Structure, composition and magnetocaloric properties in polycrystalline La1-xAxMnO $$_{3 + \delta }$$ (A = Na, K)

The polycrystalline perovskitelike manganese oxides La1-xAxMnO $$_{3 + \delta }$$ (A = Na, and K, 0.05 < x ≤ 0.20) have been fabricated by sol-gel technique. For all the compositions explored in this work, the average manganese oxidation state is practically constant, at 3.32 ± 0.02 for A = Na, and 3.40 ± 0.04 for A = K, respectively. A close relationship is confirmed to hold between the Curie temperature (Tc) and the bond distance of Mn-O. Results of magnetic measurements show that these materials can be utilized as suitable candidates for magnetic refrigerants with wide applied temperature span, for their significant entropy change and the easily tuned Curie temperature.