Practical rules for orbital-controlled ferromagnetism of 3d impurities in semiconductors

We distill from first-principles spin-polarized total-energy calculations some practical rules for predicting the magnetic state (ferromagnetic/antiferromagnetic/paramagnetic) of substitutional transition-metal impurity with different charge state in various host crystal groups IV, III-V, II-VI, I-III-VI2, and II-IV-V2 semiconductors. The basic mechanism is the stabilization of a ferromagnetic bond between two transition metals if the interacting orbitals are partially-occupied. These rules are then subjected to quantitative tests, which substantiate the mechanism of ferromagnetism in these systems. We discuss cases where current electronic structure calculations agree with these rules, and identify a few cases where conflicts exist. The effect of doping on transition-metal magnetic properties is also covered by these rules by considering the oxidation state changes due to doping. In addition, we systematically apply these rules to ideal substitutional impurities, contrasting our predictions with experiment. Discrepancies may be used to assess the role of various nonidealities such as presence of additional dopants, precipitates, clusters, or interstitial sites