Large Anisotropic Magnetocaloric Effect, Wide Operating Temperature Range, and Large Refrigeration Capacity in Single-Crystal Mn5Ge3 and Mn5Ge3/Mn3.5Fe1.5Ge3 Heterostructures.

Abstract

At present, the studies on magnetocaloric properties are mainly based on polycrystalline materials, which is not enough to reveal and understand the origin of their magnetocaloric effect. In addition, finding new room temperature magnetocaloric materials is crucial to the development and application for room temperature magnetic refrigeration. Here, we report the magnetic transitions, magnetic anisotropy, and magnetocaloric properties of single-crystal Mn5Ge3 and Mn5Ge3/Mn3.5Fe1.5Ge3 heterostructures with six (100) surfaces and the [001] growth direction prepared using the Sn flux method. Mn5Ge3 (Mn3.5Fe1.5Ge3) undergoes a sharp paramagnetic-collinear ferromagnetic transition at 299 (332) K and weak collinear-noncollinear ferromagnetic transition at 65 (35) K. Owing to the distinct spin arrangements and magnetic moments of Mn5Ge3 and Mn3.5Fe1.5Ge3, the magnetic anisotropy of the single crystal is stronger than that of the heterostructure below 299 K. Moreover, a large anisotropic magnetocaloric effect, wide operating temperature range, and large refrigeration capacity near room temperature are obtained in these two materials, especially the magnetocaloric effect of the heterostructure presents a tablelike shape due to the adjacent paramagnetic-collinear ferromagnetic transitions of Mn5Ge3 and Mn3.5Fe1.5Ge3. Under 0-3 T, the maximum magnetic entropy change, operating temperature range, and refrigeration capacity of the single crystal (heterostructure) are 5.19 (2.96) J kg-1 K-1, 43 (57) K, and 223 (169) J kg-1 when H//c, respectively. These features make them candidates for room temperature magnetic refrigeration.