HR: 0830h
AN: GP31B-0749    [PDF]
TI: Unravelling Magnetic Mixtures Using First-Order-Reversal-Curve (FORC) Diagrams: Linear Additivity and Interaction Effects.
AU: * Muxworthy, A R
EM: adrian.muxworthy@ed.ac.uk
AF: Edinburgh University, Institute of Earth Sciences, King's Buildings West Mains Road, Edinburgh, EH9 3JW United Kingdom
AU: King, J G
EM: kingjg@mopipi.ub.bw
AF: University of Botswana, Department of Physics, Private Bag 0022, Gaborone, N/A Botswana
AU: Heslop, D
EM: dheslop@uni-bremen.de
AF: Universit„t Bremen, Fachbereich Geowissenschaften Postfach 330 440, Bremen, D-28334 Germany
AU: Williams, W
EM: wyn.williams@ed.ac.uk
AF: Edinburgh University, Institute of Earth Sciences, King's Buildings West Mains Road, Edinburgh, EH9 3JW United Kingdom
AB: First-order-reversal-curve (FORC) diagrams for mixtures of different magnetic phases and bi-model distributions have been measured to examine the efficiency of the FORC method for unravelling complex magnetic signals. Mixtures of various magnetic minerals were considered; magnetite, maghemite, hematite and goethite, and the linear additivity of their FORC distributions assessed. For mixtures containing only hard magnetic minerals like hematite or goethite, which have relatively small spontaneous magnetisations (M$_s$) and large magnetocrystalline anisotropies, there is virtually no magnetostatic interactions between the phases. Because of this, FORC diagrams for mixed assemblages of hard minerals can be adequately describe by a linear addition of the two end-members. Softer minerals, i.e., relatively larger M$_s$s and smaller anisotropy like magnetite and maghemite, are more susceptible to interactions and the behaviour of soft mineral mixtures is non-linear. Discriminating between two end-members is difficult. When a magnetically weak phase like hematite is mixed with a stronger phase like magnetite, it can still be identified using the FORC technique when it could not by more standard magnetic hysteresis measurements. When the weaker phase can be identified then weak-strong mixes add linearly, however, beyond a certain critical concentration the stronger mineral swamps the magnetic signal and this linearity breaks. It is suggested that the FORC method is highly suitable for identifying small traces of hard magnetic minerals like hematite and goethite in the presence of stronger minerals such as magnetite.
DE: 1512 Environmental magnetism
DE: 1519 Magnetic mineralogy and petrology
DE: 1540 Rock and mineral magnetism
DE: 5109 Magnetic and electrical properties
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting