Open AccessAnomalous magnetic properties of brain tissue at low temperature: The 50 K anomaly
Author(s) -
Hirt Ann M.,
Brem Franziska,
Hanzlik Marianne,
Faivre Damien
Publication year - 2006
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2006jb004570
Subject(s) - condensed matter physics , magnetic susceptibility , superparamagnetism , maghemite , magnetite , magnetic anomaly , magnetic field , materials science , anomaly (physics) , phase transition , nuclear magnetic resonance , hysteresis , magnetization , physics , quantum mechanics , geophysics , metallurgy
A low‐coercivity phase, identified as magnetite and/or maghemite, is the main iron oxide in brain tissue. Measurement of susceptibility as a function of temperature ( χ –T) in brain tissue samples does not show a Verwey transition but instead shows a perturbation around 50 K. A susceptibility anomaly has been reported at this temperature in several studies of multidomain magnetite crystals, which, however, also display a Verwey transition. We have investigated the magnetic characteristics of this 50 K anomaly further in brain and tumor tissue. The magnetic measurements consist of χ –T curves, measured after cooling in zero field (ZFC) or in a field (FC), as well as hysteresis loops. The 50 K anomaly is expressed as a bump in χ –T curves over a 20 K temperature range, with a peak between 44 and 58 K. The magnetic intensity of the samples is weak; however, the anomaly signal is an order of magnitude larger than known effects related to the magnetic ordering of oxygen at 43 K. A phase transition, or magnetic ordering of another phase, does not seem a likely explanation, because both the ZFC and FC curves follow the perturbation, rather than showing a bifurcation at peak susceptibility. This explanation also precludes magnetic blocking of a superparamagnetic component. Hysteresis loops at temperature of the peak perturbation show a splitting of the descending and ascending limbs at the maximum starting field. The magnetic behavior observed in these experiments is consistent with a change in electron activity.