A chemical, crystallographic and magnetic characterisation of individual iron-oxide grains in Hawaiian lavas

Abstract

Our knowledge on the behaviour of the geomagnetic field through time critically depends on how information of the past state of the field is recorded by, and stored in iron-bearing minerals such as magnetite. For small, single domain grains these processes are described by classical Néel theory, but the magnetic behaviour of larger, pseudo-single domain or multidomain grains, still is enigmatic. Here we present a chemical, crystallographic and magnetic characterisation of three to six individual, large (~3–10 μm) iron-oxide grains from eleven different flows sampled on the Big Island of Hawai’i. These grains were all subjected to a Magnetic Force Microscopy study to characterise their magnetic domain structure; a Microprobe analyses to assess their chemical composition; and a Scanning Electron Microscopy study to identify phases and crystallographic orientations. This comprehensive dataset enables systematic analyses of their magnetic behaviour as function of chemistry and forms the basis for future micromagnetic modelling studies eventually contributing to the development of a fundamental theory of magnetic behaviour in large iron-oxide grains.