Cone phase and magnetization fluctuations in Au/Co/Au thin films near the spin-reorientation transition

Using coherent soft x-ray scattering we have measured slow magnetization fluctuations in an Au/Co/Au heterostructure near a thermally driven spin-reorientation phase transition. The intermediate scattering function is well described by a stretched exponential, suggesting cooperative motion through the transition. The decay times were found to exhibit a pronounced maximum as a function of temperature. We argue that the transition proceeds through a cone phase in which the local magnetization evolves continuously from a perpendicular to longitudinal orientation. Our results demonstrate a different and fruitful way to probe the complex spatiotemporal dynamics that arise in unusual magnetic phases with competing anisotropies.