Normal and inverse magnetocaloric effects in ferromagnetic Sm0.6−xLaxSr0.4MnO3

Abstract

We report magnetic and magnetocaloric properties of Sm0.6−xLaxSr0.4MnO3 (x = 0–0.6). A rapid increase around TC and an anomalous peak at a temperature T* ≪ TC occur in magnetization, which lead to normal and inverse magnetocaloric effects (MCE), respectively. While TC increases with increasing x (TC = 118 K for x = 0 and TC = 363 K for x = 0.6), T* increases from 30 K (x = 0) to 120 K (x = 0.4) and then decreases to 105 K (x = 0.5). The ΔSm is negative around TC and it decreases from ΔSm = −6.2 Jkg−1K−1 for x = 0 to −4.2 Jkg−1K−1 for x = 0.6 for ΔH = 5 T. The inverse MCE occurs below T* and shows a maximum value of ΔSm = +1.07 Jkg−1K−1 at T = 10 K for ΔH = 5 T at x = 0.4. This composition also shows a significant normal MCE (ΔSm = −4 Jkg−1K−1) around TC = 320 K, along with a high refrigeration capacity of 214 Jkg−1, which makes it an interesting compound for room temperature magnetic refrigeration. The inverse MCE has been suggested to be caused by the antiferromagnetic coupling between Sm 4f and Mn 3d moments. The coexistence of normal and inverse MCEs in a single material is interesting because the sample can be cooled by adiabatic magnetization and demagnetization in different temperature regions, which will enhance the refrigeration capacity.