Influences of Sintering Temperature on the Microstructure and Magnetocaloric Effect of Mn 1.15 Fe 0.85 P 0.65 Si 0.13 Ge 0.2 B 0.02 Prepared by Spark Plasma Sintering

Bulks with the same nominal composition of Mn 1.15 Fe 0.85 P 0.65 Si 0.13 Ge 0.2 B 0.02 were prepared by ball milling and subsequent spark plasma sintering (SPS) at 973, 1073, 1133 and 1173 K under a pressure of 50 MPa for 15 min. The structural and magnetocaloric properties of the compounds were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and magnetization measurements. XRD patterns indicate that all the studied compounds exhibit mainly the hexagonal Fe 2 P-type crystal structure. The lattice constants are slightly influenced by the sintering temperature ($T _{\mathbf {S}}$). As the $T _{\mathbf {S}}$ increases, crystal grains enlarge and holes become abundant. The Curie temperature monotonously decreases from 282 to 261 K when the $T _{\mathbf {S}}$ rises from 1073 to 1173 K. Under a field change from 0 to 2 T, the maximum values of isothermal entropy change are found to be 0.72, 4.4, 8.9 and 10.4 J/kgK for $T _{\mathbf {S}} = 793$, 1073, 1133 and 1173 K, respectively. The large magnetocaloric effects near room temperature in the studied compounds indicate that the SPS technique is suitable for preparing the Fe 2 P-type bulks with prominent magnetocaloric properties.