MSA AWARD LECTURE: THE MAGNETIC PERSONALITY OF MINERALS: FROM NANO-SCALE MICROSTRUCTURES TO PLANETARY-SCALE ANOMALIES

Nanoscale microstructures play a crucial role in shaping the magnetic properties of minerals. The fundamental importance of magnetism at this length scale has been overlooked in the past, leaving a number of long-standing paleomagnetic and rock-magnetic observations that could not be explained. Examples include the origin of strong and stable magnetic anomalies on Mars and the phenomenon of self-reversed thermoremanent magnetization. This gap in understanding arose because the tools required to study mineral magnetism with nanometre resolution had not been developed. We have now begun to establish quantitative links between the nanoscale microstructure of natural magnetic minerals and their macroscopic magnetic properties, by exploiting recent technological advances that have opened up the field.

Several recent advances in electron microscopy and computational mineral physics are poised to revolutionise mineral magnetism over the next five to ten years. Arguably the most significant advance is the application of off-axis electron holography, a transmission electron microscopy (TEM) technique that yields a two-dimensional vector map of magnetic flux with nanometre resolution. The technique is capable of imaging the magnetization state within individual magnetic particles, as well as the magnetostatic interaction fields between neighbouring particles. In tandem with this, advances in the application of atomistic simulations to the study of magnetic ordering in minerals with nanoscale microstructures have opened the way forward to novel interpretations and modelling.

In this talk I present an overview of how these new techniques have been applied to tackle a range of problems in rock and mineral magnetism, ranging from the magnetic properties of genetically modified bacteria to the origin of crustal magnetic anomalies.