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The unique aspect to our project, is the nanowires which we use as sources of magnetic field. These are planar permalloy nanowires, which are fabricated by our colleagues
at the University of Sheffield Department of Materials Science and Engineering. These wires have a number of useful characteristics:
- They are highly magnetic
- They are made of a soft magnetic material
- They have negligible magnetocrystalline anisotropy
- They are easily produced via microfabrication
These characteristics mean that the wires can host a number of domains, with a structure define by macroscopic anisotropies, i.e. by their shape.
Planar nanowires form domain walls
between domains of opposite orientation. At the domain wall there is a quasi-discontinuous reversal of the magnetisation.
At a domain wall, fringing fields are produced. We have developed a model for these fringing fields: Link.
The magnetisation structure of a transverse domain wall
Schematic of the nanowires that we work with Scanning Hall probe microscope image of a nanowire array
The wires are fabricated via electron-beam lithography with lift-off processing;
permalloy is thermally evaporated onto a PMMA pattern, on a silicon or MgO substrate. A schematic showing typical dimensions is shown on the left.
Imaging of the nanowires is carried out
using scanning electron microscopy. In order to image the magnetic structure of the wires, magneto-optical Kerr effect (MOKE) microscopy, or scanning Hall probe microscopy are utilised.
An example of the latter is illustrated on the right, with lighter (darker) regions representing areas with magnetic field into (out of) the plane.