Magnetocaloric effect and magnetic properties of La0.75Ba0.1M0.15MnO3 (M = Na, Ag and K) perovskite manganites

Structural, magnetic and magnetocaloric properties of La0.75Ba0.1M0.15MnO3 (M = Na, Ag and K) compounds 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. XRD analysis using Rietveld refinement reveal that the three samples, La0.75Ba0.1Na0.15MnO3 (〈rA〉 = 1.189 Å, σ2 = 5.979 × 10−3 Å2), La0.75Ba0.1Ag0.15MnO3 (〈rA〉 = 1.204 Å, σ2 = 6.984 × 10−3 Å2) and La0.75Ba0.1K0.15MnO3 (〈rA〉 = 1.238 Å, σ2 = 18.972 × 10−3 Å2), crystallize in the distorted rhombohedral system with R3¯c space group. With increasing 〈rA〉, the unit cell volume increases from 357.09 Å3 (M = Na) to 358.05 Å3 (M = Ag) and than decreases to 355.03 Å3 (M = K). Magnetization measurements versus temperature in a magnetic applied field of 50 mT showed that all our samples are ferromagnetic at low temperatures. The Curie temperature TC is found to be 233 K, 315 K and 288 K for M = Na, Ag and K, respectively. From the measured magnetization data of La0.75Ba0.1M0.15MnO3 (M = Na, Ag and K) samples as a function of magnetic applied field, the associated magnetic entropy change close to their respective Curie temperature TC and the relative cooling power (RCP) have been determined. The maximum of the magnetic entropy change |ΔSMMax| in a magnetic field change of 2 T is found to be 2.26 J/kg K, 1.72 J/kg K and 2.44 J/kg K for M = Na, Ag and K, respectively.