Magnetocaloric effect and critical behavior near the first to second-order phase transition of La0.7Ca0.3−xSnxMnO3 compounds

Abstract

The magnetocaloric effect and the critical behavior near the first to second-order phase transition of La _0.7 Ca _0.3-x Sn _x MnO _3 compounds (with x = 0–0.04), which were prepared by a conventional solid state reaction method, have been investigated. With increasing Sn-doping, a systematic decrease in the Curie temperature ( T _C ) and the magnetic entropy change (Δ S _m ) are observed. We also pointed out that the width and the order of the magnetic phase transition in La _0.7 Ca _0.3-x Sn _x MnO _3 compounds can be easily modified by changing Sn concentration. The Banerjee criterion suggests that the Sn-undoped sample ( x = 0) undergoes a first-order phase transition (FOPT). Meanwhile, Sn-doped samples ( x = 0.02 and 0.04) undergo a second-order phase transition (SOPT). Based on the Kouvel-Fisher method and the critical isotherm analyses, we have determined the values of the critical exponents ( β , γ , and δ ) and T _C for two SOPT samples. The results obtained for x = 0.02 sample are β = 0.218, γ = 0.858, and δ = 4.717, which are close to those expected for the tricritical mean field theory. Whereas, β = 0.468, γ = 1.095 and δ = 3.315 obtained for x = 0.04 sample are close to those expected for the mean field theory. This suggests that the presence of Sn favors establishing the ferromagnetic long-range interactions in the sample.

Keywords

• magnetocaloric effect
• critical behavior
• ferromagnetic interactions