Local Structures of Fe0.08Co0.92 Studied by X-ray Fluorescence Holography

At room temperature, pure Co has a hexagonal close-packed (HCP) structure. When several percent of Fe is doped into a Co crystal, it changes to the face-centered cubic (FCC) structure. However, it is not clear why the FCC structure in the FexCo1−x system is so stable even with small amounts of Fe concentration. Therefore, we carried out X-ray fluorescence holography (XFH) on a Fe0.08Co0.92 single crystal to visualize the three-dimensional atomic images around both Fe and Co atoms. The intensities of the reconstructed images by XFH around Fe atoms at both 100 and 300 K are inversely proportional to the distance from the Fe emitter, and those at 100 K were always higher than those at 300 K due to the suppression of the thermal vibrations of atoms. However, the image intensities around Co did not increase by cooling unlike those around Fe. In particular, the distance dependence of the atomic image intensities at 100 K are roughly constant up to 0.8 nm. This suggests that the lattice around Co, i.e., matrix crystal lattice of Fe0.08Co0.92, is more distorted than that around dopant Fe.