Structure and Magnetocaloric Properties in Perovskitelike La_l-xNa_xMnO_z Powders

Perovskitelike manganese oxides La_l-xNa_xMnO_z (x = 0.075, 0.100, 0.165, 0.200) have been fabricated using sol-gel technique. Structure analysis, temperature programmed reduction (TPR) technique and magnetic measurement have been used to study the effect of Na ion substituted amount on Mn-O distance, the oxygen content, and the magnetocaloric properties of these materials. Results show there is no clear correlation between the substituted amount and mean Mn valence, but a close relationship is observed between T_c and the bond distance of Mn-O. These materials have quite large magnetic entropy changes upon an application of a low magnetic field and can be utilized as more suitable candidates for magnetic refrigerants with wide temperature span.