Umbrella Structure in Pr, Nd and Yb Substituted YIG Studied by 57Fe NMR J. Englich, J. Kohout, H. Stepánková, P. Novák, M. Nekvasil and H. Lütgemeier J. Phys. IV France, 07 C1 (1997) C1-295-C1-296 DOI: 10.1051/jp4:19971117