Magnetic entropy change in the monovalent doping La0.7Ba0.2M0.1MnO3 (M = Na, Ag, K) manganites

Structural, magnetic, and magnetocaloric properties of monovalent doped La0.7Ba0.2M0.1MnO3 (M = Na, Ag, K) powder samples, synthesized using the solid state reaction at high temperature, have been experimentally investigated. The Rietveld refinement of the X-ray powder diffraction shows that all our synthesized samples are single phase and crystallize in the distorted rhombohedral system with $$ R\overline{3} c $$ space group. Lattice parameters and the unit cell volume increases with increasing average A-site ionic radius 〈r A〉. The Mn–O–Mn bond angle decreases with increasing 〈r A〉, ranging from 168.32° (M = Na) to 165.91° (M = K). All our studied samples undergo a paramagnetic–ferromagnetic transition. The Curie temperature T C, shifts slightly to a lower temperature with increasing 〈r A〉, which is consistent with large cationic disorder. Magnetic entropy change, $$ \left| {\Updelta S_{\text{M}} } \right| $$ , deduced from isothermal magnetization curves, reaches 3.04, 3.14, and 3.01 J/kg K for M = Na, Ag, and K, respectively, in a magnetic applied field change of 5T. Large relative cooling power (RCP) value of 337.9 J/kg is obtained for La0.7Ba0.2K0.1MnO3 sample, at a field change of 5T. This relatively large value associated to a Curie temperature of 311.5 K makes the present compound a promising candidate for the magnetic refrigerators around room temperature.