In the heliosphere large fluctuations of the magnetic field are sometimes observed, especially at shocks (e.g. travelling interplanetary shocks, planetary bow waves, and shocks related to corotating interaction regions). The large fluctuations very often have an amplitude that reaches easily four or five times the magnitude of the quiet magnetic field. Since the plasma mostly contains a non-negligible fraction of heavy ions (e.g. helium ions or cometary water ions), these magnetic field fluctuations are described in terms of three-fluid equations. Here electrons, protons and heavy ions are considered as separate fluids interacting with themselves by electromagnetic forces. The three-fluid equations are treated in such a way that we are searching for one-dimensional stationary waves. Thus the equations are reduced to a fully nonlinear set of ordinary differential equations, which have been evaluated numerically with respect to solitary waves. Subsequently, examples of solitary waves in a electron-proton plasma loaded with 10 % 4He2+ ions are presented. For instance, an enrichment of helium ions is observed within the solitary waves.