  The nonreciprocal propagation of spin waves in an ultrathin Pt/Co/Ni film has
been measured by Brillouin light scattering. The frequency nonreciprocity, due
to the interfacial Dzyaloshinskii-Moriya interaction (DMI), has a sinusoidal
dependence on the in-plane angle between the magnon wavevector and the applied
magnetic field. The results, which are in good agreement with analytical
predictions reported earlier, yield a value of the DMI constant which is the
same as that obtained previously from a study of the magnon dispersion
relations. We have demonstrated that our magnon-dynamics based method can
experimentally ascertain the DMI constant of multilayer thin films.
