Karolina Kutynia

A simply supported rectangular isotropic ferromagnetic plate with magnetocaloric properties subjected to convective heating on its upper surface is considered. The governing equations comprise a system of two-dimensional transient equations for the thickness-averaged temperature characteristics of the plate and the two-dimensional bending equations for isotropic plates expressed in terms of generalized displacements within the framework of first-order shear deformation theory. Closed-form solutions to the governing equations are obtained by expanding all thermal and mechanical field quantities in double Fourier sine series satisfying the prescribed boundary conditions, combined with the Laplace transform in time applied to the thermal quantities. A comparative numerical analysis is carried out for the magnetocaloric ferromagnetic plate and a carbon steel plate under ambient temperature rising at a finite rate to a prescribed value. The dependences of all quantities under investigation on the ambient temperature rise rate, time, convective heat transfer coefficient, thermal conductivity of the ferromagnetic material, and geometric parameters of the plate are analyzed and presented graphically. The results obtained provide a quantitative basis for assessing the thermoelastic state and for optimizing the geometry and operating conditions of active magnetic regenerator plate stacks with a view to enhancing their structural reliability.

In the present paper, the theoretical simulation and experimental studies of magnetic properties of the Mn0.9Zn0.1CoGe alloy was done. Field dependences of magnetization in a wide range of temperatures were collected. Based on the thermomagnetic Maxwell relation, the magnetic entropy change ΔSM was calculated. Moreover, using the phenomenological model, temperature dependences of magnetization in a wide range of fields were simulated. Values of thermomagnetic properties, such as magnetic entropy change and refrigeration capacity, were calculated.

The following article is an explanation of the phenomenon of magnetocaloric phenomenon, which describes the principle of refrig erants in modern magnetic refrigerators. The magnetocaloric effect occurs over a wide temperature range from low to high temperatures. MCE is observed in various materials such as transition metals, rare earth elements, Laves phases, manganites, La(Fe,Si)13 alloys, full and half Heusler alloys and MM'X alloys. The principle of magnetic chillers is also described.

The main goal of the present work was to study the critical behavior in the MnCoGe alloy in the vicinity of the critical temperature TC. The second-order phase transition from ferro- to paramagnetic state was preliminarily confirmed by the positive slope of the Arrott plots. The critical exponents have been revealed using the Kouvel–Fisher method and yield β = 0.474 ± 0.005, γ = 0.917 ± 0.005, and δ = 2.985 ± 0.005. The Curie temperature for the MnCoGe equals 293.3 ± 0.1 K.

In the present paper, the influence of partial substitution of Mn by Pd on structure, thermomagnetic properties, and phase transitions in the MnCoGe alloys was investigated. The studies of phase constitution revealed an occurrence of the orthorhombic TiNiSi-type and hexagonal Ni₂Ti- type phases. Deep analysis of the XRD pattern supported by the Rietveld analysis allowed us to notice the changes in lattice parameters and quantity of recognized phases depending on the Pd content. An increase of palladium in alloy composition at the expense of manganese induced a rise in the Curie temperature. The values of ΔS_M measured for the variation of external magnetic field ~5 T equaled 8.88, 23.99, 15.63, and 11.09 for Mn_0.97Pd_0.03CoGe, Mn_0.95Pd_0.05CoGe, Mn_0.93Pd_0.07CoGe, and Mn_0.9Pd_0.1CoGe alloy, respectively. The highest magnetic entropy change ΔS_M was observed for samples with Pd content x = 0.05 induced by magnetostructural transformation. The analysis of the n vs. T curves allowed confirmation of the XRD and DSC results of an occurrence of the first-order magnetostructural transition in Mn_0.95Pd_0.05CoGe and Mn_0.93Pd_0.07CoGe alloys samples.

The aim of this work was to investigate the effect of partial substitution of Mn by Nb on structure and thermomagnetic properties in the (Mn, Nb)-Co-Ge alloy. The master alloys were prepared by arc-melting in an arc furnace with high purity of constituent elements under a low pressure of Ar. The prepared specimens were studied in as-cast state. The X-ray was performed by BRUKER D8 Advance diffractrometer with Cu Kα radiation. The analysis of the XRD pattern revealed coexistence of two orthorhombic phases with different lattice constants. The analysis of the temperature dependence of magnetizaton confirmed the XRD results and showed that produced material manifested two magnetic phase transitions corresponding to detected phases. The values of the Curie temperature were 275 and 325 K. The values of magnetic entropy change ∆SM equaled 3.30 and 2.13 J/(kg K), respectively for recognized phases. Biphase structure of produced material allowed to reach relatively high refigeration capacity 307 J/(kg). Moreover, the analysis of field dependences of magnetic entropy change (∆SM = CBn) allowed to construct temperature dependence of exponent n. The analysis of elaborated n vs. T curve confirmed biphasic structure of produced material.

The aim of the present work is to study the influence of a partial substitution of Mn by Zr in MnCoGe alloys. The X-ray diffraction (XRD) studies revealed a coexistence of the orthorhombic TiNiSi-type and hexagonal Ni₂In- type phases. The Rietveld analysis showed that the changes in lattice constants and content of recognized phases depended on the Zr addition. The occurrence of structural transformation was detected. This transformation was confirmed by analysis of the temperature dependence of exponent n given in the relation ΔS_M = C·(B_MAX)ⁿ. A decrease of the Curie temperature with an increase of the Zr content in the alloy composition was detected. The magnetic entropy changes were 6.93, 13.42, 3.96, and 2.94 J/(kg K) for Mn_0.97Zr_0.03CoGe, Mn_0.95Zr_0.05CoGe, Mn_0.93Zr_0.07CoGe, and Mn_0.9Zr_0.1CoGe, respectively. A significant rise in the magnetic entropy change for samples doped by Zr (x = 0.05) was caused by structural transformation.