Magnetism of Dilute Oxides

Reports of Curie temperatures well above room temperature for wide-bandgap oxides doped with a few percent of transitionmetal cations have triggered intense interest in these materials as potential magnetic semiconductors. že origin of the magnetism is debated; in some systems, the ferromagnetism can be attributed to nanoparticles of a ferromagnetic secondary phase, but in others, properties are found that are incompatible with any secondary phase, and an intrinsic origin related to structural defects is implicated. že magnetic interactions in these materials are qualitatively di¥erent from those in magnetically concentrated compounds, and the standard "m-J paradigm" of localized magnetism seems unable to explain their behavior. In this chapter, we ¢rst summarize the established view of magnetism in the oxides before reviewing data on a selection of the most widely studied materials; then we consider the physical models that have been advanced to explain the magnetism, and raise issues that still have to be addressed. As noted in Chapter 19, some of the concepts also apply to wide-gap III-V compounds.