MEETINGS AND CONFERENCES

CONFERENCE ON THE PHYSICS OF MAGNETIC PHENOMENA

The Division of Physico-Mathematical Sciences of the Academy of Sciences of the USSR, the Magnetism Commission of the Academy of Sciences of the USSR attached to the Ural Branch, and Moscow State University named after M. V. Lomonosov held a conference on the physics of magnetic phenomena in Moscow from May 23 to 31 of this year.

This was the third broad conference on magnetism held in the USSR in the postwar years (the first two conferences took place in December 1946 and November 1951 in Sverdlovsk). In contrast to the first two, some thirty foreign physicists specializing in magnetism from 11 countries also took part in the work of this conference: England, Hungary, the German Democratic Republic, Holland, India, the Chinese People’s Republic, Poland, the United States of America, France, Czechoslovakia, and Japan.

About 700 physicists specializing in magnetism, electrical engineers, and metallurgists took part in the conference, which lasted 8 days, in its plenary and sectional sessions. They represented various scientific institutions of the academies of sciences of the USSR and the Union republics, industrial ministries, industrial enterprises, and higher educational institutions of 20 different cities of the Soviet Union: Moscow, Sverdlovsk, Serdobsk, Kharkov, Kazan, Leningrad, Krasnoyarsk, Kiev, Riga, Molotov, Chelyabinsk, Ashkhabad, Baku, and others.

At eight plenary and eight sectional sessions, more than 80 reports and communications were presented on various questions in the physics of magnetic phenomena.

The magnetic properties of matter have an extraordinarily wide range in the phenomena of nature. On the one hand, the smallest material formations—elementary particles—possess magnetism; on the other hand, the magnetic fields of intergalactic spaces play an essential role in the life of the universe. Such breadth of magnetic phenomena attracts the close attention of physicists to them. At the same time, the still-unraveled mysteries of the magnetic properties of matter open before us broad prospects for their practical use in technology. Precisely for this reason, in addition to physicists, electrical engineers, metallurgists, radio engineers, and metallurgists, as well as specialists in other natural sciences, are very much interested in magnetism. Such an important significance of magnetism in science and technology makes broad, businesslike contact among all specialists who are interested, to one degree or another, in the development of both the theory and the technical applications of magnetism highly desirable. One of the most effective forms of such contact is the organization and holding of meetings and conferences on both general and particular questions of magnetism. Naturally, of course, at one, even a broad,

meetings it is impossible to discuss all questions of this branch of science. Therefore the sessions at the Conference included papers and communications only on a limited set of the most important sections of magnetism, namely on: a) the magnetism of weakly magnetic substances and low-temperature magnetism; b) paramagnetic and ferromagnetic resonance; c) the physics of the ferromagnetic and antiferromagnetic state; d) the physics of the technical magnetization curve and of magnetic materials.

Among the problems of the magnetism of weakly magnetic substances and low-temperature magnetism, at the present stage of development of the physics of magnetic phenomena very great interest is attached to the study of oscillations of the magnetic susceptibility over a wide interval of fields (the de Haas—van Alphen effect), and also of galvanomagnetic effects (changes of resistance in a magnetic field and the Hall effect). The special interest in studying these phenomena lies in the fact that, in investigating them, it is possible most directly to elucidate the character of electron motion in crystals, and precisely, to determine the dependence of the energy on the quasimomentum for quasiparticles—current carriers of the Fermi type (the so-called dispersion relations), to clarify the form of the Fermi surface, and so on. This information is of enormous interest for testing our present-day theoretical ideas about the electronic structure of solids, on the one hand, and also for constructing more adequate theoretical models of reality for calculating electronic energy spectra in crystals, on the other.

In the paper by B. I. Verkin, B. G. Lazarev, I. M. Dmitrenko, and I. F. Mikhailov, “Magnetic Properties of Nonferromagnetic Metals at Low Temperatures,” the principal general conclusions were presented from a large number of works carried out since 1949 at the Physico-Technical Institute of the Academy of Sciences of the Ukrainian SSR. These investigations first clearly showed that the de Haas—van Alphen effect is not specific only to bismuth crystals, but is a universal phenomenon for a large aggregate of metallic crystals. Studies of the crystallographic anisotropy of the de Haas—van Alphen effect and its temperature dependence, in comparison with theory, made it possible to determine the basic parameters characterizing the state of the electrons in the metals investigated. The discovery in these experiments of a complex frequency spectrum of the “periodic” dependence of susceptibility on the field indicates the complex character of the electronic energy spectrum in the crystal (the existence of several types of current quasiparticles). The experimental data obtained indicate the possibility of determining the form of the Fermi surface for these various types of fermions.

The paper by the English scientist D. Shoenberg, “Experimental Studies in the Field of the de Haas—van Alphen Effect,” aroused great interest. In his report the author emphasized that for “weak” magnetic fields (of the order of \(2 \cdot 10^4\) oersted) one can, from measurement data, judge only the character of small portions of the Fermi surface and obtain information about the so-called “fine structure” of this surface. To obtain information on large portions of the Fermi surface, stronger fields, up to \(10^5\) oersted, are required. The author developed new, very interesting methods of measurement, with the aid of which one can observe oscillations of the magnetic susceptibility of very short period in such strong fields on a cathode oscillograph. Strong fields were obtained by pulses during the discharge of a condenser. The author’s measurements permit one to draw interesting conclusions about the form of Fermi surfaces and to carry out a broad comparison with theory.

