A. S. Ilyushin

Multifunctional Phenomena in Rare-Earth Intermetallic Compounds With a Laves Phase Structure: Giant Magnetostriction and Magnetocaloric Effect

We report on the magnetic and thermal properties [magnetization, specific heat, thermal expansion, magnetostriction, and magnetocaloric effect (MCE)] for the three multicomponent systems Tb_xDy_yGd_zCo₂, Tb_xDy_yHo_z(Co, Fe)₂, and Tb_xDy_yEr_z(Co, Fe)₂ (x + y + z = 1). We show that for Tb_xDy_yR_zCo₂, the Curie temperatures, TC (which ranged from 130 to 300 K), and order of the phase transition (first or second order) could be controlled by composition. The highest MCE values (the adiabatic temperature change ΔT_ad = 2.2-2.3 K at μ₀ΔH = 1.8 T) were observed for the compounds exhibiting the transitions of the first order. Giant volume magnetostriction of 1500-2000 and 500-600 ppm is demonstrated at a field of μ₀H = 10 and 1.2 T, respectively. Structural and magnetic entropy contributions to the total isothermal entropy change are estimated for Tb_xDy_yR_zCo₂. Regular recurrence and/or change of the physical properties across the varied composition of the compounds allows us to find the materials with desired magnetic characteristics, such as T_C, MCE, and magnetostriction, to use them in practice.

Magnetostructural phase transitions and magnetocaloric effect in Tb-Dy-Ho-Co-Al alloys with a Laves phase structure

The influence of simultaneous substitution within the rare earth (R) and Co sublattices on the structural, magnetic, and magnetocaloric properties of the Laves phase RCo2-type compounds is studied. Main attention is devoted to the studies of the magnetostructural phase transitions and the transition types with respect to the alloy composition. Multicomponent alloys Tbx(Dy0.5Ho0.5)1−xCo2 and Tbx(Dy0.5Ho0.5)1−xCo1.75Al0.25 were prepared with the use of high purity metals. Majority of the Tbx(Dy0.5Ho0.5)1−xCo2 alloys exhibit magnetic transitions of the first-order type and a large magnetocaloric effect. The substitution of Al for Co in Tbx(Dy0.5Ho0.5)1−xCo2 increases the Curie temperature (TC) but changes the transition type from first-to the second-order. The discussion of the physical mechanisms behind the observed phenomena is given on the basis of the first principles electronic-structure calculations taking into account both the atomic disorder and the magnetic disorder effects at finite temperatures. T...

Spontaneous and external magnetic field-induced magnetostriction in RCo2-based multicomponent alloys

The spontaneous and external magnetic field-induced magnetostrictions have been studied in multicomponent Tb0.3Dy0.35Ho0.35Co2 and Tb0.8Dy0.1Gd0.1Co2 alloys whose structures are isotypical to the C15 Laves phases. The temperature dependences of the lattice parameters have been measured in the range of 110–280 K. It has been found that the crystal lattice undergoes rhombohedral distortions at temperatures lower than the temperatures of magnetic ordering in these alloys (148.5 and 243 K, respectively). The temperature (4.2–280 K) and field (0–8 T) dependences of the longitudinal and transverse magnetostrictions have been studied. The high magnetoelastic effects have been detected.

Effect of coverage by carbon on the possibility of forming an interstitial solid solution in Fe(001) and Fe(111) subsurface layers

The interaction between carbon adatoms as a function of the coverage of the Fe(001) and Fe(111) surfaces by carbon has been theoretically investigated using first-principles calculations in terms of the density functional theory. It has been established for the first time that the sequential filling of the upper surface layer by carbon atoms leads to the embedding of a part of atoms in the subsurface iron layer due to the their collective interaction, which provides the possibility of forming the interstitial solid solution. It has been demonstrated that the high coverage of the (001) surface by carbon leads to a considerable decrease in the energy barrier to the diffusion of carbon atoms into the subsurface layer as compared to the diffusion barrier for single atoms.

Structural and magnetic phase transformations in the diluted laves phases Pr(Fe1 − xAlx)2

The Pr(Fe1 − xAlx)2 alloys with concentrations x = 0–1 have been synthesized under a high pressure. The phase composition and lattice parameters (a and c) have been determined as a function of x. The magnetic and Mössbauer measurements have been performed at T = 90–400 K. It has been established that the Curie temperatures of alloys linearly depend on their composition.

Magnetic and magnetostrictive properties of Tb-Dy-Ho-Fe-Co alloys

In this work, the structural and magnetic properties of single-phase TbxDyyHoz(Fe,Co)2 (x + y + z = 1) alloys have been investigated by means of X-ray diffraction, 57Fe Mossbauer spectroscopy, magnetization measurements and a standard strain gage technique. The magnetostriction of TbxDyyHoz(Fe,Co)2 was examined against an applied magnetic field up to 10 kOe in 80 - 400 K temperature range. The Co-containing compounds are found to have high values of magnetostrictive susceptibility due to compensation of magnetic anisotropy in both the rare-earth and 3d transition metals sublattices.

On the self-organization of atomic magnetic moments after application of an electric field

An attempt is made to reveal the self-organization of atomic magnetic moments in rare-earth ferrimagnets of the TbFe2 type, an effect reported on in the works of S.K. Godovikov. A careful experimental study and a critical analysis of the data reported in his publications suggest that there are no grounds to maintain that this phenomenon exists.

Mössbauer spectroscopy studies of crystal fields in YBa2(Cu1−xFex)3O7−y

Abstract Mossbauer spectra in single phase YBa 2 ( Cu 1− x Fe x ) 3 O 7− y samples with 57 Fe concentration x = 0.04, 0.08 are studied at temperatures 4.2–300 K. Partial doublet parameters are determined. Positions of 57 Fe in the crystal lattice are identified.

The Diagnostics of the Exogeneous Factor Influence on the Formation of the Teeth Solid Tissue Biomineral Stucture by X-ray Diffraction and Raman Spectrosopy

The methods of X-ray diffraction, Raman spectroscopy, and scanning electron microscopy are applied for the analysis of human biomineral tissues, i.e., healthy solid tissues of teeth and tissues formed against the background of chemotherapeutic treatment. This allows instrument certification of their morphological and substructural units to be carried out, revealing abnormal and pathological manifestations in the structure, which are important for prevention and tissue-preservation activities.

The formation of Fe–Ga–In nanocomposite particles using mechanochemical interaction of Fe with the Ga–In eutectic

Mechanochemical interaction of Fe powder with the liquid Ga–In eutectic in the Fe-rich concentration corner of the Fe–Ga–In phase diagram was studied and compared with binary Fe–Ga and Fe–In specimens. Slow formation of diluted solid solutions in the Fe–In system was confirmed. In the Fe–Ga system, the dominant concentrated A2 solid solution is formed with Heff = 236 kOe, accompanied by ordered D03 and L12 phases. The Fe–Ga–In system features a stationary equilibrium between the concentrated A2 phase and D03 in the iron matrix.