[Truncated abstract] Artificial spin ice consists of nano-patterned arrays of magnetic material, and is designed as a two-dimensional experimental model of pyrochlore spin ices such as Dy2Ti2O7. The fundamental components are elongated islands of magnetic material. These are coupled by dipolar interactions, which are frustrated by geometry. The islands are small enough to be single-domain - that is, to good approximation, the magnetic moment is aligned throughout the island - and their elongated shape constrains the magnetisation to point along the island long axis, so that the islands act as Ising macrospins with two states. The islands are large enough that their magnetisation reversal is inaccessible to thermal dynamics, and the system behaves as if at zero temperature. Accordingly, dynamics must be induced by external fields which act uniformly on all spins. These global dynamics are highly constrained and many states are inaccessible, regardless of their energy. This Thesis is a theoretical study of the athermal, driven dynamics of square artificial spin ice. The aim is to understand how dynamics are a ected not only by the complex energy landscape generated by the interactions between spins, but also disorder in the system. The work can be divided into three main strands. The first is to treat the vertices of the spin array as objects, and to consider how these interact with each other. Analysis of energetically-allowed vertex processes provides an explanation of how in an ideal system, array edge geometry and the sequence of applied elds controls dynamics. It is found that in perfect systems low-energy states can be generated by careful selection of dynamical processes, but also by the introduction of randomness into the sequence of driving fields.
|Qualification||Doctor of Philosophy|
|Publication status||Unpublished - 2012|