Effects of the Ru substitution on magnetocaloric properties have been studied for MnFeP0.8Ge0.2 and Mn1.2Fe 0.8P0.5Si0.5. The parent compounds undergo a first-order magnetic transition near room temperature accompanied by a large thermal hysteresis, ΔThys, of about 10 K. The substitution of 10-15 at.% of Ru reduces ΔThys 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 ΔThys 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.
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