Critical properties around the ferromagnetic-paramagnetic phase transition in La0.7Ca0.3-xAxMnO3 compounds (A = Sr, Ba and x = 0, 0.15, 0.3)

Influence of alkaline earth element doping in the A-site on the structure, magnetic and magnetocaloric properties of La0.7Ca0.3-xAxMnO3 (A = Sr and Ba; x = 0, 0.15 and 0.3) perovskite manganites have been investigated. X-ray diffraction data indicates that samples x = 0 and 0.15 crystallize in the orthorhombic structure (space group Pnma), whereas samples x = 0.3 belong to the rhombohedral structure (space group R-3c). Substitution of Sr or Ba for Ca plays an important role in the increase of Curie temperature (TC) and modification the nature of the magnetic phase transition in materials. Sample x = 0 exhibits the first-order phase transition (FOPT) with a large magnetic entropy change (ΔSm), whereas samples x = 0.15 and 0.3 exhibit the second-order phase transition (SOPT) characterizations and the moderate values of ΔSm. Using the modified Arrott plots method, the critical behaviors around TC for SOPT samples have been investigated through the values of critical parameters (TC, β, γ, and δ). We pointed out that Ba-doping favors establishing long-range ferromagnetic order, contrary to the case of Sr-doping.