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18 UNIVERSITÄT OSNABRÜCK, FACHBEREICH PHYSIK this system is a non-saturated spin-fluctuation system. The exchange-enhancement factors are not high enough to lead to the saturation of the amplitude of the local spin fluctuations. In the case of GdNi5-xAlx system, the aim of our study was to investigate the influence of partially replacing Ni by Al on the magnetic state of the Ni 3d-electrons in GdNi5-xAlx by using magnetic measurements and XPS technique. The valence bands of GdNi5, GdNi4Al (Fig 4) arise mainly from the Ni 3d electrons which are close to the onset of ferromagnetism. The 3d states are hybridized with 5d states. The occupied part of the valence bands are over 4eV wide. One can see also a marked feature near the maximum of the valence bands of GdNi5 and GdNi4Al. This may be explained Intensity (arb. units) GdNi 5 GdNi 4 Al GdNiAl 4 pure Ni -2 0 2 4 6 8 10 12 14 16 Binding energy (eV) as a partial quenching of the spin fluctuations by the strong magnetic moments of Gd atoms. Furthermore, the substitution of Ni by Al leads to an increase of the localization of the Ni 3d electrons, reflected by an energy shift of the valence band maximum to higher binding energies. This is also supported by the different values of the saturation temperature of the spin fluctuations T * obtained for GdNi5 and GdNi4Al. Fig 4. XPS valence spectra of the GdNi5-xAlx system. One can observe marked differences both in the shape and in the position of the valence bands in GdNiAl4 and Ni. The density of states at the Fermi level in GdNiAl4 is drastically reduced in comparison with pure Ni and the maximum of the valence band is shifted to higher binding energy, namely from 0.59 eV in Ni to 2.3eV in GdNiAl4. The states at the Fermi level have 3d and s-p character in Ni and GdNiAl4, respectively. In d-band metals and alloys the 3d states are shifted gradually to higher binding energy by increasing the d-state occupancy and consequently a decreasing density of states at EF occurs. These results reveal the complete filling of the Ni 3d-band by charge transfer of Gd 5d electrons and the s-p character of the states at the Fermi level in GdNiAl4. This conclusion is also confirmed by comparing the Ni 2p core level spectra for pure Ni and GdNiAl4. In the Ni 2p core level spectrum of pure Ni are present also satellites as an evidence for the d character in unoccupied states. The absence of these satellites in the Ni 2p spectrum of GdNiAl4, shows that the 3d-band in this compound is filled. Summarising the results, one may conclude that the Ni 3d-band in GdNi5-xAlx compounds is sensitive to the local environment, showing a large variety of magnetic behaviours by partially replacing Ni by Al atoms. Outlook We have very recently investigated the presented ferric-wheel by X-ray emission spectroscopy using synchrotron radiation. The results will be further analysed. Other magnetic molecules will be investigated by several spectroscopic methods in the next future. Other rare-earth compounds under investigation are the LaNi5-xAlx and YCo2-xSix series. References [1] See http://zeus.physik.uni-osnabrueck.de/neumann/veroeff_1.html [2] St. Uhlenbrock, PhD Thesis, Osnabrück 1994 [3] S. Lütkehoff, PhD Thesis, Osnabrück 1997 [4] S. Plogmann, PhD Thesis, Osnabrück, 2000 [5] A review on http://cmpweb.ameslab.gov/magnetic_molecules/ [6] C. Schröder, PhD Thesis, Osnabrück 1999 [7] E. Burzo, S.G. Chiuzbăian, L. Chioncel, M. Neumann, Journal