Nanoscale Imaging of High-Field Magnetic Hysteresis in Meteoritic Metal
Using X-Ray Holography
Abstract
Stable paleomagnetic information in meteoritic metal is carried by the
cloudy zone ~1-10 micron wide regions containing islands
of ferromagnetic tetrataenite embedded in a paramagnetic antitaenite
matrix. Due to their small size and high coercivity
(~2.2 T), the tetrataenite islands carry very stable
magnetic remanence. However, these characteristics also make it
difficult to image their magnetic state with the necessary spatial
resolution and applied magnetic field. Here we describe the first
application of X-ray holography to image the magnetic structure of the
cloudy zone of the Tazewell IIICD meteorite with spatial resolution down
to ~40 nm and in applied magnetic fields up to 1.1 T,
sufficient to extract high-field hysteresis data from individual
islands. Images were acquired as a function of magnetic fields applied
both parallel and perpendicular to the surface of a ~100
nm thick slice of the cloudy zone. Broad distributions of coercivity are
observed, including values that likely exceed the maximum applied field.
Horizontal offsets in the hysteresis loops indicate an interaction field
distribution with half width of ~100 mT between the
islands in their room-temperature single-domain state, providing a good
match to first-order reversal curve diagrams. The role of interactions
during the acquisition of transformation chemical remnant magnetization
as the meteorite parent body is cooled, and the implications for
extracting quantitative estimates of the paleofield, are discussed