Superparamagnetic maghemite

Moskowitz BM, Frankel RB, Walton SA, Dickson DPE, Wong KKW, Douglas T, Mann S (1997) Determination of the preexponential frequency factor for superparamagnetic maghemite particles in magneto-ferritin. J Geophys Res 102 22671-22680... 

Superparamagnetic maghemite (Fe2C>3) NPs were generated in situ in the core of the PAA-b-PnBA core-shell brushes [31, 161] as described in Scheme 12. The carboxylate groups coordinate with Fe3+ ions and form the polychelate. AFM and TEM measurements show distinct pearl-necklace conformations for the polychelates of the brushes with Fe3+. After the alkalization and oxidation reaction small maghemite NPs formed within the core of the brushes distributed in a wire-like manner and the brushes returned to the extended worm-like morphologies. 

S. Momet, J. Portier, E. Duguet, A method for synthesis and functionalization of ultra small superparamagnetic covalent carriers based on maghemite and dextran, J. Magn. Magn. Mater 2005, 93, 127-134. 

Al substitution is commonly found in soil-related maghemite. The spectra are somewhat similar to that of Al-free maghemite, but the sextet is often accompanied by a doublet (Fig. 3.16), the contribution of which decreases at lower temperatures. This typical superparamagnetic behavior is a consequence of a combined effect of particle size and diamagnetic substitution [125, 126]. 

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