单层极限下硒化锰外延薄膜的室温本征铁磁性
Room Temperature Intrinsic Ferromagnetism in Epitaxial Manganese Selenide Films in the Monolayer Limit
摘要：
单层范德华（vdW）磁体为探索二维（2D）磁性以促进科学和技术进步提供了令人兴奋的机会，但是仅在低温下观察到了固有的铁磁性。本文报道了分子束外延生长的硒化锰（MnSe $_x$）薄膜的室温铁磁性。磁性和结构表征提供了强有力的证据，表明在单层限制下，铁磁性源自vdW锰二硒化物（MnSe $_2$）单层，而对于较厚的膜，它可能源自vdW MnSe $_2$和/或$α$ -MnSe（111）的界面磁性的组合。GaSe和SnSe $_2$外延层上的单层MnSe $_x$薄膜的磁化强度测量显示具有大的饱和磁化强度（~ 4 Bohr磁子/Mn）的铁磁有序性，这与密度泛函理论计算预测的单层1 T-MnSe $_2$的铁磁性一致。在GaSe上生长MnSe $_x$膜至高厚度（~ 40 nm）产生$α$（111），以及与单层MnSe $_x$样品相比增强的磁矩（~ 2倍）.通过扫描透射电子显微镜（STEM）、扫描隧道显微镜（STM）和反射高能电子衍射（RHEED）的详细结构表征揭示了GaSe（0001）和$α$ -MnSe（111）之间的突变和干净的界面。特别是，通过STEM测量的结构与界面处存在MnSe $_2$单层一致。这些结果在节能信息存储和处理方面具有潜在的应用前景。
英文摘要：
Monolayer van der Waals (vdW) magnets provide an exciting opportunity for exploring two-dimensional (2D) magnetism for scientific and technological advances, but the intrinsic ferromagnetism has only been observed at low temperatures. Here, we report the observation of room temperature ferromagnetism in manganese selenide (MnSe$_x$) films grown by molecular beam epitaxy (MBE). Magnetic and structural characterization provides strong evidence that in the monolayer limit, the ferromagnetism originates from a vdW manganese diselenide (MnSe$_2$) monolayer, while for thicker films it could originate from a combination of vdW MnSe$_2$ and/or interfacial magnetism of $α$-MnSe(111). Magnetization measurements of monolayer MnSe$_x$ films on GaSe and SnSe$_2$ epilayers show ferromagnetic ordering with large saturation magnetization of ~ 4 Bohr magnetons per Mn, which is consistent with density functional theory calculations predicting ferromagnetism in monolayer 1T-MnSe$_2$. Growing MnSe$_x$ films on GaSe up to high thickness (~ 40 nm) produces $α$-MnSe(111), and an enhanced magnetic moment (~ 2x) compared to the monolayer MnSe$_x$ samples. Detailed structural characterization by scanning transmission electron microscopy (STEM), scanning tunneling microscopy (STM), and reflection high energy electron diffraction (RHEED) reveal an abrupt and clean interface between GaSe(0001) and $α$-MnSe(111). In particular, the structure measured by STEM is consistent with the presence of a MnSe$_2$ monolayer at the interface. These results hold promise for potential applications in energy efficient information storage and processing.
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