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 La0.67Ca0.33Mn1+δO3 (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 222K, 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 5K indicates that the saturation magnetization is lowered in the non-stoichiometric manganites. Under a magnetic field change from 0 to 5T, the maximum absolute values of isothermal entropy change (ΔST,max) are found to be 2.10, 2.94 and 2.90J/kgK for δ=−0.05, 0 and 0.05, respectively. The slight change of Mn content in the non-stoichiometric (La,Ca)MnO3 system can adjust the Curie temperature without significant degradation of the ΔST,max value, which may provide a useful approach to obtain magnetocaloric La–Ca–Mn–O materials for magnetic refrigeration near room temperature.