Composition Dependence of Magnetocaloric Effect in Pr_0.6Ca_0.4Mn_1−x Cr _x O₃ (x = 0.02–0.08)

We report the effect of varying Cr content on magnetic and magnetocaloric properties of Pr_0.6Ca_0.4Mn_1−x Cr _x O₃ samples (x = 0, 0.02, 0.04, 0.06 and 0.08). While the parent compound (x = 0) is a charge ordered and antiferromagnetic insulator, Cr doped compounds are ferromagnetic metals with nearly same Curie temperature (T _C ≈ 140 K). We find unusual field-induced metamagnetic transition above T_C in x = 0.02 and 0.04 which is absent in x = 0.06 and 0.08. It is suggested that the paramagnetic phase in these compounds is inhomogeneous with coexistence of nano-size ferromagnetic clusters and short range charge ordered clusters. Field induced growth of ferromagnetic nano-clusters and destruction of short-range charge ordering leads to the observed metamagnetic transition, which results in large magnetic entropy change of −ΔS _M = 5.043, 6, 5.509 and 4.375 J/kg K under ΔH = 5 T, for x = 0.02, 0.04, 0.06 and 0.08, respectively. In addition, large relative cooling power (RCP) found in these materials (327.384, 286.36, 272.22 and 279.936 J/kg) makes it interesting for practical applications. Our study suggests that creation of ferromagnetic nano-clusters in the paramagnetic phase by Mn-site doping in charge ordered compounds provides an alternative approach to achieve high ΔS _M and RCP values.