  Disorder induced by chemical inhomogeneity and Jahn-Teller (JT) distortions
is often observed in mixed valence perovskite manganites. The main reasons for
the evolution of this disorder are connected with the cationic size differences
and the ratio between JT active and non-JT active ions. The quenched disorder
leads to a spin-cluster state above the magnetic transition temperature. The
effect of Cu, a B-site substitution in the La0.8Sr0.2MnO3 compound, on the
disordered phase has been addressed here. X-ray powder diffraction reveals
rhombohedral (R-3c) structures for the two compounds with negligible change of
lattice volume. The chemical compositions of the two compounds were verified by
ion beam analysis technique. With the change of electronic bandwidth, the
magnetic phase transition temperature has been tuned towards room temperature
(318 K), an important requirement for room temperature magnetic refrigeration.
However, a small decrease of the isothermal entropy was observed with
Cu-substitution, related to the decrease of the saturation magnetization.

Materials Science