Effects of Ru substitution on the structural, magnetic and magnetocaloric properties of Pr_0.68Ca_0.22Sr_0.1Mn_1−xRu_xO₃ (x = 0, 0.05, 0.1 and 0.2) compounds

The structural, magnetic and magnetocaloric properties of polycrystalline Pr_0.68Ca_0.22Sr_0.1Mn_1−xRu_xO₃ (x = 0, 0.05, 0.1 and 0.2) compounds were studied. All the samples crystallized in an orthorhombic symmetry. A significant increase in the lattice parameters in the doped samples was attributed to the existence of Ru with a the mixed-valence state (Ru³⁺/Ru⁴⁺). The increase in the Curie temperature (T_c) with increasing Ru content was interpreted as Ru doping promoting the ferromagnetic interactions between Ru⁴⁺–Mn³⁺ and Ru⁴⁺–Mn⁴⁺pairs. The decrease in saturation magnetisation was attributed to an AFM interaction between the Ru³⁺–Mn³⁺ and Ru³⁺–Mn⁴⁺ pairs and smaller magnetic moments of Ru than those of Mn. The decrease in ΔS_M (from 4.66 J kg⁻¹ K⁻¹ for x = 0.05 to 2.32 J kg⁻¹ K⁻¹ for x = 0.2 at 5 T) was attributed to the nature of phase transition (from a first-order to second-order transition) and a decrease in the saturation magnetisation.