Spin-Resolved Photoemission Study of n = 2 Core Levels of Iron
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SPIN-RESOLVED PHOTOEMISSION STUDY OF n = 2 CORE LEVELS OF IRON L.E. KLEBANOFF*, D.G. VAN CAMPEN, and R.J. POULIOT Lehigh University, Department of Chemistry and Zettlemoyer Center for Surface Studies, Sinclair Laboratory, 7 Asa Drive, Bethlehem, PA 18015 ABSTRACT The first spin-resolved x-ray photoelectron spectroscopy (SRXPS) study of the n = 2 core levels of ferromagnetic Fe are reported. The 2P 312, 2p, 1 2 and 2s core levels all display interesting spin-dependent structures and splittings. The spectral complexity predicted by a purely atomic picture is not observed in the data. The results indicate that theories incorporating the delocalization of the 3d valence band are more applicable to the description of core-level photoemission in iron. Introduction Spin-resolved photoemission has played an important role in elucidating the nature of interface magnetism. The majority of such studies have been spin-resolved ultra-violet photoemission (SRUPS) investigations of the valence-band structure of metallic surfaces [1-41. These studies have provided a wealth of information concerning the valence electronic structure of ferromagnetic metals. SRUPS has also been used to measure the spin dependence of the rather shallow 3s and 3p core levels of Fe [5-8] and the 3p level of Co [11. A disadvantage of using SRUPS for core-level study is that the low-energy ultra-violet radiation can photoionize only very shallow core levels, leaving the more tightly bound n = 2 levels of the 3d ferromagnets inaccessible. While SRUPS is ideal for valence-band study, valence-band investigations do not usually afford the element specificity that is often required to investigate heterogeneous magnetic interfaces. We present here the first spin-resolved photoemission study employing a high photon energy (1253.6 eV) often used in x-ray photoelectron spectroscopy (XPS) studies of core levels. Spin-resolved XPS (SRXPS) results for the Fe 2P312 , 2p,/ 2 , and 2s levels are reported. The results show that intra-atomic exchange effects are important for these tightly bound levels, despite their small radial extent. The SRXPS data also clarify the nature of core-level initial states involved in soft x-ray magnetic circular dichroism (MCD) spectroscopic studies [9-11] of Fe. Experimental Our Fe sample was a thin film prepared by evaporating high-purity Fe in ultra-high vacuum onto the surface of a sputter-cleaned cobalt-based ferromagnetic metallic glass of composition Co 66 Fe4 NilB 1 4Si 15 [121. The glass substrate consisted of a loop that was easily magnetized to saturation by passing current through coils wrapped around the legs of the loop. This arrangement allowed the preparation of high-purity polycrystalline Fe films with thicknesses of 20-30A with very little oxygen contamination [131. The ferromagnetic exchange coupling between the Co metallic glass substrate and the Fe thin film conveniently leads to an in-plane magnetically saturated Fe film (with negligible stray magnetic field) that is required for SRXPS study. A fresh Mat. Res. Soc. Sy
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