1. Institut NÉEL, CNRS & Université Joseph Fourier, BP166, F-38042 Grenoble Cedex 9, France
2. National
Center for Electron
Microscopy, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California 94720, United States
3. SPINTEC, CEA/CNRS/UJF-Grenoble 1/Grenoble-INP, INAC, Grenoble, F-38054,
France