Exchange and anisotropy effects on spin waves in epitaxial Co films

Using Brillouin scattering we have investigated the effect of large in-plane anisotropy on magnetic excitations in b axis-oriented epitaxial 50-nm Co films. For in-plane fields along the easy axis the magnon frequencies increase monotonically with increasing field. For in-plane fields along the hard axis, nonmonotonic behavior is observed in which the surface to bulk spin-wave character of one magnon mode changes as a function of applied field. Although fits to the data based on a full theoretical treatment are consistent with parameters in the literature and with parameters extracted from the magnetization data, we show that uncertainties in crystal orientation (as small as 1 degrees) can produce dramatic effects in the quantitative data interpretation.