Magnetocaloric properties and magnetic refrigerant capacity of MnFeP _1-xSi_x

Magnetic entropy change, ΔS_M, and the refrigeration capacity, q, of MnFeP_1-xSi_x have been examined. In accordance with the previous report, the compounds with 0.30 ≤ x ≤ 0.60 undergo a first-order magnetic transition near room temperature. The Curie temperature is increased linearly from 210 K to 360 K with increasing x from 0.30 to 0.60. The compounds display large thermal hysteresis. This hysteresis decreases with increasing x. We have carefully estimated ΔS_M of the compounds with large thermal hysteresis from the Maxwell relation using the magnetization-temperature curves. It was found the peak values of ΔS _M in a field change of 2 T is 7-13 J/K kg, which are much smaller than the values reported previously. On the other hand, the q values of the compounds over the temperature range 30 K were found to be 1.5 times as large as that of metallic Gd. These results demonstrate excellent magnetic refrigerant capacity of MnFeP_1-xSi_x near room temperature. To expand the working temperature range of magnetic refrigerant materials, a design of a composite material is also proposed.