Magnetic properties of single and multi-domain magnetite under pressures from 0 to 6 GPa

Abstract

Using novel experimental methods, we measured the acquisition of isothermal remanent magnetization, direct field demagnetization, and alternating field demagnetization of multi-domain (MD) and single domain (SD) magnetite under hydrostatic pressures to 6 GPa. We find that the saturation remanence of MD magnetite increases 2.8 times over initial, non-compressed values by 6 GPa, while its remanent coercivity remains relatively constant. For SD magnetite, remanent coercivity and saturation remanence vary little from 0 to 1 GPa, increase markedly from 1 to 3 GPa, then plateau above 3 GPa. These new findings suggest that by 3 GPa, SD magnetite either undergoes a magnetic phase transition, or that it reaches an optimal magnetic state where magnetostriction and/or magnetocrystalline energy constants attain some threshold state without reorganization of the pre-existing magnetic lattices. Similar behavior is not observed in MD magnetite, likely due to domain wall effects. Copyright 2004 by the American Geophysical Union.