Non-collinear magnetization structure at the thickness and

Non-collinear magnetization structure at the thickness and
temperature driven spin reorientation transition in ultrathin epitaxial Fe
films on W(110)
Ślęzak T.1, Ślęzak M.1, Kozioł-Rachwał A.1, Matlak K.1, Freindl K. 3, Spiridis N. 3, E. PartykaJankowska4, D. Wilgocka-Ślęzak3, Zając M. 1,2, Rüffer R.2, Korecki J.1,3
1
Faculty of Physics and Applied Computer Science, AGH, Kraków, Poland
European Synchrotron Radiation Facility, BP 220, 38043 Grenoble Cedex, France
3
Institute of Catalysis and Surface Chemistry, PAN, ul. Niezapominajek 8, Kraków, Poland
4
Faculty of Physics, University of Vienna, A-1090 Wien, Austria
2
Thickness and temperature induced in-plane spin reorientation transition (SRT) in epitaxial
Fe films on W(110) [1] was studied in situ using the nuclear resonant scattering of synchrotron
radiation. NRS is a synchrotron analogue of Mössbauer spectroscopy (MS), in the sense that
recoilless excitation (induced by the resonant x-rays with energy 14.4 keV for 57Fe) of the nuclear
energy levels, split due to the hyperfine interactions, is involved [2]. In this method, the hyperfine
parameters can be obtained from a characteristic beat pattern seen in the time evolution of the
intensity of nuclear resonant scattering (the so called time spectrum). The well defined polarization
of the synchrotron x-rays provides high sensitivity to the orientation of the hyperfine magnetic field
and electric field gradient. The numerical analysis of the NRS time spectra measured during Fe
evaporation, indicates that transition from the uniform [1-10] oriented magnetization state observed
at lower thickness to the [001] magnetization orientation at higher thickness undergoes via
formation of non-collinear spin structure. It is clear that with increasing film thickness the bottom
Fe(110) atomic layers initiate SRT while the surface magnetization reverses at the end. This
thickness induced SRT originates at the Fe/W(110) interface and proceeds via a non-collinear spin
structure resembling a planar domain wall that propagates towards the surface with increasing film
thickness. It was shown that thickness induced SRT process at 250°C proceeds also trough the
intermediate, vertically non-collinear magnetic state but in contrast to the room temperature
thickness driven reorientation the spin spiral state has opposite sense of rotation namely: with
increasing thickness magnetization reorientation from [1-10] to [001] direction is initiated by the top
most atomic layers and completed at the Fe/W(110) interface.
The nature of the temperature induced transition is also non-collinear and with increasing
temperature surface magnetization switches first from [1-10] to [001] direction.
[1] Gradmann U., Korecki J., Waller C., Appl. Phys. A 39 101 (1986)
[2] Sturhahn W., Hyperfine Interact. 125, 149 (2000)
This work was supported by the Team Program of the Foundation for Polish Science cofinanced by the EU European Regional Development Fund.