Band coupling model of electron and hole mediated ferromagnetism in Semiconductors: The case of GaN

Transition metal (TM) doped diluted magnetic semiconductors (DMSs) have many unique physical properties that can be used for magneto-optical and spintronic applications. The DMSs exhibit a wide range of magnetic ordering behavior. For example, Mn doped GaN can be either ferromagnetic or antiferromagnetic, depending on the Mn concentration, carrier density, or pressure. A unified band coupling model based on the p-d and d-d level repulsions between the TM and host elements are developed to explain the hole-induced ferromagnetism. We show that kinetic s-d coupling can be introduced through chemical ordering and strain, thus leading to electron-mediated ferromagnetism. Moreover, by using rare-earth elements (e.g., Gd) as magnetic dopants, the symmetry-allowed s-f coupling can also lead to a large splitting at the conduction band edge, producing electron-mediated ferromagnetism. Our model, therefore, provides a simple guideline for future band structure engineering of magnetic semiconductors.