Effects of the core-shell structure on the magnetic properties of partially oxidized magnetite grain. Experimental and micromagnetic investigations
Abstract
The relationship between hysteresis parameters and oxidation of ultrafine magnetic particles is determined though a series of experimental measurements and micromagnetic simulations, as a function of gradual oxidation of magnetite. In the experiment, both coercivity (Bc) and the ratio of saturation remanence to saturation magnetization (Mrs/Ms) versus oxidation parameter z display similar trends, which slowly increase before z = 0.9, ranging from ~17 mT to ~21 mT and ~0.22 to ~0.28, respectively. But thereafter both parameters are seen to decrease sharply before magnetite becomes completely oxidized. Numerical simulations using a micromagnetic model with a simple core-shell geometry exhibit good agreement with the experimental observations. The numerical simulations show three broad categories of behavior. Firstly, uniformly magnetitzed single domain (SD) size particles become increasingly unstable as the oxidation degree grows, but that their remanence remains almost unchanged. Secondly, slightly larger grains near the boundary between SD grains and pseudo-single-domain (PSD) sized particles, the coercivity initially decreases before growing again with increasing oxidation before finally decreasing sharply upon complete transformation to maghemite. Finally, larger PSD grains demonstrate far less sensitivity to the oxidation and do not show any clear trend. These results can be interpreted as the partially oxidized magnetic grains being controlled by both the oxidized shell and un-oxidized core as well as the effects of exchange and magnetostatic coupling.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMGP43B..04W
- Keywords:
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- 5109 PHYSICAL PROPERTIES OF ROCKS Magnetic and electrical properties;
- 1540 GEOMAGNETISM AND PALEOMAGNETISM Rock and mineral magnetism;
- 1952 INFORMATICS Modeling