Effect of non-stoichiometry on the structural, magnetic and magnetocaloric properties of La0.67Ca0.33Mn1+δO3 manganites

Abstract In this paper, the structural, magnetic and magnetocaloric properties of a series of manganites with non-stoichiometric composition of La 0.67 Ca 0.33 Mn 1+ δ O 3 ( δ =0,±0.05 and±0.1) are reported. Polycrystalline manganites were synthesized using the sol–gel method. The X-ray diffraction results reveal that slight excess or deficiency of Mn does not modify the orthorhombic crystal structure with the space group Pbnm . The non-stoichiometry of Mn content has significant influence on the magnetic properties of the manganites. The manganites with δ =−0.05, 0, 0.05 and 0.1 undergo ferromagnetic–paramagnetic phase transitions at 220, 240, 248 and 222 K, respectively. Antiferromagnetic order could happen in the sample with δ =−0.1 due to the observation of quite small magnetization even at low temperature and strong magnetic field. The magnetization measurement at 5 K indicates that the saturation magnetization is lowered in the non-stoichiometric manganites. Under a magnetic field change from 0 to 5 T, the maximum absolute values of isothermal entropy change ( Δ S T , max ) are found to be 2.10, 2.94 and 2.90 J/kg K for δ =−0.05, 0 and 0.05, respectively. The slight change of Mn content in the non-stoichiometric (La,Ca)MnO 3 system can adjust the Curie temperature without significant degradation of the Δ S T , max value, which may provide a useful approach to obtain magnetocaloric La–Ca–Mn–O materials for magnetic refrigeration near room temperature.