1. Department of Physics, University of Trieste, Via Valerio 2, I-34127 Trieste, Italy
2. Peter Grünberg Institute (PGI-6), Research Centre Jülich, 52425 Jülich, Germany
3. Abdus Salam International Centre for Theoretical Physics, Strada Costiera 11, Trieste I-34151, Italy
4. IOM-CNR Laboratorio TASC, S.S. 14 km 163.5 in AREA Science Park, Basovizza, I-34149 Trieste, Italy
5. Elettra - Sincrotrone Trieste, S.S. 14 km 163.5 in AREA Science
Park, Basovizza, I-34149 Trieste, Italy
6. IOM-CNR Democritos, Trieste I-34151, Italy