Double resonance mechanism of ferromagnetism and magnetotransport in (Ga-Mn)As

We calculate the electronic states of the Mn-doped semiconductors and show that resonant states are formed at the top of the down spin valence band du e to magnetic impurities and that they give rise to a strong and long-range d ferromagnetic coupling between Mn moments. We propose that the coupling o f the resonant states, in addition to the intra-atomic exchange interaction between the resonant and nonbonding states, is the origin of the ferromagn etism of (Ga-Mn)As. The mechanism is thus called "double resonance." The re sonant states bring about the spin-dependent resistivity to produce magneto resistive properties in (Ga-Mn)As and their junctions.