Magnetocaloric effect in La1-xSrxCoO3 undergoing a second-order phase transition

We have prepared rhombohedral La1-xSrxCoO3-δ (x = 0.2-0.5) compounds with a mass density ρ ≈ 5.5 g/cm3. Their magnetocaloric (MC) effect is studied via the magnetic-entropy change (ΔSm) and relative cooling power (RCP), which are calculated from initial magnetization data recorded at different temperatures. Results reveal that the ΔSm magnitude is maximum (ΔSmax) around the ferromagnetic-paramagnetic phase transition and dependent on both the applied-field (H) magnitude and Sr content (x). For H = 50 kOe, |ΔSmax| can be tuned in the range of 1.6-2.7 J/kg K, corresponding to RCP values of 89-141 J/kg. Among the studied La1-xSrxCoO3-δ samples, the samples with x = 0.3-0.5 have the largest |ΔSmax| values. If combining these samples as MC blocks in refrigeration application, the working temperature range of a cooling device could range from 204 to ~280 K, with |ΔSmax| stable at ~2.6 J/kg K and RCP ≈ 198 J/kg. We have also assessed the phase-transition type and magnetic order and found La1-xSrxCoO3-δ undergoing a second-order phase transition. Magnetic order tends to change from the long-range type to the short-range one when x varies from 0.2 to 0.5. This is in good agreement with the results obtained from the analysis of critical behavior.