Making SiMn and TiO2 ferromagnetic at room temperature

During the last two decades the enormous efforts were put into the creation, understanding and manipulation of room temperature ferromagnetism (RT FM) in semiconductors. The utilization of spin functionality hand in hand with electrical charge-based electronics opens the wide field of phenomena combining brand-new physics and extensive potential for applications in the next generation logic device and storage. In this talk, recent experimental results on RT FM in Si1-xMnx and Ti1-xCo(V)xO2, the promising materials for hybrid semiconductor spintronics will be reported. Si1-xMnx mosaic (polycrystalline) thin films prepared by pulsed laser deposition exhibit unusual magnetic characteristics - The Curie temperature TC in nonstoichiometric Si1-xMnx alloys (x ~ 0.52-0.55) is one order of magnitude higher (TC ~ 300 K) as compared to stoichiometric MnSi (TC ~ 30 K). The mechanism of the high-temperature FM is still not clear. The FM exchange is associated with the formation of defects with localized magnetic moments coupled via spin fluctuations of itinerant electrons in the host. Also we suppose that structural defects caused, in particular, by small sizes of crystallites have a strong influence on the formation of Si1-xMnx phase with high temperature FM. In case of TiO2, Co and V dopants have been used to create a RT FM dilute magnetic oxide. The study of magnetic, magnetotransport and magneto-optical properties of magnetron sputtered Ti1-xCo(V)xO2–δ (x ∼ 1 at. %) revealed a different mechanism responsible for ferromagnetic response at RT. For Ti1-xVxO2−δ the magnetic properties are determined mainly by structural defects, whereas in Ti1-xCoxO2−δ the magnetic moments of Co play a main role.