Berlin 2005 – scientific programme

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HL: Halbleiterphysik

HL 3: Spintronik I

HL 3.9: Talk

Friday, March 4, 2005, 12:45–13:00, TU P164

Hybrid ferromagnet/semiconductor nanostructures on a cleaved (110) InAs surface: spin-valve effect and extraordinary magnetoresistance — •Andreas Wittmann and Dirk Grundler — Institut für Angewandte Physik und Zentrum für Mikrostrukturforschung, Universität Hamburg, Jungiusstrasse 11, D-20355 Hamburg, Germany

We present a novel design for a ferromagnet/semiconductor hybrid transistor. For this, a ferromagnetic film is deposited on a cleaved InAs/InGaAs heterostructure incorporating a two dimensional electron system (2DES). As no Shottky barrier is present we obtain an excellent Ohmic interface contact with a measured resistance close to the Sharvin resistance.

To separate the FM layer on the cleaved edge into a source and a drain electrode we have used a shadow evaporation technique. This allowed us to tailor the separation length down to about 0.2 µm which was shorter than the mean free path in the 2DES. We have performed magnetotransport experiments and observe hysteretic spin–valve–like effects and a large positive magnetorestistance. We attribute the latter to the extraordinary magnetoresistance effect.

Currently we perform experiments on samples which are cleaved in situ right before evaporation. Source and drain are nanostructured by scratching the film with the tip of an atomic force microscope. This results in smaller separation lengths of the contacts. We present our latest results in this direction.

We acknowledge financial support by the DFG and the BMBF.