The effects of annealing and concentration on the hysteresis properties of magnetite around the PSD-MD transition |
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| Authors: | P Dankers N Sugiura |
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| Institution: | Geomagnetic Laboratory, Earth Physics Branch, 1 Observatory Crescent, Ottawa, Ont. K1A 0Y3 Canada;University of Toronto, EPS Room 3023, Erindale College, Mississauga, Ont. L5L 1C6 Canada |
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| Abstract: | Hysteresis parameters Hcr, Hc, Jrs, Js, and their ratios Hcr/Hc, Jrs/Js have been measured for a large number of accurately prepared grain size fractions of magnetite in the range between 5 and 150 μm. For several grain size fractions three different concentrations of magnetite are used: 100, 0.1, and 0.002 vol.%. Most of the measurements were repeated after annealing the specimens to 600°C. For some specimens in the pseudo-single (PSD) and multidomain (MD) range Hc and Hcr have been measured as functions of temperature. Plots of the results from Hc, Hcr/Hc and Jrs/Js versus the grain size reveal curves with a convex and a concave part. Concentration and annealing affects the values of the hysteresis parameters, especially for grains coarser than 25 μm but the shape of the curves remains the same. The inflection point from convex to concave for all curves occurs at 25 μm and it appears to be independent of concentration and annealing. It is therefore proposed to define the transition from PSD to MD as the inflection point of these curves. |
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