817 words - 4 pages

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, the Grüneisen parameters at atmospheric and applied pressures (Γ^at=0.13 and Γ^app) were adjusted (see table 1) leading to the calculated curves shown in the fig.1 and fig.2 for P=1.5,2.0 and 2.9 kbar. The dotted curves are due to the variation of pressure (from atmospheric to P = 1.5, 2.5 and 2.9 kbar), simultaneously under the intensity of the applied magnetic field change from zero to 5 T.

Figure 4 shows the thermal hysteresis for...

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