Magnetocaloric effect and critical field analysis in Eu substituted La0.7-xEuxSr0.3MnO3 (x=0.0, 0.1, 0.2, 0.3) manganites

Highlights: • Crystal structure changes from rhombohedral (x = 0.0) to orthorhombic (x ≥ 0.1). • An enhancement in $\Delta S_{\text{m}}^{\text{max}}$ is observed with the decrease in A-site average ionic radius. • The critical nature of phase transition has been understood with different methods. • The universal master curve is used as a probe to review the nature of phase transition. In this study, we have investigated magnetic behavior, magnetocaloric effect and critical exponent analysis of La_0.7-xEu_xSr_0.3MnO₃ (x = 0.0, 0.1, 0.2, 0.3) manganites synthesized through solid state reaction route. The crystallographic data obtained from refinement of X-ray diffraction patterns reveal that crystal structure changes from rhombohedral (for x = 0.0) to orthorhombic (for x ≥ 0.1). The average ionic radius of A-site is decreased from 1.384 Å (for x = 0.0) to 1.360 Å (for x = 0.3) with Eu³⁺ substitution which in turn decreases the Mn-O-Mn bond angles. Magnetization measurements are performed in the vicinity of T_C to determine magnetocaloric effect (MCE) and critical field behavior. The maximum magnetic entropy change $\left(\Delta S_M^{\text{max}}\right)$ (for μ₀ΔH = 6T) increases with the Eu³⁺ substitution from 3.88 J/kg K (for x = 0.0) to 5.03 J/kg K (for x = 0.3) at the transition temperature. The critical field behaviour of compounds was analysed using various methods such as modified Arrott plots, Kouvel-Fisher method and critical isotherm to determine critical temperature and critical exponents (β, γ and δ). The obtained critical exponents are in good accordance with scaling relation. The temperature dependence of the order parameter n, for different magnetic fields, is studied using the relation ΔS_MαHⁿ. The values of n are found to obey the Curie-Weiss law for temperatures above the transition temperature. The rescaled change in entropy data for all compounds collapses into the same universal curve, revealing a second order phase transition.