Stokes anti-Stokes peak intensity interchange across a first-order phase transition

We discuss the interchange of the acoustical peak intensity between the Stokes and the anti-Stokes side of Brillouin light scattering spectra in an asymmetric Fe(20إ)/Cr(20إ)/Fe(20إ)/Cr(9إ)/Fe(100إ) ferromagnetic trilayer which takes place at a critical applied magnetic field H=0.4 kOe. This sudden interchange is due to a first-order magnetic phase transition involving the outermost Fe layer static magnetization. It is shown that this effect is a consequence of a reversal of the sense of precession of dynamic magnetization in the outermost Fe layer.