Effects of competing ferro- and antiferromagnetic interactions in

magnetic semiconductors

Tomasz Dietl

Laboratory for Cryogenic and Spintronic Research, Institute of Physics,

Polish Academy of Sciences, Warszawa, Poland; also Institute of Theoretical Physics, Warsaw University, Poland (dietl@ifpan.edu.pl)

In the recent years a considerable effort has been devoted to understand the nature of hole-controlled ferromagnetism in tetrahedrally coordinated diluted magnetic semiconductors. In these materials conceptual difficulties of charge transfer insulators and strongly correlated disordered metals are combined with intricate properties of heavily doped semiconductors, such as Anderson-Mott localisation and defect creation by self-compensation mechanisms. Moreover, in these disordered magnetic systems, the ferromagnetic portion of the RKKY interaction competes with the antiferromagnetic coupling coming from the RKKY interaction itself as well as from a strong intrinsic superexchange.

In the talk, arguments [1], which indicate why such a competition is much more important in p-type (II,Mn)VI compounds as compared to (III,Mn)V materials systems will be recalled. It will then be argued, based on massive Monte Carlo simulations [2], that this competition accounts for non-standard characteristics of ferromagnetism in modulation-doped p-type (Cd,Mn)Te quantum wells [3], such as the presence of nano-scale magnetic domains. Finally, results of inelastic neutron scattering will be presented [4], which reveal the influence of the holes on the antiferromagnetic coupling between the nearest neighbour Mn pairs in p-(Zn,Mn)Te. It will be shown that the magnitude of the effect provides direct information on the ferromagnetic interactions driven by the carriers at the localisation boundary.

The work was partly supported by AMORE and FENIKS EC projects, by ERATO Semiconductor Spintronics Project of JST, and by Humboldt Foundation.

1. T. Dietl, H. Ohno, and F. Matsukura, Phys. Rev. B 63, 195205 (2001).

2. D. Kechrakos, N. Papanikolaou, K. N. Trohidou, and T. Dietl Phys. Rev. Lett. 94, 127201 (2005).

3. H. Boukari, P. Kossacki, M. Bertolini, J. Cibert, S. Tatarenko, D. Ferrand, A. Wasiela, J.A. Gaj, and T. Dietl, Phys. Rev. Lett. 88, 207204 (2002).

4. H. Kępa, Le Van Khoi, C.M. Brown, M. Sawicki, J.K. Furdyna, T.M. Giebułtowicz, and T. Dietl, Phys. Rev. Lett. 91, 087205 (2003).