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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 transition at T = Tc 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 ferromagnetic metal below Tc 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 compound show a cusp at a temperature T* much below Tc. While the Tc 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 Sm) was estimated from magnetization isotherms. The sign of delta Sm is found to change from negative above T* to positive below T* indicating the coexistence of normal and inverse magnetocaloric effects. delta Sm is nearly composition independent (-delta Sm is about 1.5 J/Kg K for delta H = 1 Tesla) and refrigeration capacity lies between 50 and 80 J/kg K for x = 0.1-0.6. The tunability of Curie temperature with a nearly constant delta Sm value along with high refrigeration capacity makes this series of compounds interesting for magnetic refrigeration over a wide temperature range.