Effect of Cu doping on the structural, magnetic and magnetocaloric properties of La0.7Sr0.25Na0.05Mn1−xCuxO3 manganites

The effect of Cu doping on structural, magnetic and magnetocaloric properties in La0.7Sr0.25Na0.05Mn1−xCuxO3 (x = 0, 0.05, 0.10, 0.15, 0.20) has been investigated. The samples were prepared by conventional solid-state reaction. Analysis of XRD patterns indicates that the samples are crystallized in a rhombohedral perovskite structure with R 3̅ c space group. Rietveld refinements reveal that the lattice parameter a and unit cell volume gradually increase up to x = 0.10 then decrease, while parameter c decreases with increasing Cu content. XPS spectra exhibit the coexistence of the Cu2+ and Cu3+ ions in the samples with x=0.15 and 0.20. Magnetization measurements show the Curie temperature Tc and the maximum magnetic entropy change ΔSM decrease with the increase in the Cu content, whereas the relative cooling power (RCP) is basically unaffected. The La0.7Sr0.25Na0.05Mn0.9Cu0.1O3 sample shows a maximum ΔSM of 1.75 J kg−1 K−1 and a RCP of 87 J kg−1 at 320 K under a magnetic field change of 20 kOe, and can be one of the potential magnetic refrigerant materials for near room temperature application.