Open AccessOn the magnetocrystalline anisotropy of greigite (Fe 3 S 4 )
Author(s) -
Winklhofer Michael,
Chang Liao,
Eder Stephan H. K.
Publication year - 2014
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1002/2013gc005121
Subject(s) - greigite , magnetocrystalline anisotropy , authigenic , ferrimagnetism , superparamagnetism , anisotropy , magnetite , magnetic anisotropy , geology , magnetization , grain size , condensed matter physics , mineralogy , materials science , nuclear magnetic resonance , magnetic field , metallurgy , physics , diagenesis , quantum mechanics
Abstract The ferrimagnetic mineral greigite (cubic Fe 3 S 4 ) is well known as an intracellular biomineralization product in magnetic bacteria and as a widely occurring authigenic mineral in anoxic sediments. Due to the lack of suitable single‐crystal specimens, the magnetic anisotropy parameters of greigite have remained poorly constrained, to the point where not even the easy axis of magnetization is known. Here we report on an effort to determine the anisotropy parameters on the basis of ferromagnetic resonance (FMR) powder spectroscopy on hydrothermally synthesized, chemically pure greigite microcrystals dispersed in a nonmagnetic matrix. In terms of easy axis orientations, the FMR data are consistent with <111> or <100>, or less likely, a more general type. With a g factor of 2.09, the anisotropy field is about 90 mT and in some samples may reach 125 mT, compared to 30 mT for cubic magnetite. This confirms the dominating role of cubic anisotropy on the magnetic properties of greigite, which we show to be responsible for large SIRM/k values. K 1 is in the range −15 … −23 J/m 3 (<111>) or +10 … +15 kJ/m 3 (<100>), yielding upper limits of 44 or 34 nm for the superparamagnetic grain size, respectively.