1School of Physics, Peking University, Beijing 100871 2Beijing Key Laboratory for Magnetoelectric Materials and Devices, Beijing 100871 3Collaborative Innovation Center of Quantum Matter, Beijing 100871
Abstract：Mn-based Heusler alloys have attracted significant research attention as half-metallic materials because of their giant magnetocrystalline anisotropy and magnetocaloric properties. We investigate the crystal structure and magnetic properties of polycrystalline, [101]-oriented, and [100]-oriented Mn$_{2-\delta}$Sn prepared separately by arc melting, the Bridgeman method, and the flux method. All of these compounds crystallize in a Ni$_{2}$In-type structure. In the Mn$_{2-\delta}$Sn lattice, Mn atoms occupy all of the 2$a$ and a fraction of the 2$d$ sites. Site disorder exists between Mn and Sn atoms in the 2$c$ sites. In addition, these compounds undergo a re-entrant spin-glass-like transition at low temperatures, which is caused by frustration and randomness within the spin system. The magnetic properties of these systems depend on the crystal directions, which means that the magnetic interactions differ significantly along different directions. Furthermore, these materials exhibit a giant magnetocaloric effect near the Curie temperature. The largest value of maximum of magnetic entropy change ($-\Delta S_{\rm M})$ occurs perpendicular to the [100] direction. Specifically, at 252 K, maximum $-\Delta S_{\rm M}$ is 2.91 and 3.64 J$\cdot$kg$^{-1}$K$^{-1}$ for a magnetic field of 5 and 7 T, respectively. The working temperature span over 80 K and the relative cooling power reaches 302 J/kg for a magnetic field of 7 T, which makes the Mn$_{2-\delta}$Sn compound a promising candidate for a magnetic refrigerator.
2019, Vol. 36 
