Influence of Crystallite Size on Magnetocaloric Effect and Critical Behavior La0.7Sr0.3Mn0.92Co0.08O3 Nanoparticles

Four samples of La_0.7Sr_0.3Mn_0.92Co_0.08O₃ (LSMCO) with different crystallite sizes were prepared by the combination of solid-state reaction and mechanical milling methods. Based on isothermal magnetization data, M(H), temperature dependences of magnetic entropy change, ΔS_mT, of the samples under a magnetic field change of 10 kOe were calculated. The maximum values of magnetic entropy change (|ΔS_max|) at room temperature are in the range of 0.9-1.4 J · kg^-1 · K^-1, corresponding to ferromagnetic (FM)-paramagnetic phase transition. In addition, M² versus H/M curves at temperatures around TC prove the samples exhibiting a second-order magnetic phase transition. The critical exponents β, γ, and δ were determined using the modified Arrott plot method and critical isotherm analysis. Here, these exponent values are located in between those expected for the mean-field theory and 3-D Heisenberg model. It means the coexistence of short-range and long-range FM interactions in LSMCO nanoparticles.