MEETINGS AND CONFERENCES

In the report by E. S. Borovik, “Galvanomagnetic Phenomena and the Properties of Conduction Electrons in Metals,” experimental results obtained by the author in comprehensive studies of the Hall effect and of changes in resistance in a magnetic field were presented.

For the theoretical interpretation the author resorts to a two-zone model of a metal with mixed conductivity (holes and electrons).

In the report by N. E. Alekseevskii, N. B. Brandt, and T. I. Kostina, “Galvanomagnetic Properties of Bismuth,” the authors’ data were presented on the measurement of the strong reversible influence of all-round compression on the galvanomagnetic properties and electrical conductivity of bismuth. The experimental results are interpreted by means of a two-zone model of the metal.

In the report by I. M. Lifshits, M. Ya. Azbel, and M. I. Kaganov, “On the Theory of Galvanomagnetic Phenomena,” the foundations were set forth of a general theory of galvanomagnetic phenomena in nonferromagnetic metals without any special assumptions about the law of electron dispersion of the conductivity and about the nature of their interaction with the crystal. The theory was presented in two variants: classical (without taking into account the quantization of levels in a magnetic field) and quantum. The authors showed that the behavior of the specific electrical conductivity and of the Hall constant in strong magnetic fields is determined by the topology of the isoenergetic surfaces situated near the boundary surface of the Fermi surface. The theory, in its most general form, explains the existence of two groups of metals (see the report by E. S. Borovik), as well as the linear increase of resistance in a magnetic field at intermediate fields, discovered by P. L. Kapitza. The theory also gives an explanation of the de Haas—van Alphen effect.

M. Ya. Azbel and E. A. Kaner, in their report “The Theory of Cyclotron Resonance in Metals,” discussed the theory of a peculiar resonance phenomenon that arises in a metal when a high-frequency electromagnetic field and a constant magnetic field are applied. This phenomenon differs substantially from diamagnetic resonance in semiconductors, since in the latter the depth of the skin layer is considerably greater, whereas in metals, on the contrary, it is considerably smaller than the radius of the Larmor orbit of the electron. The study of this effect can provide valuable information about the energy spectrum of electrons in a metal.

The report by the Japanese physicist R. Kubo, “The Theory of Galvanomagnetic Effects in Metals in Strong Magnetic Fields,” was devoted to the theoretical study of electron motion in strong magnetic fields. The author refrains from using the usual Boltzmann—Bloch kinetic equation in strong fields and has developed his own original method of calculation, which consists in expressing the conductivity tensor through the spin-density correlation function of the current component.

The report by I. M. Lifshits, A. M. Kosevich, and A. V. Pogorelov, “The Energy Spectrum of Electrons in a Metal and the de Haas—van Alphen Effect,” was devoted to an exposition of the quantum-mechanical theory of the motion of a charged quasiparticle in a homogeneous magnetic field for an arbitrary dispersion law. Along with the spin paramagnetic and diamagnetic part of the magnetic moment, its oscillating part was obtained. It was shown that the period of the oscillation is determined by the character of the Fermi surface (by the extremal values of the cross-sectional area of the boundary surface of Fermi). The authors gave methods for calculating the shape of the boundary surface and the velocities of electrons on it.

Certain magnetic properties of semiconductors were touched upon in the report by Ya. G. Dorfman, “On the Determination of the Individual Components of the Magnetic Susceptibility of a Semiconductor,” in which a new comprehensive method is proposed for the experimental determination of the individual components of the susceptibility (of electrons, holes, and impurity atoms). In the report by I. K. Kikoin and Yu. A. Bykovskii, “On the Popе-

…transverse photomagnetic effect in germanium” dealt with the properties of a new and interesting phenomenon discovered earlier by I. K. Kikoin; in particular, the observed transverse photomagnetic emf depends in a very complicated way on the magnitude of the field and on the temperature.

To this same group of reports one may also assign the communication by E. F. Gross, B. P. Zakharchenya, and N. M. Reinov, “The Linear and Quadratic Zeeman Effect and the Diamagnetism of Excitons in Cuprous Oxide.” These experiments provide clear evidence of the large magnitude (up to 200 Å) of the effective dimensions of Mott excitons in semiconductors.

Questions of magnetochemistry were the subject of reports by the Indian physicist A. Bose, “The Paramagnetic Properties of Some Compounds of the Iron Group with Similar Structure,” who studied in detail the paramagnetic anisotropy of a large number of single crystals of hydrated salts with Cu++ and Ni++ ions; on the basis of experimental data the author draws definite conclusions about the character of the chemical bonds in the compounds studied; Ya. G. Dorfman, in the report “Magnetochemistry of Diamagnetic Compounds and the Role of the Polarization-Paramagnetic Term,” established the essential significance of this type of magnetism in carrying out magnetochemical investigations and in their theoretical interpretation.

The behavior of magnets in high-frequency electromagnetic and ultrasonic fields, as well as questions of magnetic relaxation, are of great scientific and practical interest. The latter is due to the fact that, by observing the influence of high-frequency fields in the resonant regime or relaxation effects, we obtain detailed and direct information about the finest details of electron motions in atoms, molecules, and condensed bodies. It is precisely for this reason that methods of magnetic resonance have already found wide practical application in various branches of physics and chemistry. It should also be particularly noted that high-frequency methods make it possible to approach the solution of those important theoretical problems that arise in the study of galvanomagnetic phenomena (see above).

