Critical Behavior and Magnetocaloric Effect in La2NiMnO6 Nanocrystals

In this paper, we present a detailed study on the magnetocaloric effect (MCE) and the critical behavior of La₂NiMnO₆ (LNMO) nanocrystals. Cubic-structured LNMO samples with different crystallite sizes (d = 200 to 26.4 nm) were prepared by a combination of solid-state reaction and mechanical milling with milling time (t_m) changing from 0 to 30 min. The results show that all the samples undergo the second-order phase transition. Using the modified Arrott plot and critical isotherm analysis methods, we have analyzed the critical behavior for nanocrystals to obtain the optimal values of the critical parameters (β, γ, δ, and T_C). The results indicate that shortand long-range ferromagnetic interactions coexist in the samples. In addition, we also assess the MCE of the samples via the magnetic entropy change (ΔS_M). Based on the obtained ΔS_M(T, H) data, we have also described the universal master curve for ΔS_M, which as a function of ΔS_M(T)/ΔS_M^P versus rescaled temperature θ = (T - TC)/(Tr - TC), where Tr is the reference temperature. Interestingly, all the ΔS_M (T, H) data points are collapsed into a universal curve in the whole temperature range.