Large magnetocaloric effect and critical behavior in La0.7Ba0.2Ca0.1Mn1−xAlxO3

Abstract

The structural, magnetic and magnetocaloric properties of La_0.7Ba_0.2Ca_0.1Mn_1−xAl_xO₃ (0 ≤ x ≤ 0.1) perovskite manganite oxides have been investigated. X-ray diffraction (XRD) analysis using Rietveld refinement has shown that all of the samples under investigation crystallize with a rhombohedric structure in the Rc space group (N°167). Paramagnetic (PM) to ferromagnetic (FM) transitions have been observed in all of the synthesized samples. In addition, the maximum magnetic entropy change (ΔS^max_M) for the x = 0 sample was found to reach ∼5.8 J kg⁻¹ K⁻¹ under an applied magnetic field of 5 T, which is sufficient for potential applications in magnetic refrigeration. For the same applied magnetic field (μ₀H = 5 T), the relative cooling power (RCP) value is found to be 167 J kg⁻¹. The critical properties of manganites La_0.7Ba_0.2Ca_0.1Mn_1−xAl_xO₃ (0 ≤ x ≤ 0.1) are investigated through various techniques, such as modified Arrott plots, Kouvel–Fisher methods and critical isotherm analyses around the paramagnetic–ferromagnetic phase transition (T_c). The values of critical exponents, derived from magnetic data using the above methods, yield 0.246 ≤ β ≤ 0.253, 1.01 ≤ γ ≤ 1.12 and 4.76 ≤ δ ≤ 4.9 with a T_c of 300–350 K. The exponent values are close to those expected for tricritical mean field model ferromagnets with short-range dipole–dipole interactions.