Structural and magnetocaloric properties of La1−yNayMnO3compounds prepared by microwave processing

Polycrystalline samples of sodium doped lanthanum manganites of the type La 1− y Na y MnO 3 (0 < y ⩽ 0.15) having nanometric crystallite size have been prepared by microwave processing. The Curie temperature T C of the prepared pellets is strongly dependent on the sodium content in the compound and ranges between 196 and 312 K. A detailed structural analysis has been performed on the prepared samples using the Rietveld FULLPROF program and important structural parameters are estimated. Close to T C , a significant change in magnetic entropy has been observed in all the studied samples. The maximum entropy change at 0.8 T field (µ 0 H ) for the La 0.90 Na 0.10 MnO 3 compound shows an enhancement by ∼158% over that measured for a sample with Na content of 0.05 and is ∼67% of that known for the prototype magnetic refrigerant (pure Gd). The maximum adiabatic temperature change (Δ T ad ) is estimated to be ∼2 K. The temperature dependence of the magnetic entropy change for La 1− y Na y MnO 3 compounds, measured under various magnetic fields, could be explained fairly well by including the contributions from the magnetoelastic and electron interaction in the expression for the Landau theory of phase transition.