Dispersion Relation in a Ferrofluid Layer of Any Thickness and Viscosity in a Normal Magnetic Field; Asymptotic Regimes B. Abou, G. Néron de Surgy et J.E. Wesfreid J. Phys. II France, 7 8 (1997) 1159-1171 DOI: 10.1051/jp2:1997178