Dual Manipulation of Ferromagnetism in Co-Doped ZnO Thin Films by Surfactant and n-Type Carriers

We present a conceptually-new approach “dual manipulation effect” using the surfactant passivation and the electron carrier doping for mediating intrinsic ferromagnetism in Codoped ZnO dilute magnetic semiconductor (DMS) thin films. The first-principles calculations show that the surface passivation by hydrogen serves as a magnetism switch for the Co-O-Co magnetic coupling at the surface of the thin film, and thus can control the spin polarization of the doped Co atoms. Meanwhile, the electron carrier doping can further function as an effective layerlike ferromagnetism mediator for the underneath layer. The dual manipulation effect sheds light on the essential magnetism origin of n-type Co:ZnO DMS thin films, and may be used as an alternative strategy for enhancing the ferromagnetism in other n-type DMS oxides thin films.