Magnetocaloric Effects and Critical Behavior of La0.7Ca0.3−xSrxMnO3.

In this study, polycrystalline samples of La_0.7Ca_0.3−xSr_xMnO₃ (x = 0.00, 0.10, and 0.25) were prepared using the conventional solid-phase reaction method. The magnetocaloric effects and critical behavior of this series of polycrystalline materials were investigated. The research results indicate that all the samples are single-phase with an orthorhombic structure, belonging to the space group Pbnm. Under a magnetic field of 7 T, the maximum magnetic entropy changes of the samples were 9.74, 7.37, and 6.11 J·kg⁻¹·K⁻¹, respectively, and the relative cooling power are 360.53, 361.04, and 366.50 J·kg⁻¹, respectively. The doped samples demonstrate superior magnetic refrigeration ability compared to the parent phase. It is noteworthy that the Curie temperature increases from 243 K (x = 0.00) to 295 K (x = 0.10) and 350 K (x = 0.25). In addition, there is a transition from a first-order to a second-order phase transition in the sample with x = 0.25. The critical behavior of the compounds with x = 0.25 was analyzed using various methods, including modified Arrott plots, the Kouvel-Fisher method, and critical isotherm, to determine critical exponents (β, γ, and δ). The results obtained from both methods are close and indicate that the critical behavior of the sample crosses between mean field model and 3D-Heisenberg model. The temperature dependence of the order parameter n for different magnetic fields is studied using the relation |∆S_M|∝ Hⁿ. The values of n not only reveal the type of phase transition of the system but also validate the critical exponents. The results indicate that La_0.7Ca_0.3−xSr_xMnO₃ (x = 0.10, and 0.25) ceramics have the potential to be used as room-temperature magnetic refrigeration materials. [ABSTRACT FROM AUTHOR]