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Theoretical investigation on the barocaloric and magnetocaloric properties in the Gd5Si2Ge2 compound

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Figure 1 shows the temperature dependence of magnetization in Gd5Si2Ge2 compound at and at atmospheric pressure. Open symbols are the experimental data and the solid symbols represent the theoretical curve. The circles are for sample heating and triangles are for sample cooling. The value of saturation magnetization at 8 K in the theoretical curve was normalized with the experimental data. The values of and were adjusted according to the critical temperatures from the M vs. T curves (Fig. 1) at atmospheric pressure for sample heating and cooling (table 1). It is worth noticing that fixes the Curie temperature and is responsible for the existence of first order magnetic phase transition and fixes the thermal hysteresis of about 5 K.
Table 1 shows the values of our model parameters adjusted to fit the experimental data for the pressures 1.5, 2.0 and 2.9 kbar. Values of model parameters used in the theoretical curves adjusted at zero magnetic field.
Figure 2 shows the isothermal entropy changes heating the sample (a), (b) and (c) and (the figure 3 cooling the sample (a), (b) and (c)). The solid curves are due to the variations from atmospheric pressure (P^at) to applied pressure, P=1.5 kbar (fig.2a and fig.3a), P=2.0 kbar (fig.2b and fig.3b), P=2.9 kbar (fig.2c and fig.3c) without applied magnetic field (µ_0 h_0=0 T) for sample heating and cooling, as indicated by the arrows. The open circles and open squares represent 〖ΔS〗_T vs. T experimental data for Gd5Si2Ge2 which are in good agreement with our theoretical curves for sample heating and cooling, respectively [19]. The value was used for this compound in our theoretical curves [28], value that we kept in our model in all theoretical curves. For all pressure changes, th...

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...ing applied pressure, in fact only the 〖ΔS〗_T-peak intensity increases with increasing pressure. We predict an increase in the 〖ΔS〗_T-peak intensity on average of 58% compared to 〖ΔS〗_T-peak intensity for P^at→P (at zero applied magnetic field). The open symbol show 〖ΔS〗_T vs. T for variation of pressure (P^at→P) keeping the fixed applied field (µ_0 h_(0 (fixed))=5 T), for sample heating (triangles) and cooling (inverted triangles), respectively. That intensity of the applied field, each applied pressure P=1.5,2.0 and 2.9 kbar it is provided that the phase change occurs in T=289.0,289.1 and 289.4 K, and that the intensity of the peaks are 〖ΔS〗_T=-2.3,-3.4 e -3.9 J/kg.K, respectively. The reduction in the peak intensities of 〖ΔS〗_T can be ascribe to the loss of first order phase transition (at µ_0 h_(0 (fixed))=5 T) once we notice the loss of thermal hysteresis.
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