Diluted Magnetic Semiconductors. Above Room Temperature Ferromagnetism in Si:Mn and TiO(2-x):Co
CIC nanoGUNE Seminars
- Speaker
-
Alexander Granovsky, Magnetism Department, Moscow State University, Moscow, Russia
- When
-
2010/03/02
12:00 - Place
- nanoGUNE seminar room, Tolosa Hiribidea 76, Donostia - San Sebastian
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Abstract:
We present recent experimental results on the structural, electrical and
magnetic properties of Mn-implanted Si. and Co-doped TiO2 magnetic oxides.
Si wafers, both n- and p-type, with high and low resistivity, were used as the
starting materials for implantation with Mn ions at the fluencies up to 5 x
1016 cm-2. After implantation and vacuum annealing at 850C, the materials were
investigated with SIMS, SRP, TEM, XRD, XAS, XMCD, VSM, SQUID and magneto-
optical techniques. The saturation magnetization was found to
show the lack of any regular dependence on the Si conductivity type, type of
impurity and the short post- implantation annealing.
According to XMCD Mn impurity in Si does not bear any appreciable magnetic
moment at room temperature. The obtained results indicate that above room
temperature ferromagnetism in Mn-implanted Si originates not from Mn impurity
but rather from structural defects in Si .
The TiO(2-x): Co thin films were deposited on LaAlO3 (001) substrates by
magnetron sputtering in the argon–oxygen atmosphere at oxygen partial
pressure of 2.10-6-2.10-4 Torr. It was obtained that Transversal Kerr Effect
(TKE) spectra in ferromagnetic samples are extremely sensitive to the Co
volume fraction, the crystalline structure, and technology parameters. The
observed well-pronounced peaks in TKE spectra for anatase Co-doped TiO(2-x)
films at low Co (<1%) volume fraction are not representative for bulk Co or Co
clusters in TiO(2-x) matrix that indicates on intrinsic ferromagnetism in
these samples. With increase of Co volume
fraction up to 5-8% the fine structure of TKE spectra disappears and the
magneto-optical response in reflection mode becomes larger than that for thick
Co films. Moreover, the TKE increases further in the case of the films
fabricated onto SrTiO3 substrates.
We discuss possible mechanisms of ferromagnetic order at room temperature in
magnetic oxides based on TiO(2-x) and in ferromagnetic semiconductors based on
Si, as well as perspectives of applications of these novel materials in
spintronics and magnetophotonics.