CoSi(001)∥MgO(001)薄膜电子结构和铁磁性的第一性原理计算

First principles calculations of the electronic structure and ferromagnetism of CoSi(001)∥MgO(001)thin films

使用了基于密度泛函理论的第一性原理的方法,计算了外延关系为CoSi(001)∥MgO(001)的薄膜生长体系的电子结构和磁矩,以及分析了其电荷密度与差分电荷密度。结果发现当CoSi晶体的晶格常数a,b设定为0.84224 nm,c=0.28135 nm时,体系的能量最低,达到最稳定的平衡态。由自旋极化能带图、总电子态密度以及分态密度可知,该CoSi外延薄膜的导带底与价带顶发生明显的交叠从而表现出金属性同时在费米能级附近产生了明显的自旋裂化现象;价带顶主要是由Co的3d^(7)态电子构成,而导带底主要由Si的3p态电子构成,同时由态密度可知其产生了赝能隙现象,Co-3d态电子不仅主要贡献了态密度,也是薄膜产生磁性的主要因素。由计算结果的密里根电荷以及电荷密度可知,电子由Si转移到Co,Co作为电子受主,Co之间形成反键态,Co、Si之间形成共价键结构。经计算该外延关系下的CoSi具有铁磁性,总磁矩为0.52μB。

In this paper,the first principle method based on density functional theory is used to calculate the electronic structure,magnetic moment,and charge density and differential charge density of the thin film growth system whose epitaxial relation is CoSi(001)∥MgO(001).The results show that when the lattice constants a and b of CoSi crystal are set as 0.84224 nm and C=0.28135 nm,the energy of the system is the lowest and the most stable equilibrium state is reached.It can be seen from the spin polarization band diagram,total electron state density and fractal density that the guide band bottom and valence band top of the CoSi epitaxial film overlap significantly,thus showing the gold property and producing obvious spin cracking phenomenon near the Fermi level.The valence band top is mainly composed of THE 3d^(7)state electrons of Co,while the conduction band bottom is mainly composed of the 3p state electrons of Si.At the same time,it can be seen from the state density that the phenomenon of pseudo energy gap is generated.The Co-3d state electrons not only mainly contribute to the state density,but also are speculated to be the main factor for the magnetic generation of the film.According to the calculated Mulliken charge and charge density,electrons are transferred from Si to Co,and Co ACTS as the electron acceptor,forming an anti-bonding state between Co and Si,and forming a covalent bond structure between Co and Si.The CoSi under this epitaxial relationship is ferromagnetic and the total magnetic moment is 0.52μB.