[Zurück]

W. Rupp:
"Ion beam induced magnetism of thin Fe films on Cu(100)";
Vortrag: Seminar Institut für Allgemeine Physik (IAP), TU Wien; 30.01.2007.

We have added a SMOKE (Surface Magneto Optical Kerr Effect) system in an existing UHV chamber equipped with conventional surface analytic systems like LEED (Low Energy Electron Diffraction), LEIS (Low Energy Ion Scattering) and AES (Auger Electron Scattering). The sample is placed between an air gap of a closed iron core with coils outside the vacuum chamber. So we can produce a constant homogeneous magnetic field of about ±100 mT.
The structure and magnetism of ultra thin epitaxial Fe films grown on Cu(100) at 300 K (RT) will be discussed. 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 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. 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 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) as the films becomes bcc during ion bombardment.
The magnetic properties and crystallographic structure of such treated films depending on ion dose and ion energy and ion mass will be discussed.