Defect-induced magnetism in oxides

The so called ``d$^0$ magnets'' are a class of materials which, lacking any magnetic ions with open $d$ or $f$ shells, should in principle not be magnetic, but nevertheless exhibit signatures of room temperature ferromagnetism. The most widely studied class of d$^0$ magnets is that of medium to wide gap oxides. Since ferromagnetism is generally observed in highly defective samples, it is expected that the magnetism must be somehow defect-related. However, at the present, there is no clear explanation of the experimental observations. We then present the results of a detailed research which combines Density Functional Theory (DFT) with model Hamiltonian calculations. In particular we consider whether ferromagnetism might be due to carrier-mediated long-range coupling between magnetic moments residing on cation vacancies or to a Stoner-like splitting of an impurity band in defect-rich regions of the samples.