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Theory of exchange splittings of bands in diluted magnetic semiconductors

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Giant magneto-optical and magneto-transport effects specific to diluted magnetic semiconductors as well as carrier-mediated ferromagnetism in these systems are known to originate from the presence of a sizable spin-dependent coupling between effective mass carriers and electrons localised on the open d shells of transition metal impurities. A series of recent photoemission and magneto-optical experiments, particularly on magnetically doped nitrides and oxides, but also on (Ga,Mn)As, points to our limiting understanding of the physics governing the sp-d exchange interactions in diluted magnetic semiconductors.

I will present a revisited theory of magneto-optical effects in diluted magnetic semiconductors1 and show that it explains the unexpected antiferromagnetic sign of the apparent s-d exchange coupling found for photoelectrons in (Ga,Mn)As2 and the apparent ferromagnetic p-d exchange interaction reveled by magnetooptical studies for (Zn,Co)O, (Ga,Mn)N, and (Ga,Fe)N3 as well as, a long time ago, for (Ga,Mn)As on the insulator side of the metal-to-insulator transition4.

These findings have important consequences on ferromagnetism in these systems and help to understand the evolution of the Curie temperature on going from arsenides to phosphides and to nitrides containing a few percent of randomly distributed Mn ions.

1 C. Śliwa, T. Dietl, Phys. Rev. B 78, 165205 (2008); T. Dietl, Phys. Rev. B 77, 085208 (2008).

2 R. C. Myers et al., Phys. Rev. Lett. 95, 017204 (2005); M. Poggio et al., Phys. Rev. B 72, 235313 (2005); N. P. Stern et al., Phys. Rev. B 75, 045329 (2007).

3 W. Pacuski et al., Phys. Rev. B 73, 035214 (2006); ibid. 76, 165304 (2007); Phys. Rev. Lett. 100, 037204 (2008).

4 J. Szczytko et al., Solid State Commun. 99, 927 (1996).

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