Magnetocaloric and phase coexistence in La_0.5Ca_0.5–xSr_xMnO₃ manganites

Structural, magnetic, and magnetocaloric properties of the phase separated La_0.5Ca_0.5–xSr_xMnO₃ (x = 0, 0.2, 0.3, 0.4, and 0.5) manganites have been studied. The results show that the phase coexistence state can be investigated by magnetocaloric studies (especially the field dependence of magnetic entropy change at constant temperature). Magnetic entropy change (△S_M) shows positive (negative) peak at the vicinity of T_N (T_C). However, in the intermediate temperatures between T_N and T_C, both the sign and magnitude of △S_M are strongly dependent on temperature and magnetic field, manifesting the competition of ferromagnetic (FM) (negative △S_M) and non-FM (positive △S_M) phases. This behavior is more pronounced in the parent compound, La_0.5Ca_0.5MnO₃, in which the intermediate phase separation ranges between 160 and 225 K. The substitution of Ca by Sr enhances the ferromagnetic state, weakens the phase separation, and thus narrows the temperature range in which the field related effects (such as the sign change of △S_M) are observed.