Spin-fluctuation mediated high-temperature ferromagnetism in Si:Mn dilute magnetic semiconductors

We discuss a possible route to explain high-temperature ferromagnetism in Si:Mn dilute magnetic semiconductors. We argue that most Mn atoms are segregated within nanometer-sized regions of magnetic precipitate and form the alloy, or compound, MnSi 2 -z with z ≈ (0.25 $\div$ 0.30), whereas a small minority of Mn atoms forms Ångström-sized magnetic defects embedded in the host. Assuming that MnSi 2 -z is a weak itinerant ferromagnet which supports sizable spin fluctuations (paramagnons) far above the intrinsic Curie temperature, we show that the Stoner enhancement of the exchange interaction between the local magnetic moments of the defects occurs. As a result, a significant increase of the temperature of global ferromagnetic order in the system is achieved. We develop a phenomenological approach, to qualitatively describe this effect. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2010

Si-Based Magnetic Semiconductors

The efforts over the past decade to identify and characterize magnetic semiconducting systems that would be compatible with present-day silicon technologies are reviewed. Investigations that have explored transition metal doping of the group IV semiconductors silicon and germanium are discussed along with intermetallic compounds such as silicides and germanides that may play the role of a magnetic semiconducting source of polarized electrons. Thin films and nanostructures of these materials have been grown by a number of synthesis techniques, and the resulting structural properties, including the important issue of homogeneity of dopants, are critically surveyed. The resulting magnetic and carrier transport properties are also reviewed