Sodium - Deficiency effects on the structural, magnetic and magnetocaloric properties of La0.8Na0.2−x□xMnO3 (0 ≤ x ≤ 0.15)

In this paper, we report the magnetocaloric effect of Na vacancies in La0.8Na0.2−x□xMnO3 (0 ≤ x ≤ 0.15) powder samples synthesized using the sol-gel technique. Structural investigations using X-ray diffraction show that all the elaborated compounds crystallise in the rhombohedral structure with R3¯c space group. Magnetic measurements versus temperature reveal a magnetic transition from ferromagnetic (FM) to paramagnetic (PM) phase when increasing temperature. The Curie temperature TC shifts to lower values with increasing sodium-deficiency. The Arrott plots indicate that a second order phase transition takes place. The effect of sodium-deficiency on the magnetocaloric properties has also been investigated. The maximum values of the magnetic entropy changes, |−ΔSM|max, under a magnetic field change of 5T are found to be 4.74; 4.13; 6.14 and 4.55 J/kg K for x = 0; 0.05; 0.1 and x = 0.15 respectively. The relative cooling power (RCP) and its field dependence are also analyzed. The obtained magnetic entropy changes are compared to calculated ones based on the Landau theory and a good concordance is observed.