XPCS Study of Antiferromagnetic Domain Fluctuation*

We have studied magnetic domain fluctuations in Yttrium-Dysprosium-Yttrium trilayer films using X-ray Photon Correlation Spectroscopy (XPCS) in conjunction with resonant soft X-ray magnetic scattering. Dysprosium thin film possesses a helical antiferromagnetic phase below Tn = 180 K and a ferromagnetic phase below Tc = 64 K. With coherent soft x-rays we observed magnetic speckle in the scattering from the antiferromagnetic domains. We determined critical points and found a shift of Curie temperature from the bulk value. Hysteresis associated with a first order phase transition was also observed. We observed magnetic speckle around the magnetic satellite peak at (0,0,q$_{m})$ due to static disorder as well as magnetic domains. At temperatures above Tn the system showed static behavior on times scales up to $\sim $ 300 sec which is indicative of non-fluctuating static disorder that persists above Tn. Close to Tc, there appears to be time-dependent fluctuations due to slow domain wall motion and these will be discussed.