In the report of the well-known American physicist A. Kip, “Cyclotron and Plasma Resonance in Solids,” it was shown that, under certain conditions, experiments on diamagnetic resonance in semiconductors make it possible to determine the effective mass of current carriers. The experiments were carried out on germanium–silicon alloys in the frequency range from 9000 to 60,000 Mc and at a temperature of about 4°K. With an increase in the concentration of current carriers \((>10^{13})\), cyclotron resonance changes into plasma resonance. This case was studied by the author in a crystal of antimony-indium of type \(n\).

In the report of the well-known Dutch physicist C. J. Gorter, “New Investigations in the Field of Paramagnetic Relaxation,” it was noted that recent measurements of low-frequency relaxation at helium temperatures showed that it is not connected with spin-lattice interaction and that, in many cases, energy absorption is effected by oscillations of the lattice. At liquid-hydrogen temperatures a slow, temperature-independent relaxation within the spin system was found, which cannot be explained by the Waller–Brur theory, but requires for its interpretation the old theory of Kronig–Bouwkamp.

The report by I. G. Shaposhnikov, “Phenomenological Theory of Nonresonant Paramagnetic Relaxation Phenomena,” was of a survey character with regard to research in this field, including the author’s own work.

MEETINGS AND CONFERENCES

The report by A. A. Manenkov and A. M. Prokhorov, “Fine and hyperfine structure of paramagnetic resonance in divalent europium,” the report by N. S. Garif’yanov, “Hyperfine structure of paramagnetic-resonance lines in single crystals of salts of elements of the iron group,” and, finally, the report by the German physicist A. Lösche, “Application of paramagnetic nuclear resonance to the investigation of certain salts,” dealt with specific questions of nuclear and electron resonance in various substances. The results of these works are of interest both for nuclear physics (determination of nuclear spins and magnetic moments) and for magnetochemistry. To this same group of reports one may also assign the report by B. M. Kozyrev, “Electron paramagnetic resonance in electrolyte solutions.” The most interesting result of this work is the conclusion that a sufficiently stable short-range order exists in solutions.

In the reports by N. N. Neprimerov, “Some magneto-optical phenomena at microwaves,” G. S. Krinchik, “Magneto-optical properties of ferromagnets in the infrared region,” and G. V. Skrotskii, V. F. Zakharchenko, and L. V. Kurbatov, “On the theory of the Faraday and Kerr effects at radio frequencies,” interesting questions were touched upon concerning the properties of gyrotropic media, which at present are acquiring great practical importance in high-frequency radio engineering.

The report by the Indian physicist J. C. Sanyal, “Permeability of ferromagnets at centimeter wavelengths,” and that by L. A. Fomenko, “Radio-frequency magnetic spectra of mixed ferrites,” dealt with the behavior of ferromagnets in high-frequency fields.

Questions of the theory of high-frequency magnetic materials (magnetodielectrics) were touched upon in the report by K. M. Polivanov, B. M. Fradkin, N. G. Katkov, and V. V. Skugarev, “On the theory of artificial magnetodielectrics made of metallic powders.” The theoretical calculations of the authors of the report make possible certain regulation of the frequency characteristics of a magnetodielectric by changing its granulometric composition. Experimental verification of the calculations gave satisfactory results.

Questions of the magneto-optics of centimeter waves in ferrites were also touched upon in the report by K. M. Polivanov, Ya. N. Kolli, L. K. Mikhailovskii, and V. A. Fabrikov, “Magnetodielectrics in waveguide devices.” The authors established an unambiguous dependence of Faraday rotation on magnetization, a nonlinear relation with the thickness of the washer, and found the influence of the mechanical structure on the effect under study (when the material is crushed).

In the report by S. A. Al’tshuler, V. I. Avvakumov, and L. Ya. Shekun, “Resonant paramagnetic absorption of ultrasound in certain salts of rare-earth elements,” the results of theoretical calculations were presented, the purpose of which was to clarify the question of which salts of which elements may be expected to exhibit the greatest resonant absorption of ultrasound—a phenomenon previously predicted by S. A. Al’tshuler. The calculation showed that the greatest effect should be expected in salts containing rare-earth ions with an even number of \(4f\)-electrons.

Among the various questions of magnetism, questions of ferromagnetism are of especially great importance. This is due to the fact that the phenomenon of ferromagnetism has found the broadest practical application in modern technology: not a single electrical machine or apparatus, not a single radio-engineering device can do without the use of one or another magnetic material made from ferromagnetic substances. At the same time, the study of the ferromagnetic properties

the substance is also of great prospective scientific interest, since this phenomenon is connected with the very complex and subtle properties of the electronic system of solids, and therefore its study opens up possibilities for investigating the great totality of other physical properties of solids and, consequently, the prospects for their practical use. At the Conference the subject of discussion was the following problems of ferromagnetism: studies of the nature of the ferromagnetic and antiferromagnetic states of matter and their connection with other (nonmagnetic) properties; study of the magnetic structure of ferromagnets, which determines their technical magnetic properties; and also questions of the physics of magnetic materials.

