Carrier-controlled ferromagnetism in diluted magnetic semiconductors (DMS) allows one to explore the physics and possible applications of semiconductor quantum structures in which magnetisation can be manipulated by strain and light as well by electric fields and currents [1].
In the talk, we will first present the current understanding of ferromagnetism in DMS, including the nature of high temperature ferromagnetism observed often in nitrides and oxides [2]. We will argue that in these systems, structures with spatially modulated ferromagnetic order can be obtained either by engineering appropriate layer structures or in a self-organised way. We will then discuss a series of recent experiments that has made it possible to determine both extrinsic and intrinsic domain wall resistance [3] as well as to observe and examine in details the current-induced domain-wall displacement and creep [4]. Mechanisms controlling domain-wall resistance, pinning, and velocity will be specified and compared to theoretical expectations. In particular, theory of domain-wall resistance developed by combining multi-orbital tight-binding approximation and Landauer-Büttiker approach [5] will be presented. Recent application of the theory for the description of experimentally observed large magnitudes of electron current spin polarization in Zener-Esaki diodes and tunnelling magnetoresistace in trilayer structures will also be shown [6].
1. see, T. Dietl and H. Ohno, Materials Today 9 (11) (2006) 18.
2. T. Dietl, Nature Mat. 5 (2006) 673.
3. D. Chiba, M. Yamanouchi, F. Matsukura, T. Dietl, and H. Ohno, Phys. Rev. Lett. 96 (2006) 096602.
4. M. Yamanouchi, D. Chiba, F. Matsukura, T. Dietl, and H. Ohno, Phys. Rev. Lett. 96 (2006) 096601.
5. R. Oszwa³dowski, J. A. Majewski, and T. Dietl, Phys. Rev. B 74 (2006) 153310; cond-mat/0701398.
6. P. Sankowski, P. Kacman, J. A. Majewski, and T. Dietl, Phys. Rev. B 75 (2007) 045306.
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