Papers by Keyword: Curie Point

Abstract: In this work, we investigated the dynamics of nanocrystallization from the amorphous state of the Fe_72.5Cu₁Nb₂Mo_1.5Si₁₄B₉ alloy together with magnetic phase transformations. The thermomagnetic analysis was performed with the simultaneous recording of the temperature inside the core by a thermocouple and the inductance of the winding wound over the core. It was found that the permeability of the core after the crystallization peak first increases rapidly, and then decreases and stabilizes at some level. Permeability growth begins at a temperature that coincides with the Curie point of the Fe₈₀Si₂₀ solid solution. A decrease in permeability was associated with stabilization of the structure of the amorphous and crystalline phases upon cooling. With decreasing temperature, the active redistribution of chemical elements is suppressed, and silicon atoms occupy a stable position in the crystal lattice of iron. Nanocrystalline cores have different Curie temperatures in the state after the peak of crystallization and 300 seconds after the peak. This indicates the continuation of the diffusion of silicon from the amorphous matrix into Fe-Si nanocrystals for some time after the crystallization peak.

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: An experimental method is suggested for the determination of the rate of magnetic phase transitions. The method is based on the measurement of the change of magnetic susceptibility of a ferromagnetic sample in the vicinity of the phase transition in response to an abrupt change of the sample temperature. This paper describes the measurement of the change of the magnetic susceptibility of a thin gadolinium plates, cooled by water-flow at a temperature below the Curie point (T_C=292 K). It was found that the relaxation time of the magnetic susceptibility of gadolinium in the temperature range from 289.9 to 291.3 K can be approximated using the Landau-Khalatnikov equation with a kinetic coefficient value γ = 3.9×10^-8 cm³/(erg×s). The linear approximation does not fit well in the range from 291.3 to 293.2 K. The fundamental restriction of specific power of the magnetocaloric refrigerator (made by gadolinium plates) was estimated.

Abstract: Heating of a magnetizable body in an alternating magnetic field near the Curie point due to non-equilibrium magnetizing is theoretically investigated. The body is of a spherical shape and surrounded by a non-magnetizable unbounded medium. The heat generation power density is regarded as a piecewise linear function with a fracture at the Curie point. The steady temperature distribution within the body and outside it is found.

Abstract: In the present work we report our studies of temperature dependence of magnetization and structure analysis of Lu2Fe17 samples. The samples revealed various, coarse grained, submicrocrystalline, and nanocrystalline microstructures. It was found that in nanocrystalline state the Lu2Fe17 compound has a higher coercive force, retains phase composition and does not disintegrate during heating. The curves of the temperature dependence of magnetization were recorded for all investigated structural states and indicated that nanocrysatlline sample had a higher Curie point.

Abstract: Investigations of the influence of synthesis procedures and LaSr-manganite stoichiometries on the Curie point and other magnetic characteristics of the material, being the topic of this work, are attractive since they present a necessary primal step in the intended development of nano-magnetic drug carriers based on these materials. In the course of such an investigation, differences in the mechanisms of the formation of desired manganite compounds by following a classical solid-state preparation method, depending on various stoichiometries used, were noticed, with the reaction pathways thereof outlined onward.

Abstract: Phase transformations during the heating of amorphous Fe-Si-B alloys were investigated. The differential thermomagnetic analysis and X-ray method are used for the studies. The intervals of phase transformations are revealed, and the magnetic properties of phases are determined. The method of calculation of magnetic effects during the phase transformations, registered by differential technique is suggested.