Tuning the Curie temperature and thermal hysteresis of giant magnetocaloric (MnFe)₂PX (X = Ge and Si) compounds by the Ru substitution

Effects of the Ru substitution on magnetocaloric properties have been studied for MnFeP_0.8Ge_0.2 and Mn_1.2Fe _0.8P_0.5Si_0.5. The parent compounds undergo a first-order magnetic transition near room temperature accompanied by a large thermal hysteresis, ΔT_hys, of about 10 K. The substitution of 10-15 at.% of Ru reduces ΔT_hys down to 2-3K. On the other hand, a sharp magnetic transition is preserved by the Ru substitution up to 15% and, as a result, a large magnetic entropy change and a small ΔT_hys are achieved. It is found that the refrigerant capacity of the Ru substituted compounds is 1.6-1.8 times as large as that of Gd. These results have proved that the Ru substitution is an effective method to realize Mn-based magnetic refrigerant materials.