  Interdigitated transducers were used to generate and detect surface acoustic
waves on a thin layer of (Ga,Mn)(As,P). The out-of-plane uniaxial magnetic
anisotropy of this dilute magnetic semiconductor is very sensitive to the
strain of the layer, making it an ideal test material for the dynamic control
of magnetization via magneto-striction. The time-domain measurement of the
amplitude and phase of the transmitted SAW during magnetic field sweeps
indicated a clear resonant behavior at a field close to the one calculated to
give a precession frequency equal to the SAW frequency. A resonance was
observed from 5K to 85K, just below the Curie temperature of the layer. A full
analytical treatment of the coupled magnetization/acoustic dynamics showed that
the magneto-strictive coupling modifies the elastic constants of the material
and accordingly the wave-vector solution to the elastic wave equation. The
shape and position of the resonance were well reproduced by the calculations,
in particular the fact that velocity (phase) variations resonated at lower
fields than the acoustic attenuation variations.
