碱金属和碱土金属掺杂二维GaN材料电磁特性的第一性原理计算

First-principles study of magnetic properties of alkali metals and alkaline earth metals doped two-dimensional GaN materials

基于密度泛函理论和投影缀加波赝势方法,采用广义梯度近似算法研究了碱金属(Li, Na, K和Rb)和碱土金属(Be, Mg和Sr)掺杂二维GaN单层的电子结构和磁学性质.研究表明,除Be原子位于GaN单层平面内之外,其余掺杂原子均略微隆起于平面.通过比较七种掺杂体系在不同环境下的形成能,发现在富N环境中更易实现掺杂.能带结构表明:四种碱金属原子掺杂体系是磁性半导体,总磁矩为2μB;三种碱土金属掺杂体系呈半金属性,总磁矩为1μB.磁耦合计算表明,七种元素掺杂体系均存在长程铁磁耦合.采用海森伯平均场模型估算双掺杂体系的居里温度,发现Li, Be, Mg和Sr的长程铁磁耦合态居里温度均高于室温,表明这4种原子掺杂的二维GaN单层是很好的室温铁磁性备选材料.

We systematically study the electronic structure and magnetic properties of alkali metals(Li, Na, K and Rb) and alkaline earth metals(Be, Mg and Sr) doped two-dimensional GaN monolayers using the firstprinciples calculations based on density functional theory. The results show that Be atom is located in the plane of the GaN monolayer, and the other doped atoms reside slightly above the plane. It is found that doping is easier to achieve under the N-rich condition. The total magnetic moment of the alkali metals doped system and the alkaline earth metals doped system are 2μB and 1μB, respectively, which are presented mainly by the spinpolarized holes of the nearest N atoms of the impurity atoms. The band structures indicate that the four alkali metal atoms doped systems are magnetic semiconductors, and the three alkaline earth metal doped systems are all semi-metallic. For a double M-doped GaN monolayer system, there is a long-range ferromagnetic coupling in the seven elements doped systems, which are realized by the hole-mediated p-p hybrid interaction. The Heisenberg mean field model is used to estimate the Curie temperature. It is found that the long-range ferromagnetic coupling states of Li, Be, Mg and Sr are existent at higher than room temperature, indicating that the four atom-doped two-dimensional GaN monolayers are very good candidates for the room temperature ferromagnetic candidate materials. The alkali metals and alkaline earth metals doped two-dimensional GaN monolayers are expected to play an important role in the studying of spintronics.