Yu. I. Spichkin

A pressure-induced magnetic phase transition in Y2Fe17 intermetallic compound

Abstract The results of the investigation of the influence of pressure on the magnetic properties of Y 2 Fe 17 intermetallic compound are reported. The Curie temperature is established as T c =320 K and its pressure derivative as d T c /d p =−47K/GPa. Th action of the hydrostatic pressure is found to produce a new magnetic phase. A Ginzburg-Landau functional is used to describe the origin of the non-collinear magnetic structure. The field-induced volume magnetostriction is calculated on the basis of the experimental data obtained.

Magnetic entropy and phase transitions in Gd, Tb, Dy and Ho

Abstract An experimental investigation of magnetization and magnetic entropy change in the vicinity of the magnetic phase transitions in Gd, Tb and Dy has been made. The nature of the transition in the paramagnetic state was established on the basis of experimental results and nonlinear molecular field theory.

Iron(III) Oxide Nanoparticles in a Polyethylene Matrix

A method is proposed for the preparation of iron(III) oxide nanoparticles via thermal decomposition of iron(III) acetate in a high-temperature solution of polyethylene. The nanoparticles were characterized by EXAFS, EPR, and Mössbauer spectroscopy. The nearest neighbor environment of Fe in the nanoparticles was shown to be similar to that in the structure of γ-Fe2O3 . According to the Mössbauer results, the material contains iron(III) oxide in superparamagnetic and ferromagnetic states similar to γ-Fe2O3 . The particle size determined by high-resolution transmission electron microscopy is consistent with x-ray diffraction data. Experimental data are presented on the field-dependent magnetization of the material.

The effect of atomic volume on the Curie temperature and exchange integrals in amorphous R-Fe alloys

Abstract Curie temperatures and the dependence of exchange inegrals on the atomic volumes in amorphous R-Fe alloys were obtained by means of magnetization measurements under hydrostatic pressure and calculations based on molecular field theory. The hydrostatic pressure leads to decreasing of the ferromagnetic exchange interactions inside the iron magnetic subsystem and to increasing of the inferromagnetic exchange interactions between iron and the rare-earth subsystems. The results obtained for the amorphous alloys were compared with the results for the crystalline R-Fe compounds

Magnetic properties and exchange interactions in amorphous and crystalline Y-Fe alloys

Abstract The effects of pressure on the magnetization and ac susceptibility of amorphous Y 0.19 Fe 0.81 alloy and crystalline Y 2 Fe 17 . The results show that two phase transitions para-ferromagnetic-spin-glass-like state transform under pressure to the single phase transition paramagnetic-spin glass in amorphous Y 0.19 Fe 0.81 alloy. The temperature range within which pressure induces the noncollinear ordering of Fe magnetic moments in crystalline Y 2 Fe 17 compound was obtained.

Magnetic part of specific heat in high-purity Dy single crystal

Abstract The specific heat and spontaneous magnetization of high-purity Dy single crystal are measured in the temperature range 4.2–300 K. The magnetic contribution to the specific heat is determined and the magnetic part of the entropy is calculated. The magnetic ordering in the paramagnetic region above the Neel temperature is discussed.

Effect of uniform pressure on magnetization and magnetic phase diagram of terbium single crystal

Abstract The effect of uniform pressure on magnetization of a terbium single crystal (Δσ-effect) in the temperature range 80–330 K in magnetic fields up to 14 kOe has been studied. Terbium volume magnetostriction which in the vicinity of the Neel temperature in the magnetic field H = 13 kOe acquires enormous values of ω = 650 × 10 −6 , was concluded on the basis of experimental data for Δσ-effect. It has been shown that in terbium the dependence of the magnetic anisotropy constant on pressure in the base-plane is well described by the magnetic anisotropy single-ion theory. The terbium magnetic phase diagram exhibits an anomaly in the vicinity of T ≈223 K caused by helicoid angle passage of 18° value. The effect of pressure on temperatures of magnetic phase transitions, critical fields of helicoidal antiferromagnetic ordering destruction, paramagnetic Curie temperature and efficient magnetic moment has been studied.

Relationship of adiabatic, isothermal and field constant changes of a magnetic entropy

The character of a magnetic entropy change under the influence of the magnetic field for different isobaric thermodynamic processes is discussed. The general equations describing the relationship of adiabatic, isothermal and field constant ways of changing of magnetic entropy are presented. It is shown that a value of total magnetic entropy adiabatic change of can be close to isothermal one (for, example, at elevated temperature and/or a small value of magnetocaloric effect) as well as to constant field one (in the case of large magnetocaloric effect and/or a small value of magnetization and low temperature).

Chapter 170 Static and dynamic stresses

Publisher Summary This chapter discusses properties of lanthanide metals, their alloys and compounds which can be studied using static and alternating mechanical stresses. The effects related to magnetoelastic interactions are discussed. These interactions in magnetic materials can display themselves in static magnetostriction deformations and in the changing of the magnetic state under mechanical stress. The influence of hydrostatic and uniaxial pressure on the transition temperatures of magnetic phase transformations, magnetization, magnetic phase diagrams and spin structures in the lanthanide metals and their alloys, and compounds with 3d transition metals (TM) and nonmagnetic elements is considered. Pressures causing elastic strains without nonreversible deformations are considered. The chapter discusses the sound attenuation and internal friction in lanthanide metals arising from the existence of magnetic order. The anomalies of the elastic constants and moduli in these metals and their alloys and compounds with Fe and Co and their origin are discussed. The influence of commensurate magnetic structures on elastic properties and sound attenuation in lanthanide metals is discussed. The higher-order elastic constants which characterize the anharmonic properties of crystal lattices and explain the dependence on pressure of elastic constants is described in the chapter. The magnetic phase diagrams obtained from magnetization and elastic properties measurements are discussed.

Magnetocaloric effect near the first-order phase transitions in compounds of rare earth and transition metals

The results of the calculations and the experimental values of the magnetocaloric effect (MCE) in a group of compounds that are promising for use in magnetic coolers are reported. In the materials studied, MCE reaches the largest values near the magnetic first-order phase transitions and is mainly determined by the evolving latent heat of the transition. Contributions of different processes, occurring at the first-order phase transitions, to the observed MCE value have been separated on the basis of the thermodynamic model.