1. Department of Materials Physics, GFMC, Universidad Complutense de Madrid, Fac. CC. Físicas, 28040 Madrid, Spain
2. Institute of Sensor and Actuator Systems, TU Wien, Gusshausstrasse 27-29, 1040 Vienna, Austria
3. Hahn-Schickard, Wilhelm-Schickard-Str. 10, 78052 Villingen-Schwenningen, Germany