Postprint version. Published in Hyperfine Interactions, Volume 66, Issue 1-4, November 1, 1991, pages 71-82.
The definitive version is available at https://doi.org/10.1007/BF02395857.
The average blocking temperatures of ferritin molecules containing differing amounts of iron were determined by Mossbauer spectroscopy. The results imply that the magnetic anisotropy of the ferritin core particles is a function of particle volume. By addition of 57Fe to ferritin core particles it was determined that, at a given temperature within the superpara-magnetic temperature region, the “last-in” ferric ions have average relaxation times that are shorter than those of the bulk ferric ions.