[en] The ion dynamics in perpendicular nonlinear magnetosonic waves in a plasma containing two ion species is studied through theory and simulation using a one dimension, electromagnetic particle code with full ion and electron dynamics; in the simulations the density of heavier ions was set to be 10% of that of lighter ions. As in a single-ion-species plasma, some of the light ions can be accelerated by the longitudinal electric field formed in a wave. It is found that the bulk of heavy ions are accelerated by the transverse electric field. For a large-amplitude wave, the maximum speed of heavy ions is about the wave propagation speed, which exceeds the Alfven speed. Theoretical estimates of maximum speeds are given for small- and large- amplitude waves. They are in good agreement with the simulation results. (author)