With regard to the first problem, a number of papers were devoted to questions of the quantum-mechanical theory of the phenomena of ferromagnetism and antiferromagnetism, and first of all to the theory of spin waves (ferromagnons), which explains the behavior of these properties of matter at low temperatures. These were the following papers: N. N. Bogolyubov and S. V. Tyablikov, “Approximate methods of secondary quantization in the quantum theory of magnetism,” in which the authors gave a survey of a series of their works on the quantum-mechanical theory of ferromagnetism and antiferromagnetism; S. V. Vonsovskii, “Quantum-mechanical treatment of the problem of ferromagnetism of metals of the transition groups,” where an exposition was given of the work of the Sverdlovsk physicists on the quantum theory of crystals of the transition groups, whose electronic energy spectrum has two branches: a Bose branch (for spin waves) and a Fermi branch (for conduction electrons). In the paper of the Polish physicist S. O. Shenevskii, “Remarks on the theory of spin waves,” critical comments by Z. Semadeni on the incorrectness of replacing sums by integrals in F. Bloch’s first work on the theory of spin waves were presented, as well as a generalization of the semiclassical theory of spin waves given by G. Tsopf.

The discussion report of the German physicist G. Geber, “On the statistics of spin waves,” was devoted to clarifying the question of the statistics of elementary excitations in ferromagnets. In V. L. Bonch-Bruevich’s paper “On the theory of ferromagnetism in a nonideal lattice,” the question was considered of the influence of various distortions of the crystal lattice of a ferromagnet on its spontaneous magnetization. G. S. Krinchik, in the paper “Ferromagnetism of conduction electrons,” set forth his ideas that ferromagnetism is caused not by the exchange interaction of internal electrons, but by the interaction of external conduction electrons among themselves and with internal electrons. The author carries out his calculations within the framework of a two-zone one-electron model.

The paper of the Czechoslovak physicist L. Valenta, “On the theory of spontaneous magnetization of thin films,” follows his calculations, which are a further generalization of the work of Klein and Smith on the theory of the spontaneous-wave magnetization of thin ferromagnetic layers. In the paper of S. V. Tyablikov and A. A. Gusev, “On the dependence of the magnetic anisotropy constants of cubic crystals on temperature and field,” the authors’ calculations were presented, in which, taking account of a spin-wave model, they accounted for the magnetic interaction of electrons in a crystal and which they then applied to calculating the energy of magnetic anisotropy of ferromagnetic crystals of cubic symmetry.

In A. I. Akhiezer’s paper “Theory of relaxation and kinetic processes in ferrodielectrics at low temperatures,” the interaction between two types of elementary excitations—phonons and ferromagnons—was considered. This interaction is decisive not only for the thermal conductivity of ferrodielectrics, but also for the phenomena of sound absorption in them (ferroacoustic resonance and magneto-

acoustic oscillations). In the report by E. A. Turov, “On the spectrum of elementary excitations in certain kinetic processes in ferromagnetic crystals,” the results of more exact calculation of the energy spectrum of the spin-lattice field in a ferrodielectric were presented, in which the independence of the phonon and ferromagnon branches of this spectrum is not assumed.

V. L. Ginzburg, in his communication “On superconducting ferromagnets,” showed that the presence of spontaneous magnetization makes it difficult to detect the phenomenon of superconductivity in ferromagnets, even if it exists, and indicated certain possibilities for observing it.

A number of reports dealt with questions of the thermodynamics of ferromagnetic and antiferromagnetic substances, as well as the study of the temperature dependences of their principal properties.

In the report by the Dutch physicist C. J. Gorter, “On the thermodynamics of antiferromagnetism,” the results of a thermodynamic investigation of the phase diagram field–temperature for antiferromagnetic crystals with rhombic symmetry were presented. The case in which the external magnetic field is parallel to the preferred axis of the antiferromagnet was considered in detail. It was shown that on the phase diagram there are two types of second-order transition lines and three of first order. The development of the theory agrees well with the experimental data.

In the report by the well-known French scientist L. Néel, “Metamagnetics or antiferromagnetics with a threshold field,” a theory was presented of the magnetic properties of antiferromagnets of the type of chlorides of elements of the iron group, developed by the author within the framework of the molecular-field model and of certain other substances. In these calculations both direct and indirect exchange interactions between magnetic sublattices are taken into account, and a detailed thermodynamic investigation of phase transitions under various conditions is carried out.

In the report by L. Néel, F. Bertaut, F. Forrer, and R. Pauthenet, “A new type of ferromagnetic substances: ferrites of rare-earth elements with a garnet-type structure,” it was noted that the ferrites of rare-earth elements have a structure not of the perovskite type, but of the garnet type, with the general formula \(\mathrm{Fe}_2'\mathrm{Fe}_3''\mathrm{M}_3\mathrm{O}_{12}\) (\(M\) is a rare-earth element, \(\mathrm{Fe}'\) and \(\mathrm{Fe}''\) are trivalent iron ions in different magnetic sublattices). On the basis of a molecular-field model and of a representation of the subdivision of the crystal into magnetic sublattices, the atomic magnetic moment of these compounds is determined.

In the report by the well-known American scientist R. M. Bozorth, “On certain magnetic properties of ferrites and cyanides at low temperatures,” the results were presented of his joint studies with G. J. Williams and Dorothy E. Walsh on the temperature dependence of the magnetization of rare-earth ferrites and cyanides of the iron group in the temperature interval from room temperature to \(1.3^\circ\mathrm{K}\). The investigations showed that among these compounds there are ferromagnetics, antiferromagnetics, and paramagnetics. Interesting features in the temperature course of magnetization were observed. The atomic magnetic moments of these substances were determined.

In the report by A. S. Borovik-Romanov, V. R. Karasik, N. M. Kreines, and M. P. Orlova, “Experimental investigation of the temperature dependence of the magnetic susceptibility of certain antiferromagnets,” the results of temperature investigations of the magnetic susceptibility of anhydrous sulfates of nickel, iron, cobalt, and copper, as well as carbonates of manganese and cobalt, were presented.

