Effect of Structural Disorders on Magnetocaloric Effect in La2/3-xGdxSr1/3-yBayMnO3

Cation disordering in ABO(3) perovskite manganites plays the import role on their magnetism and transport properties. In the present, single phase of La2/3-xGdxSr1/3-yBayMnO3 ploycrystals are synthesized with fixing the averaged A-site ionic size of 1.247 angstrom. Subtle structural variations have been studied by Rietveld refinements using X-ray powder diffraction data. The unit cell symmetry remains unchanged with doping while the lattice parameters, Mn-O bond length, the Mn-O-Mn bond angle vary with the dopants. With increasing the Ba content, Mn-O bond length decreases while Mn-O-Mn bond angle increases, which indicates that the double-exchange interaction increases with Ba content. However, the ferromagnetic-to-paramagnetic transition temperature, T-c, decreases with Ba content, which confirms the strong suppression effect of cations disordering on magnetic ordering. The first-order to second-order magnetic phase transition is manipulated by a rival ship between A-site size-disorder degree and electron-lattice coupling for the sample system. In this system, we easy adjust the T-c above the room temperature. The transition temperature may be easily broadened by adjusting the cations disordering. It may be used as a promising candidate for magnetic refrigerant near room temperature.