1. Peter Gruenberg Institute 9 (PGI-9) and JARA-Fundamentals of Future Information Technologies, Forschungszentrum Juelich, Juelich 52428, Germany
2. Dipartimento di Fisica, Università di Pisa, Largo Bruno Pontecorvo 3, Pisa 56127, Italy
3. IHP - Leibniz Institut für innovative Mikroelektronik, Frankfurt (Oder) 15236, Germany
4. CNR − ISMN, Via P. Gobetti 101, Bologna 40129, Italy
5. Pollard Institute, School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom
6. Dipartimento di Scienze, Università degli Studi Roma Tre, Viale G. Marconi 446, Roma 00146, Italy