Photoemission study of electron correlation in M₇X₈ (M=Fe, Co; X=S, Se)

The occupied and unoccupied states of ferrimagnetic metals Fe₇S₈ and Fe₇Se₈, and a paramagnetic metal Co₇Se₈ have been studied by photoemission and X-ray inverse photoemission spectroscopies. Compared with the density of states (DOS) given by the band-structure calculation, the photoemission spectra of Fe 3d and Co 3d are narrowed. While the Fe 3d photoemission spectrum has a strong intensity at the higher binding energy side, it is significantly suppressed near the Fermi level. Self-energy corrections to the DOS's have been done for Fe₇Se₈ and Co₇Se₈. Disagreements between experimental and theoretical spectra have become small, indicating the importance of electron correlation effect.