Non-collinear magnetism of Transition metal linear clusters

过渡金属纳米材料由于其特殊的磁性而引起了人们的广泛兴趣。在本项目中，我们利用非共线第一性原理分子动力学理论研究了铁纳米团簇的原子结构和磁性结构，并阐明了以下几点。（1）裸Fe链：在裸Fe线性链中，随着原子间距离的改变，磁性排列从共线变为非共线（反之亦然）。结果表明，磁取向的变化不仅是由3d电子之间的反铁磁相互作用引起的，而且也是由4s和3d电子之间的类RKKY相互作用引起的.在优化的原子间距离，发生二聚化，特别是在链与偶数原子，和磁矩排列在二聚体的单位反平行。(2)Fe碳纳米管中的铁链：为了稳定线性结构，铁链被封装在由五角环终止的管状碳纳米管中。球囊中的Fe原子是不稳定的，但管囊中的Fe链是稳定的，保持其线性结构。由于Fe和C原子之间的超交换作用，在胶囊中反平行磁排列占主导地位。（3）氧化铁团簇FenOm：当n>m时，出现平行的大磁矩，而当n<m时，出现反平行的零磁矩或小磁矩。这是由于Fe和O原子之间的超交换作用。研究了n= 1，2和m=1-6时氧化铁阴离子团簇的原子结构和电离能。

Transition-metal nano materials have been attracting many researchers interests because of their anomalous magnetic properties. In the present project, we have theoretically studied the atomic and magnetic structures of iron nano clusters by using the non-collinear first principles molecular dynamics, and clarified the following points.(1)Bare Fe chains : In bare Fe linear chains, magnetic alignment changes from collinear to non-collinear (and vice versa) with changing the interatomic distances. It is suggested that the change in the magnetic alignment is caused not only from the antiferromagnetic interaction between 3d electrons but also from RKKY-like interaction between 4s and 3d electrons. In the optimized interatomic distances, a dimerization occurs, especially in chains with even-number atoms, and the magnetic moments align antiparallel in unit of the dimer.(2)Fe chains in carbon nanocapsules : To stabilize the linear structures, Fe chains are encapsulated in tubal carbon nanotubes terminated by pentagonal rings. A Fe atom in the global capsule is not stable, but Fe chains are stable in tubal capsules, keeping their linear structures. Antiparallel magnetic alignments are dominant in the capsules because of the super exchange interaction between Fe and C atoms.(3)Iron oxide cluster FenOm : Parallel large magnetic moments appears for n>m, while antiparallel aliments with zero or small net magnetic moments appears for n<m. This is due to the superexchange interaction between Fe and O atoms. The atomic structures and ionization potential of iron oxide anion clusters also investigated for n=1,2 and m=1-6.