We report a theoretical analysis of x-ray magnetic circular dichroism (XMCD) at the Cr-$L$ edge in half-metallic ferromagnetic ${\mathrm{CrO}}_2$. First, since the XMCD spectrum is the difference between the x-ray absorption spectra (XAS) for right- and left-handed circularly polarized x rays, a general perturbative method of calculating XAS spectra is developed by means of the Keldysh Green's function technique for nonequilibrium states. Subsequently, it is applied to the analysis of XMCD of half-metallic ferromagnetic ${\mathrm{CrO}}_2$. Calculated XAS and XMCD spectra are compared with several previous experimental data. It is clearly shown that effects of the atomiclike Coulomb interaction between the $2p$ and $3d$ states are indispensable ingredients to yield good agreement with the experiments. Such strong $2p\text{−}3d$ correlation may originate from a peculiarity of the half-metallic ferromagnetic state. Evaluation of the validity of sum rules is made within our framework.

中文翻译：

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半金属铁磁体CrO2的X射线磁圆二色性分析

我们报告了 Cr- 处 X 射线磁圆二色性 (XMCD) 的理论分析$L$半金属铁磁边缘${\mathrm{氧化铬}}_2$。首先，由于 XMCD 光谱是右旋和左旋圆偏振 X 射线的 X 射线吸收光谱 (XAS) 之间的差异，因此通过 Keldysh Green 函数技术开发了计算 XAS 光谱的通用微扰方法：非平衡状态。随后，将其应用于半金属铁磁体的XMCD分析${\mathrm{氧化铬}}_2$。计算出的 XAS 和 XMCD 光谱与之前的几个实验数据进行了比较。清楚地表明，类原子库仑相互作用的影响$2p$和$3d$状态是与实验产生良好一致性的不可或缺的成分。这么强$2p\text{-}3d$相关性可能源于半金属铁磁态的特性。求和规则有效性的评估是在我们的框架内进行的。