The authors acknowledge Y. Nagamine, H. Maehara and K. Tsunekawa of CANON ANELVA for preparing the MTJ films. Financial support by the CNRS and the ANR agency (NANOMASER PNANO-06-067-04, ALICANTE PNANO-06-064-03, VOICE PNANO-09- P231-36) and EU grant MASTER No. NMP-FP7-212257 is acknowledged. B. G. is sup- ported by a PhD grant from the DGA. 

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