Abstract We have prepared rhombohedral La 1-x Sr x CoO 3-δ ( x = 0.2–0.5) compounds with a mass density ρ ≈ 5.5 g/cm 3 . Their magnetocaloric (MC) effect is studied via the magnetic-entropy change (Δ S m ) and relative cooling power ( RCP ), which are calculated from initial magnetization data recorded at different temperatures. Results reveal that the Δ S m magnitude is maximum (Δ S max ) around the ferromagnetic-paramagnetic phase transition and dependent on both the applied-field ( H ) magnitude and Sr content ( x ). For H = 50 kOe, |Δ S max | 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 La 1-x Sr x CoO 3-δ samples, the samples with x = 0.3–0.5 have the largest |Δ S max | 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 |Δ S max | 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 La 1-x Sr x CoO 3-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.

中文翻译：

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La 1-x Sr x CoO 3 中发生二阶相变的磁热效应

摘要 我们制备了质量密度 ρ ≈ 5.5 g/cm 3 的菱形 La 1-x Sr x CoO 3-δ ( x = 0.2–0.5) 化合物。它们的磁热 (MC) 效应是通过磁熵变 (Δ S m ) 和相对冷却功率 ( RCP ) 来研究的，它们是根据在不同温度下记录的初始磁化数据计算得出的。结果表明，在铁磁-顺磁相变附近，Δ S m 量级最大（Δ S max ），并且取决于外加场 ( H ) 量级和 Sr 含量 ( x )。对于 H = 50 kOe，|Δ S max | 可以在 1.6–2.7 J/kg K 的范围内调整，对应于 89–141 J/kg 的 RCP 值。在研究的La 1-x Sr x CoO 3-δ 样品中，x = 0.3-0.5 的样品具有最大的|Δ S max | 值。如果在制冷应用中将这些样品组合为 MC 块，冷却装置的工作温度范围可以从 204 到 ~280 K，其中 |Δ S max | 稳定在 ~2.6 J/kg K 和 RCP ≈ 198 J/kg。我们还评估了相变类型和磁序，发现 La 1-x Sr x CoO 3-δ 经历了二阶相变。当 x 从 0.2 变化到 0.5 时，磁序往往从长程型变为短程型。这与从关键行为分析中获得的结果非常一致。