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1 2007

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Photoemission study of Eu 2+/3+ ions in ferromagnetic (Eu,Gd)Te semiconductor layers

Dziawa P., Orłowski B. A., Osinniy V., Pietrzyk M., Taliashvili B., Story T., Johnson R. L.

Materials Science Poland

2007

Vol. 25, No. 2

377--382

(Eu,Gd)Te ferromagnetic semiconductor layers grown by molecular beam epitaxy technique on BaF2 (111) monocrystalline substrates were investigated by resonant photoemission spectroscopy using synchrotron radiation. In n-(Eu,Gd)Te layers, a ferromagnetic transition induced by electron concentration is observed. Magnetic as well as electrical properties of this material depend strongly on the charge state (2+ vs. 3+) of Eu and Gd ions known to be sensitive to crystal stoichiometry and formation of oxide complexes. The relative concentration of Eu2+ and Eu3+ ions was determined from the analysis of the resonant photoemission energy distribution curves (EDC), measured at photon energies close to 4d-4f resonance. After various in-situ annealing and Ar sputtering procedures, a clear improvement of crystal stoichiometry of (Eu,Gd)Te layers was observed as manifested by the increase of Eu2+ intensity in the spectra. Contribution of Eu 4f shell to the total density of states was also analyzed and found at the valence band edge for Eu2+ ions and about 6 eV lower for Eu3+ ions.