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Magnetic properties of meteorite ‘cloudy zones’ revealed

last modified Feb 13, 2019 08:29 AM

A team led by Cambridge Earth Sciences' Joshua Einsle and Richard Harrison have used advanced microscopy techniques and numerical simulations to gain new insight into the formation, composition and magnetic behaviour of the meteoritic composite known as the ‘cloudy zone’.

The iron-nickel composite material known as the 'cloudy zone' is only found in meteorites, originating from planetesimal parent bodies which had a molten core - like our Earth - in the early days of the solar system.

Due to their small size, planetesimals are unable to maintain a fluid core for billions of years. This resulted in them slowly solidifying over millions of years, before eventually being broken up through collisions with other planetesimals. Through this cooling process, iron-nickel alloys form a series of unique metallic phases.

The cloudy zone consists of tightly-packed, nanoscale 'islands' of tetrataenite, an ordered phase of alternating iron and nickel layers which forms during slow cooling. The nanoscale magnetic properties of the material allow it to record the magnetic fields generated by the planetesimal it came from.

Einsle commented "Previously, interpretation of magnetic measurements relied on assumptions about the composition and structure of the two phases in the cloudy zone. The experiments presented here identify a new chemically ordered phase, and model for how the magnetic information is recorded in the composite as it forms."

The team's data showed that magnetic information was recorded in the cloudy zone when the islands became chemically ordered, unlike previous models which understood this as being locked-in when the islands formed at high temperature.

"This changes our understanding of how this phase operates to encode data, and so how to interpret the recording of the magnetic evolution of a planetesimal it stores" continued Einsle.

Tetrataenite makes an excellent permanent magnet. This improved understanding of its nanoscale magnetic properties within the meteorite cloudy zone could also provide a model for a low-cost replacement for rare-earth permanent magnets used in wind turbines and other green technologies.

More to follow...

Nanomagnetic properties of the meteorite cloudy zoneJoshua F. Einsle et al. is published in Proceedings of the National Academy of Sciences.