Magnetocaloric Effect and Critical Behavior in a Disordered Ferromagnet La0.7Sr0.3Mn0.9Ti0.1O3

The critical phenomena around the Curie temperature (T_C) of a polycrystalline La_0.7Sr_0.3Mn_0.9Ti_0.1O₃ were studied based on magnetic field and temperature dependence of magnetization. Using the modified Arrott plot method, we determined the critical parameters T_C≈234 K, β = 0.372 ± 0.012, γ = 1.171 ± 0.112, and δ = 4.15 ± 0.01. With these critical values, the M(H) data of the sample fall onto two universal branches of the scaling function M(H, ε) = |ε|^β f_±(H/|ε|^β+γ), where ε = (T - T_C)/T_C, and f₊ for T > T_C and f_- for T <; T_C. This pointed to the existence of a short-range ferromagnetic (FM) order in La_0.7Sr_0.3Mn_0.9Ti_0.1O₃, which is attributed to FM clusters persisting in a wide temperature range, even above T_C. Electron-spin-resonance spectra affirmed the presence of the FM clusters at temperatures as high as T = T_min (≈1.3 T_C), above which the sample is completely paramagnetic. Based on the M(H) data, we also calculated the magnetic-entropy change (ΔS_m), which reached a maximum (|ΔS_max| ≈ 4.3 J/kg · K) around the T_C, corresponding to the relative cooling power of ~200 J/kg for a field change ΔH = 50 kOe. A linear relationship |ΔS_max(H)| ∝ Hⁿ is achieved with a local exponent n = 0.59 determined from n = 1+ (β - 1)/(β + γ), indicative of a short-range FM system.