Oscillatory domain wall motion in a single-crystal ultrathin Au/Co/Au system

We have used x-ray photon correlation spectroscopy together with resonance soft x-ray scattering to measure domain dynamics in a Au/Co/Au system that exhibits a spin reorientation phase transition (SRT) in the temperature range of 200-300 K. The incoming photon energy was tuned at the Co L$_{3}$ edge and the coherence is established with a $\sim$10 um pinhole. The resultant speckle pattern is measured with a CCD camera in time as a function of temperature 200 K to 300 K. The correlation coefficient, which is an indicator of domain wall dynamics, shows damped oscillatory behavior in time. The period of the oscillations is approximately 120 sec. The frequency and damping constant were found to depend on the length-scale and temperature changes through the phase transition. Our results show that the SRT dynamics on a mesoscopic length scale and slow time scale can be surprisingly complex.