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Magnetismus Poster: Do., 13:00–15:30 D-P244
X-ray Resonant Magnetic Scattering on Diluted Magnetic Semiconductors
Alexei Nefedov 1 , Numan Akdogan 1 , Rustam Khaibullin 2 , Lenar Tagirov 2,3 ,
Hartmut Zabel 1
1 Institut für Experimentalphysik/Festkörperphysik, Ruhr-Universität Bochum,
Bochum, Germany – 2 Kazan Physical-Technical Institute of RAS, Kazan, Russia –
3 Kazan State University, Kazan, Russia
Diluted magnetic semiconductors (DMS) are key materials for spintronics, which are
intended to manipulate both the spin and charge degree of freedom by coupling the
spins of the magnetic ions and the charge carriers of the host semiconductors. Recently
several oxide-based DMS have been reported to be robust, room temperature
ferromagnets. In particular, the Co-doped TiO2 system, first reported to be ferromagnetic
by Matsumoto [1], has received much attention. However, a consensus on the
origin of the ferromagnetic coupling has not yet been reached. To clarify this situation
we have studied in detail the magnetic properties of Co-doped TiO2 synthesized by
ion implantation with doses of 0.25-1.50·10 17 ions/cm 2 using x-ray resonant magnetic
scattering (XRMS) in a temperature range of 4.2-295 K. The XRMS experiments were
carried out at BESSY II using the ALICE diffractometer [2].
Firstly, a two-component hysteresis curve was observed at the Co L3 edge (E=778 eV)
for the sample implanted with the dose of 1.50·10 17 ions/cm 2 . However, variation of
the photon energy leads to a change of the relative intensities of these two components
and at the photon energy of E=780 eV only a one-component hysteresis curve has been
observed. This allows to separate magnetic contributions from Co ions incorporated in
TiO2 and contributions from Co metallic clusters. We found that the Curie temperature
increases from 12 K for the lowest implantation dose (D=0.25·10 17 ions/cm 2 ) to
above room temperature for samples implanted with a dose of 1.00·10 17 ions/cm 2 .
Within our sensitivity no magnetic signal was found at the Ti edges, however at the
O K edge a small, but clearly visible magnetic signal was observed. From this we
infer that oxygen atoms which are close to Co atoms are polarized. This observation
could imply that the ferromagnetism observed for Co-doped rutile (100)TiO2 samples
is mediated by a superexchange mechanism through oxygen atoms.
N. Akdogan acknowledges a fellowship through the International Max-Planck Research
School “SurMat”. We gratefully acknowledge BMBF for the financial support through
Contracts No. 05KS4PCA (ALICE diffractometer) and No. 05ES3XBA/5 (travel to
BESSY).
[1] Y. Matsumoto et al., Science 291 (2001) 854.
[2] J. Grabis et al., Rev. Sci. Instr. 74 (2003) 4048.