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

In this paper, the structural, magnetic and magnetocaloric properties of a series of manganiles with non-stoichiometric composition of La0.67Ca0.33Mn1+delta O3 (delta=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 Photo. The non-stoichiometry of Mn content has significant influence On the magnetic properties of the manganites. The manganites with delta=-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 (delta= -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 (Delta S-T,S-max) are found to be 2.10, 2.94 and 2.90 J/kg K for delta=-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 Delta S-T,S-max value, which may provide a useful approach to obtain magnetocaloric La-Ca-Mn-O materials for magnetic refrigeration near room temperature. (C) 2015 Elsevier B.V. All rights reserved.