First to Second Order Phase Transformation in La<inf>0.7-x</inf>Sm<inf>x</inf>Ca<inf>0.3</inf>MnO<inf>3</inf>Compounds

Abstract

The magnetocaloric effect (MCE) was discovered a long time ago. It is the response of a magnetic material to the applied magnetic field change and appearing the maximum value when the material is near its magnetic ordering temperature. In recent years it has attracted the attention of researchers and the amount of publications in this topic increases quickly. It is known that first order magnetic phase transition La 0.7 Ca 0.3 MnO 3 compound exhibits a giant MCE around the Curie temperature $(T_{\mathrm{C}})$ . However, MCE in this compound only occurs in a narrow temperature range, which limits its applicability. In this work, we point out that the width and the nature of the magnetic phase transition, $T_{\mathrm{C}}$ value, and as well as MCE in this material is easily modified through Sm-doped into La-site. With an increasing Sm concentration in La 0.7-x Sm x Ca 0.3 MnO 3 compounds, a systematic decrease in the magnetization, $T_{\mathrm{C}}$ , and magnetic entropy change $(\Delta S_{\mathrm{m}})$ are observed. The Banerjee criterion suggests that the sample with $x=0.1$ considered undergoes a first order magnetic phase transition. Meanwhile, $x=0.2$ sample undergoes a second order magnetic phase transition. A detailed analysis of the critical behavior based on the modified Arrott plots, the Kouvel-Fisher, and the scaling hypothesis methods has been done. Our results indicate a coexistence of long-range and short-range ferromagnetic interactions in La 0.5 Sm 0.2 Ca 0.3 MnO 3 compound. Besides, a further method, a phenomenological universal curve for magnetic entropy change, has been applied as a supplementary criterion to discriminate between the first and second order phase transition in these samples. The essence of changes in the order of magnetic phase transition, magnetic and magnetocaloric properties is thoroughly discussed by means of the crystal structure.