[1] Univ Nottingham, Sch Phys & Astron, Nottingham NG7 2RD, England
[2] CNRS, Grenoble High Magnet Field Lab, F-38042 Grenoble, France
[3] Univ Sheffield, Dept Elect & Elect Engn, Sheffield S3 3JD, S Yorkshire, England
[4] Russian Acad Sci, Inst Phys Microstruct, Nizhnii Novgorod 603950, Russia