical constant energy surfaces for the case of the applied static magnetic field perpendicular to the propagation direction (Voigt-type Kerr effect). The analysis is in terms of R_v, the complex polarization factor of the reflected wave. The behavior of R_v is considered in detail for low magnetic fields. Multiple-carrier conduction and energy-dependent scattering are shown to give rise to major contributions to R_v. Computer curves for |R_v|vs. μ_eB, $\text{n}\text{p}$ and ω are presented for parameters corresponding to InSb. Approximate expressions for R_v, which are valid for low magnetic field, high-loss conditions, are given and compared with curves computed from the more complex expressions. Room temperature data for R_v are presented for TE₁₁ waves in a circular waveguide. The dependence of R_v on magnetic flux density is shown for intrinsic InSb. The data are compared with the plane wave predictions. Experimental data for the magneto-Kerr effect are also given for magnetic fields slightly misaligned from the Voigt orientation. An empirical model is introduced which describes these data in terms of data for the Faraday and Voigt orientations of the magnetic field. This model is shown to be of value for alignment of the magnetic field in the Voigt orientation, and for measurement of the Voigt-type Kerr effect in the presence of any small, remaining longitudinal magnetic field component.     

Electron-phonon scattering in potassium at high magnetic fields

We have measured the temperature dependence of both the zero-field resistivity and the transverse magnetoresistance of polycrystalline potassium wires (?(300 K)/?(4.2 K)=140 to 6000) in fieldsH?35 kG and at temperaturesT?4.2 K. Our principal findings are: 1) The presence of a large magnetic fieldH=35 kG does not alter the temperature dependence of ? from that observed atH=0; below 4.2 K theT-dependent part of the resistivities,_?T (H=0) and_?T (H=35 kG), fit well to the function exp (?Θ*/T) with the same Θ*=23K. 2) Deviations from Matthiessen's rule are significantly reduced in a strong field so that the magnitude of_?T (H=0) approaches that of_?T (H=35 kG) as sample purity decreases. 3) The slope of the high-field linear magnetoresistance increases slightly (?8%) from 1.5 K to 4.2 K. We attribute the exponential temperature dependence of_?T (H) to the freezing out of electron-phonon umklapp processes as has been shown for the zero-field resistivity. The reduction in deviations from Matthiessen's rule at high fields can be understood within semiclassical theory, but the latter cannot explain the failure of_?T (H) to saturate at high fields. A proposal by Young that electron-phonon umklapp scattering may contribute aT-dependent high-field linear magnetoresistance in potassium is considered.     

The ground state of two-dimensional electrons in a nonuniform magnetic field

An exact solution to the Schrödinger equation for the ground state of two-dimensional Pauli electrons in a nonuniform transverse magnetic field H is presented for two cases. In the first case, the field H depends on a single variable, H = H(y), while in the second case, the field is axially symmetric, H = H(ρ), ρ²=x ²+y ². The electron density distributions n = n(y) and n = n(ρ) that correspond to a completely filled lower level are found. For quasiuniform fields of fixed sign, the functions n(y) and n(ρ) are locally related to the magnetic field: n(y) = H(y)/?₀ and n(ρ) = H(ρ)/?₀, where ?₀ = hc/|e| is a magnetic flux quantum. Magnetic fields are considered that are periodic, singular, and bounded in the plane xy. Finite electron objects in a nonuniform magnetic field are analyzed.     

Effect of an external magnetic field and a trapped magnetic flux on the current-voltage characteristics of a granular high-temperature superconductor YBa2Cu3O7−δ

A comparative study of the current-voltage characteristics of the high-temperature ceramic superconductor YBa₂Cu₃O_～6.95 at T = 77.3 K is performed over wide ranges of external magnetic fields H _ext and “treatment” fields H _treat. It is found that the field dependences of the parameters a and j _c involved in the exponential equation E = a(j ? j _c)^v describing the current-voltage characteristics depend substantially on the method used for applying the magnetic field, whereas the exponent v ～ 2 depends on neither the method of application nor on the magnetic field strength. The field dependence of the trapped magnetic field H _trap is determined.