The report by K. P. Belov, A. N. Goryaga, and Ya. Paces, “Thermodynamic investigations of ferromagnets in the region of the Curie temperature,”

was devoted to presenting the results of the authors’ measurements of magnetization, electrical resistance, and its variation in a longitudinal magnetic field in a series of nickel alloys (with silicon, copper, manganese, and iron) in the region of the Curie temperature, as well as to a thermodynamic analysis of these data on the basis of the theory of phase transitions of the second kind.

Analogous studies of the magnetization of ferrites near the Curie point and a thermodynamic analysis of the measurement results were described in the report by K. P. Belov, K. M. Bolshova, and T. A. Elkina, “Studies of the magnetization of ferrites in the region of the Curie temperature.”

In the report by the Hungarian physicists L. Pala and T. Tarnoczi, “Temperature dependence of the differential susceptibility of cobalt in strong magnetic fields,” the results of the authors’ experimental investigations were presented. On the experimental curve of the temperature dependence under study, the authors found two maxima. It proved possible to explain these features of the curves completely with the aid of the theory of rotation processes. In addition, the influence of a phase transformation in cobalt (transition from the face-centered cubic structure to the hexagonal structure) on the course of the differential-susceptibility curve was also investigated.

In the report by I. M. Puzei, “Temperature dependence of the magnetic-anisotropy energy,” the results of studies of the temperature variation of the magnetic-anisotropy constant of single crystals of nickel, nickel alloys with iron of composition $\mathrm{Ni}_3\mathrm{Fe}$, and alloys of the molybdenum and chromium permalloy type at various degrees of ordering in the temperature interval from 20 to 550° K were presented. It was found that in alloys the temperature dependence of the anisotropy constant is weaker than in pure nickel, and is affected by the degree of ordering. The latter circumstance opens up possibilities for using the ordering phenomenon in ferromagnetic alloys to obtain temperature-stable materials.

The report by L. N. Fedotova, “Influence of temperature and loading on the magnitude of magnetic saturation of specimens of ferromagnetic alloys,” was devoted to presenting the results of the author’s experiments on iron–nickel and iron–aluminum alloys. In the case of the latter it was shown that, in the temperature interval from 14 to 190° K, the temperature dependence does not obey Stoner’s formula ($\sim T^2$), but follows the law ($\sim T^{3/2}$) predicted by spin-wave theory.

L. V. Kirenskii, R. S. Nosova, and N. V. Reshetnikova, in the report “Temperature dependence of the magnetic properties of nickel,” set forth the results of their studies of the dependence of the magnetic-anisotropy constant of a nickel single crystal on the intensity of the magnetic field in fields up to 6670 oersted and at temperatures from room temperature to 300° C. It was shown that this dependence has a hyperbolic character with respect to the quantity inverse to the field intensity ($1/H$). In addition, the authors investigated the temperature dependence of the galvanomagnetic effect in nickel at its magnetic saturation in the temperature interval from $-196^\circ$ C to the Curie point. The data obtained are of interest for refining the theory of the processes of rotation of spontaneous magnetization in ferromagnetic crystals.

In the report by D. I. Volkov and V. I. Chechernikov, “Temperature dependence of the paramagnetic susceptibility of nickel-based alloys,” the results of precision studies of the temperature dependence of the paramagnetic susceptibility of a series of nickel alloys in the temperature interval from the Curie point to $\sim 1200^\circ$ C were presented. The results of this work are of substantial interest for refining the thermodynamic theory of the ferromagnetic transition, as well as for

theory of interacting external and internal electrons of ferromagnetic metals and alloys.

A series of reports and communications was devoted to questions of the study of the nonmagnetic properties of ferromagnets. These investigations are of special interest, since they open up new possibilities both for refining our ideas about the nature of the ferromagnetic and antiferromagnetic state of matter and for elucidating regularities in a solid body connected with its other properties (electrical, thermal, mechanical, etc.).

In the report by N. P. Grazhdankina and I. G. Fakidov, “The Relation between the Magnetic and Electrical Properties of Chromium Sulfides,” the authors described highly interesting properties of ferromagnetic and antiferromagnetic compounds. Namely, in studying the temperature dependence of the electrical resistance of these substances, the authors found that the ferromagnetic compounds possess metallic conductivity, while the antiferromagnetic compounds possess semiconducting conductivity, whose temperature dependence is characteristic of semimetals (at a temperature of approximately 300° K the temperature coefficient of electrical resistance changes sign). This circumstance indicates the existence of differences in the electronic energy spectra of ferromagnetic and antiferromagnetic compounds of this type.

The report by E. I. Kondorskii, O. S. Galkina, and L. A. Chernikova, “Galvanomagnetic Effects in Nickel Alloys at Low Temperatures,” was devoted to presenting the results of measurements of the temperature dependence of electrical resistance and of its change caused by magnetization to saturation, in the temperature intervals from 2 to 4.2° K and from 14 to 20° K in nickel, and also in nickel alloys with copper (5, 10, 15, 20, 25% copper), chromium (1, 2, and 3% chromium), and manganese (25.6% manganese). These investigations confirm A. P. Komar’s general conclusion concerning the essential connection between ordering in alloys and the magnitude of the galvanomagnetic effect in ferromagnets.

