1. Peter Grünberg Institute 9, Forschungszentrum Jülich & JARA Jülich-Aachen Research Alliance, 52425 Jülich, Germany
2. JARA-Institute for Green IT, RWTH Aachen University, 52056 Aachen, Germany
3. Blackett Laboratory, Imperial College London, South Kensington Campus, London SW7 2AZ, UK