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.