Bulk Mn_(1.2)Fe_(0.8)P_(0.76)Ge_(0.24) alloy was prepared by mechanical milling and subsequent spark plasma sintering technique.Effect of annealing on the structure and magneto-caloric properties of the alloy was investigated.XRD results show that both sintered and annealed samples possess a hexagonal Fe_2P-type crystal structure.After annealing,ferromagnetic impurity Fe_3Mn_4Ge_6,which exists in the sintered sample,was eliminated from the alloy.Furthermore,the lattice constants a and c change noticeably,leading to a decrease in c/a ratio,while the cell volume almost remains invariable.As a result,the Curie temperature of the alloy increases from 253 K to 298 K,but the maximum magnetic entropy change decreases from 37.5 to 11.7 J·kg·K^(-1) for 2 T magnetic field change.On the other hand,the thermal hysteresis of M-T curves around T_C upon heating and cooling is 14 and 8 K for the as-sintered and the annealed sample,respectively,showing evident change.
展开▼
