Tuning of normal and inverse magnetocaloric effect in Sm0.35Pr0.15Sr0.5MnO3 phase separated manganites

Abstract

Magnetic and magnetocaloric properties of Sm0.35Pr0.15Sr0.5MnO3 polycrystalline manganite (bulk and nanometric samples) are investigated in detail. It has been observed that all the particle sizes (bulk to nano) show first order ferromagnetic→paramagnetic phase transition at low magnetic field. Ferromagnetic transition temperature also decreases with decreasing the particle size. This suggests that ferromagnetism is weakened and the first order magnetic phase transition is softened. We have investigated the magnetocaloric effect (MCE) of both bulk and nanometric samples around their spin glass-like transition temperature, Tg and Curie temperature, TC. It has been found that bulk sample exhibits both normal (i.e., negative ΔSM) and inverse (i.e., positive ΔSM) MCE around TC and after Tg, respectively. The value of ΔSM (+3.17Jkg−1K−1) at TC is almost three times larger than at Tg (ΔSM=−0.52Jkg−1K−1) for a magnetic field change of 7T. The bulk sample also exhibits a large relative cooling power (RCP) of 43.5J/kg for a magnetic field of 1T. The corresponding adiabatic temperature change of bulk sample is observed to be ∼1.5K for a magnetic field change of 3T. The value of ΔSM also decreases with reduction of particles sizes. The temperature width of ΔSM broadens with decreasing particle size. The value of ΔSM and the adiabatic temperature change vary with temperature and it is also found to be significant at all applied magnetic fields. Our results suggest that Pr3+ doping induces ferromagnetic clusters in the charge ordered matrix exhibiting large normal MCE at TC and the antiferromagnetic coupling between the Sm 4f and Mn 3d moments is most likely responsible for the inverse MCE below Tg. The co-existence of normal and inverse MCEs is technologically potential and interesting as the sample can be cooled by adiabatic magnetization and demagnetization in different temperature regions enhancing the refrigeration capacity.