Structure and magnetocaloric properties of La_(0.8)Ag_(0.2-x)K_xMnO_3 perovskite manganites

摘要

In the present study we report the effect of K doping on the structural, magnetic and magnetocaloric properties in La_(0.8)Ag_(0.2-x)K_xMnO_3 (0≤x≤0.15) powder samples synthesized using the solid state reaction method at high temperature. X-ray diffraction analysis using Rietveld refinement show that all our samples crystallize in the rhombohedral structure 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 (EDX), respectively. Magnetization measurements versus temperature in a magnetic applied field of 50 mT showed that all our investigated samples display a paramagnetic-ferromagnetic transition with decreasing temperature. The Curie temperature T_C increases with increasing K content from 278.5 K forx= 0-330 K for x = 0.15. A large magnetic entropy change |△S_m|, deduced from isothermal magnetization curves, has been observed in our samples with a peak centered around their respective 7c. The maximum of the magnetic entropy change |△S_M~(Max)| in a magnetic field change of 5T is found to be 6.12, 5.28, 4.92 and 4.26Jkg~(-1) K~(-1) for x = 0, 0.05, 0.1 and 0.15 respectively. Large relative cooling power (RCP) value of 258.3 J kg~(-1) is obtained for La_(0.8)Ag_(0.05)K_(0.15)MnO_3 sample, at a field change of 5T. This relatively large value associated to a Curie temperature of 330 K make the present compound a promising candidate formagneticrefrigerators around room temperature.