Effects of Cr substitution on structural and magnetic properties in La_(0.7)Pr_(0.3)Fe_(11.4)Si_(1.6) compound

摘要

In an effort to explore the effect of substitution Fe by Cr in NaZn_(13)-type La_(0.7)Pr_(0.3)Fe_(11.4-x)Cr_xSi_(1.6) (x = 0, 0.06, 0.12, 0.26, and 0.34) compounds, the structure and magnetic properties have been investigated by high intensity of x-ray and neutron diffraction, scanning electron microscopy, specific heat, and magnetization measurement. It has been found that a substitution of Cr for Fe in this compounds leads to decrease in the lattice parameter a at room temperature but variation on Curie temperature (T_C). While the first order nature of magnetic phase transition around T_C does not change with increasing Cr content up to x = 0.34. High intensity x-ray and neutron diffraction study at variable temperatures for highest Cr concentration x = 0.34 confirmed the presence of strong magneto-volume effect around T_C and indicated the direct evident of coexistence across magnetic transition as characteristic of first order nature. The values of - ΔS_M around T_C decrease from 17 J kg~(-1)K~(-1) for x = 0 to 12Jkg~(-1) K~(-1) for x = 0.06 and then increases with further increasing Cr content up to 17.5 Jkg~(-1) K~(-1) for x = 0.34 under a change of 0-5 T magnetic field. Similar behavior on relative cooling power which is decrease from 390Jkg~(-1) for x = 0 to 365 J kg~(-1) for x = 0.06 at the beginning and then increases up to 400 J kg~(-1) for x = 0.34. From the point of this view with the highest Cr concentration (x = 0.34) exhibits favourable material candidate for magnetic refrigerator application therefore should inspire further study concerning on higher Cr concentration in this compound.