Effect of the oxygen deficiency on the physical properties of La0.8Na0.2MnO3-δ oxides (δ=0 and 0.05)

This paper presents the effects of oxygen deficiency on the structural, magnetic and magnetocaloric properties of La0.8Na0.2MnO3-delta where delta=0 and 0.05. The Polycrystalline La0.8Na0.2MnO3-delta samples were synthesized by a new method. The introduction of the oxygen deficiency in our samples leads to an increase of Mn3+ content according to the electronic formula La0.3+Na0.2+Mn0.6+2 delta 3+Mn0.6-2 delta 4+O3-delta. The X-ray diffraction analysis shows a phase transition from a rhombohedral system with R (3) over barc space group for delta=0.00 to an orthorhombic with Prima space group for delta=0.05. It also induces a great variation in the magnetic properties. The magnetization versus temperature study has shown that all samples exhibit a magnetic transition from ferromagnetic (FM) to paramagnetic (PM) phase with the increase in temperature. However, it can be clearly seen that the oxygen deficiency induces an increase in the magnetization and a decrease in the Curie temperature T-C. Besides, the magnetocaloric effect (MCE) as well as the Relative Cooling Power (RCP) has been estimated. As an important result, the values of MCE and RCP in our oxygen deficiency manganites are reported to be close to those found in gadolinium that is considered as magnetocaloric reference material. (C) 2015 Elsevier B.V. All rights reserved.