Effect of annealing on the structure and magnetic properties of Mn1.1Fe0.9P0.8Ge0.2 compound

Effect of homogenization of the chemical composition and crystal structure on the magnetocaloric effects have been studied for bulk Mn1.1Fe0.9P0.8Ge0.2 alloy prepared by mechanical alloying and subsequent spark plasma sintering method. After optimal homogenization treatment, the ferromagnetic impurity, Ge6Fe3Mn4 phase was completely eliminated from the alloy; furthermore, the crystal lattice constant of the MnFePGe main phase, which possesses a hexagonal Fe2P-type structure, varies obviously compared with that of the sintered sample. As a result, the Curie temperature, TC, of the alloy increases from 253 to 267.5 K and the maximum magnetic entropy change, |ΔSm|, also increases from 36.36 to 44.35 J/kg K under 3 T magnetic field. Furthermore, the thermal hysteresis of M-T curves around TC upon heating and cooling, a signature of a first-order magnetic phase transition, reduces from 15 K for as-sintered sample to 9 K for annealed sample.