The electronic structure of the Co-doped indium tin oxide (ITO) diluted magnetic semiconductors (DMSs) were investigated theoretically from first principles, using the fully relativistic Dirac linear muffin-tin orbital band structure method. The X-ray absorption spectra (XAS) and X-ray magnetic circular dichroism (XMCD) spectra at the Co , In , Sn , and O edges were investigated theoretically from first principles. The origin of the XMCD spectra in these compounds was examined. The calculated results are compared with available experimental data. 1. Introduction Spintronics or spin-transport electronics has attracted much of attention due to its technologically potential applications. Dilute magnetic semiconductors (DMS), obtained by doping a host semiconductor with magnetic impurities, can be used for spintronic devices [1]. In DMS, apart from electron degree of freedom, one uses the spin degree of freedom which can lead to new class of devices and circuits. The starting materials, which were expected to be the promising candidates for spintronics, are Group III–V materials, such as (Ga, Mn)As [2, 3] with the Curie temperature of ~110？K [4]. Recently Chen et al. [5] reported the Curie temperature as high as 200？K in nanostructures of (Ga, Mn)As. Other candidates, which can show this property, are transition metal doped Group III nitrides, phosphides, and semiconducting oxides. Dietl et al. [6] predicted theoretically a Curie temperature higher than room temperature for transition element doped semiconducting materials, such as GaN and ZnO. After the report of ？K in ( )O [7], there have been many reports on ZnO-based DMSs showing high [8]. Both theoretical and experimental studies suggested that wide bandgap oxide semiconductors with high-carrier density are one of the most favorable host compounds for ferromagnetic DMS with higher Curie temperature [9–12]. Compared to nonoxide semiconductors, the advantages of oxide semiconductors are (1) wide bandgap suited for applications with short wavelength light, (2) transparency and dyeability with pigments, (3) high n-type carrier concentration, (4) capability to be grown at low temperature even on plastic substrate, (5) ecological safety and durability, (6) low cost, and so forth. In addition, large electronegativity of oxygen is expected to produce strong exchange coupling between band carriers and localized spins. Such advantages make oxide semiconductors attractive. Actually, many studies on oxide-based DMS have been reported [13], where most of the research employed ZnO and TiO2 as host semiconductors. To
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