Magnetic semiconductors are attracting great interest because of their potential use for spintronics, a new technology that merges electronics with the manipulation of conduction electron spins. (GaMn)As and (GaMn)N have recently emerged as the most popular materials for this new technology, and although their Curie temperatures are rising toward room temperature, these materials can only be fabricated in thin film form, are heavily defective, and are not obviously compatible with Si. In this talk I will show that it is productive to consider transition metal monosilicides as potential alternatives. In particular I will concentrate on the bulk metallic magnets derived from doping the narrow gap insulator FeSi with Co. We have discovered several interesting and important differences in the magneto-conductivity, optical conductivity, and anomalous Hall effect of these materials with Mn doped II-V and II-VI semiconductors due to disorder and preponderance of d-electron character of bands close to the Fermi level.
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