Introduction

Figure 5.1 shows an array of nanodots created using the novel ``double template'' method imaged using a scanning electron microscope.

Figure 5.2 shows the experimentally measured hysteresis loop for such an array of nickel nanodots (see section 5.1.1) with a bounding sphere diameter $d$ of 500nm (Zhukov, 2004) obtained through magneto-optical Kerr effect (Argyres, 1955) microscopy. The motivation here is to reveal the physics in this hysteresis loop through micromagnetic simulation.

Although the precise shape of the nanodot is not known, we do know the manufacturing method (see section 5.1.3) and from this we can derive an approximate representation of the nanodot.

It is not feasible to perform a three-dimensional micromagnetic simulation of a large array of nanodots so instead a single nanodot is modelled numerically. Despite some inevitable dipolar interaction in the real system, particularly when the nanodots are close together, it remains of interest to investigate the magnetisation of an independent nanodot.

Figure 5.1: Scanning electron microscope image of a droplet array

Figure 5.2: Normalised MOKE measurements for a nickel dot array of diameter 500nm

Figure 5.3: The double-template self-assembly technique. First, an aqueous suspension of latex spheres (top left) of diameter $d$ is poured onto a substrate. As the water evaporates, the latex spheres are attracted to each other (top centre), forming a regular close-packed structure. This template can be filled with a non-magnetic material (top right) and the latex spheres etched away (bottom left). The resulting gaps can be filled with a magnetic material to a varying height $h$ (bottom right) to form arrays of connected or disconnected part-spherical nanodots.