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Title: Magnetic properties of arrays of magnetite particles produced by the method of electron beam lithography (EBL)
Author: King, James Gagwane
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1996
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This study involves the production of arrays of parallelepiped magnetite particles in the size range 0.1 - 1 μm. This was achieved by utilising electron beam lithography techniques which are often employed in the design of semi-conductor devices. These particles are required in order to understand the mechanism of reversal of magnetisation for pseudo-single-domain (PSD) particles important to paleomagnetic studies. The samples used by previous researchers are magnetite powders. In such samples, despite attempts to disperse the particles onto non-magnetic matrix, there is no way of eliminating particle clumping, and magnetostatic interaction. Low temperature magnetic measurements obtained using samples of cubic arrays of magnetite particles shows that the effect of particle clumping is to increase the amount of saturation isothermal remanence (SIRM) lost at the Verwey transition. The dependence of SIRM lost at the Verwey transition on particle size in the PSD size range, is consistent with the vortex domain structure predicted for unconstrained 3-D micromagnetic studies. The results shows that 'true' magnetic memory is a stress related phenomenon. Magnetic properties of cubic arrays of magnetite particles measured at room temperature are not consistent with the mechanism of magnetic reversal of coherent rotation of atomic magnetic moments, but are generally in good agreement with that of vortex nucleation and propagation in general. The method of domain classification using the coercivity ratio often used in rock magnetism, is shown to be not useful in classifying PSD in the submicron size range. Magnetic properties of rectangular parallelepiped magnetite particles are more complex than expected from the simple demagnetisation shape anisotropy contribution.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available