Tunable spin reorientation transition and magnetocaloric effect in Sm0.7-xLaxSr0.3MnO3 series

We report electrical resistivity, magnetic, and magnetocaloric properties in Sm0.7-xLaxSr0.3MnO3 series for x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.65, and 0.7. All the compounds show second order paramagnetic to ferromagnetic (FM) transition at T = T-c, which is tunable anywhere between 83 K and 373 K with a proper choice of the doping level (x). The insulating ferromagnet x 0 transforms to a ferromagnetic metal below T-c for x 0.1, and the insulator-metal transition temperature shifts up with increasing x. The magnetization (M) exhibits an interesting behavior as a function of temperature and doping level. The field-cooled M(T) of all but x 0.7 compounds show a cusp at a temperature T* much below T-c. While the T-c increases monotonically with increasing x, T* increases gradually, attains a maximum value (T* 137 K) for x 0.6 and decreases rapidly thereafter. It is suggested that the decrease of M(T) below T* is due to ferrimagnetic interaction between Sm(4f) and Mn(3d) sublattices that promotes spin-reorientation transition of the Mn-sublattice. The observed anomalous feature in M(T) does not have impact on the dc resistivity. Magnetic entropy change (Delta S-m) was estimated from magnetization isotherms. The sign of Delta S-m is found to change from negative above T* to positive below T* indicating the coexistence of normal and inverse magnetocaloric effects. Delta S-m is nearly composition independent (-Delta S-m 1.2 +/- 0.2 J/Kg K for mu(0)Delta H = 1 Tesla) and refrigeration capacity lies between 40 and 50 J/kg K for 0.1 <= x <= 0.6. We show scaling of magnetic entropy change under different magnetic fields and analysis of critical exponents associated with the phase transition in x 0.6 compound. The tunability of Curie temperature with nearly constant Delta S-m value along with high refrigeration capacity makes this series of compounds interesting for magnetic refrigeration over a wide temperature range. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4773337]