Abstract
It is shown that the charge-orbital ordered antiferromagnetic insulating state of the parent compound (y=0) in Nd0.5Ca0.5Mn1−yRuyO3 (y=0, 0.03, 0.05, & 0.10) series is destabilized and a ferromagnetic metallic state is induced by Ru substitution as small as 3%. The ferromagnetic transition temperature (TC) increases with Ru content from 215 K (y=0.03) to 255 K (y=0.10). The magnetic entropy change (ΔSm) of y=0 changes sign from negative to positive as the temperature is lowered below the charge ordering temperature. However, ΔSm is negative and exhibits a peak close to TC in Ru-doped samples. The peak values of ΔSm are −0.33, −3.8, −3.6, and −3.5 J kg−1 K−1 for y=0, 0.03, 0.05, & 0.10 respectively, for a field change of ΔH=5 T. The relative cooling power (RCP) decreases with increasing Ru content from 268 J/kg for x=0.03 to 234 J/kg for x=0.10 for ΔH=5 T whereas the y=0 sample shows 17 J/kg. The large RCP and ΔSm found in Ru-substituted samples will be interesting for magnetic refrigeration below room temperature.
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