HR: 0800h
AN: MR31B-0372    [Abstracts]
TI: Magnetic transition and sound velocities of Fe3C at high pressure
AU: * Gao, L
EM: liligao2@uiuc.edu
AF: Department of Geology, University of Illinois at Urbana-Champaign, 247 NHB 1301 W.Green St., Urbana, IL 61801, United States
AU: Chen, B
EM: binchen2@uiuc.edu
AF: Department of Geology, University of Illinois at Urbana-Champaign, 247 NHB 1301 W.Green St., Urbana, IL 61801, United States
AU: wang, J
EM: jwang11@uiuc.edu
AF: Department of Geology, University of Illinois at Urbana-Champaign, 247 NHB 1301 W.Green St., Urbana, IL 61801, United States
AU: lerche, M
EM: lerche@aps.anl.gov
AF: Advanced Phonon Source (APS), Argonne National Laboratory, Advanced Phonon Source (APS), Argonne National Laboratory 9700 S Cass Ave, Lemont, IL 60439, United States
AU: lerche, M
EM: lerche@aps.anl.gov
AF: Carnegie Institution of Washington, Carnegie Institution of Washington 5251 Broad Branch Rd., N.W, Washington, DC, DC 20015, United States
AU: Zhao, J
EM: jzhao@aps.anl.gov
AF: Advanced Phonon Source (APS), Argonne National Laboratory, Advanced Phonon Source (APS), Argonne National Laboratory 9700 S Cass Ave, Lemont, IL 60439, United States
AU: Sturhahn, W
EM: sturhahn@aps.anl.gov
AF: Advanced Phonon Source (APS), Argonne National Laboratory, Advanced Phonon Source (APS), Argonne National Laboratory 9700 S Cass Ave, Lemont, IL 60439, United States
AU: Ding, Y
EM: yding@hpcat.aps.anl.gov
AF: Advanced Phonon Source (APS), Argonne National Laboratory, Advanced Phonon Source (APS), Argonne National Laboratory 9700 S Cass Ave, Lemont, IL 60439, United States
AU: Ding, Y
EM: yding@hpcat.aps.anl.gov
AF: Carnegie Institution of Washington, Carnegie Institution of Washington 5251 Broad Branch Rd., N.W, Washington, DC, DC 20015, United States
AU: Ding, X
EM: xding@gig.ac.cn
AF: Department of Geology, University of Illinois at Urbana-Champaign, 247 NHB 1301 W.Green St., Urbana, IL 61801, United States
AU: Scott, H P
EM: hpscott@iusb.edu
AF: Department of Physics and Astronomy, Indiana University South Bend, Department of Physics and Astronomy, Indiana University South Bend, South Bend, IN 46634, United States
AU: Bass, J
EM: jaybass@uiuc.edu
AF: Department of Geology, University of Illinois at Urbana-Champaign, 247 NHB 1301 W.Green St., Urbana, IL 61801, United States
AU: Li, J
EM: jackieli@uiuc.edu
AF: Department of Geology, University of Illinois at Urbana-Champaign, 247 NHB 1301 W.Green St., Urbana, IL 61801, United States
AB: Carbon is a candidate light element in the Earth's core. Fe3C (cementite) has the lowest carbon content among all known Fe-C compounds. Under ambient conditions, Fe3C is ferromagnetic. A pressure-induced magnetic transition from a magnetic phase to non-magnetic phase has been found in previous studies; however, there is a controversy concerning the transition pressure. In this study, we carried out synchrotron Mossbauer spectroscopy (SMS) and nuclear resonant inelastic x-ray scattering (NRIXS) studies on Fe3C up to 52 GPa at room temperature at Sector 3 of the Advanced Photon Source (APS), Argonne National Laboratory. The starting material was synthesized from 57Fe-enriched iron powder and graphite powder. X-ray diffraction measurements revealed that the run product contains a non-negligible amount of iron. Our 1 bar SMS spectrum is well fitted by assuming one iron site with a magnetic hyperfine field of 20 T, consistent with that of Fe3C. Above 9.3 GPa our Mossbauer spectra revealed the disappearance of the 20 T site, indicating that Fe3C has lost its magnetism around 9.3 GPa or below. This is consistent with the magnetic transition at pressure of around 10 GPa reported in a Fe K-edge x- ray circular dichroism study (Duman et al., 2005), and is consistent with x-ray emission spectroscopy data (Lin et al., 2004), showing a significantly reduced magnetic moment at 12 GPa. A magnetic to paramagnetic phase transition is also observed at 483 K under room pressure (Wood et al., 2004). The observed magnetic transition under high pressure and high temperature indicates that the ferromagnetic phase is not stable under the Earth's core condition, and that the non-magnetic phase of Fe3C is more applicable to the Earth's core. We have also derived the Debye velocity of the sample from parabolic fitting to the low-energy range of the nuclear resonance inelastic x-ray scattering spectra at ambient condition. Combined with equation of state of Fe3C (Scott et al., 2001, Li et al., 2002), the compressional and shear wave velocities of Fe3C at ambient condition have also been derived.
DE: 1540 Rock and mineral magnetism
DE: 3924 High-pressure behavior
DE: 4465 Phase transitions
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting