Ni_n(n=2-6)原子簇的电子结构和磁性研究

ELECTRONIC STRUCTURE AND MAGNETISM OF CLUSTERS Nin(n=2-6)

采用MS-Xa方法研究了Nin(n=2-6)原子簇的电子结构和原子磁矩,发现团簇的几何对称性对原子磁矩和电子态 密度的分布有重要影响.具有Oh点群对称的八面体原子簇Ni6的3Eg轨道上存在很强的负交换耦合。呈现反铁磁耦合趋势; 具有C3v点群对称的三边金字塔结构的原子簇Ni5位于塔顶点的Ni原子与基面上的Ni原子磁矩方向相反,但大小不等,呈现 出亚铁磁交换耦合特征.与金属Ni相比,有些Ni原子团簇磁性增强,有些团簇磁性减弱.这一结果能够较好地解释铁磁超微颗 粒呈现出的表面磁性异常现象.

The electronic structure and magnetism of clusters Ni-n(n=2-6) have been studied by spin-polarized MS-X-alpha method. The results show that the effect of the cluster symmetry on its atomic magnetic moment and electronic density of states is very notable. Ni-6 cluster is an octahedron belonging to O-h point group. Its E-3(g) orbital presents strong negative exchange coupling and has a trend of antiferromagnetic couplings. Ni-5 Cluster is of three-side pyramidal structure belonging to point group C-3v. The magnetic moment direction of Ni atom lying on vertex of the pyramid is antiparallel to the moment direction of the Ni atoms lying on underside of the pyramid, which present the characteristic of ferrimagnetic couplings. Compared with metal nickel, the magnetic moments of some clusters are enhanced and some are weakened. The abnormal phenomenon of surface magnetism of ferromagnetic superfine particles can be well explained using this result.