[1] Stanford Univ, Dept Appl Phys, Stanford, CA 94305 USA
[2] IBM Corp, Thomas J Watson Res Ctr, Yorktown Hts, NY 10598 USA
[3] Univ British Columbia, Dept Phys & Astron, Vancouver, BC V6T 1Z1, Canada
[4] Argonne Natl Lab, Div Chem & Mat Sci, Argonne, IL 60439 USA
[5] ISMRA Univ Caen, CRISMAT, F-14050 Caen, France
[6] Univ Tokyo, Inst Solid State Phys, Minato Ku, Tokyo 106, Japan