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- Title
Demagnetization Energy and Internal Stress in Magnetite From Temperature‐Dependent Hysteresis Measurements.
- Authors
Béguin, Annemarieke; Fabian, Karl
- Abstract
The magnetization state of magnetite controls acquisition and stability of remanent magnetization in Earth and planetary rocks. Although commonly interpreted in terms of grain size, also stress, grain shape, and magnetostatic interactions can substantially modify magnetic stability. Here, we show that scaled reversible work (SRW) in the approach‐to‐saturation (ATS) of hysteresis curves is temperature independent if anisotropy is due to demagnetizing energy. Stress anisotropy vanishes with increasing temperature. With a new measurement and evaluation procedure stress‐induced anisotropy is separated from demagnetization effects. We calibrated the new method using theoretical ATS curves for different stress and demagnetization regimes. Experimental results for synthetic magnetite samples underpin the validity of the method and provide insight into the relationship between magnetostatic, magnetocrystalline, and stress energies. The SRW method provides a new tool to study the reliability of paleomagnetic recording mechanisms, and enables quantitative investigation of stresses due to tectonics, meteorite impacts, oxidation, exsolution, or quenching. Plain Language Summary: Magnetic particles in rocks store information about past magnetic fields and about the physical conditions during formation of the magnetic minerals. Magnetic measurements are sensitive which makes them useful for understanding magnetic minerals and their recording mechanisms. Magnetite is the most abundant natural magnetic mineral in Earth's crust and understanding its magnetic recording properties is a central task of rock magnetism. Here, a temperature‐dependent measurement technique is developed and tested that can determine internal stress in magnetite crystals that was generated during crystal growth or by later mechanical forces due, for example, to tectonics or meteorite impacts. Also, chemical or thermal gradients, produced by oxidation or rapid cooling can generate internal stresses. It was previously difficult to separate stress from other parameters that influence the properties of magnetite particles. Our new method makes it possible to study stresses in magnetite in relation to tectonic, paleomagnetic, and paleointensity studies in Earth and planetary magnetism. Key Points: Scaled reversible work from temperature‐dependent hysteresis measurements quantifies demagnetizing energy and stress in magnetiteInternal stress due to oxidation or mechanical crushing can reach 350 MPaDemagnetizing energy reflects shape anisotropy, particle interaction, and increasing alignment of the magnetization structure
- Subjects
GEOMAGNETISM; DEMAGNETIZATION; MAGNETITE; REMANENCE; MAGNETITE crystals; MAGNETIC measurements
- Publication
Geophysical Research Letters, 2021, Vol 48, Issue 24, p1
- ISSN
0094-8276
- Publication type
Article
- DOI
10.1029/2021GL096147