Influences of Sintering Temperature on the Microstructure and Magnetocaloric Effect of Mn1.15Fe0.85P0.65Si0.13Ge0.2B0.02 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 Fe2P-type crystal structure. The lattice constants are slightly influenced by the sintering temperature (T
_S
). As the T
_S
increases, crystal grains enlarge and holes become abundant. The Curie temperature monotonously decreases from 282 to 261 K when the T
_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
_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 Fe2P-type bulks with prominent magnetocaloric properties.