Abstract
In this work, we present a detailed study on the magnetocaloric effect near the first-to-second order magnetic phase transformation of La0.7Ca0.25Ba0.05MnO3 nanoparticles with averaged crystallite sizes D = 39–79 nm. The ferromagnetic-paramagnetic phase-transition region of the bulk sample (exhibiting the first-order nature) becomes more broadened in nanoparticles (exhibiting the second-order nature). Based on isothermal magnetization data, M(H), we calculated magnetic entropy change versus temperature, ΔSm(T), of the samples under magnetic-field changes ΔH = 0–30 kOe. As a result, |ΔSm| reaches the maximum value (|ΔSmax|) around TC = 258–262 K. With ΔH = 30 kOe, |ΔSmax| values obtained from the samples are located in the range 4.38–5.63 J·kg−1·K−1, corresponding to refrigerant-capacity values RC = 138–141 J·kg−1. Field dependences of |ΔSmax| and RC can be expressed by a power law, with |ΔSmax| = a·Hn and RC = b·HN. Interestingly, all the ΔSm(T) curves of the samples undergoing the second-order phase transition at different applied fields are collapsed onto a universal curve, which is obtained by normalizing the ΔSm(T, H) curves to their respective ΔSmax value, and rescaling the temperature axis above and below TC with θ = (T − TC)/(Tr − TC), where Tr is the reference temperature.
