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

Low-frequency low-field magnetic susceptibility measurements were made on four samples of mammalian tissue iron oxide deposits. The samples comprised: (1) horse spleen ferritin; (2) dugong liver hemosiderin; (3) thalassemic human spleen ferritin; and (4) crude thalassemic human spleen hemosiderin. These samples were chosen because Mössbauer spectroscopic measurements on the samples indicated that they exemplified the variation in magnetic and mineral structure found in mammalian tissue iron oxide deposits. The AC-magnetic susceptometry yielded information on the magnetization kinetics of the four samples indicating samples 1, 2, and 3 to be superparamagnetic with values of around 10(11) s(-1) for the pre-exponential frequency factor in the Néel-Arrhenius equation and values for characteristic magnetic anisotropy energy barriers in the range 250-400 K. Sample 4 was indicated to be paramagnetic at all temperatures above 1.3 K. The AC-magnetic susceptometry data also indicated a larger magnetic anisotropy energy distribution in the dugong liver sample compared with samples 1 and 3 in agreement with previous Mössbauer spectroscopic data on these samples. At temperatures below 200 K, samples 1-3 exhibited Curie-Weiss law behavior, indicating weak particle-particle interactions tending to favor antiparallel alignment of the particle magnetic moments. These interactions were strongest for the dugong liver hemosiderin, possibly reflecting the smaller separation between mineral particles in this sample. This is the first magnetic susceptometry study of hemosiderin iron deposits and demonstrates that the AC-magnetic susceptometry technique is a fast and informative method of studying such tissue iron oxide deposits.