Send to

Choose Destination
Proc Natl Acad Sci U S A. 2019 Feb 5;116(6):1984-1991. doi: 10.1073/pnas.1810797116. Epub 2019 Jan 22.

Thermomagnetic recording fidelity of nanometer-sized iron and implications for planetary magnetism.

Author information

Geosciences Research Division, Scripps Institution of Oceanography, La Jolla, CA 92093;
Institute of Earth and Planetary Science, School of Geosciences, University of Edinburgh, Edinburgh EH9 3FE, United Kingdom.
Geosciences Research Division, Scripps Institution of Oceanography, La Jolla, CA 92093.
Natural Magnetism Group, Department of Earth Science and Engineering, Imperial College London, London SW7 2AZ, United Kingdom.


Paleomagnetic observations provide valuable evidence of the strength of magnetic fields present during evolution of the Solar System. Such information provides important constraints on physical processes responsible for rapid accretion of the protoplanetesimal disk. For this purpose, magnetic recordings must be stable and resist magnetic overprints from thermal events and viscous acquisition over many billions of years. A lack of comprehensive understanding of magnetic domain structures carrying remanence has, until now, prevented accurate estimates of the uncertainty of recording fidelity in almost all paleomagnetic samples. Recent computational advances allow detailed analysis of magnetic domain structures in iron particles as a function of grain morphology, size, and temperature. Our results show that uniformly magnetized equidimensional iron particles do not provide stable recordings, but instead larger grains containing single-vortex domain structures have very large remanences and high thermal stability-both increasing rapidly with grain size. We derive curves relating magnetic thermal and temporal stability demonstrating that cubes (>35 nm) and spheres (>55 nm) are likely capable of preserving magnetic recordings from the formation of the Solar System. Additionally, we model paleomagnetic demagnetization curves for a variety of grain size distributions and find that unless a sample is dominated by grains at the superparamagnetic size boundary, the majority of remanence will block at high temperatures ([Formula: see text]C of Curie point). We conclude that iron and kamacite (low Ni content FeNi) particles are almost ideal natural recorders, assuming that there is no chemical or magnetic alteration during sampling, storage, or laboratory measurement.


lunar magnetism; micromagnetics; paleomagnetism; thermal stability

[Available on 2019-08-05]

Conflict of interest statement

The authors declare no conflict of interest.

Supplemental Content

Full text links

Icon for HighWire
Loading ...
Support Center