Mapping magnetic signals of individual magnetite grains to their
internal magnetic configurations using micromagnetic models
Abstract
Micromagnetic Tomography (MMT) is a technique that combines X-ray micro
computed tomography and scanning magnetometry data to obtain information
about the magnetic potential of individual grains embedded in a sample.
Recovering magnetic signals of individual grains in natural and
synthetic samples provides a new pathway to study the remanent
magnetization that carries information about the ancient geomagnetic
field and is the basis of all paleomagnetic studies. MMT infers the
magnetic potential of individual grains by numerical inversion of
surface magnetic measurements using spherical harmonic expansions. The
magnetic potential of individual particles in principle is uniquely
determined by MMT, not only by the dipole approximation, but also more
complex, higher order, multipole moments. Here we show that such complex
magnetic information together with particle shape and mineralogy
severely constrains the internal magnetization structure of an
individual grain. To this end we apply a three dimensional micromagnetic
model to predict the multipole signal from magnetization states of
different local energy minima. We show that for certain grains it is
even possible to uniquely infer the magnetic configuration from the
inverted magnetic multipole moments. This result is crucial to
discriminate single-domain particles from grains in more complex
configurations such as multi-domain or vortex states. As a consequence,
our investigation proves that by MMT it is feasible to select
statistical ensembles of magnetic grains based on their magnetization
states, which opens new possibilities to identify and characterize
stable paleomagnetic recorders in natural samples.