B. Swinnen, J. Dekoster, J. Meersschaut, S. Cottenier, S. Demuynck, G. Langouche, M. Rots Applied Physics Letters 70 (24), 33021997A1Published while none of the authors were employed at the CMMDOI http://link.aip.org/link/doi/10.1063/1.119144