Anomalous Moessbauer fraction in superparamagnetic systems

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1992

OSTI ID:7233108

Mohie-Eldin, M E.Y.

The biological molecule ferritin and its proven synthetic counterpart polysaccharide iron complex (P.I.C.) have been shown to contain small (<100[degrees] in diameter) antiferromagnetic cores at their centers. Moessbauer studies of these molecules have revealed an anomalous drop in the Moessbauer fraction (f-factor) as the temperature rises above 30[degrees]K for mammalian ferritin and 60[degrees]K for P.I.C. Above the blocking temperature, superparamagnetic relaxation results in the disappearance of hyperfine splitting. This thesis investigates and attempts to resolve this Lamb-Moessbauer f-Factor anomaly in these superparamagnetically relaxing systems. The long range order technique of magnetization measurements is used to compare magnetic properties of both molecules and to verify the suggestion that the P.I.C. molecule is a good biomimic to ferritin based on the identification of ferrihydrite as the major mineral in both, by short range probing techniques such as X-ray diffraction. The anomaly is confirmed in P.I.C.'s Moessbauer spectra. Different absorbers are used to experimentally investigate the absorber thickness effect on the Moessbauer spectra. The anomaly persists for thin absorbers. Data that is treated with FFT procedures to eliminate the thickness effect still exhibit this anomaly. The authors then investigated the effect of superparamagnetic relaxation on the f-factor. Spin-lattice relaxation was excluded based upon a calculation of the rate of energy transfer from the spin system to the lattice. The authors introduce a theory as a plausible explanation of the anomaly: Superparamagnetic relaxation brings about a dynamical displacement of the Moessbauer nucleus through magnetostriction. These displacements produce a Doppler broadening of the Moessbauer spectrum that reduces the apparent f-factor. The temperature dependence of the theoretically calculated f-factor agrees qualitatively with experiment.

• Research Organization: Tufts Univ., Medford, MA (United States)
• OSTI ID: 7233108
• Country of Publication: United States
• Language: English

Related Subjects

664000* -- Atomic &amp; Molecular Physics-- (1992-)
74 ATOMIC AND MOLECULAR PHYSICS
CARBOHYDRATES
COMPLEXES
FERRITIN
IRON COMPLEXES
MAGNETISM
METALLOPROTEINS
MOESSBAUER EFFECT
ORGANIC COMPOUNDS
ORGANOMETALLIC COMPOUNDS
PARAMAGNETISM
POLYSACCHARIDES
PROTEINS
RELAXATION
SACCHARIDES
TEMPERATURE DEPENDENCE
TRANSITION ELEMENT COMPLEXES