Fe4N电子结构及其磁性

(湖北汽车工业学院 理学院,湖北 十堰 442002)

凝聚态物理; 电子结构; 磁性; 密度泛函理论; 态密度; Mulliken电荷分布

Electronic structure and magnetic property of Fe4N
WU Yun-pei,HU Yong-jin,ZHOU Wang-huai

(School of Science,Hubei University of Automotive Technology,Shiyan 442002,China)

:condensed matter physics; electronic structure; magnetic property; density functional theory; density of states; mulliken charge distribution

DOI: 10.13800/j.cnki.xakjdxxb.2018.0522

备注

铁粉在高温氮化氛围下能够形成强磁性铁氮化合物Fe4N,为了研究其材料中不同占位Fe的磁性差异,文中运用基于密度泛函理论下的第一性原理平面波赝势方法,通过实验上测量出的空间结构群、晶格常数和原子坐标来建立Fe4N晶体结构,然后进行几何优化。由最稳定的几何构型,计算出了电子结构和磁性的大小。结果 表明:N、顶角Fe(Ⅰ)和面心Fe(Ⅱ)的磁矩大小分别为0.06,2.94和2.32 μB.根据Mulliken电荷分布情况,详细分析了各位置原子特别是Fe的磁矩来源情况。可以看出,面心处的Fe(Ⅱ)磁矩大小明显要弱于顶角处Fe(Ⅰ),这个数据与实验和其他人的计算结果都符合得很好,证明本计算结果是有效的。通过分析各原子的自旋劈裂态密度图,发现Fe(Ⅰ)和Fe(Ⅱ)都出现了不同程度的自旋劈裂,在费米能级附近,Fe(Ⅰ)劈裂更明显,这很好地解释了顶角Fe(Ⅰ)有较大磁矩。由于中心N和面心Fe(Ⅱ)之间存在着比较强的共价作用,远大于N和顶角Fe(Ⅰ)之间的相互作用力,从而导致不同位置Fe的磁性强弱不同。

Iron nitride Fe4N with ferromagnetism was formed when nitrogen was incorporated in the iron powder under high temperature.To study the magnetism difference of iron in the different sites,the crystal structure of Fe4N was built based on experimental space structure,crystal parameter and atomic coordinate,then optimized structurally.Based on the most stable geometrical configuration,the electronic structure and magnetic property were calculated.The results show that the magnetic moments of N,Fe(Ⅰ)in the corner angle and Fe(Ⅱ)in the face center are 0.06,2.94 and 2.32 μB,respectively.The source of magnetic moment of all the atoms,especially iron,was analyzed through Mulliken charge distribution.It is seen that the magnetic moment of Fe(Ⅱ)in the face center is lower than that of Fe(Ⅰ)in the corner angle.The results agree well with the previous experimental and theoretical values,which are proven to be effective.Through analyzing the figure of density of states,spin-split case occurs to different degrees in Fe(Ⅰ)and Fe(Ⅱ),and the spin-split in Fe(Ⅰ)is more obvious near the Femi energy level,which explains Fe(Ⅰ)in the corner angle has more larger magnetic moment.Moreover,there exists more stronger covalent interaction between N and Fe(Ⅱ)than that between N and Fe(Ⅰ), thus leading to the magnitude difference of magnetic moment of Fe in different sites.