Abstract
It is shown that substitution of C or N for O recently proposed as a way to create ferromagnetism in otherwise nonmagnetic oxide insulators is curtailed by formation of impurity pairs, and the resultant C2 spin=1 dimers as well as the isoelectronic N2(2+) interact antiferromagnetically in p-type MgO. For C-doped ZnO, however, we demonstrate using the Heyd-Scuseria-Ernzerhof hybrid functional that a resonance of the spin-polarized C2 ppπ* states with the host conduction band results in a long-range ferromagnetic interaction. Magnetism of open-shell impurity molecules is proposed as a possible route to d(0)-ferromagnetism in oxide spintronic materials.
Highlights
It is shown that substitution of C or N for O recently proposed as a way to create ferromagnetism in otherwise nonmagnetic oxide insulators is curtailed by formation of impurity pairs, and the resultant C2 spin 1⁄4 1 dimers as well as the isoelectronic N22þ interact antiferromagnetically in p-type MgO
Local-density approximation (LDA) calculations predicted that group-II oxides MO (M 1⁄4 Mg, Ca, Sr, Ba) become FM when doped with C or N [4,5]
Our calculations suggest that the d0 magnetism observed in the C-doped ZnO may well be due to a magnetic interaction between these species mediated by conduction band electrons
Summary
It is a FM half-metal (FMHM) as reported in the literature [4,15]. For the Mg32O30C2 supercell with the longest C-C distance, our LDA calculation gives the same FMHM solution (due to the 1=3 filled C-2p down-spin impurity band, not shown here) as reported in the literature [4]. (a) Total and C 2p DOS for two nearestneighbor C impurities in a Mg32O30C2 supercell It is an insulator with a molecular spin 1⁄4 1. (We note that this value would be somewhat reduced if in the calculations the true band gap rather than the smaller LDA gap and a larger supercell were used) Such an AFM coupling was found in the molecular magnets SrN [21] and Rb4O6 [23].
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