Dataset associated with 'Vogel-Fulcher-Tammann Freezing of a Thermally Fluctuating Arti cial Spin Ice Probed by X-ray Photon Correlation Spectroscopy'

We report on the crossover from the thermal to athermal regime of an arti cial spin ice formed from a square array of magnetic islands whose lateral size, 30 nm 70 nm, is small enough that they are superparamagnetic at room temperature. We used resonant magnetic soft x-ray photon correlation spectroscopy (XPCS) as a method to observe the time-time correlations of the uctuating magnetic con gurations of spin ice during cooling, which are found to slow abruptly as a freezing temperature T0 = 178 5 K is approached. This slowing is well-described by a Vogel-Fulcher-Tammann law, implying that the frozen state is glassy, with the freezing temperature being commensurate with the strength of magnetostatic interaction energies in the array. The activation temperature, TA = 40 10 K, is much less than that expected from a Stoner-Wohlfarth coherent rotation model. Zero- eld-cooled/ eld-cooled magnetometry reveals a freeing up of uctuations of states within islands above this temperature, caused by variation in the local anisotropy axes at the oxidised edges. This Vogel-Fulcher-Tammann behavior implies that the system enters a glassy state on freezing, which is unexpected for a system with a well-defined ground state..