Solid State Phenomena Vol. 190

Abstract: Magnetic properties of the hydrides of an intermetallic compound Ho₂Fe₁₄B are studied in the temperature range 78 700 K. The temperature dependencies of magnetization σ (Т) are obtained under continuous control of the hydrogen content in the samples investigated. The dependence of the Curie (T_C) and the spin-reorientation transition (T_SR) temperatures on hydrogen pressure (P) and its concentration (x) are determined. The dependence of hydrogen concentration on pressure at constant temperatures (isotherms x (P)) in the vicinity of T_C and the temperature variation of hydrogen concentration at a constant pressure (isobars x (T)) are investigated.

Abstract: In this study, the coil-less fluxgate effect in Co₇₁Fe₁Mo₁Mn₄Si₁₄B₉ amorphous ribbon was investigated. The coil-less fluxgate is a new type of fluxgate sensor without a coil. It is based on helical anisotropy and deep circumferential magnetic saturation in the ferromagnetic fluxgate core. Coil-less fluxgate measurements were performed in as-cast and annealed ribbons at 480 mA current with 3, 12.5 and 25 rad/m torsion. The second harmonic of the output voltage detected from the ends of the wire show a linear variation in the low magnetic field region. The sensitivity of the current annealed ribbons in the presence of 25 rad/m torsion is about 570 V/T, which is comparable with previously reported fluxgate sensitivity values. The presented sensor has no coil so it is much easier to reduce the size of the sensor and easy to fabricate it.

Abstract: Magnetic properties of the La_1xR_xMn₂Si₂ (R is Gd, Tb, Dy; 0 x 1) compounds were investigated using magnetic measurements on quasi-single crystals. The x-T concentration magnetic phase diagrams are constructed. All obtained x-T magnetic phase diagrams are found to be similar. Six magnetic structures are realized in the compounds at different concentrations x. It was shown that all the compounds have strong magnetic anisotropy with the c-axis as the easy direction. For the compounds with x = 0.2, the irreversible magnetization processes are observed which can be attributed to the existence of a compensation point at which the R and Mn magnetic sublattices compensate each other. The nature of various spontaneous and field-induced phase transitions is also discussed.

Abstract: A method of measuring crystal field parameters by means of a rotating-sample magnetometer is presented. The measurement is performed by registering 2nd, 4th and 6th harmonics of the signal that is proportional to magnetization change due to rotation of the sample in a magnetic field. Experimentally measured temperature dependence of the amplitudes of these harmonics is used to determine the crystal field parameters within the framework of the theoretical model proposed in [. The signal is detected by a digital lock-in amplifier, while temperature is controlled by a PID controller. The sample and pickup coils are located in the bore of a Halbach permanent magnet. The measurements are fully automated. Magnitude of the expected signal was estimated. Test measurements of magnetization of the Tb single crystal along a axis (in the easy crystallographic plane a-b) in the permanent magnetic field 2.7 T at room temperature were performed. The results show that sensitivity of the instruments and the proposed design of the equipment allows us to determine crystal field parameters of heavy rare-earth metals. Testing of the control software showed that computer-device communications and execution of the software blocks are correct.

Abstract: A method for direct measuring the magnetostriction of ferromagnetic films (deposited on nonmagnetic substrates) in using an atomic force microscope was suggested. In measuring the magnetostriction for films 10 [mm] in length and 0,2 [μm] in thickness, which were deposited on substrates 200 [μm] thick, the minimum measured magnetostriction magnitude is ~10^-7. The procedure was tested for Ni and Fe films. The magnetostriction magnitudes measured for the films are comparable with those obtained by other magnetostriction-measuring methods. The effect of alloying with zirconium and nitrogen on the magnetostriction of nanocrystalline Fe films was studied.

Abstract: In the present work, the structure and magnetic properties of strontium hexaferrite powder during milling in various media and subsequent annealing were studied. The milling of the powder leads to an abrupt decrease in the powder particle size and the average crystallite sizes as well as an increase in lattice microstrains of the SrFe₁₂O₁₉ phase. During milling in toluene, no changes in the phase composition were observed, whereas, during milling in water, the Fe₂O₃ phase (type H1.1) is formed. In the powder milled in oleic-acid-containing toluene a small quantity of α-Fe was found. After milling, the saturation magnetization and remanence decrease; at the same time, the coercive force of the powder milled in toluene is unchanged with increasing milling time, but slightly increases after milling in water and in oleic-acid-containing toluene. The annealing allowed us to increase the magnetic properties of the powder. It is conditioned by formation of nanocrystalline state. Moreover, the magnetic properties values depend on the medium and time of milling. The annealed powders are characterized by the following magnetic properties: μ₀Н_ci = 0.42 ÷ 0.49 T, B_r = 0.23 ÷ 0.24 T, (BH)_max = 8-9.6 kJ/m³.

Abstract: The work presents a Mossbauer study of changes in the structure and phase composition of Fe-Cr-Co-W-Ga alloys with mechanical and magnetic properties appropriate for a new application of them as materials for rotors of high-speed engines. The changes are traceable to variations of the initial composition. A comparison of the latter with the changes in the Mossbauer parameters and a combined analysis of the data with the mechanical and magnetic characteristics are performed.

Abstract: The bulk nanostructured Co-P alloys were prepared by dynamic compaction and a plasma spray deposition techniques. The magnetic characteristics, such as the saturation magnetization, M₀, the Bloch constant, B, the local magnetic anisotropy field, H_a, the ferromagnetic resonance linewidth, ΔH, the coercivity, H_c, were investigated. A comparison between the magnetic properties of the Co-P alloys prepared by dynamic compaction and a plasma spray deposition techniques was carried out.

Abstract: The influence of powder particle size on behaviour of hot plastic deformation, structure and magnetic properties of Nd–Fe–B die-upset magnets have been examined. It was found, that powder particle size strongly affected plastic properties of material during hot deformation process. Precursors made of powder with the smallest particles (d < 32 μm) shown bigger plastic resistance than those made of powder with the larger ones (32 – 88 or 88 – 350 μm). For the same pressing force and temperature, applied within hot plastic deformation process, precursors made of the smallest particle powder allowed to obtain only 56 % deformation, while the another, made of larger particle powder: 65% deformation.

Abstract: Abstract. The valence state of Ce and Eu was investigated by X-ray absorption near-edge structure (XANES) spectroscopy above L3-Ce and L3-Eu absorption edges in series of RCo₂P₂ (R = La, Ce, Pr, Eu) magnetic intermetallics. At the same time under similar conditions the rearrangement of Co and Pr local environment vs. temperature was studied by extended X-ray absorption ¯ne structure (EXAFS) spectroscopy above K-Co and L3-Pr absorption edges.