| In the first part of this article a review of relevant papers dealing with the magnetic properties of nickel doped titanium dioxide is presented. Each paper is shortly described, including information about sample preparation method, used magnetic detection techniques, and the main results from the investigated materials. A short summary of the reviewed papers is presented and the main ideas relevant to the room temperature ferromagnetism (RTFM) observed in many samples of Ni:TiO2 are discussed and possible mechanisms of RTFM are formulated. In the second part, the investigations of nickel and nitrogen co-modified titanium dioxide nanocomposites, nNi, N-TiO2 (where n = 1, 5, and 10 wt.% of Ni), by dc magnetisation measurements in 2-300K range and in external magnetic field up to H=7 T, are presented. Complex magnetic behavior of the studied nanocomposites has been revealed. The samples showed weak ferromagnetism with Curie temperature above room temperature. No superparamagnetic behavior was registered in the studied temperature range. Comparison of the obtained magnetic parameters (saturation magnetisation, remanent magnetisation and coercive field) of nNi,N-TiO2 with previously studied similar nanocomposites, nFe,N-TiO2 and nCo,N-TiO2, is presented and the conclusions about the nature of their ferromagnetism are drawn. Small value of Ni magnetic moment indicate that RTFM in nNi,N-TiO2 nanocomposites originate mostly from metallic nickel nanoparticles. |
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