Above room temperature magnetocaloric properties of La0.7Ba0.3-zNazMnO3 compounds

Magnetocaloric effect (MCE) in fine grained perovskite manganites of the type La0.7Ba0.3-zNazMnO3 (0 < z < 0.15) prepared by pyrophoric method has been investigated. The prepared samples remain single phase and exhibit paramagnetic to ferromagnetic phase transition (TC) at 317, 313 and 312 K for z = 0.05, 0.10 and 0.15, respectively. From the measured magnetization data of La0.7Ba0.3-zNazMnO3 compounds as a function of field (0.8 T), the associated magnetic entropy change close to their respective Curie temperatures, the refrigeration capacity and the relative cooling power (RCP) have been determined. The maximum magnetic entropy change |ΔSMmax| exhibits a linear dependence with applied magnetic field. Estimated adiabatic temperature change at TC at 0.8T field is ∼1.18 K (z = 0.05). ΔTad obtained for La0.7Ba0.3-zNazMnO3 compounds compare favorably with those reported for other doped lanthanum manganites. The observed field dependence of magnetic entropy change is explained reasonably well in light of Landau theory of phase transition which takes into account the contributions of magnetoelastic and electron interaction