Do 8 nm Co Nanocrystals in Long-Range-Ordered Face-Centered Cubic (fcc) Supracrystals Show Superspin Glass Behavior?

Here, we show evidence for superspin glass behavior in long-range-ordered face-centered cubic (fcc) supracrystals of 8 nm Co nanocrystals as has been well-demonstrated for disordered 3D assemblies. The dynamic behavior shows a critical slowing down, and the characteristic relaxation time is found to diverge to a finite static glass temperature. The collective nature of the glass state is supported by the existence of a memory effect. We conclude that, in the case of magnetic nanocrystal assemblies where the individual nanocrystal anisotropy is low, superspin glass behavior is observed whatever the mesoscopic order is.