[1] Univ Cambridge, Dept Mat Sci & Met, 27 Charles Babbage Rd, Cambridge CB3 0FS, England
[2] Max Planck Inst Eisenforsch GmbH, Dept Microstruct Phys & Alloy Design, Max Planck Str 1, D-40237 Dusseldorf, Germany
[3] Leibniz Inst Hochstfrequenztech, Ferdinand Braun Inst, Gustav Kirchhoff Str 4, D-12489 Berlin, Germany
[4] Univ Ulster, Nanotechnol & Integrated Bioengn Ctr, Newtownabbey BT37 0QB, North Ireland
[5] CNRS, Lab Photon & Nanostruct, Route Nozay, F-91460 Marcoussis, France