Dresden 2011 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 37: Magnetic Semiconductors II

MA 37.7: Vortrag

Mittwoch, 16. März 2011, 16:15–16:30, HSZ 401

F-centres and ferromagnetism in oxides — •Aurab Chakabarty and Charles Patterson — School of Physics, Trinity College Dublin, Dublin 2, Ireland

We present Hybrid and LDA calculations to explain the ferromagnetism (FM) observed in oxide thin films[1]. A model is proposed where FM can occur in oxides with F-centre defects when defect levels are partially filled and can be described by a single band Hubbard model. The model predicts room-temperature FM in large Hubbard-U limit[2]. We show that positively charged oxygen vacancy is metastable[3], but in oxygen poor and n-type conditions, oxygen and zinc vacancies are strongly bound together to form a ZnO divacancy, which is an F-centre with a Hubbard-U large enough to support ferromagnetism at room temperature. The Hubbard-U value is estimated from defect transition levels and from total energy calculations on divacancy pairs with parallel and anti-parallel magnetic moments. This model may also explain ferromagnetism in other nonmagnetic oxides such as MgO, as the MgO divacancy is an F-centre [4] with a large U.

References:

1. J.M.D. Coey et al, nat. mater. 4, 173 (2005)

2. J. A. Henderson et al, Phys. Rev. B. 46, 6328 (1992)

3. C. H. Patterson, Phys Rev. B, 74, 144432 (2006)

4. D. Ricci et al, J. Chem. Phys, 117, 2844 (2002)