Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Material Science and Engineering, Northeastern University, Shenyang, 110819, China.
Department of Physics, Freie Universität Berlin, Berlin, 14195, Germany.
Nanoscale. 2023 May 11;15(18):8278-8288. doi: 10.1039/d3nr00346a.
Two-dimensional ferrovalley materials should simultaneously possess three characteristics, that is, a Curie temperature beyond atmospheric temperature, perpendicular magnetic anisotropy, and large valley polarization for potential commercial applications. In this report, we predict two ferrovalley Janus RuClX (X = F, Br) monolayers by first-principles calculations and Monte Carlo simulations. The RuClF monolayer exhibited a valley-splitting energy as large as 194 meV, perpendicular magnetic anisotropy energy of 187 μeV per f.u., and Curie temperature of 320 K. Thus, spontaneous valley polarization at room temperature will be present in the RuClF monolayer, which is nonvolatile for spintronic and valleytronic devices. Although the valley-splitting energy of the RuClBr monolayer was as high as 226 meV with magnetic anisotropy energy of 1.852 meV per f.u., the magnetic anisotropy of the RuClBr monolayer was in-plane, and its Curie temperature was only 179 K. The orbital-resolved magnetic anisotropy energy revealed that the interaction between the occupied spin-up states of d and the unoccupied spin-down states of d dominated the out-of-plane magnetic anisotropy in the RuClF monolayer, but the in-plane magnetic anisotropy of the RuClBr monolayer was mostly contributed by the coupling of the d and d orbitals. Interestingly, the valley polarizations in the Janus RuClF and RuClBr monolayers appeared in their valence band and conduction band, respectively. Thus, two anomalous valley Hall devices are proposed using the present Janus RuClF and RuClBr monolayers with hole and electron doping, respectively. This study provides interesting and alternative candidate materials for the development of valleytronic devices.
二维铁谷材料应同时具备三个特点，即居里温度超过大气温度、垂直磁各向异性和大谷极化，以满足潜在的商业应用需求。在本报告中，我们通过第一性原理计算和蒙特卡罗模拟预测了两种铁谷 Janus RuClX（X = F、Br）单层。RuClF 单层表现出高达 194 meV 的谷分裂能、187 μeV/ f.u. 的垂直磁各向异性能和 320 K 的居里温度。因此，在 RuClF 单层中会存在室温下的自发谷极化，这对于自旋电子学和谷电子学器件来说是非易失性的。尽管 RuClBr 单层的谷分裂能高达 226 meV，磁各向异性能为 1.852 meV/ f.u.，但其磁各向异性为面内，居里温度仅为 179 K。轨道分辨磁各向异性能表明，RuClF 单层中占据的自旋向上的 d 态和未占据的自旋向下的 d 态之间的相互作用主导了其面外磁各向异性，而 RuClBr 单层的面内磁各向异性主要由 d 和 d 轨道的耦合贡献。有趣的是，Janus RuClF 和 RuClBr 单层中的谷极化分别出现在它们的价带和导带中。因此，我们分别使用本征的 Janus RuClF 和 RuClBr 单层，通过空穴和电子掺杂，提出了两种异常谷霍尔器件。本研究为谷电子学器件的发展提供了有趣的替代候选材料。
