Magnetic and magnetocaloric properties of lanthanum manganites with monovalent elements doping at A-site

In this study, magnetic and magnetocaloric properties of La0.8K0.1M0.1MnO3 with M=Na and Ag compounds have been investigated. X-ray diffraction analysis using Rietveld refinement reveals that La0.8K0.1Na0.1MnO3 and La0.8K0.1Ag0.1MnO3 samples crystallize in the distorted rhombohedral system with R (3) over barc spacegroup. The surface morphology and elemental analysis of both samples were carried out by scanning electron microscopy(SEM) and energy dispersive X-ray technique( EDAX), respectively. EDAX spectra taken from the surface of the synthesized powders show a nominal composition near the desired one for M=Na sample whereas some vacancies are present in the A-site in the case of Ag substitution as will be discussed in this paper. Magnetization measurements versus temperature in a magnetic applied field of 50 mT showed that our samples are ferromagnetic at low temperatures. Curie temperature T-C is found to be 330 and 310 K for M=Na and Ag, respectively. Arrott plots deduced from isothermal magnetization curves indicate that our samples exhibit a second order magnetic phase transition. From the measured magnetization data of La0.8K0.1M0.1MnO3 with M=Na and Ag samples as a function of magnetic applied field, the associated magnetic entropy change, vertical bar Delta S-M vertical bar, close to their respective Curie temperature T-C and the relative cooling power RCP have been determined. The maximum magnetic entropy change, vertical bar Delta S-M(Max)vertical bar, reaches 4.39 and 4.92 J/kg K for M=Na and Ag, respectively, in a magnetic applied field change of 5T. For both samples, the vertical bar Delta S-M vertical bar values determined by the Maxwell theory agree well with those calculated by the Landau theory. (C) 2010 Elsevier B.V. All rights reserved.