Affiliation: | (1) Facultad de Fisica, Pontificia Universidad Catolica de Chile, V. Mackenna 4860, Macul, Casilla 306, 6904411, Santiago 22, Chile;(2) Laboratorium voor Vaste-Stoffysica en Magnetisme, K.U. Leuven, Celestijnenlaan 200 D, 3001 Leuven, Belgium;(3) Present address: K.U. Leuven, Celestijnenlaan 200 D, 3001 Leuven, Belgium;(4) Present address: Physics Department, West Virginia University, Hodges Hall, Box 6315, Morgantown, WV 26506, USA |