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

• Structural and magnetic properties of La0.67Ca0.33Mn1+δO3 manganites were studied.
• The manganites with deficient and excessive Mn crystallized in the same orthorhombic structure.
• The concentration of Mn has important influences on the magnetic properties.
• The manganites exhibit significant magnetocaloric effect in broad temperature range.
• The magnetocaloric effect of the manganites can be interpreted by Landau model.

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 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 (ΔST,maxΔST,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)MnO3 system can adjust the Curie temperature without significant degradation of the ΔST,maxΔST,max value, which may provide a useful approach to obtain magnetocaloric La–Ca–Mn–O materials for magnetic refrigeration near room temperature.