HR: 0830h
AN: GP31B-0747    [PDF]
TI: Thermoremanence and Stable Memory in Multidomain Hematite
AU: * Ozdemir, O
EM: ozdemir@physics.utoronto.ca
AF: Ozden Ozdemir, Physics Department, University of Toronto, 3359 Mississauga Road North, Mississauga, ON L5L 1C6 Canada
AB: Thermal demagnetization of thermoremanence (TRM) imparted parallel to the (0001) basal plane of a large natural single crystal of hematite revealed very high unblocking temperatures. Most demagnetization occurs between 670 C and the Neel temperature. In contrast, the decay curve of 1-mT TRM drops exponentially with increasing alternating field, characteristic multidomain (MD) behaviour. Such exponential decay is due to hematite's weak spontaneous magnetization and self-demagnetizating field. Domain walls in MD hematite move almost unhindered to their limiting positions and the TRM intensity approaches to the saturation remanence. This also explains the observed high Mtrm = 1.1 kA/m. The TRM memory recovered after low-temperature cycling (LTC) is parallel to the original TRM and equally resistant to thermal demagnetization. The surviving thermoremanence after LTC is about 30 percent of the original remanence, very similar to single-domain hematites with grain sizes 0.12-0.42 micrometer. Stable TRM and memory with very high unblocking temperatures are due to hard spin-canted ferromagnetism, not to defect ferromagnetism. However, the defect moment seems to couple to the spin-canted moment and renucleate memory in warming through the Morin transition.
DE: 1517 Magnetic anomaly modeling
DE: 1519 Magnetic mineralogy and petrology
DE: 1540 Rock and mineral magnetism
DE: 5109 Magnetic and electrical properties
DE: 6225 Mars
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting