HR: 0800h
AN: GP21A-12    [Abstracts]
TI: Thermal Fluctuation Tomography: Analysis of Single-Domain Grain Populations
AU: * Jackson, M
EM: irm@umn.edu
AF: Institute for Rock Magnetism University of Minnesota, 291 Shepherd Labs 100 Union St SE, Minneapolis, MN 55455, United States
AU: Carter-Stiglitz, B S
EM: cart0196@umn.edu
AF: Institute for Rock Magnetism University of Minnesota, 291 Shepherd Labs 100 Union St SE, Minneapolis, MN 55455, United States
AU: Chen, A P
EM: chen0653@umn.edu
AF: Institute for Rock Magnetism University of Minnesota, 291 Shepherd Labs 100 Union St SE, Minneapolis, MN 55455, United States
AU: Moskowitz, B M
EM: bmosk@umn.edu
AF: Institute for Rock Magnetism University of Minnesota, 291 Shepherd Labs 100 Union St SE, Minneapolis, MN 55455, United States
AU: Solheid, P A
EM: peat@umn.edu
AF: Institute for Rock Magnetism University of Minnesota, 291 Shepherd Labs 100 Union St SE, Minneapolis, MN 55455, United States
AB: In Néel's thermal-activation theory for the magnetization of single-domain grains, the thermal fluctuation field varies strongly with temperature T and with particle volume V. Thermal fluctuation tomography uses this relationship to calculate the joint distribution f(V,H_k0) of particle volumes and microcoercivities from backfield remanence curves measured over a range of temperatures. We have previously applied the method to shape-anisotropy-dominated nanoparticle populations that span the boundary between the superparamagnetic and stable-single-domain states at room temperature, using low-temperature backfield data sets. Here we extend the approach to larger single-domain populations that are thermally stable at room temperature, using new data sets for different strains of magnetotactic bacteria and for the Tiva Canyon Tuff, measured both below and above room temperature. We address some of the issues that become increasingly important with larger particle sizes, including incoherent reversal modes and alteration related to the required high-temperature measurements. We also apply thermal fluctuation tomography to characterize materials in which the anisotropy is dominantly magnetocrystalline rather than shape-controlled, for example the monoclinic magnetite polymorph at temperatures below the Verwey transition.
DE: 1512 Environmental magnetism
DE: 1540 Rock and mineral magnetism
DE: 1594 Instruments and techniques
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Joint Assembly