Table of contents

A review is given of the experimental investigations of the magnetocaloric effect (MCE) in rare-earth magnetic materials of different classes: heavy rare-earth metals and their alloys, iron garnets, and intermetallic compounds. The results of measurements of the MCE near phase transitions are given for the vicinity of the Curie and Neél temperatures, and also near magnetic compensation points in the case of ferromagnetism-helicoidal antiferromagnetism and helicoidal ferromagnetism–paramagnetism transitions. The contributions to the MCE made by the various magnetic sublattices in rare-earth ferromagnets are identified. Measurements of the MCE in single crystals of alloys of heavy rare-earth metals have made it possible to identify the main energy contributions to the helicoidal antiferromagnetism-ferromagnetism phase transitions and their energy dependences. The concluding section of the review deals with the technical applications of the MCE exhibited by rare-earth magnetic materials. An analysis is made of the potential applications as refrigerants in magnetic refrigerators, in thermodynamic cycles, and in structures of various types.

The experimental data on the electrical, thermal, and optical properties of high-boron compounds and modifications of boron—refractory crystals distinguished by specific and complicated structure—are reviewed. It is shown that depending on the complexity of the crystalline structure the properties of the materials transform, systematically approaching the properties characteristic of amorphous semiconductors; a new class of materials is thus identified—quasiamorphous semiconductors. In the limiting case of the most complicated structures, they can be regarded as natural structural models of amorphous semiconductors.

A review is made of research on geomagnetic pulsations, which are hydromagnetic waves of natural origin in the frequency range 10⁻³–5 Hz. Methods for diagnostics of the earth's magnetosphere and methods for electromagnetic sounding of the earth's crust on the basis of data from the observation of pulsations are described. It is believed that the electrical properties of the earth's crust are pertinent to the diagnostics of the magnetosphere, while consideration of the spatial structure of the inducing field is useful in geosounding. The fluctuation and critical properties of magnetic storms and pulsations are discussed on the basis of phenomenological models. Estimates of the properties of the magnetosphere and of the interplanetary medium at the earth's orbit can be made more accurate by taking account of the fluctuations in the diagnostic approach of a black box without an input.

This review is devoted to polarization phenomena observed in the x-ray range. It is noted that x-ray polarization effects are due to two physical factors, namely, the diffraction of x-rays and the anisotropy of the x-ray susceptibility of atoms in crystals. Diffraction-induced birefringence, dichroism, and change in polarization state are very dependent on the degree of imperfection of the crystal. Effects associated with the anisotropy of x-ray susceptibility, which have not been adequately investigated so far, are discussed in some detail. The anisotropy can lead to a qualitatively new effect, namely, the appearance of additional reflections with unusual polarization properties that provide information about crystal structure and chemical bonding. Magnetic scattering of synchrotron x-rays has become a powerful tool for the investigation of magnetic ordering in crystals. Practical applications discussed in this review include different modern x-ray polarizers, analyzers, and quarter-wave plates for obtaining and analyzing circular polarizations.

Three types of systems in which the excitation of oscillations due to high-frequency energy sources is possible have been considered. Despite widely held ideas, one can classify such systems as self-oscillatory. Systems with times of interaction with the energy source that are short in comparison with the period of the oscillations which arise are the first type. Systems of the second type are those having two degrees of freedom, one of which is high-frequency and the other is low-frequency. Transfer of the energy of the high-frequency source to the energy of low-frequency oscillations is achieved by the formation of combination frequencies. Thermomechanical systems are the third type. The role of the high-frequency energy source is to maintain the necessary temperature of the element being heated. Self-modulation of the parameters is the cause of oscillation excitation in such systems.