Observing Thermomagnetic Stability of Non-Ideal Magnetite Particles: Good Paleomagnetic Recorders?

Almeidal, Trevor P., Takeshi Kasama, Adrian R. Muxworthy, Wyn Williams, Lesleis Nagy and Rafal E. Dunin-Borkowski, 2014
Fusion TEM holder tip
Image courtesy of Geophys. Res. Lett.

Abstract

The thermomagnetic behavior of remanence-induced magnetite (Fe3O4) particles in the pseudo-single-domain (PSD) size range (~0.1–10 µm), which dominate the magnetic signature of many rock lithologies, is investigated using off-axis electron holography. Construction of magnetic induction maps allowed for the visualization of the vortex domain state in an individual Fe3O4grain (~200 nm in diameter) as a function of temperature. Acquisition of a series of electron holograms at 100°C intervals during in situ heating up to 700°C demonstrates the vortex state of the Fe3O4 grain, in this instance, remains thermally stable close to its unblocking temperature and exhibits a similar in-plane remanent state upon cooling; i.e., the particle is effectively behaving like a uniaxial single-domain particle to temperatures near TC. Such particles are thought to be robust magnetic recorders. It is suggested that evidence for PSD behavior should therefore not preclude paleomagnetic investigation.

Impact Statement

The analysis of remanence-induced magnetite (Fe3O4) particles’ thermomagnetic behavior using off-axis electron holography. The Fe3O4 grain’s vortex state is demonstrated with electron holograms taken at 100° C intervals through in situ heating.