In the report by E. I. Kondorskii and I. E. Ozhigov, “Electrical Resistance and Its Change in a Strong Magnetic Field in Iron–Nickel Alloys in the Region of Low (14–77° K) Temperatures,” the authors presented the results of their investigation of the temperature dependence of electrical resistance and of its change in a magnetic field, as well as the influence on these quantities of heat treatment capable of producing ordering in iron–nickel alloys with nickel concentrations of 40–100% in the temperature interval from 14 to 90° K. The authors found that both the resistance and its relative change in a magnetic field depend quadratically (\(\sim T^2\)) on temperature in the region investigated.

R. G. Annaev, R. A. Mikhailov, M. Mamaev, V. Myndaev, and B. Bulatov, in the report “Investigation of Even and Odd Effects in the Nickel–Copper Alloy System,” reported on the results of an experimental verification of the main conclusions of the theory of even and odd effects in two-component ferromagnetic alloys.

In the report by G. P. D’yakova, “The Law of Approach to Saturation for Even Effects,” a generalization of the law of approach to saturation was presented for magnetostriction and other even effects within the framework of the theory of rotational processes.

In the report by N. S. Akulov, “On a New Method for Calculating the Magnetostriction of Single Crystals,” a generalization was given of the statistical theory of regions of spontaneous magnetization for single crystals with four axes of easiest magnetization; this theory was applied to the calculation of linear magnetostriction.

The report by K. B. Vlasov, “Some Questions in the Theory of Elastic Ferromagnetic (Magnetostriction) Media,” was devoted to an exposition of the foundations of the thermodynamic theory of a polarized ferromagnetic elastic ...

of the medium. Expressions were obtained for the tensors of the modulus of elasticity, magnetic permeability, the magnetostriction constant, etc., as well as relations connecting these tensors for various processes (isothermal, adiabatic). The results obtained are of great importance for elucidating the regularities of magnetostriction oscillations in ferromagnets.

Among the problems in the theory of the technical magnetization curve of ferromagnetic substances, a very large—and in a number of cases decisive—place belongs to studies of the structure of regions of spontaneous magnetization (domains). The magnitude and shape of ferromagnetic regions, the conditions for the nucleation and variation under the influence of various actions, the nature of the boundary layers between regions—all this determines the character of the course of magnetization processes in a ferromagnet, the form of its magnetization curve and hysteresis loops, i.e., the totality of its technical magnetic properties. It is precisely for this reason that so much attention is now being given to the direct comprehensive study of the structure of ferromagnetic regions. In view of the small scales of these formations, their often complex configuration, and also their sharp structural sensitivity, their experimental observation proves to be very difficult. These difficulties inevitably lead to the search for various methods of investigation that would make it possible to study the properties of the regions from different sides. One of the simplest and most direct ways of observing ferromagnetic regions from the surface of specimens is the so-called method of powder patterns. This method is based on the fact that the inhomogeneities in the deposition of ferromagnetic powder on the surface of ferromagnetic specimens are in direct connection with the inhomogeneities of the stray magnetic field near the surface, which in turn are associated with the presence of ferromagnetic regions and boundary layers between them. Improvement of the technique of powder deposits (discovered as early as 1931—1932 by Bitter and Akulov) makes it possible at present to elucidate very fine details of ferromagnetic regions under various conditions, their connection with the crystallography of specimens, the influence of crystal distortions, the regularities of the appearance of regions (nuclei) of remagnetization, etc. A number of reports of the Conference were devoted to this important question of the theory of the technical magnetization curve.

The well-known English physicist-magnetologist L. F. Bates, in his report “On Certain New Experiments with Powder Patterns,” set forth new results obtained in the laboratory he directs on the study of complex powder patterns on the surfaces of single crystals of silicon iron. Supplementing powder investigations by the use of an electron microscope made it possible experimentally to estimate the width of the boundary layer between regions. The fine structure of deposits (“closure” regions) and the connection between the structure of regions and magnetization processes were specially investigated.

The report of Ya. S. Shur and R. V. Abels, “Investigation of the Magnetic Structure of Crystals of Silicon Iron by Means of Powder Patterns,” was devoted to an exposition of the authors’ investigations of the magnetic structure of crystals of silicon iron. The authors give a clear classification of the patterns of powder deposits, establishing their connection with the crystallography of the specimens. The closure regions are investigated in detail—their shape and their changes under the influence of various factors (field, stresses, changes in specimen thickness, etc.). The connection between magnetization processes and the structure of the regions and the character of its change in a field is investigated. It is shown that the special properties of very thin sheets of materials, as compared with massive specimens, are to a considerable extent determined by the peculiarities of the structure of the ferromagnetic regions of thin specimens. The connection of the closure regions was investigated in detail

with reversal nuclei. It was shown that the reversal nuclei are not closed regions arising near various internal inhomogeneities in the crystals, but rather regions at the boundaries of domains. The retarding influence of closed regions on the processes of displacement of the boundaries between the main domains was shown. Study of the structure of the domains clearly shows that even in strong fields, along with rotation processes, there also occur “delayed” displacement processes, which account for the existence of magnetic hysteresis in these fields. The results of the observations are in good qualitative agreement with the theory. Some results of the work were demonstrated by the authors as a motion picture, giving a very vivid picture of the observed processes of change in the structure of the domains.

The results of analogous studies of the dynamics of the structure of ferromagnetic domains were presented in the report by L. V. Kirenskii, V. L. Dylgerov, and M. K. Savchenko, “Dynamics of the Domain Structure in Crystals of Silicon Iron.” The authors also used motion-picture recording to illustrate their observations.

