The atomic order and its effect on the electronic structure is a key issue in the application of half-metallic Heusler alloys as spin-polarized electron sources. In this study, we investigated the atomic ordering and electronic structures of $\mathrm{C}{\mathrm{o}}_2\mathrm{Fe}\left(\mathrm{G}{\mathrm{e}}_{0.5}\mathrm{G}{\mathrm{a}}_{0.5}\right)$ (CFGG) Heusler alloy thin films at various annealing temperatures using anomalous x-ray diffraction (AXRD) and hard x-ray photoelectron spectroscopy (HAXPES). AXRD measurements clearly showed that the Co-Fe disorder is large in the as-deposited state, which is reduced to almost zero by annealing at $T_{\mathrm{an}}=500{}^{\circ }\mathrm{C}$ for 30 min. The reduction of the Co-Fe disorder explains the observed increase in the spin polarization of currents estimated by ordinary and anisotropic magnetoresistance measurements. The photoelectron spectra of the valence band in CFGG thin films with different $T_{\mathrm{an}}$ agree well with the first-principles calculations that considers the atomic disorder. We also found that the characteristic peaks appearing in the valence band HAXPES spectra shifted to higher binding energies, compared to the calculated density of states for stoichiometric $\mathrm{L}{2}_1$-ordered CFGG. This indicates that the Fermi level is shifted and located in the vicinity of the conduction band edge in the present CFGG thin film due to electron doping by a mildly Co-rich chemical composition. Our first-principles calculations of partial density of state of $sp$ electron predicted that the high spin-polarization is obtainable in a wider energy region near Fermi level in the $\mathrm{L}{2}_1$-ordered structure than the B2 structure, which explains the enhancement of spin-polarization by promoting $\mathrm{L}{2}_1$-ordering in the present CFGG film.

中文翻译：

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原子序数对Co2Fe（Ga0.5Ge0.5）Heusler合金薄膜中半金属电子结构的影响

原子序及其对电子结构的影响是将半金属赫斯勒合金用作自旋极化电子源的关键问题。在这项研究中，我们研究了原子的原子序和电子结构$\mathrm{C}{\mathrm{Ø}}_2铁（\mathrm{G}{\mathrm{Ë}}_{0.5}\mathrm{G}{\mathrm{一种}}_{0.5}）$（CFGG）使用异常X射线衍射（AXRD）和硬X射线光电子能谱（HAXPES）在各种退火温度下的Heusler合金薄膜。AXRD测量清楚地表明，在沉积状态下，Co-Fe紊乱很大，通过在200℃下退火可以将其减少到几乎为零。${Ť}_{\mathrm{一个}}=500{}^{\circ }\mathrm{C}$30分钟 Co-Fe紊乱的减少解释了观察到的通过常规和各向异性磁阻测量估计的电流的自旋极化增加。CFGG薄膜不同价带的光电子能谱。${Ť}_{\mathrm{一个}}$与考虑原子无序的第一性原理计算非常吻合。我们还发现，与计算出的化学计量态密度相比，在价带HAXPES光谱中出现的特征峰移至更高的结合能$\mathrm{大号}{2}_{\mathrm{1个}}$订购的CFGG。这表明费米能级由于存在轻度富钴化学成分的电子掺杂而移动并位于本CFGG薄膜中的导带边缘附近。我们的第一性原理计算部分状态密度$sp$ 电子预测高自旋极化可以在费米能级附近更宽的能量区域获得 $\mathrm{大号}{2}_{\mathrm{1个}}$有序结构比B2结构更好，这说明了通过促进自旋极化的增强 $\mathrm{大号}{2}_{\mathrm{1个}}$本CFGG胶片中的光点序。