[Zurück]

W. Rupp:
"Ion beam induced magnetism of thin Fe films on Cu(100)";
Vortrag: CMS Seminar, TU Wien; 09.06.2006.

The structure and magnetism of ultra thin epitaxial Fe films grown on Cu(100) at 300 K (RT) have been investigated by STM (scanning tunnelling microscopy), low-energy electron diffraction (LEED) and by surface magneto-optical Kerr effect (SMOKE) [1]. Hysteresis loops in longitudinal and polar geometry can be determined. Depending on the film thickness, three regimes with different magnetic properties and different orientation of the magnetic anisotropy are known [2] and could be confirmed. Further it is also known that the fcc phase, which has no magnetic moment, can be achieved at room temperature (RT) only for a thickness of 5 to 10 monolayers (ML). In these films small (needle-like) nuclei of the bcc structure were found [3]. We have observed that in these Fe films the phase transition from the fcc phase to the bcc phase can be induced and promoted by Ar+ ion bombardment. By LEED measurements we observe the structural change from fcc to bcc-like structures after ion bombardment (e.g. ion dose around 0,4 Ar ions / surface atom). At RT, the structural transition is accompanied by a change of in-plane magnetization from paramagnetic to ferromagnetic behaviour. Additionally, our SMOKE data show the disappearance of the low temperature surface ferromagnetism (with perpendicular magnetic anisotropy) [2, 4] as the films becomes bcc during ion bombardment.
The magnetic properties and crystallographic structure of such treated films depending on Ar+ ion dose and ion energy will be discussed.


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[2] J. Thomassen, F. May, B. Feldmann, M. Wuttig and H. Ibach, Phys. Rev. Lett. 69, 3831 (1992)
[3] A. Biedermann, M. Schmid and P. Varga, Phys. Rev. Lett. 86, 464 (2001)
[4] A. Biedermann, R. Tscheließnig, Ch. Klein, M. Schmid and P. Varga, Surf. Sci. 563, 110-126 (2004)