B. Swinnen, J. Dekoster, J. Meersschaut, S. Demuynck, S. Cottenier, G. Langouche, M. Rots Journal of Applied Physics 81 (8), 43431997A1Published while none of the authors were employed at the CMMDOI http://link.aip.org/link/doi/10.1063/1.364763