Magnetoelastic interactions in hematite: Implications for geophysics
Abstract
Domain wall-stress interaction causes pronounced increases in attenuation and decreases in the velocities of ultrasonic (30 MHz) waves in hematite at 298°K relative to the values in a saturating magnetic field. For compressional modes, these effects are about 10 db/cm in attenuation and less than 1% in velocity and may be eliminated by the application of a magnetic field of 2 kilogauss in the basal (c) plane. At zero applied field, it was not possible to propagate shear waves in the single crystal; as the field is varied from 2 to 4 kG, the attenuation decreases by about 30 db/cm, and the velocities increase by as much as 10%. These data are consistent with the fact that hematite exhibits weak ferromagnetism at room temperature, with the spins largely contained in the c plane. The large fields needed to saturate the crystal indicate the presence of a hard component of magnetization. These magnetoelastic interactions can also be eliminated by cooling through the Morin temperature (TM=261°K), below which point the spins are aligned parallel to the trigonal c axis and the weak ferromagnetism vanishes. At low pressures, TM increases by 3.6°K/kb and occurs at 298°K near 30 kb. The results of this study have important consequences for ultrasonic studies of the elastic properties of third-transition metal oxides, for static compression experiments on these materials, and for studies of phase transitions in solids.
- Publication:
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Journal of Geophysical Research
- Pub Date:
- April 1971
- DOI:
- Bibcode:
- 1971JGR....76.2735L
- Keywords:
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- Elastic Properties: Hematite;
- Magnetic Properties: Hematite;
- Minerals: Oxides;
- Mineralogy;
- Petrology;
- and Physical Properties of Rocks: Elasticity;
- fracture;
- and flow;
- Mineralogy;
- Petrology;
- and Physical Properties of Rocks: Magnetic and electrical properties;
- Seismology: Body waves