The magnetocaloric effect in hydrogen-doped Nd<Subscript>2</Subscript>Fe<Subscript>14</Subscript>B and Er<Subscript>2</Subscript>Fe<Subscript>14</Subscript>B intermetallic compounds

The nature of the magnetocaloric effect (MCE) in compounds R₂Fe₁₄B (R = Nd, Er) and their hydrides in a wide temperature range is investigated. The investigation is carried out on initial samples of a special purity including single-crystalline ones. The highest value of the magnetocaloric effect is established in the Curie-temperature region. The hydrogenation of samples affects the value of the MCE. The model explaining the dependence of the value and sign of the magnetocaloric effect on the hydrogen contents in R₂Fe₁₄B compounds with participation of erbium and neodymium is proposed.     

Development of nanostructured magnetic materials based on high-purity rare-earth metals and study of their fundamental characteristics

The effect of the structural state on magnetic and hysteretic properties of compounds with high contents of a 3d transition metal, i.e., R ₂Fe_{14 ? x} Co _x B and RFe_{11 ? x} Co _x Ti (where R = Y, Sm; 0 ≤ x ≤ 8), was studied. Alloys were prepared using high-purity rare-earth metals by two different methods: induction melting and argon-arc melting. Severe plastic deformation and rapid melt-quenching allowed preparation of nanostructured samples. Structural studies of the samples were performed by X-ray powder diffraction and atomic-force microscopy methods. Magnetic hysteretic properties were studied using a PPMS magnetometer in the temperature range of 4.2–300 K in fields to 20 kOe. It was shown that the dependences of fundamental magnetic parameters (Curie temperature, saturation magnetization, and magnetocrystalline anisotropy constant) on the cobalt content exhibit a similarity for both systems. It was found that, depending on sample treatment, the grain size varies from 30 to 70 nm after severe plastic deformation and in wider ranges (from 10 to 100 nm) after rapid quenching, not exceeding the single-domain size. The interrelation between the microstructure and magnetic characteristics was investigated. It was revealed that the concentration dependence of the coercivity for both systems has a maximum at the same cobalt content, i.e., x = 2.     

A study of nanostructure magnetosolid Nd–Ho–Fe–Co–B materials via atomic force microscopy and magnetic force microscopy

Nanostructure Nd–Ho–Fe–Co–B alloys have been probed via atomic force microscopy and magnetic force microscopy (AFM and MFM, respectively). The ribbon samples with a thickness of ~30 μm are prepared via the rapid solidification on a rotating copper barrel. A part of samples has been subjected to hydration, whereas another one has undergone severe plastic deformation. AFM was mainly used to study the contact and free surface of ribbon samples. This has enabled us to establish the topography, structure, defects of both sides, morphology of magnetic inclusions of the initial quenched samples and the materials subjected to the subsequent external effects. The AFM and MFM data allowed the magnetic hysteresis properties of the bulk samples with the identical composition to be interpreted.     

Magnetic phase diagrams of the Tm<Subscript>2</Subscript>Fe<Subscript>17</Subscript>–H system

The compound Tm₂Fe₁₇, the only one among R₂Fe₁₇ (where R is a rare earth metal), exhibits uniaxial magnetic anisotropy at cryogenic temperatures. Its Curie temperature is close to room temperature, T_C = 295 K. Magnetic phase diagrams for the Tm₂Fe₁₇–H system have been constructed on the basis of measuring the temperature and field dependences of magnetization performed for different crystallographic directions of single-crystalline samples of Tm₂Fe₁₇ and its hydrides Tm₂Fe₁₇H_x (x = 1, 2, 3, 4). It has been found that the hydrogen atoms, located in the interstices of the crystal lattice of this compound, have a significant effect on both its Curie temperature and the type of magnetic anisotropy.     

The rate of cyclization of 2′- and 4′-substituted diphenylamine-2-carboxylic acids in sulfuric acid as a function of the electronic properties of substituents

The kinetic regularities of cyclization of 2′- and 4′-substituted diphenylamine-2-carboxylic acids in sulfuric acid were determined. The rate of cyclization of diphenylamine-2-carboxylic acids is linearly dependent on the nature of substituents in the meta-position relative to the reaction site in accordance with the two-parameter Hammett equation.     

Remagnetization of permanent magnets in closed and open magnetic circuits

The homogeneity of the strength of the magnetic field on the surface of a magnet placed in open and closed magnetic circuits is investigated using a program for modeling the remagnetization processes in highly anisotropic uniaxial ferromagnets. It is shown that the inhomogeneity of the magnetic field on the surface of a magnet is a consequence of magnetostatic interaction between the magnet’s microvolumes. A comparison of the calculation results and experimental data shows their close resemblance.