School of Electronic Engineering, Xi'an University of Posts and Telecommunications, Xi'an 710121, People's Republic of China.
Science, Mathematics and Technology (SMT), Singapore University of Technology and Design (SUTD), 8 Somapah Road, Singapore 487372, Singapore.
J Phys Condens Matter. 2023 Jul 5;35(40). doi: 10.1088/1361-648X/ace1c1.
Coexistence of ferromagnetism, piezoelectricity and valley in two-dimensional (2D) materials is crucial to advance multifunctional electronic technologies. Here, Janus ScXY (X≠Y = Cl, Br and I) monolayers are predicted to be piezoelectric ferromagnetic semiconductors with dynamical, mechanical and thermal stabilities. They all show an in-plane easy axis of magnetization by calculating magnetic anisotropy energy (MAE) including magnetocrystalline anisotropy energy and magnetic shape anisotropy energy. The MAE results show that they intrinsically have no spontaneous valley polarization. The predicted piezoelectric strain coefficientsand(absolute values) are higher than ones of most 2D materials. Moreover, the(absolute value) of ScClI reaches up to 1.14 pm V, which is highly desirable for ultrathin piezoelectric device application. To obtain spontaneous valley polarization, charge doping are explored to tune the direction of magnetization of ScXY. By appropriate hole doping, their easy magnetization axis can change from in-plane to out-of-plane, resulting in spontaneous valley polarization. Taking ScBrI with 0.20 holes per f.u. as an example, under the action of an in-plane electric field, the hole carriers of K valley turn towards one edge of the sample, which will produce anomalous valley Hall effect, and the hole carriers of Γ valley move in a straight line. These findings could pave the way for designing piezoelectric and valleytronic devices.
二维（2D）材料中同时存在铁磁性、压电性和谷自由度对于推进多功能电子技术至关重要。本文预言 Janus ScXY（X≠Y = Cl、Br 和 I）单层是具有动力学、机械和热稳定性的铁磁半导体。通过计算磁各向异性能（包括磁晶各向异性能和磁形状各向异性能），它们都表现出面内易磁化轴。MAE 结果表明，它们本质上没有自发谷极化。预测的压电应变系数绝对值高于大多数 2D 材料。此外，ScClI 的绝对值高达 1.14 pm V，非常适合用于超薄压电器件。为了获得自发谷极化，可以通过电荷掺杂来调节 ScXY 的磁化方向。通过适当的空穴掺杂，可以使它们的易磁化轴从面内转变为面外，从而产生自发谷极化。以每个原胞 0.20 个空穴的 ScBrI 为例，在面内电场的作用下，K 谷的空穴载流子会转向样品的一个边缘，这将产生反常谷霍尔效应，而 Γ 谷的空穴载流子则会沿直线运动。这些发现为设计压电和谷电子器件铺平了道路。
