Light-Induced Magnetic Precession in (Ga,Mn)As Slabs: Hybrid Standing-Wave Damon-Eshbach Modes

Coherent oscillations associated with spin precessions were observed in ultrafast optical experiments on ferromagnetic (Ga,Mn)As films. Using a complete theoretical description of the processes by which light couples to the magnetization, values for the exchange and anisotropy constants were obtained from the field-dependence of the magnon frequencies and the oscillation-amplitude ratios. Results reveal a relatively large negative contribution to the energy due to surface anisotropy leading to excitations that are a mixture of bulk waves and surface modes.