Spontaneous Domain Wall Fluctuation in Artificial Square Spin Ice Studied with Soft X-Ray Photon Correlation Spectroscopy*

Artificial spin ice (ASI) systems, initially introduced to model spin ice systems in nature, are 2D array of frustrated dipolar-coupled nanomagnets. We performed soft x-ray photon correlation spectroscopy (XPCS) on the antiferromagnetic Bragg peak of thermally active square ASI and studied its domain wall dynamics as functions of temperature. Our result shows seconds-to-milliseconds timescale nucleation and annihilation of a single domain wall in the region under-study. We calculated the respective autocorrelation functions of domain fluctuation, whose characteristic curvatures indicates the distinct fluctuation time scale of the ASI systems that are coupled through dipole interaction.