Here, we show evidence for superspin glass behavior in long-rangeordered 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 themesoscopic order is.
Source : Do 8nm Co nanocrystals in long range ordered face-centered cubic (fcc) supracrystals show super-spin glass behavior ? Parker, I. Lisiecki, M.P. Pileni J. Phys. Chem. Lett., 2010, 1, 1139–1142.