晶体电场对离子自旋─轨道耦合参数的影响

THE EFFECT OF THE CRYSTAL FIELD ON THE SPIN ORBIT COUPLING PARAMETER OF THE 4F ELECTRONS OF RARE-EARTH TRIVALENT IONS IN RCL_3

晶体电场对三价稀土离子自旋─轨道耦合参数有影响，是人们长期怀疑但尚无人作过定量分析与计算的问题．本文从相对论Ｄｉｒａｃ方程式给出的电子自族─轨道耦合参数表达式出发，以稀土氯化物为例，首次详细计算了晶体电场对稀土离子（Ｃｅ３＋、Ｐｒ３＋、Ｎｄ３＋、Ｓｍ３＋、Ｅｕ３＋、Ｇｄ３＋、Ｄｙ３＋、Ｅｒ３＋、Ｙｂ３＋）４ｆ自旋─轨道耦合参数贡献的相对大小．计算结果表明：晶体电场对电子自旋─轨道耦合参数的贡献至多占稀土离子核库仑场贡献的万分之一，因此可以忽略不计．寻找电子自旋─轨道耦合参数实验值与理论值差别的途径，应该从离子的电子结构本身着手来研究．

The Spin-orbit coupling parameter of the 4f electron of rae-earth trivailent ions was early calculated by Freeman. A.J. et al., and used to explain its energy spectrum and paramagnetic resonance spectrum in crystal. The difference between the theory and experiments is about 15% to 20%. Theoretically, the crystal electrical field should have influence on the Spin-orbit parameter if the ions. It has long been suspeded that the influence may be over 1% but little quantitative analysis or caluculation has been done.Based on eleCtron spin-orbit coupling parameter expression as given by Dirac equahon of relativity, taking the RCl crystal as an example, this paper for the first time gives the detailed calculation of the ralative contribution of crystal field to the spin-orbit coupling parameter of 4f electrons of rare-earth trivalent ions in RCl, (R = Ce3+, Pr3+, Nd3+, Sm3+,Eu3+, Gd3+, Dy3+, Er3+, Yb3+).It has been shown that comparing the Coulumb field due to the nucleus, the contribution of the crystal field at most 1 / 1000 and thus negligible. The reason for the difference between the dates of the theory and the experiment may be the other effects of ionic structure, not the enviroment of the crystal field.