Acquisition of high-temperature rock-magnetic instruments

University Of Minnesota-Twin Cities, Minneapolis MN

Investigators

Abstract

The project will expand experimental capabilities at the Institute for Rock Magnetism (IRM) through the acquisition of two new instruments: The first is a Asylum Research MFP-3D Magnetic Force Microscope. This instrument maps the spatial distribution of magnetic field gradients at a controlled height above the surface of a magnetic material sample, with a resolution of a few tens of nanometers, over areas up to ~100 micrometers, thereby allowing observation of the micromagnetic structure of the material (domains and domain walls). In addition to room-temperature imaging, the MFP-3D also allows high-temperature imaging up to 400°C. This is accomplished with a separate high temperature environmental stage (PolyHeater) that sits on the MFP-3D XY scanning stage. Heating and cooling can be done in air or controlled atmospheres (e.g., He, Ar, CO, etc). Sample temperature can be maintained to better than 0.2°C precision with accuracy to 0.5°C and temperature overshoots less than 0.2°C. All control and measurement functions are fully programmable for custom heating-cooling imaging experiments. The second is an AGICO MFK1-FA Kappabridge and CS4 Furnace. This instrument measures both ?real? (in-phase) and ?imaginary? (quadrature) components of complex susceptibility, with three AC operating frequencies (976, 3904 and 15616 Hz) and a range of applied AC field intensities from 2 A/m up to a maximum of 700 A/m (depending on frequency). High spatial uniformity of both applied fields and the instrument response function allow accurate measurement of the magnetic anisotropy of geological samples having various sizes and shapes, and an integrated specimen rotator in the MFK1-FA enables rapid automated acquisition of orientation-dependent data. The CS4 furnace, integrated with the MFK1-FA, will enable measurements of frequency- and amplitude-dependent susceptibility at elevated temperature, which will be important new capabilities. The new high-temperature capabilities of these two instruments will allow resident and visiting researchers at the Institute for Rock Magnetism to probe the fundamental physical origins of magnetic ?memory? in geologically significant magnetic materials such as magnetite, titanomagnetite, hematite, hemoilmenite, and pyrrhotite. The nonuniform magnetizations in micrometer-to-millimeter sized particles of these minerals provide us with the paleomagnetic ?recordings? of past geomagnetic field strength and orientation that allow us to study the evolution of the earth?s deep interior, the motion of tectonic plates, and other significant problems in the geosciences, biosciences, planetary geology, and meteoritic studies. Observation of the micromagnetic configurations within mineral grains, and their changes with experimentally applied fields and controlled temperatures, allows us to study the mechanisms of natural magnetic recording, to understand their sensitivity to thermal or chemical overprinting over geologic time, and to devise optimized laboratory methods for the recovery of paleomagnetic field data from natural recording media.