A combination of magnetic domain imaging, laboratory magnetic measurements, and numerical modeling studies will be used to study the low-temperature (120 K) phase transition of magnetite. The major goal of the proposed activity is magnetic imaging of micromagnetic structures in magnetite particles below the Verwey transition. Low temperature domain states will be imaged using (1) a dried Bitter method adapted for cryogenic temperatures and (2) low-temperature magnetic force microscopy. A unique aspect of this study will be to complement the domain imaging with in situ crystallographic orientation of magnetite particles by electron back scatter diffraction analysis. With the additional crystallographic information, the relative importance of magnetocrystalline, magnetoelastic, and magnetostatic anisotropies to micromagnetic structures at room temperature and below the Verwey transition can be investigated.
The research activity will improve our understanding of the magnetic behavior of magnetite below room temperature. Further, the behavior of magnetic domain structures during cooling or warming through the Verwey transition will provide insights into the mechanisms responsible for the "permanent" magnetic memory of fine (1-20 micrometer) particles of magnetite, the primary source of information about past geomagnetic field behavior. Finally, the project will provide critical experimental testing of theoretical micromagnetic models, provide new and important data on micromagnetic structures and advance our understanding of the physical basis of paleomagnetism.
Broader Impacts: The proposed work will provide professional training of a post doctoral student, design and construct a new scientific instrument adding to research infrastructure, and the furthering of research partnerships among collaborators in geology, physics, and microbiology. Moreover, the research will likely lead to new "tools" which can be exploited by other investigators, and produce data that will be appropriate for inclusion in the rock magnetic database currently under development.
