Low-frequency low-field magnetic susceptibility of ferritin and hemosiderin

Low-frequency low-field magnetic susceptibility measurements were made on f our samples of mammalian tissue iron oxide deposits. The samples comprised: (1) horse spleen ferritin; (') dugong liver hemosiderin; (3) thalassemic h uman spleen ferritin; and (4) crude thalassemic human spleen hemosiderin. T hese samples were chosen because Mossbauer spectroscopic measurements on th e samples indicated that they exemplified the variation in magnetic and min eral structure found in mammalian tissue iron oxide deposits. The AC-magnet ic susceptometry yielded information on the magnetization kinetics of the f our samples indicating samples 1, 2, and 3 to be superparamagnetic with val ues of around 10(11) s(-1) for the preexponential frequency factor in the N eel-Arrhenius equation and values for characteristic magnetic anisotropy en ergy barriers in the range 250-400 K. Sample 4 was indicated to he paramagn etic at all temperatures above 1.3 K. The AC-magnetic susceptometry data al so indicated a larger magnetic anisotropy energy distribution in the dugong liver sample compared with samples 1 and 3 in agreement with previous Moss bauer spectroscopic data on these samples. At temperatures below 200 K, sam ples 1-3 exhibited Curie-Weiss law behavior, indicating weak particle-parti cle interactions tending to favor antiparallel alignment of the particle ma gnetic moments. These interactions were strongest for the dugong liver hemo siderin. possibly reflecting the smaller separation between mineral particl es in this sample. This is the first magnetic susceptometry study of hemosi derin iron deposits and demonstrates that the AC-magnetic susceptometry tec hnique is a fast and informative method of studying such tissue iron oxide deposits. (C) 2000 Elsevier Science B.V. All rights reserved.