B. Swinnen, J. Meersschaut, J. Dekoster, S. Demuynck, S. Cottenier, M. Rots Physica B: Condensed Matter 237-238, 244-2461997A1Published while none of the authors were employed at the CMMDOI http://dx.doi.org/10.1016/S0921-4526(97)00139-7