Large enhancement of elastic light scattering due to random fluctuations of the magnetization

We have observed the field dependence and enhancement of the intensity of polarized elastic light scattering, from ultrathin magnetic films with perpendicular magnetic anisotropy (PMA). High-resolution Brillouin spectroscopy elucidates that this enhancement reaches its maximum at a critical field (H_crit) where the magnetization starts to incline toward out-of-plane due to the strong PMA. We attribute this new effect to the microscopic instability due to random fluctuations of the magnetization near H_crit, since this elastic scattering has no frequency shift from the excitation light and thus the correlation of each spin decays monotonically. The enhancement factor depends on the PMA strength as well as the film thickness, and we obtain an enhancement as large as a factor of 20 at room temperature with a low external field of 0.18 kOe.