Impact of amorphization on the magnetic state and magnetocaloric properties of Gd3Ni

Rapid quenching and ball milling have been used to modify the magnetic state and magnetocaloric properties of the intermetallic compound Gd₃Ni. The melt-spun and ball-milled Gd₃Ni samples are found to exhibit a soft ferromagnetic-like behavior below 120 K, whereas in the crystalline state, the Gd₃Ni compound is an antiferromagnet with a Néel temperature of about 99 K. The reduced value of the saturation magnetization observed in amorphous Gd₃Ni samples is ascribed to the appearance of a magnetic moment on Ni atoms. After amorphization, the Gd₃Ni samples exhibit substantially improved magnetocaloric properties in a low field region in comparison with crystalline Gd₃Ni.     

Relaxation nature of a current settling upon the application of an electric voltage in LaMnO3 crystals

The electrical conductivity of LaMnO₃ crystals was measured at room temperature to determine that the transition to a stable magnitude of electric current corresponding to the applied voltage has a relaxational nature with a characteristic time of about 10 min. The steady-state value of the current depends on the preceding voltage applied to the sample. The effect was observed in both dc and ac measurements. Detailed characterization of the crystals was performed using magnetic and x-ray methods.     

The concentration metamagnetic transition in Tm1−x TbxCo2 compounds

The Tm_1?x Tb_xCo₂ (0 ≤ x ≤ 1) system was studied by measuring the magnetic susceptibility, electrical resistance, and neutron diffraction. In the compounds with 0 < x ≤ 0.15, an inhomogeneous magnetic state characterized by the existence of large regions (up to 100 Å in size) with short-range ferrimagnetic order was found to occur. The maximum of the residual electrical resistance observed in the compound with x = 0.1 at the magnetic ordering temperature was established to be due to the scattering of conduction electrons by localized spin fluctuations associated with f-d exchange fluctuations caused by the substitution of terbium for thulium. The increase in the terbium concentration to x ≥ 0.15 leads to a sharp increase in the Co sublattice magnetization and the establishment of a long-range ferromagnetic order, which indicates a concentration metamagnetic transition in the band subsystem.     

Relaxational polarization of dielectrics

Conclusion It follows from the foregoing that the main equations for the static and complex dielectric permittivity have now been sufficiently completely formulated, allowing the permittivity to be rigorously determined with short-range interaction taken into account. In the first case, this involves the use of the Gibbs distribution, and in the second the Kubo formalism. However, although ... the development of equilibrium statistical mechanics may be regarded as complete (from the American foreword to [14]), the reduction of the Gibbs distribution to take into account only the dipole -dipole interactions of nearest-neighbor molecules, as is done in the Kirkwood and Fröhlich theories, cannot be regarded as entirely satisfactory. For such an approach, it is necessary to know the accurate structure of the molecule and the position of the nearest-neighbor molecules, which requires special investigations. In addition, other forms of interaction are omitted, and elastic polarization is not taken rigorously into account.A much more difficult problem confronts theories of nonequilibrium relaxational polarization, in that the development of nonequilibrium statistical mechanics is much worse, since it considers considerably more difficult time-dependent problems and the fundamental question of irreversibility (from the same foreword). In the present review it has been shown that the basic problem of the theory of nonequilibrium relaxational polarization is to find the relation between the macroscopic and molecular distribution functions and to determine the explicit form of these functions. Rigorous solution of this problem for specific materials will allow the laws governing the establishment of relaxational polarization to be determined, together with the corresponding dispersion relations. To this end, in turn, it is necessary to know the relation between the molecular relaxation function and those defects which determine the relaxational process [74].Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 56–73, January, 1979.     

Neutron diffraction investigation of a metamagnetic transition in the Tb<Subscript>0.1</Subscript> Tm<Subscript>0.9</Subscript>Co<Subscript>2</Subscript> compound

The Tb_0.1Tm_0.9Co₂ compound is investigated using neutron diffraction. It is shown that this compound undergoes an irreversible band metamagnetic transition induced by an external magnetic field. The magnetization of the Co sublattice increases from 0.2 to 0.6 μ_B. The critical field strength is approximately equal to 1 T at temperatures of 1.8 and 4.0 K. As the temperature increases, the effect of the magnetic field on the magnetic state of the sample weakens and, at 25 K, no noticeable changes are observed in an external field of 0.75 T. The metamagnetic transition at 1.8 K is accompanied by the disappearance of rhombohedral distortions and brings about a lattice expansion by approximately 1%.     

Quantitative interpretation of EELS and REELS spectra

A critical analysis of the present day Electron Energy Loss Spectroscopy (EELS) data interpretation methods has been done. The necessity for the consideration of a target as a multilayered structure with different inelastic energy loss cross sections in the surface and the bulk layers has been shown to be a reality both for the transmission EELS and the reflection EELS (REELS). A method to reconstruct inelastic energy loss cross sections in various target layers from the experimental data has been presented. Essential qualitative and quantitative dependence of the path length distribution function for reflected electrons as a function of scattering angle has been revealed. The tested method for extraction of the information from REELS experiments with angular resolution has been presented.Received: 9 October 2003, Published online: 19 February 2004PACS: 34.80.-i Electron scattering - 34.50.Bw Energy loss and stopping power - 25.30.Fj Inelastic electron scattering to continuum     

Numerical analysis of isothermal space-charge relaxation in a dielectric with blocking electrodes

For a dielectric with blocking electrodes, the system of continuity and Poisson's equations is numerically solved in the nonsteady case. The distribution of the mobile-charge concentration and field inside an electrically neutral dielectric at various times, both after the potential is switched on and after the short-circuiting the latter. The time dependences of the isothermal polarization and depolarization currents are calculated. It is established, in particular, that these dependences for a dielectric with one type of mobile charge carrier are not approximated by an exponential.