Critical Behavior and Magnetocaloric Effect of Pr1-xSrxCoO3

The modified Arrott plot method was used to analyze magnetic-field dependences of magnetization, \(M\) ( \(H\) ), for two polycrystalline samples Pr1-x Srx CoO3 with \(x = 0.4\) and 0.5. The analyses determined the values of critical parameters \(T_{C} \approx 204\) K, \(\beta = 0.654~\pm ~0.016\) , \(\gamma = 1.11~\pm ~0.009\) , and \(\delta = 2.70~\pm ~0.009\) for \(x = 0.4\) , and \(T_{C} \approx 218\) K, \(\beta = 0.495~\pm ~0.004\) , \(\gamma =0.991~\pm ~0.003\) , and \(\delta = 2.86~\pm ~0.009\) for \(x = 0.5\) . With these critical values, the \(M(H\) ) data around the \(T_{C}\) of the samples fall into two universal branches of a scaling function \(M(H\) , \(\varepsilon ) ={} \vert \varepsilon \vert ^{\beta }\!f_{\pm }\) ( \(H/ \vert \varepsilon \vert ^{\beta +\gamma }\) ), where \(\varepsilon =(T\) – \(T_{C}\) )/ \(T_{C}\) , and \(f_{+}\) for \(T > T_{C}\) and \(f_{-}\) for \(T < T_{C}\) . Here, the \(T_{C}\) increase with the increasing Sr content is ascribed to an increase of ferromagnetic (FM) double-exchange interaction pairs of Co3+–Co4+, and to the \(\beta \) change from 0.654 (for \(x = 0.4\) ) to 0.495 (for \(x = 0.5\) ). This corresponds to the change in FM interactions from short-range to nearly long-range FM orders. Based on the \(M(H)\) data, we also determined the magnetic-entropy change, which reaches a maximum value ( \(\vert \Delta S_{\max } \vert \) ) around the \(T_{C}\) ; \(\vert \Delta S_{\max } \vert \,\approx ~1.9\) and 2.2 J/kg \(\cdot \) K for \(x =0.4\) and 0.5, respectively, for a magnetic field change \(\Delta H = 50\) kOe. The relative cooling power thus increases from 52 J/kg (for \(x = 0.4\) ) to 84 J/kg (for \(x = 0.5\) ). In particular, field dependences of the magnetic-entropy change ( \(\Delta S_{m}\) ) obey a power function \(\vert\Delta S_{m}\) ( \(H\) ) \(\vert ~\propto H^{\mathbf {n}}\) , where the magnetic-ordering parameter ( \(n\) ) slightly decreases from 0.75 for \(x = 0.4\) to 0.70 for \(x = 0.5\) .