High-temperature hysteresis and other magnetic properties of synthetic monodomain titanomagnetites |
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| Authors: | ? ?zdemir W O&#x;Reilly |
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| Institution: | Department of Geophysics and Planetary Physics, School of Physics, The University, Newcastle upon Tyne NE1 7RU Great Britain |
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| Abstract: | A suite of synthetic titanomagnetites of composition Fe2.4?δAlδTi0.6O4 and Fe2.6?δAlδTi0.4O4 (δ = 0, 0.1 and 0.2 in both cases) have been prepared by a method of partial self-buffering and pulverized in a ball mill to particle size of about 200–500 Å. Magnetic hysteresis parameters-saturation and remanent magnetizations and coercive force were measured between room temperature and the Curie temperatures and other parameters-X-ray cell edge, initial susceptibility and coercive force of remanence were determined at room temperature. The intrinsic magnetic “hardness” increases with increasing content of Al3+ and Ti4+, both probably corresponding to an increase in the concentration of Fe2+ ions on the tetrahedral sites of the spinel structure. The room-temperature hysteresis properties were compared with those resulting from monodomain models for the work done to magnetically saturate an assemblage of grains and the approach to saturation, and the separate contributions from coexisting anisotropies of cubic and uniaxial symmetries (assumed present) inferred. The cubic anisotropy energy constants so derived are larger than those determined from multidomain single crystals. The derived cubic constants are also larger than the derived uniaxial anisotropy constants. The latter, however, dominate the behaviour (e.g., coercive force) because of the lower symmetry. The materials appear to be entirely in the stable monodomain state at room temperature. |
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