Journal of Electron Spectroscopy and Related Phenomena 78 (1996) 95-98 zyxwvutsrqponmlkjihgfedcbaZY Electronic band structure and photoemission spectra of Fe& M. Shirai”, N. Suzuki” and K. Motizukib aDepartment of Material Physics, Faculty of Engineering Science, Osaka University, Machikaneyama-cho l-3, Toyonaka 560, Japan bDepartment of Applied Physics, Faculty of Science, Okayama University of Science, Ridai-cho l-l, Okayama 700, Japan First-principles electronic band structure calculations are performed for a cation-deficient NiAs-type ferrimagnet Fe& (pyrrhotite) by using the linearized augmented-plane-wave (LAPW) method based on the local density approximation for the exchange-correlation potential. The magnetic moment, the magnetic hyperfine field, the isomer shift, and the Fe 3s core-level spin-splitting are evaluated for each iron-site. Valence-band ultraviolet photoemission and inverse photoemission spectra are calculated for the ferrimagnetic state of Fe,Ss and the results are compared with recent observations. 1. INTRODUCTION Transition-metal compounds with the NiAs- type crystal structure have been attracting much interest due to their rich variety of electrical, magnetic, and optical properties [l]. It is nec- essary for understanding of these properties to elucidate their electronic states microscopically. Based on the theory of spin fluctuations [2], vari- ous magnetic properties of NiAs-type transition- metal pnictides, such as MnAs and FeAs, can be well explained by taking account of charac- teristic features of their electronic band struc- tures [3]. On the other hand, for a NiAs-type transition-metal chalcogenide NiS, the electronic band structure calculation based on the local density-functional formalism [4] can not explain the magnitude of the magnetic moment, the in- sulating behavior, and the valence-band photoe- mission spectra in the antiferromagnetic state [5]. Previously we have calculated the electronic band structures of the NiAs-type transition-metal chalcogenides, MX (M = Fe, Co; X = S, Se), in order to provide an insight into the magnetic and optical properties of these chalcogenides [6]. However, these chalcogenides tend to be defi- cient in cations and form various kinds of su- perstructures associated with ordering of cation- vacancies. For more quantitative argument, therefore, it is necessary to consider the effect of ordered cation-vacancies. Recently valence-band ultraviolet photoemis- sion and inverse photoemission spectra [7] as well as core-level x-ray absorption spectra [S] have been measured extensively for FeTSs and its isostructural selenide Fe;rSes. In order to ana- lyze these observed spectra, it is desired to per- form first-principles electronic band structure cal- culations for these chalcogenides. In the present paper the electronic band structure calculated for Fe7Ss is reported and is compared with the observed photoemission spectra. The result for Fe;lSes has been published elsewhere [9]. Fe& is the main ingredient of the natural min- eral, pyrrhotite, which has turned out to be of some importance in geophysics. Due to the or- dering of iron-vacancies and the slightly mono- clinic distortion Fe& takes the 2fia x 2a x 4c- type superstructure [lo], where zyxwvutsrqponmlkjihgf a and c denote the lattice constant,s for the original NiAs-type structure. Fe7Ss becomes ferrimagnetic below TN N 580 K, where magnetic moments on de- ficient iron-layers and those on complete iron- layers align in the opposite direction from each 0368-2048/%/$15.00 0 1996 Elsevier Science B.V. All rights reserved zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJI PII SO368 - 2048 (%) 02686-2