Magnetic and Magnetocaloric Properties of Dy-Substituted (La1−xDyx)0.7Ba0.3MnO3 Perovskites

We examine the effect of average cation radius at the A site of the perovskite structure on the structural, magnetic and magnetocaloric properties of barium-doped lanthanum manganites. The A site cation radius is varied by partially replacing La⁺³ ions by smaller Dy⁺³ ions in the parent compound, for x up to 15%, in a nominal formula (La_1-xDy_x)_0.7Ba_0.3MnO₃. The barium doping level and thus the ratio Mn⁺⁴/(Mn⁺³ + Mn⁺⁴) was kept constant at 30%. The substitution of La⁺³ by the smaller Dy⁺³ ions causes a larger misfit in the ionic radius between the A and B sites of the perovskite structure which results in a phase transformation from rhombohedral to orthorhombic. All samples exhibit a ferromagnetic to paramagnetic transition. Transition temperature decreases with the percentage x of substitution from 275 to 203 K. Arrott-Belov plots show that all samples follow the behavior expected for a conventional second-order transition. The magnetic entropy change has been determined using isothermal magnetization curves in the vicinity of Curie temperature using Maxwell´ s equation. For a field change of 2 T the maximum IΔS_M^PEAK| decreases from 2.25 to 1.74 J/K/kg.