Micromagnetic study of the influence of crystal defects on coercivity in magnetite
1993
Loading...
Persistent link to this item
Statistics
View StatisticsJournal Title
Journal ISSN
Volume Title
Title
Micromagnetic study of the influence of crystal defects on coercivity in magnetite
Authors
Published Date
1993
Publisher
Journal of Geophysical Research (American Geophysical Union)
Type
Article
Abstract
A one-dimensional micromagnetic model is used to calculate the thermal dependence of microcoercivity (hc) produced by the unpinning of a domain wall (DW) from various types of defects in magnetite. Equilibrium solutions are found that minimize the magnetoelastic, anisotropy, exchange, magnetostatic, and external field energies with respect to the wall width (w) and position of the wall relative to the defect. The defect may be a single dislocation, dislocation dipole, planar defect, or planar defect bounded by two parallel dislocations. Wall pinning is produced by (1) microstress fields of dislocations, (2) local changes in exchange and anisotropy constants within a planar defect region, or (3) a combination of both effects. The calculations, using temperature-dependent parameters, predict the thermal dependence of hc (T) as a function of grain size, domain wall width, defect spacing, and type of defect. Results show that, for grain sizes between 1 and 100 μm, hc(T) is usually a function of the wall width raised to some power n. The particular value of n is found to be a function of the DW-defect interaction spacing (d/w), type of defect, and grain size. Also, within this size range, the wall width expands with temperature more gradually than classical theory predicts. The microcoercivity results are used with the theory of Xu and Merrill (1990) to predict the thermal dependence of the macroscopic coercivity Hc in magnetite. For grains with low defect densities, such as recrystallized magnetites, negative dislocation dipoles with d/w≈0.1–1 produce a thermal dependence of coercivity that agrees with experimental results. In the high defect density limit, a population of positive and negative dislocation dipoles with a distribution of dipole widths produce an Hc (T) dependence consistent with experimental data from crushed and glass ceramic magnetites.
Keywords
Description
Related to
Replaces
License
Collections
Series/Report Number
Funding information
This research was supported by National Science Foundation grant EAR-9017389. Support for the IRM is provided by grants from the Keck Foundation and the National Science Foundation. This is contribution 9206 of the Institute for Rock Magnetism.
Isbn identifier
Doi identifier
10.1029/93JB01719
Previously Published Citation
Moskowitz, B. M. (1993), Micromagnetic study of the influence of crystal defects on coercivity in magnetite, J. Geophys. Res., 98(B10), 18011–18026, doi:10.1029/93JB01719.
Suggested citation
Moskowitz, Bruce. (1993). Micromagnetic study of the influence of crystal defects on coercivity in magnetite. Retrieved from the University Digital Conservancy, 10.1029/93JB01719.
Content distributed via the University Digital Conservancy may be subject to additional license and use restrictions applied by the depositor. By using these files, users agree to the Terms of Use. Materials in the UDC may contain content that is disturbing and/or harmful. For more information, please see our statement on harmful content in digital repositories.