Influence of Ge and Bi substitution on the magnetic and magnetocaloric properties of LaFe_(11.4)Si_(1.6)

摘要

In this work, the magnetic and magnetocaloric properties of LaFe _(11.4)Si_(1.6-x)Ge_x (x = 0.05, 0.1 and 0.2) and La_(1-x)Bi_xFe_(11.4)Si_(1.6) (x = 0, 0.1 and 0.2) compounds have been investigated. X-ray results indicate that the samples with lower Ge and Bi contents mainly consist of the NaZn_(13)-type phase with a small amount of α-Fe impurity phase. The α-Fe impurity phase increases with increasing concentrations of Ge and Bi. The Curie temperature of the samples also increases slightly with increasing Ge and Bi contents. The spin-wave dispersion coefficient D, exchange constant J and average mean-square range of exchange interaction ()~(1/2) have been calculated. The increase in Curie temperature is attributed to an increase in the average Fe-Fe distance and ferromagnetic interactions. The peak values of the magnetic entropy change |ΔS_m| are found to decrease with increasing Ge and Bi contents. This is attributed to a change of the phase transition from first order to second order. The peak values of |ΔS _m| are 22.38 J/kg K for LaFe_(11.4)Si_(1.6), 12.58 J/kg K for LaFe_(11.4)Si_(1.5)Ge_(0.1) and 14.25 J/kg K for La_(0.9)Bi_(0.1)Fe_(11.4)Si_(1.6) at a magnetic field of 6 T.