Hyperfine quenching of polarized two-electron ions in an external magnetic field

The hyperfine quenching mechanism of metastable states in polarized heliumlike heavy ions is considered. The lifetime dependence of these states on the ion polarization in an external magnetic field is established. This dependence is presented for the ²³P₀ state of the europium (Z=63) ion and is proposed as a method for the measurement of the ion polarization in experiments for the search of parity violating effects.     

Pattern of the induced magnetic field in high-temperature superconducting ceramics

Our experiments performed earlier have shown that, when an external magnetic field is absent, the transport critical current in 3-d superconducting ceramics is a homogeneous function of the sample transverse sizes. The transport critical current density and magnetic field induced by the current are homogeneous functions of a point on the sample cross-section. Using these experimental results equations describing the induced magnetic field pattern in ceramic sample have been derived. The distributions of the transport critical current density and induced magnetic field in the samples having polygonal, diamond-shaped cross-sections illustrate the results.     

Inverse beta decay of arbitrarily polarized neutrons in a magnetic field

We calculate the cross-section of the inverse beta decay process,v _e+n → p+e, in a background magnetic field which is much smaller than m _p ^2/e . Using exact solutions of the Dirac equation in a constant magnetic field, we find the cross-section for arbitrary polarization of the initial neutrons. The cross-section depends on the direction of the incident neutrino even when the initial neutron is assumed to be at rest and has no net polarization. Possible implications of the result are discussed.     

多结超导环在外磁场中的行为

分析和计算了双结超导环在无偏置电流时的磁通、环流、自由能与外磁场的关系.发现双结环与单结环在磁场中的行为有所不同.当两个结的Ic相等时，双结环在1＜β=2πLIcΦ0＜2时，若无偏置电流，总磁通Φ、环流I与外磁通Φe的关系仍然是非回滞的曲线.仅当β≥2时，曲线才出现回滞.另外双结环有两支解，并且每支解的周期为2Φ0. 关键词： 双结环 双支解 2Φ0周期 回滞     

Circular polarized coherent thermal radiation from semiconductor layers in an external magnetic field

We investigated, both theoretically and experimentally, the polarization properties of coherent thermal radiation from thin semiconductor planar layers in a weak external magnetic field. For the Faraday configuration, it is shown that the spectrum of thermal radiation is a superposition of two oscillating spectra which correspond to radiation of electromagnetic waves with right- and left-hand circular polarization.     

Phase transition in a plasma with anisotropic electron distribution in an external magnetic field

A phase transition is discussed that can occur in a plasma with substantially different transverse and longitudinal temperatures of electrons moving in a magnetic field, ?. The Debye cloud surrounding an ion sharply contracts as T_∥ decreases or the magnetic field increases. The effect of larger radiative electron-ion recombination cross sections compared with their theoretical values is explained; this effect is observed in storage rings with electron cooling systems (coolers). The role played by the phase transition in the crystallization of ion beams is discussed.     

Surface currents of a superconducting axisymmetric body that screen an external coaxial magnetic field

A time-saving method to find currents on the surface of a superconducting axisymmetric body is suggested for the case when the axis of the body and the symmetry axis of an external magnetic field coincide. The method is based on solving a one-dimensional integral equation. Analytical solutions are derived for the superconductor in the form of an ellipsoid of revolution that is placed in a uniform magnetic field and in the form of a sphere placed in a magnetic field varying as a polynominal at the symmetry axis. To find the current density on the surface of an arbitrarily shaped axisymmetric body placed in an arbitrarily varying magnetic field, a method of numerically solving the integral equation is proposed. It is a combination of the iterative regularization method and the projective method with a projector in the form of B splines. The results of numerical reconstruction of the sought functions by the latter method for a number of particular cases are presented.     

Effect of annealing in an external magnetic field on the magnetic texture of Mo-containing nanocrystalline alloys

The magnetic texture of (Fe_1?x Co_x)₇₆Mo₈Cu₁B₁₅ (x = 0, 0.5) nanocrystalline alloys is studied for different amounts of nanocrystalline grains. The originally amorphous alloys were annealed in external longitudinal and transverse magnetic fields of 0.025 T and 0.8T, respectively. Mössbauer measurements were carried out at room and liquid nitrogen temperatures in order to gain information on the hyperfine interactions and the orientation of the magnetization. The obtained results are compared with those received from zero-field annealed samples. Magneto-optical Kerr effect (MOKE) was applied for the investigation of possible changes at the surface of the x = 0 ribbon as a function of annealing temperature and applied magnetic field. A combination of uniaxial anisotropy, which originates from the shape anisotropy, and four-fold anisotropy, which is a contribution from crystallites of nanometre size embedded in the residual amorphous matrix, is unveiled.     

