Na-doped La0.7Ca0.3MnO3 compounds exhibiting a large magnetocaloric effect near room temperature

In this work, we have investigated the magnetic properties and the magnetocaloric effect of La0.7-xNaxCa0.3MnO3 compounds, which were prepared by a conventional solid-state reaction technique. The Rietveld refinement results suggested that the samples are single phase belonging to an orthorhombic structure (space group Pnma). Analyzing temperature dependence of magnetization M(T) revealed that the Curie temperature (T-C) increases with increasing Na content (x). Their T-C value is found to be 260-298 K for x= 0.0-0.1, respectively. Base on M(T) data measured at different applied magnetic fields (H), temperature dependence of magnetic entropy change Delta S-m(T) data for all the samples was calculated by using a phenomenological model. In the vicinity of T-C, -Delta S-m(T) curve reaches a maximum value (denoted as vertical bar Delta S-max vertical bar), which gradually increases with increasing H. Under 12 kOe, the value of vertical bar Delta S-max vertical bar is in a range of 1.47-5.19 J/kg K corresponding to the relative cooling power RCP=57.12-75.88 J/ kg. Applied the universal master curve method for the magnetic entropy change, we concluded that Na-doped in La0.7-xNaxCa0.3MnO3 compounds leads to modification the nature of the magnetic phase transition from the first-to the second-order.