Evidence of oxygen ferromagnetism in ZnO based materials

Discoveries of room-temperature ferromagnetism (RTFM) in semiconductors hold great promise in future spintronics technologies. Unfortunately, this ferromagnetism remains poorly understood and the debate concerning the nature, carrier-mediated versus defect-mediated, of this ferromagnetism in semiconducting oxides is still open. Here, by using X-ray absorption (XAS) and X-ray magnetic circular dichroism (XMCD), it is demonstrated that the oxygen ions have a ferromagnetic response in different ZnO-based compounds showing RTFM behavior: ZnO nanoparticles capped with organic molecules and ZnO/ZnS heterostructures. These results demonstrate the intrinsic occurrence of RTFM in these systems, and point out that it is not related to the metallic cation but it relays on the conduction band of the semiconductor.This work was partially supported by Spanish MAT2011–27573-C04–04, MAT2010–16022, CSD2009–00013, MAT2011–27470-C02–02, MAT2010– 09346-E, the Madrid Government project NANOBIOMAGNET S2009/MAT-1726, and by the Aragón DGA NETOSHIMA grant. The synchrotron radiation experiments were performed at SPring-8 (Proposal Numbers: 2011B3873, 2011B1700 and 2011B0024) and at APS (Proposal No. GUP-10283). Use of the Advanced Photon Source was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02–06CH11357. The authors acknowledge to J. Freeland for his assistance during the SR experiments at APS. C.G. acknowledges the Ministerio de Educación y Ciencia of Spain for a PhD. Grant. M.A.L.-M. acknowledges to CSIC for a JAE-Doc contract within the Junta para la Ampliación de Estudios program. N.C. acknowledges the financial support of the FSE-MEC, Ramón y Cajal program (ref. RYC-2007–01715). E.C. acknowledges the Ministerio de Educación of Spain for a postdoctoral grant in foreign research centres.Peer reviewe