R_2Fe_(17)Mx化合物的磁性研究

Study of the Magnetism in R_2Fe_(17)M_x Compounds

用自旋极化的MS－Xa方法计算了Nd_2Fe_(17)Nx（x=0,3)化合物中含哑铃Fe原子对的Fe8及合Nd原子的NdFe_6。原子簇的电子结构和磁矩．计算结果显示，Nd_2Fe_(17)化合物内在Fe（c）和Fe（f）间的分子轨道中，有三个奇宇称轨道呈现负交换耦合。通过比较a－Fe的MS－Xa计算结果，能够很好地说明R_2Fe_(17)化合物居里温度较低的原因。在化合物Nd_2Fe_(17)N_3中Fe（c）－Fe（f）间分子轨道只剩下一个奇宇称轨道呈现弱的负交换耦合，通过比较N_2Fe_(17)，与N_2Fe_(17)N_3化合物Fe_8原子簇的计算结足，能够很好地说明间隙原子M（=N、H或C）对R_2Fe_(17)M化合物居里温度产生影响的物理机理。对R_2Fe_(17)型化合物中影响Fe-Fe交换作用大小的主要因素，本文也作了讨论。

The electronic structure and magnetic moments of cluster NdFe_6 and cluster Fe_8 with a dumbbell atom-pair in Nd_2Fe_(17)Nx(x = 0,3) have been studied by spin-po1arized MS-Xa method. The results showed that (l) There are negative exchange couplings between Fe(f) and Fe (c) atoms in Nd_2Fe_(17), which occur at three odd parity orbitals. Compared to the results of a-Fe calculated by MS-Xa method,the 1ow Curie temperature of compounds R_2Fe_(17) can be explained satisfactorily. (2) There is on1y one weaker negative exchange coupling orbital leaving in between Fe(f) and Fe(c) in Nd_2Fe_(17)N_3. These results may be helpful for understanding the effect of inter- stitial atom M (=N,H or C) in R_2Fe_(17)Mx on Curie temperature. The other key factors affecting the Fe-Fe exchange coupling in R_2Fe_(17) compounds were also discussed in this paper.