The effect of magnetostatic interactions on the magnetisation structure and magnetic properties of magnetite grains for the size range 0.03 - 0.15 microns has been examined. The understanding of magnetostatic interactions is important because magnetite that occurs naturally by some precipitation process and in sedimentary rocks containing magnetosomes may form as magnetostatic interacting clumps of grains. This has implications in the way we perceive magnetic signals are recorded in rocks, bacterial magnetosomes found in sedimentary rocks, and also in magnetic recording media. The examination of magnetostatic interactions has been achieved by using a three-dimensional micromagnetic model which considers arrays of 4x4x4 cubic magnetite grains with uniaxial shape anisotropy and arrays of 6x6 or 4x4 cubic grains, arranged analogous to arrays of particles that may be produced by a method of electron beam lithography. The grains have a maximum spacing of one grain width, when they are seen to be non-interacting: or a minimum where they are almost touching, when they are interacting. Using this method it is possible to see how grain interactions alter the magnetic domain structure of uniform and non-uniform grains. The effect of interactions on bulk properties, such as coercivity and remanence can be examined from simulated hysteresis cycles. Properties are examined when the grains are arranged within the arrays such that their easy axes of magnetocrystalline anisotropy are aligned parallel with every other grain in the array, and in the case where the axes are in a randomly differing orientation from every other grain within the array. Hysteresis parameters for non-interacting and interacting arrays of grains are calculated, and these theoretical values are compared with previous theoretical micromagnetic models and experimental work. The results from this study are in good agreement with previous work.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:663289 |
| Date | January 1999 |
| Creators | Virdee, D. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/14612 |
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