The recent discovery of magnetism in a variety of diverse non-magnetic materials containing defects has challenged conventional thinking about the microscopic origin of magnetism in general. Especially intriguing is the complete absence of d electrons that are traditionally associated with magnetism. By a systematic microscopic investigation of two completely dissimilar materials (namely, ZnO and rhombohedral-C_(60) polymers) exhibiting ferromagnetism in the presence of defects, we show that this new phenomenon has a common origin and the mechanism responsible can be used as a powerful tool for inducing and tailoring magnetic features in systems which are not magnetic otherwise. Based on our findings, we propose a general recipe for developing ferromagnetism in new materials of great technological interest. The recipe is quite general, although its realization is system specific. In each case, the required basic step is to find two synergistic codopants, one for providing the unpaired electrons and the other for facilitating the ferromagnetic coupling.
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