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

Abstract

In this study, magnetic and magnetocaloric properties of La 0.8K 0.1M 0.1MnO 3 with M=Na and Ag compounds have been investigated. X-ray diffraction analysis using Rietveld refinement reveals that La 0.8K 0.1Na 0.1MnO 3 and La 0.8K 0.1Ag 0.1MnO 3 samples crystallize in the distorted rhombohedral system with R3¯c space group. 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 La 0.8K 0.1M 0.1MnO 3 with M=Na and Ag samples as a function of magnetic applied field, the associated magnetic entropy change, | Δ S M | , close to their respective Curie temperature T C and the relative cooling power RCP have been determined. The maximum magnetic entropy change, | Δ S M M a x | , reaches 4.39 and 4.92 J/kg K for M=Na and Ag, respectively, in a magnetic applied field change of 5 T. For both samples, the | Δ S M | values determined by the Maxwell theory agree well with those calculated by the Landau theory.