  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.
