Magnetic properties and magnetocaloric effect of Ti-doped La0.7Sr0.3MnO3

Abstract

We have studied the influence of Ti doping on the magnetic properties and the magnetocaloric effect of La0.7Sr0.3Mn0.92Ti0.08O3 prepared by using solid-state reaction. The temperature dependence of magnetization reveals that the presence of the Ti dopant strongly reduces the Curie temperature (TC) to a value of ∼235 K. The magnetic-entropy change (ΔSm) has been assessed by means of isothermal-magnetization data versus the magnetic field, M-H curves, recorded at different temperatures. Around TC, −ΔSm reaches maximum values of 1.1, 2.0, and 2.7 J/(kg·K) for applied fields of 10, 20, and 30 kOe, respectively. A relative cooling power (RCP) of 135 J/kg is, thus, achieved for an applied field of 30 kOe. Detailed analyses of the M-H curves around TC indicate that the sample exhibits a second-order magnetic phase transition, where the variations of the saturation magnetization (Ms) and the inverse initial susceptibility (χ0−1) versus temperature obey asymptotic relations. Using the Arrott-Noakes method, we have obtained the critical exponents β = 0.425 ± 0.016, γ = 1.017 ± 0.055, and δ = 3.393 ± 0.039. These exponents are in good agreement with the magnetic equation of state. The β value determined in our case is between those expected for the mean-field (β = 0.5) and the 3D Heisenberge (β = 0.365) models, demonstrating the existence of ferromagnetic clusters.