Silicide Nanowires from Coordination Compound Precursors

In the last two decades there has been a great interest in the synthesis and characterization of one-dimensional materials. A variety of inorganic materials have been prepared in the form of nanowires and nanobelts with a diameter of a few nanometer and lengths going up to several hundreds of microns (Xia et al., 2003). The two main techniques used for nanowire growth are vapor-assisted (Wagner, 1964) and solution-based growth (Stejny, 1981; Stejny, 1979; Kruyt & Arkel, 1923; Gates et al., 2002; Mayers & Xia, 2002; Messer et al., 2000; Song et al., 2001) processes. Nanowires, nanorods and nanobelts constitute an important class of 1D nanostructures, which provide models to study the relationship between electrical transport, optical, magnetic and combined properties such as electro-optic and magneto-electronic properties with dimensionality and size confinement. In recent decades strong interest has been drawn to explore silicides (Murarka, 1983; Miglio & d’Heurle, 2000), which are chemical compounds of silicon with different metals. Considerable amount of studies are carried out on transition metal silicides such as CoSi2, NiSi, MnSi, CrSi2, FeSi (Maex & Rossum, 1995). The magnetic properties of MnSi and FeSi are studied extensively. MnSi has a helical spin structure at low fields below 29 K and it is paramagnetic above that temperature (Ishikawa et al., 1976; Belitz, 1999). CrSi and NiSi are either weakly paramagnetic or diamagnetic. The transition-metal monosilicides such as MnSi, CoSi and FeSi are a group of highly correlated electron materials (Aeppli & DiTusa, 1999; Riseborough, 2000). In the case of MnSi, application of external magnetic fields results in field-induced phase transitions from the helimagnetic phase to a conical spin structure at low fields and then to a ferromagnetic state at higher magnetic fields (Ishikawa et al., 1976; Belitz, 1999). The temperature dependence of high field magnetization of field-induced ferromagnetic states of MnSi shows signatures indicating the role of both spin wave excitations and stoner band excitations related to itinerant electron ferromagnetism (Aeppli & DiTusa, 1999). In another manganese-based silicide, Mn5Si3, the magnetic structure has been studied for many years (Lander et al., 1967; Brown & Forsyth, 1995; Silva et al., 2002). Mn5Si3 shows two different antiferromagnetic configurations with a low temperature highly non-collinear phase (Lander et al., 1967; Brown & Forsyth, 1995; Silva et al., 2002). It was previously reported that antiferromagnetic Mn5Si3 can be driven into a ferromagnetic or ferrimagnetic state by insertion of carbon into the voids of Mn octahedra of the hexagonal structure (Senateur, 1967). Thin films of Mn5Si3Cx with x = 0.8 have a Curie temperature TC = 350 K (Surgers, 2003) well above room temperature. FeSi is a Kondo insulator (Aeppli &