Solid State Phenomena Vols. 233-234

Abstract: The magnetic, transport, optical, and elastic properties of the electron-doped manganites CaMn1-xMxO3 with Mn-site doping (M=Mo or W, x≤0.20) are studied and the results are compared with those of Ca-site substituted manganites with the same Mn3+ concentration. If Mn3+ concentration is lees than 10%, the charge carriers' localization due to lattice distortions in the Ca-site doped samples is stronger than the localization caused by magnetic dilution in the case of Mn-site substitution. At higher Mn3+ concentration, the magnetic dilution plays a key role.

Abstract: The temperature dependence of electronic and magnetic properties of the organic charge-transfer salt (DOEO)₄[HgBr₄]·TCE was investigated using magnetometry. The magnetic susceptibility shows a maximum at 40 K followed by an onset of a pronounced increase at 70 K and a constant behavior above 120 K. Implications on the charge carrier density are discussed. Combining the magnetometry with resistivity and ESR measurements we propose a sequence of insulating, metallic and semiconducting behavior with increasing temperature. Our results indicate that (DOEO)₄[HgBr₄]·TCE is close to the boundary between an insulating and conducting ground state.

Abstract: We report on the influence of short annealing treatments at 923 K and 1073 K during 10min on both martensitic transformation and exchange bias effect for the Ni_50.0Mn_36.5Sn_13.5 Heusler alloy ribbon by means of magnetic measurements. We have observed that the martensitic transformation is shifted towards higher temperatures with increasing annealing temperature. Furthermore, isothermal M(H) hysteresis loops performed under field-cooling protocol show an exchange bias effect for as-quenched and two annealed ribbons, which indicates the existence of ferromagnetic-antiferromagnetic interactions at low temperatures. In particular, we observe that H_C diminishes with the increasing of the annealing temperature, but H_E is not affected by the heat treatment.

Abstract: The magnetocaloric effect (MCE) in Ni_1.81Mn_1.64In_0.55 Heusler alloy has been measured by the direct method. The field dependences of the magnetization were obtained. The phase transition temperatures were determined. The maximal adiabatic temperature change ΔT_ad near the Curie temperature is 1.8 K under the magnetic field change ∆H = 18 kOe. The inverse MCE (∆T_ad = -3.72 K) in the same field change takes place near the temperature of martensitic transformation.

Abstract: In this work the magnetic and structural properties of quaternary Fe-Ni-Mn-Al Heusler alloys are studied. We use first principles calculations to investigate crystal lattice relaxation of alloys and their coupling to the magnetic order, with a particular focus on the tetragonal distortions characterized by the c/a ratio. It follows from our calculations that Fe-Ni-Mn-Al alloys have very interesting magnetic properties and can be good candidates as multifunctional magnetic materials.

Abstract: On the base of the model S–T projection of S–T–P surface for FeRh alloy one of the possible of the heat pump cycles type is drawn up: with acquisition by the alloy the heat from external heat source. Corresponding efficiency of these cycle as functions of temperature at various differences between initial and final temperatures (permanent thermal load ΔT) and as a function of pressure at various differences between initial and final temperatures are analyzed. It is found, particularly, that within the temperature range (320 – 370) K and pressure range (0.4 – 1.0)∙10⁹ Pa efficiency of the heat-pump cycles takes the values from the interval from 30 to 35. These values are comparable to those found recently with using the tensile stress up to ψ = 1∙10⁹ Pa and with using the magnetic field up to H = 2∙10⁶ A/m.

Abstract: The melt-spun Y₂(Fe,Mn)₁₇ ribbons were synthesized by rapid quenching from the melt. The phase composition, crystal structure and magnetocaloric effect (MCE) in low-cost iron-based pseudo-binary Y₂(Fe,Mn)₁₇ ribbons were investigated respectively by using x-ray diffraction and direct measurements of MCE. It was found that crystal structure of the as-spun ribbons retains hexagonal Th₂Ni₁₇-type because of the weak glass-forming ability. The Y₂Fe₁₄Mn₃ and Y₂Fe₁₃Mn₄ nanostructured ribbons demonstrate higher MCE compare to polycrystalline alloys.

Abstract: We report the magnetic and magneto-optical (MO) properties of the Heusler Ni43.7Mn43.6In12.7 alloy ribbon in martensitic and austenitic states. The samples were produced by rapid solidification using the melt-spinning technique. The difference between the transformation temperatures obtained from magnetization and transverse Kerr effect (TKE) measurements shows that the chemical composition and/or microstructure are not identical in the bulk and at the ribbon surface. The TKE spectra profile in the spectral energy range of 0.5-3.5 eV does not change significantly at the martensitic transformation that indicates on a very similar electronic structure in martensitic and austenitic states.

Abstract: The direct measurements of the magnetocaloric effect (MCE) and the magnetization for R₂Fe₁₇ (R = Y, Tb, Dy) compounds are reported. The maximal values of the MCE for different R₂Fe₁₇ compounds are almost the same at the Curie temperature and are equal to 0.8 – 0.85 K at ΛH = 13.5 kOe. The field dependencies of the magnetization and MCE and the dependence of MCE via magnetization deviates from the classical regularities and describes by the thermodynamic theory attracting the higher terms. Obviously the occurrence of the mixed exchange interactions in these compounds leads to the requirement of consideration both thermal and local fluctuations of the exchange integrals near the magnetic transition temperature.

Abstract: The purpose of this work was the complex investigation of magnetic, magnetocaloric and magnetoelastic properties of compounds based on Gd₅Si₂Ge₂ with small In substitutions in p-sublattice. The conducted measurements revealed that both the magnetocaloric effect and the volume magnetostriction upon cooling reach the higher values than upon heating. Indium substitution leads to the appearance of the second maximum on the temperature dependence of the magnetocaloric effect resulting in the increase of the refrigerant capacity.