Theoretical Study of Spin-Orbit Coupling in Metallic Ferromagnetism

自旋-轨道耦合是唯一的一种相互作用，它将自旋系统固定在晶格上，但对于3d过渡金属来说，它太小了，无法进行可靠的定量计算。本文研究了稀土(R)和三维过渡金属的间质修饰金属间化合物以及X/Co或Fe （X=Pd, Pt, Ag, Au）铁磁多层体系的磁性各向异性能（MAE）的第一性原理带计算。用FLAPW方法计算了GdCo_5、GdFe_<12>、Gd_2Fe_<17>、GdFe_<12>N和Gd_2Fe_<17>N_3的电子结构，并对R离子周围的电荷分布进行了细致的研究。氮间隙离子与周围的铁和R离子形成强键。与Fe成键会导致更大的自旋饱和矩，而与R成键会使R周围的电荷呈强的非球面分布，晶体场（CF）与SmCo_5一样大。我们发现这个大CF是这些氮化物中强单轴磁各向异性的微观起源。对于X/Co或Fe体系，用LMTO方法系统地计算了MAE，包括自旋轨道相互作用。我们发现这些系统中MAE的一般趋势可以用第一性原理计算很好地解释。研究了复合材料对Co层厚度和应变的依赖关系。

The spin-orbit coupling is the only one interaction, which fixes the spin system to the lattice, but it is too small to make a reliable quantitative calculations in the case of 3d-transition metals. We have investigated the magnetic anisotropy energy (MAE) from the first-principles band calculations in the two cases : interstitially modified intermetallics of rare-earth (R) and 3d transition metals and X/Co or Fe (X=Pd, Pt, Ag, Au) ferromagnetic multilayr system. In the former case, the electronic structures of GdCo_5, GdFe_<12>, Gd_2Fe_<17>, GdFe_<12>N and Gd_2Fe_<17>N_3 were calculated by FLAPW method and the charge distribution around R ions were investigated carefully. Nitrogen interstitial ions make strong bondings with surrounding Fe and R ions. The bonding with Fe leads to a larger spin saturation moment, but that with R makes a strong aspherical charge distribution around R and a crystalline field (CF) as large as that of SmCo_5. We found that this large CF is the microscopic origin of the strong uniaxial magnetic anisotropy in these nitrides. In the case of X/Co or Fe system, the MAE were calculated systematically by the LMTO method including the spin-orbit interaction. We found that the general tendency of the MAE in these systems are well explained by first-principles calculations. The thickness of Co layr dependence and the strain dependence of the MAE were also investigated.