Journal
GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS
Volume 12, Issue -, Pages -Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1029/2011GC003538
Keywords
FORC; domain wall; low temperature; pinning; susceptibility; titanomagnetite
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Funding
- European Science Foundation (ESF) of the European Commission [ERAS-CT-2003-980409]
- DG Research
- NERC [NE/D522203/1]
- IRM
- Directorate For Geosciences
- Division Of Earth Sciences [1028690] Funding Source: National Science Foundation
- Natural Environment Research Council [NE/D522203/1] Funding Source: researchfish
- NERC [NE/D522203/1] Funding Source: UKRI
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Domain wall pinning in titanomagnetite has been investigated at low temperatures using first-order reversal curve (FORC) diagrams, AC magnetic susceptibility, and Lorentz transmission electron microscopy. A discontinuous transition from a low-coercivity extrinsic pinning regime to a high-coercivity intrinsic pinning regime is evident in low-temperature FORC diagrams on cooling from 100 to 50 K. Intrinsic pinning is characterized by a crescent moon FORC distribution with narrow coercivity distribution centered on 10-20 mT. This crescent-shaped FORC distribution is reproduced using a modification of Neel's (1955) one-dimensional theory of domain wall pinning in a random field. The pinning transition coincides with a thermally activated relaxation process (activation energy 0.13 +/- 0.01 eV), attributed to electron hopping. The relaxation and intrinsic pinning are explained as a magnetoelastic aftereffect caused by enhancement of magnetocrystalline anisotropy due to rearrangement and localization of Fe(2+)-Fe(3+) cations within the domain walls. This study provides experimental verification that Neel's theory is an appropriate quantitative framework for the analysis of FORC diagrams in multidomain titanomagnetite and suggests a potential method for the quantitative unmixing of multidomain signals from FORC diagrams in rock and environmental magnetic studies.
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