Magnetocaloric effect in Ba-doped LaCoO3 cobaltites showing second-order phase transitions

Abstract

The magnetocaloric effect in the R-3c rhombohedral La1-xBaxCoO3 samples (x = 0.2-0.4) prepared by the mechanical milling and ceramic methods has been studied through the dc magnetization measurements. The results have revealed the magnetic phase-transition temperature (T-C) changing from 185 to about 200 K when x changes from 0.2 to 0.4. Around T-C, the samples show a large change in the magnetic entropy (Delta S-m). The value of.Sm depends on both x and the applied-field magnitude. Under an applied field H = 30 kOe, the maximum magnetic-entropy changes are about 1.1, 1.7 and 1.6 J/Kg center dot K for x = 0.2, 0.3 and 0.4, respectively, corresponding to the relative cooling power ranging between 63 and 73 J/kg. Our studies have also found La1-xBaxCoO3 exhibiting a second-order phase transition and short-range magnetic order. We suggest that short-range order is related to the interaction competition between two ferromagnetic and anti-ferromagnetic phases due to the coexistence of Co3+ and Co4+ ions.