In the report by J. Kaczer (Czechoslovakia), “A New Method for Investigating the Domain Structure of Ferromagnets and Its Application at High Temperatures,” an account was given of a new original method, developed by the author, for studying the structure of domains on the surface of ferromagnetic specimens. The method consists in measuring the change in the induction current in an oscillating permalloy probe as it moves along the surface near the boundaries of the layers of domains. The measurement results are in good agreement with the data from powder patterns. The advantages of this method become apparent in studies of domain structure over wide temperature intervals, for which the method of magnetic suspensions cannot be used.

Still another new method for studying the structure of ferromagnetic domains was described in the report by G. V. Spivak, N. G. Kanavina, I. S. Sbitnikova, I. N. Prilezhaeva, T. N. Dombrovskaia, and V. K. Azovtsev, “On the Direct Visualization of Ferromagnetic Domains by Means of a Secondary-Emission Electron Microscope and an Electron Mirror.” The authors propose two modifications of this method, based on the principle of modulation of both the direct and the reflected (from the surface) electron beam by local magnetic fields at the surface of the ferromagnet. In the first case the reflected electron beam, by means of the corresponding electron-optical device, is focused and gives an enlarged image of the region on the screen of a secondary-emission microscope; in the second case, of an electron mirror. Both these techniques are based on the use of the phenomenon of “magnetic contrast,” produced on a cold flat cathode containing magnetic inhomogeneities that are a kind of magnetic “microlenses.” The report presented the first results of experiments for a single crystal of cobalt and their comparison with powder-pattern images. Prospects for the development of this method were also discussed.

In the report by the Polish scholar St. Loria, “Magneto-Optical Polarization Phenomena in Ferromagnetic Crystals and the Contemporary Problems of Ferromagnetism,” the most important questions of the theory of magneto-optical phenomena in ferromagnets were enumerated, and the possibilities of using these phenomena for study, by means of measurements of the effects under consideration, of the structure of ferromagnetic domains were also analyzed in detail; implementation of this method has already begun in practice.

Questions of the theory of boundary layers between ferromagnetic domains were touched upon in the report by the American physicist K. P. Bean, “The Nature of Ferromagnetic Domain Boundaries.” The author proposed a new method

of precisely measuring the energy of domain walls between regions. This method amounts to studying magnetization processes in iron–nickel wire (65% nickel) with uniaxial anisotropy produced by stretching. Similar questions in the theory of domain walls were also touched upon in the report of the Czechoslovak physicist Ya. Kacer, “The Theory of the Coercive Force of Thin Plates,” in which the author presented the results of his calculations on the influence of domain-wall energy on the process of remagnetization, taking into account the structural features of the boundaries of ferromagnetic regions near the surface of thin specimens.

In the report by the English scientist L. F. Bates, “Temperature Changes Associated with Magnetization,” a survey was given of an improved method for measuring temperature changes associated with magnetization processes in weak and medium fields, developed in the laboratory headed by the author. In addition, the report presented the results of an investigation of temperature changes and attempts to separate them into reversible and irreversible parts in highly coercive materials. For certain ferrites and silicon iron, in the region of weak and zero fields, peculiarities were found in the thermal changes under study which have not yet received a theoretical interpretation.

The subsequent reports of this section of the Conference (on the physics of magnetic materials) were devoted to questions concerning the influence of phase transformations, crystallographic and magnetic texture on the magnetic properties of ferromagnetic materials, to phenomena of magnetic hysteresis, questions of magnetic viscosity of ferromagnets, and certain problems in the physical theory of magnetic measurements.

In the survey report by the Japanese physicist R. Kubo, “Some Recent Advances in the Field of Magnetism in Japan,” the principal results were presented of studies by Japanese physicists (Chikazumi, Taniguchi, Yamamoto, Iida, Suzuki, Kaya, and others), mainly on the study of magnetic anisotropy caused by processes of directional ordering of atoms in the crystal lattice of ferromagnetic alloys of the iron–nickel system.

In the report by the Hungarian physicist P. Denes, “Anisotropic Magnetic Cores Made of Pressed Materials,” an analysis is given of various possibilities for improving the magnetic properties of such cores, and methods are set forth for calculating the magnetic permeability in them.

The report by Ya. S. Shur, E. B. Shtol’ts, and G. S. Kandaurova, “The Magnetic Properties and Magnetic Structure of Specimens Made of Highly Coercive Powders,” was devoted to presenting the results of such studies in powders of manganese–bismuth and cobalt–chromium alloys and in pure cobalt, with average linear particle sizes from 1 mm to 1–2 microns. Magnetic texture in the specimens was created by orienting the particles in a magnetic field. The particles were embedded in an insulating nonmagnetic binding substance; the hardening of the specimen was carried out in the presence of a field. The authors investigated in detail the magnetization curves and hysteresis loops of the specimens studied and drew a number of conclusions about the features of the magnetic structure and magnetization processes in them.

N. N. Buinov, L. I. Podrezov, and M. F. Komarova, in their report “Investigation of Decomposition in a Nickel–Beryllium Alloy (1.9% beryllium),” reported on a study of the influence of phase transformations in this alloy on the magnitude of its coercive force.