of Physics: Condensed Matter, 12 (2000) 5897 [8] D. Ginoux, D. Givord, and A del Moral, Solid State Communications 19 (1978) 891 [9] J. Palleau and G. Chouteau, Physical Review Letters 41 (1980) L227 [10] M. Coldea, S. Chiuzbaian, M. Neumann, D. Todoran, M. Demeter, R. Tetean, V. Pop, accepted for publication in Acta Physica Polonica [11] T. Moriya, Journal of Magnetism and Magnetic Materials 100 (1991) 261 and the references therein [12] A. Caneschi, D. Gatteschi, C. Sangregorio, R. Sessoli, L. Sorace, A. Cornia, M.A. Novak, C. Paulsen, W. Wernsdorfer, J. Magn. Magn. Mater. 200 (1999) 182
GRADUIERTENKOLLEG MIKROSTRUKTUR OXIDISCHER KRISTALLE 19 [13] R.W. Saalfrank, I. Bernt, E. Uller and F. Hampel, Angew. Chem. 109 (1997) 2596 [14] O. K. Andersen and O. Jepsen, Physical Review Letters 53 (1984) 2571 Publications ♦ V. Simon, S.G. Chiuzbaian, M. Neumann, D. Eniu, E. Indrea, A. Török-Kiss, S. Simon, Photoelectron spectroscopy on iron containing CaO-SiO2-P2O5 glass ceramics, accepted for publication in Modern Physics Letters B ♦ L. Chioncel, E. Burzo, S. Chiuzbaian, Induced transition metal moments in rare-earth compounds, accepted for publications in Balkan Physics Letters ♦ S.G. Chiuzbaian, M. Neumann, O. Waldmann, B. Schneider, I. Bernt, R.W. Saalfrank, X-ray photoelectron spectroscopy of a cyclic hexanuclear cluster, submitted for publication in Surface Science ♦ V. Pop, M. Coldea, M. Neumann, S. Chiuzbaian, D. Todoran, X-ray photoelectron spectrosopy and magnetism of Gd3Ni8Al, submitted for publication in Journal of Alloys and Compounds ♦ M. Coldea, S. Chiuzbaian, M. Neumann, D. Todoran, M. Demeter, R. Tetean, V. Pop, Magnetic and Electronic Properties of GdNi5-xAlx Intermetallic Compounds, accepted for publication in Acta Physica Polonica ♦ A. Slebarski, M.B. Maple, E.J. Freeman, C. Sirvent, D. Tworuszka, M. Orzechowska, A. Wrona, A. Jezierski,S. Chiuzbaian, M. Neumann, Weak ferromagnetism induded by atomic disorder in Fe2TiSn, Physical Review B, 62 (2000) 3296 ♦ E. Burzo, S.G. Chiuzbaian, L. Chioncel, M. Neumann, Magnetic and electronic properties of LaNi5-xCux system, Journal of Physics: Condensed Matter, 12 (2000) 5897 Attended lectures & seminars Ringvorlesung des Graduiertenkollegs Seminar des Kollegs Kolloquium des SFB 225 Vorlesungen: Prof. Dr. M. Coldea, Magnetism and magnetic properties of materials, 1999 Prof. Dr. E. A. Kotomin, Introduction into theory of defects in oxide solids, 1999 Conferences, meetings, summer schools • Measurements on ferric-wheel at the Advanced Light Source in Berkeley, USA, November 2000 • Ames Laboratory, Iowa State University, USA, meetings and discussions related to the magnetic molecules (2 weeks) October-November 2000. • 19th European Conference on Surface Science, ECOSS-19, Madrid, Spain, poster September 2000 • International Conference: Condensed Matter Physics, Ustron-Jaszowiec, Poland, poster, May 2000 • Frühjahrstagung des Arbeitskreises Festkörperphysik bei der DPG, Regensburg, Germany, poster, March 2000 • 10. NRW-Mitarbeitertreffen "Physik und Chemie an Oberflächen", Münster, Germany, talk, October 1999 • International Sommer School on Thin Films Magnetism, Cluj-Napoca, Romania, participant, August 1999 • Frühjahrstagung des Arbeitskreises Festkörperphysik bei der DPG, Münster, Germany, participant, March 1999 • 9. NRW-Mitarbeitertreffen "Physik und Chemie an Oberflächen", Köln, Germany, participant October 1998
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