Effect of an external magnetic field on Landau damping in carbon nanotubes

A quantum-mechanical formula for describing the dependence of the longitudinal permittivity of a nanotube on its characteristic parameters and the magnetic field strength was derived. The imaginary part of the permittivity was isolated, and the cases of a Boltzmann and degenerate electron gas were examined. For a degenerate electron gas, asymptotic expressions for absorption in the short- and long-wave ranges were obtained. It was demonstrated that the absorption coefficient for a longitudinal electromagnetic wave exhibits Aharonov-Bohm oscillations.     

Noncollinear orientation of external magnetic field and flux lines penetrating an isotropic hard superconductor

Penetration by Abrikosov flux lines of an isotropic hard superconductor in the critical state induced by changes in the orientation of external magnetic field has been theoretically investigated. The analysis has been based on the microscopic nonlocal model taking into account forces of bulk and surface pinning, alongside magnetic forces of interaction of the row of penetrating vortices with existing flux lines, Meissner currents, and vortex images. New vortices penetrate a superconductor only when the angle through which the field is rotated is larger than a certain critical value. It has been determined that the alignment of entering vortices is essentially different from that of the applied magnetic field. The feasibility of detecting noncollinearity effects is discussed. Zh. éksp. Teor. Fiz. 114, 1804–1816 (November 1998)     

Effect of an external magnetic field on the propagation velocities of magnetoacoustic waves in a magnetic fluid

Theoretical results on the propagation of magnetoacoustic waves in an ideal magnetic fluid with frozen magnetization are generalized. Expressions for the propagation velocity of fast and slow magnetoacoustic waves and Alfven waves are derived. Agreement between the theoretical and experimental results is demonstrated for the fast magnetoacoustic waves propagating in a water-based magnetic fluid.     

Interaction of neutrons with layered magnetic media in oscillating magnetic field

New experimental possibilities of investigating layered magnetic structures in oscillating magnetic fields are discussed. Spin-flip and nonspin-flip neutron reflection and transmission probabilities show a frequency dependency near the magnetic neutron resonance condition. This allows to increase the precision of the static magnetic depth profile measurements of the magnetized matter. Moreover, this opens new possibilities of measuring the induction of the oscillating field inside the matter and determining the magnetic susceptibility of the oscillating magnetic field. Refraction of neutrons as they pass through a magnetic prism in the presence of an oscillating magnetic field is also investigated. A non-polarized neutron beam splits into eight spatially separated neutron beams, whose intensity and polarization depend on the strength and frequency of the oscillating field. Also, it is shown that the oscillating magnetic permeability of an angstrom-thick layer can be measured with a neutron wave resonator.     

The dynamics of the Heisenberg-Mattis model with an external magnetic field

We have obtained the energy of spin waves for disordered magnetic systems in an external magnetic field which are described by the Heisenberg-Mattis model.     

Effect of sample shape on nonlinear magnetization dynamics under an external magnetic field

Effect of sample shape on the nonlinear collective dynamics of magnetic moments in the presence of oscillating and constant external magnetic fields is studied using the Landau–Lifshitz–Gilbert (LLG) approach. The uniformly magnetized sample is considered to be an ellipsoidal axially symmetric particle described by demagnetization factors and uniaxial crystallographic anisotropy formed some angle with an applied field direction. It is investigated as to how the change in particle shape affects its nonlinear magnetization dynamics. To produce a regular study, all results are presented in the form of bifurcation diagrams for all sufficient dynamics regimes of the considered system. In this paper, we show that the sample's (particle's) shape and its orientation with respect to the external field (system configuration) determine the character of magnetization dynamics: deterministic behavior and appearance of chaotic states. A simple change in the system's configuration or in the shapes of its parts can transfer it from chaotic to periodic or even static regime and back. Moreover, the effect of magnetization precession stall and magnetic moments alignment parallel or antiparallel to the external oscillating field is revealed and the way of control of such “polarized” states is found. Our results suggest that varying the particle's shape and fields’ geometry may provide a useful way of magnetization dynamics control in complex magnetic systems.     

Effect of an alternating field on the relaxation of effect of an alternating field on the relaxation of magnetic flux in a Josephson medium

We establish how trapped magnetic flux depends on the frequency and amplitude of an alternating field and how such a field affects the relaxation rate of the flux. We find that the nature of the flux creep changes in the process and that relaxation of the flux stops after the external field is switched off. We examine the dynamics of flux relaxation in a ring in the approximation in which the current density is assumed homogeneous, for various density dependences of the effective vortex activation energy. The critical current density and the vortex activation energy are obtained as functions of the external field strength. Finally, we explain the observed behavior in terms of the different field profiles emerging in the rings. Zh. éksp. Teor. Fiz. 111, 1047–1056 (March 1997)