In the report by B. G. Livshits, “Changes in the Structure and Properties of Nickel Solid Solutions during Heat Treatment,” a survey was given of the results of an experimental study of alloys: nichrome, molybde-

CONFERENCES AND MEETINGS

pure permalloy and invar. On the basis of an analysis of the measurement results, the conclusion is drawn that in solid solutions of transition metals there are inhomogeneities of atomic order that are a consequence of selective interatomic bonding. The need for more direct structural investigations and for the development of the thermodynamics of intraphase aging is pointed out.

The question of studying the structure of the most important system of high-coercivity alloys—iron-nickel-aluminum—was discussed in the report by B. G. Livshits and B. S. L’vov, “The structure of iron-nickel-aluminum alloys in their high-coercivity state.”

Problems of the influence of atomic ordering on the magnetic properties of ferromagnetic alloys were discussed in the reports: by B. G. Livshits and B. V. Molotilov, “The magnetic investigation of the ordered alloy \( \mathrm{Ni}_3\mathrm{Mn} \)”; by M. V. Dekhtyar’, “The temperature dependence of magnetic properties and ordering processes in an iron-nickel-molybdenum alloy”; by V. E. Rode, “The kinetics of superstructural transformations of the alloy \( \mathrm{Fe}_3\mathrm{Al} \)”; by V. I. Ivanovskii, “On the magnetic properties of ordering alloys \( \mathrm{Fe}_3\mathrm{Al} \).” In all these reports, the results of specific investigations of the influence of the atomic ordering of alloys, achieved by various heat treatments, on their magnetic properties were presented, as well as the influence of alloying additions on this process, the results of studies of temperature changes in magnetic properties, the kinetics of phase transformations, and so on.

In the report by Ya. S. Shur and I. E. Startseva, “The stability of the magnetic structure of residually magnetized soft magnetic materials,” the results of experimental investigations were presented on the influence of various treatments on the magnitude of residual magnetization and the conditions of its destruction under the influence of various methods of demagnetization (alternating field, mechanical vibrations, and temperature oscillations). Methods are indicated for regulating the magnitude of residual magnetization and its stability in soft magnetic materials.

The following reports were devoted to the investigation of the regularities of irreversible processes (jumps) of magnetization reversal, hysteresis loop, in longitudinal and rotating fields: by the Czechoslovak physicist K. Votruba, “The dependence of the Barkhausen effect on plastic deformation in ferromagnets”; by V. F. Ivlev, V. L. Il’yushenko, L. I. Aseeva, and A. E. Lipkin, “Investigation of irreversible jumps of magnetization reversal in ferromagnetic wires”; by R. I. Yans and V. P. Kartashev, “On the structure of the family of symmetric hysteresis loops of ferromagnets”; by L. V. Kirenskii, A. Ya. Vlasov, N. I. Vtyurin, and V. F. Ivlev, “Temperature and rotational hysteresis in ferromagnets”; by N. L. Bryukhatova, “Investigation of hysteresis losses in the rotating magnetic fields of a molybdenum single crystal before and after a phase transformation.” In these reports the results of concrete measurements by the authors in various ferromagnetic materials were presented.

In the report by Ya. S. Shur, M. G. Luzhinskaya, and L. A. Shubina, “The influence of repeated stressing and thermomechanical treatment on the magnetic properties of high-coercivity alloys,” new methods for obtaining textured high-coercivity alloys of the vicalloy type (from the iron-cobalt-vanadium system) were described, and a qualitative theoretical explanation of the results obtained was given.

The report by R. V. Teleshina, I. A. Lepeva, and A. G. Shishkova, “Magnetic viscosity of nickel-zinc ferrites under free and forced change of magnetization,” was devoted to presenting the results of a study of the temperature dependence of magnetic viscosity in specimens of nickel-zinc ferrites of various compositions and various heat treatments in the temperature interval from \(78^\circ\mathrm{K}\) to the Curie point, in a regime

free and forced variation of magnetization. It was found that at 78° K all specimens possess magnetic aftereffect with viscous processes lasting up to several minutes.

In the report by Yu. S. Vail’, “Regularities in the Decay of Reversible Permeability,” the phenomenon of disaccommodation in soft magnetic materials (silicon iron, Armco iron) was investigated. The results obtained by the author are in contradiction with the “first rule of magnetic viscosity.” The author gives an interpretation of his results on the basis of the theory of Néel, Street, and Woolley.

The well-known Chinese physicist Ko Ting-sui, in his report “Measurements of Internal Friction as a Method of Magnetic Research,” pointed out the possibility of fruitful use of measurements of internal friction in ferromagnetic materials for the study of their magnetic properties.

In the reports by S. Sh. Dolginov and L. N. Zhuzgov, “A Miniature Magnetometer for Measuring Very Weak Magnetic Fields,” and by L. Kh. Fridman and V. I. Drozhzhina, “Ferrosonde Magnetometers for Measuring the Magnetic Properties of Small Specimens,” certain questions in the physics of magnetic measurements were presented and specific apparatus designs were described.

Many questions were asked on all the reports and communications, and lively debates took place, which continued not only at the official sessions of the Conference but also in personal meetings among the participants.

The significance of the present Conference lies not only in the fact that many interesting and important questions in the physics of magnetic phenomena were discussed there, that certain results of the work of physicists and magnetologists were summed up, and that paths for further research were outlined, but also in the fact that, in the course of the Conference, close scientific contacts were established between Soviet physicists and physicists from a number of foreign countries. The broad exchange of opinions, the friendly atmosphere during the sessions, and the mutual exchange of information will undoubtedly exert a fruitful influence on further progress in the science of magnetism in all countries.

S. V. Vonsovskii