Magnetic domains and other forms of quasistatic spontaneous disorder drive nonergodic behaviors that can lead to unusual material properties. We examine these behaviors near a spin spiral stripe melting transition in an amorphous FeGe thin film using coherent resonant soft x-ray scattering. We find that the system is ergodic very close to the transition, as reflected by a nearly Gaussian distribution of fluctuations. At slightly lower temperature the distribution is skewed, implying nonergodicity. The distributions can be resolved into two distinct components reflecting two different kinds of fluctuating spin structures, one at a shorter and one at a longer length scale. Our results delineate an approach to evaluate the statistics of fluctuations in many classes of nanoscale heterogeneous materials.

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• Dynamical phase transitions
• Magnetic phase transitions
• Magnetic thin films
• Noncollinear magnets
• X-ray photon correlation spectroscopy
• X-ray scattering
• X-ray techniques