Resonant photoemission studies on Fe-Ni alloys

This paper investigates the electronic structure of Fe1−xNix (x = 0.32, 0.36, 0.4, 0.5) alloys employing high resolution photoelectron spectroscopy using synchrotron radiation. The valence bands and the core levels have been recorded at various on-resonance and off-resonance photon energies of Fe and Ni. An anti-resonance dip observed in the valence bands taken at Fe 3p → 3d resonance lies closer to the Fermi level compared to that observed at Ni 3p → 3d resonance, indicating larger density of itinerant Fe 3d electrons. Whereas, Ni 3d states are comparatively less itinerant in these alloys. The hybridization effects increase with increase of Fe content in the alloy system. The intensity of Ni L3M4,5M4,5 Coster-Cronig Auger transition observed with 853 eV (Ni 2p → 3d resonance) photon energy, drops down drastically for the Invar alloy (Fe0.64Ni0.36) as compared to other Fe-Ni alloys due to the existence of Ni in more than one local chemical surroundings as expected for Invar alloy. The electron-electron interaction energy (Udd) of Ni 3d shell is found to decrease with the decrease of Ni concentration. The 3p and 3s core levels of Fe and Ni recorded at 707 eV (Fe 2p → 3d resonance) are overwhelmed by various intense resonant Auger features such as Fe L3M2,3M2,3, Fe L3M2,3M4,5 and Fe L3M1M4,5. The 1S state of Fe L3M2,3M2,3 is greatly enhanced in the Invar alloy as compared to other alloys. The microscopic compositional in-homogeneity present in Invar alloy plays a crucial role in the screening of holes in Ni sites but does not contribute in screening the holes in Fe sites.