Determination of f0 for fine magnetic particles

• Published in: Journal of magnetism and magnetic materials Vol. 125; no. 3; pp. 345 - 350
• Main Authors: Dickson, D.P.E., Reid, N.M.K., Hunt, C., Williams, H.D., El-Hilo, M., O'Grady, K.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.08.1993; Elsevier Science
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Magnetic resonances and relaxations in condensed matter, mössbauer effect; Mossbauer effect; other γ-ray spectroscopy; Mössbauer effect; other γ-ray spectroscopy; Physics; Moessbauer effect; Arrhenius equation; Iron hydroxides; Superparamagnetism; Experimental study; Iron oxides; Relaxation time
• ISSN: 0304-8853
• DOI: 10.1016/0304-8853(93)90109-F

In this paper we have determined a value for the pre-exponential factor in the Néel-Arhennius equation for the iron oxyhydroxide particles found in the protein ferritin. The data were obtained using a combination of zero field magnetic and Mössbauer spectroscopy studies yielding a value for f0 of (9.5±2.7)X1011 Hz. This value is significantly different to that of 2.8 X 109 Hz commonly used and in closer agreement to that of 1013 Hz obtained for iron particles using an analogous technique. Using our experimental value for f0 gives a revised superparamagnetic criterion for DC magnetic measurements on a 100 second time-scale of KV < 32 kT and a Mössbauer spectroscopy criterion for a measurement time-scale of 10-9 s of KV < 8 kT. Our results together with other published data would suggest that a more appropriate estimate for the value of f0 would lie in the range 1012 to 1013 Hz.