Regensburg 2007 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 23: Spin controlled transport II
HL 23.8: Talk
Tuesday, March 27, 2007, 15:45–16:00, H14
Giant anisotropic magnetoresistance in ultrathin (Ga,Mn)As films — •R.R. Gareev, M. Döppe, M. Schlapps, J. Sadowski, M. Sperl, G. Bayreuther, W. Wegscheider, and D. Weiss — 1Institut für Experimentelle und Angewandte Physik, Universität Regensburg, Universitätsstraße 31 D-93040 Regensburg
We report on the giant anisotropic magnetoresistance (GAMR) effect, which we observed in ultrathin (Ga,Mn)As films close to the metal-insulator transition (MIT). We prepared 5nm-thick Ga0.95Mn0.05As films ontop (Al,Ga)As buffer layer followed by subsequent annealing. Finally, for films with optimized carrier-mediated ferromagnetism and a well-defined MIT we obtained the Curie temperature Tc≈90K and hole concentration p≈4*1020cm−3. We studied magneto-transport properties using Hall bars for different orientations of magnetic field H and both longitudinal Rxx and transverse Rxy components of resistance. We found that below MIT (T<20K) both Rxx and Rxy components become comparable. Moreover, both components show enhanced magnetization-regulated magnetoresistance, which we relate to delocalization of carriers dependent on orientations of magnetization and current. In the planar geometry of H both Rxx and Rxy demonstrate reproducible multi-step switching patterns, which are symmetric to the direction of H. In the planar geometry of H the AMR is enhanced and exceeds 100