The identification by 57Fe internal field nuclear magnetic resonance of hyperfine

fields at four Fe sites in the (average) tetragonal unit cell of vacancy-ordered γ-

Fe2O3 (maghemite) was reported. The effects of vacancy redistribution due to

annealing the partially vacancy-ordered form was observed in the 57Fe lineshape. In

addition, the reduction of the particle size of the vacancy-ordered form was

observed to gradually eliminate the vacancy ordering and then to cause a transition

from ferrimagnetism to superparamagnetism.

Vacancy Ordering in γ-Fe2O3 Nanocrystals Observed by 57Fe NMR. T.J.Bastow,

A.Trinchi, M.R.Hill, R.Harris, T.H.Muster: Journal of Magnetism and Magnetic

Materials, 2009, 321[17], 2677-81