The effects of Si substitution for As on the magnetic and magnetocaloric properties of MnFeP0.5As0.5−xSix compounds have been investigated. The Si-substituted compounds MnFeP0.5As0.5−xSix with x=0, 0.1, 0.2, and 0.3 have been prepared by high-energy ball milling and solid-state reaction. X-ray diffraction shows that all the MnFeP0.5As0.5−xSix compounds crystallize in the Fe2P-type structure. Magnetic measurements show that the compounds are ferromagnetic with a nonlinear dependence of TC on Si content. All compounds exhibit a field-induced first-order magnetic phase transition. The magnetic-entropy change is derived from the magnetization data by using the Maxwell relations. The maximum magnetic-entropy change observed in this system reaches about 32J∕kgK for a field change from 0to2T for x=0.2, at temperature around 294K.

Powder and sintered samples of La0.9MnO3 (LMO) and La0.62Y0.07Ca0.31MnO3 (LYCMO) are used in this study. The two initial calcined in air powders have almost identical ferromagnetic properties with Tc≈250 K, and saturation magnetization of σ≈90 emu/gm corresponding to Mn4+(0.3)/Mn3+(0.7). Heating the calcined powders in argon to high temperatures lowers Tc to ≈120 K; however, subsequent oxygen annealing brings back the high Tc form. The LYCMO remains ferromagnetic with σ≈90 emu/gm in both heat treatments but only has a colossal magnetoresistance (MR) for Tc≈120 K. In contrast the LMO with Tc≈120 K has σ reduced to one-half its ferromagnetic value and the MR is almost zero. Neutron diffraction shows only the ferromagnetic structure below Tc for LYCMO but the low magnetization of LMO is best interpreted as a mixed ferro–antiferromagnetic structure rather than a canted one.