Magnetocaloric effect in polycrystalline La0.65Ba0.3M0.05MnO3 (M=Na, Ag, K) manganites

The effects of monovalent doping on the crystallographic, magnetic and magnetocaloric properties of La0.65Ba0.3M0.05MnO3 (M = Na, Ag, K) powder samples, elaborated using the solid state reaction method at high temperature, have been investigated. In our three samples the Mn4+ amount remains constant equal to 40%. 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 (3) over barc space group. All our studied samples undergo a paramagnetic-ferromagnetic transition with decreasing temperature. Using the Arrott plot, the second-order transition Curie temperature T-C for M = Na, Ag and K is found to be 310, 300 and 290 K, respectively. The magnetic entropy change, deduced from isothermal magnetization curves, exhibits a maximum |Delta S-M(Max)| of about 2.65, 2.82 and 2.66 J/kg K for M = Na, Ag and K, respectively, in a magnetic applied field change of 5T. Although these values are modest, the magnetocaloric effect extends over a large temperature range leading to an important value of the relative cooling power (RCP). The RCP values exhibit an early linear dependence with the magnetic applied field. The refrigeration capacity in a magnetic applied field of 1T is found to be 28.8, 27.8 and 25.6 J/kg for M = Na, Ag and K compounds. (C) 2009 Elsevier B.V. All rights reserved.