Magnetocaloric effect above room temperature in the K-doped La0.8Na0.2−xKxMnO3 manganites

Structural, magnetic and magnetocaloric properties of La0.8Na0.2−xKxMnO3 (0 ≤ x ≤ 0.2) powder samples have been investigated by X-ray diffraction (XRD) and magnetic measurements. Our samples have been synthesized using the solid state reaction method at high temperature. Rietveld refinements of the X-ray diffraction patterns show that all our samples are single phase and crystallize in the distorted rhombohedral system with R3¯c space group. Magnetization measurements versus temperature in a magnetic applied field of 50 mT show that all our samples exhibit a paramagnetic–ferromagnetic transition with decreasing temperature. Although K doping in our samples leads to an increase in the average ionic radius 〈rA〉, the Curie temperature is found to remain almost constant around 330 K. From the measured magnetization data of La0.8Na0.2−xKxMnO3 (0 ≤ x ≤ 0.2) samples as a function of magnetic applied field, the associated magnetic entropy change |ΔSM| close to the Curie temperature TC has been determined. The parent compound (x = 0) exhibits a maximum entropy change |ΔSMMax| of 1.32 J/kg K at 325 K in a magnetic applied field of 1 T. |ΔSMMax| decreases to 0.92 J/kg K at 335 K for x = 0.2 in the same field magnitude.