Effects of A-site cation disorder on structure and magnetocaloric properties in Y and Sr codoped La_(2/3)Ca_(1/3)MnO_3 compounds

摘要

Structural and magnetocaloric properties for the perovskite manganite La_(2/3-x)T_xCa_(1/3-y)MnO_3 (x < 0.2) have been studied. These compounds with the fixed A-site average ionic radii of 1.204 A and Mn~(4+)/Mn~(3+) ratio were prepared by conventional solid-state reaction technique. The lattice parameters were obtained from refining x-ray diffraction diagrams preformed by Rietveld refinement method. The ferromagnetic ordering temperature T_C increases abruptly owing to the increase in the competition between A-site size-disorder degree σ~2 and double-exchange interaction resulting from Mn-O-Mn bond angle. Phase transition may be broadened due to the cation disordering at A-site. Sample with x=0.01 appears a large magnetic entropy △S_M=3.3 J kg~(-1) K~(-1) at the Curie temperature T_C=274 K, which may be used as a promising candidate for magnetic refrigerant near room temperature.