  The utility of nanoscaled ferromagnetic particles requires both stabilized
moments and maximized switching speeds. During reversal, the spatial modulation
of the nanoparticle magnetization evolves in time, and the energy differences
between each new configuration are accomodated by the absorption or emission
spin waves with different wavelengths and energy profiles. The switching speed
is limited by how quickly this spin wave energy is dissipated. We present here
the first observation of dispersing spin waves in a nanoscaled system, using
neutron scattering to detect spin waves in the CoO shells of exchange biased Co
core- CoO shell nanoparticles. Their dispersion is little affected by finite
size effects, but the spectral weight shifts to energies and wave vectors which
increase with decreasing system size. Core-shell coupling leads to a
substantial enhancement of the CoO spin wave population above its conventional
thermal level, suggesting a new mechanism for dissipating core switching
energy.
