Magnetite Under Pressure: Direct Magnetic Measurements and Consequences for Meteorite Impacts

HR: 14:10h
AN: GP22A-03 [PDF]
TI: Magnetite Under Pressure: Direct Magnetic Measurements and Consequences for Meteorite Impacts
AU: * Gilder, S A
EM: gilder@ipgp.jussieu.fr
AF: Institut de Physique du Globe, Laboratoire de Paleomagnetisme, 4 place Jussieu, Paris, 75252 France
AU: LeGoff, M
EM: legoff@ipgp.jussieu.fr
AF: Institut de Physique du Globe, Laboratoire de Paleomagnetisme, 4 place Jussieu, Paris, 75252 France
AU: Chervin, J
EM: JClaude.Chervin@pmc.jussieu.fr
AF: Universite Pierre et Marie Curie, Physique des Milieux CondensＴ, 2 place Jussieu, Paris, 75252 France
AU: Peyronneau, J
EM: peyronno@ipgp.jussieu.fr
AF: Institut de Physique du Globe, Laboratoire de Paleomagnetisme, 4 place Jussieu, Paris, 75252 France
AB: New diamond anvil cell technology now makes it possible to directly measure magnetic properties of extremely small sample volumes under high pressures. Specifically, we have developed a "non-magnetic" beryllium-copper, membrane-type diamond cell that houses a system designed to measure the reversible magnetic susceptibility of micron-sized samples under pressures in excess of 30 GPa. By placing the cell in the confines of an electromagnet, we can measure reversible susceptibility as a function of applied field, with H varying from -1.2 T to +1.2 T. Because the integral of Xrev(H)dH is proportional to the magnetic moment (of the reversible part of the remanence, or Mrev), we can measure the reversible hysteresis parameters of ferromagnetic materials as a function of pressure. We find that magnetite reversible hysteresis parameters vary little below 1.0 GPa, while at higher pressures significant increases occur in bulk coercivity (Hc) and the ratio of saturation remanent magnetization (Mrs) to saturation magnetization (Ms). The magnetic properties of magnetite are not reversible upon pressure release. Moreover, the magnetic properties of magnetite under pressure and after pressure release are highly dependent on both domain state and the presence or absence of an external magnetic field. These factors should be taken into account when studying the magnetic signatures of meteorite impacts.
DE: 1540 Rock and mineral magnetism
DE: 3924 High-pressure behavior
DE: 3994 Instruments and techniques
DE: 5440 Magnetic fields and magnetism
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting