Publications

1. Zoe Budrikis, Paolo Politi, and R. L. Stamps. Vertex dynamics in finite two-dimensional square spin ices. Phys. Rev. Lett. 105 017201, June 2010. (arXiv)
   
2. Zoe Budrikis, R. L. Stamps, Nils Wiese and John Chapman. Disordered chain model of cross tie wall spacing. Phys. Rev. B 84 024423, July 2011.
3. Zoe Budrikis, Paolo Politi and R. L. Stamps. Diversity enabling equilibration: disorder and the ground state in artificial spin ice. Phys. Rev. Lett. 107 217204, November 2011 (arXiv)
4. Zoe Budrikis, Paolo Politi, and R. L. Stamps. Disorder regimes and equivalence of disorder types in artificial spin ice. J. Appl. Phys. 111 07E109, February 2012. (arXiv)
5. Zoe Budrikis, K. L. Livesey, J. P. Morgan, J. Akerman, A. Stein, S. Langridge, C. H. Marrows, R. L. Stamps. Domain dynamics and fluctuations in artificial square ice at finite temperatures. New J. Phys. 14 035014, March 2012.
6. Zoe Budrikis, Paolo Politi, and R. L. Stamps. A network model for field and quenched disorder effects in artificial spin ice. New J. Phys. 14 045008, April 2012.
   
7. Zoe Budrikis, K. L. Livesey, J. P. Morgan, J. Akerman, A. Stein, R. L. Stamps, Paolo Politi, S. Langridge, C. H. Marrows. Disorder strength and field-driven ground state domain formation in artificial spin ice: experiment, simulation and theory. (arXiv)

Further reading

CNR highlights: Dynamics and ordering process in artificial spin ice

My research

Magnetic systems are an ideal setting in which to study a variety of physics models. Many fascinating phenomena occur naturally, and nanopatterning technologies make it possible to construct arrays of magnetic islands coupled by stray fields, with desired geometries. My research deals with both these aspects, the former in a study of cross tie magnetic domain walls and the latter in ongoing work on artificial spin ice.

In both cases, my theoretical work has emphasised finding simple models with wide applicability, in order to understand the essential physics of the system and to relate it to other phenomena. The aim of these models is always to explain and predict experimental results, and much of my work so far has been in collaboration with experimentalists at the University of Glasgow and the University of Leeds.

Cross tie domain walls

In my Honours year, I used coupled Langevin equations describing periodic chains of elastically coupled particles to model cross-tie magnetic domain walls. Cross tie domain walls separate domains with a 180° shift in magnetization. They have a complex internal structure consisting of a periodic line of vortices and antivortices. Although the micromagnetic structure is complex, the simple model of coupled particles serves well to describe the system and was used to extract a measure of the strength of disorder in an experimental system. This was done using micromagnetic modelling to derive the mean coupling between vortex cores and using this as a parameter to fit experimental data to the particle chain model. (Phys. Rev. B, 84 024423)

Artificial spin ice

My PhD research has focussed on ‘artificial spin ice’. Artificial spin ice consists of nanofabricated arrays of magnetic islands, which act like Ising (two-state) spins due to shape anisotropy. The islands are positioned so their interactions are frustrated. However, in square artificial spin ice, geometry-imposed differences in couplings lead to a well-defined ground state, which is antiferromagnetically ordered. However, unlike conventional Ising antiferromagnetics, artificial spin ice allows a wide variety of excitations above this ground state. My work has dealt with the driven dynamics of artificial spin ice, and how these dynamics are affected by quenched disorder.

My work can be divided into two broad approaches. The first is to treat the vertices of the array of spins as objects, and to consider how these interact with each other. This makes it possible to write down a set of equations describing how the population fractions of these vertex objects changes when an external magnetic field is applied, under the assumption that vertices are well mixed and only interact with their nearest neighbours. The solution of these equations agrees well with simulations in the field regime where the assumptions are expected to hold. (Phys. Rev. Lett., 105 017201)

The effects of quenched disorder on vertex dynamics can be studied via numerical simulation. Intriguingly, simulations show that different sources of disorder lead to similar effects on the dynamics, and the strength of disorder – rather than its origin – is the best way to characterise it. (J. Appl. Phys. 111 07E109)

An alternative approach to studying disorder is to characterise its effects on the configurational phase space of the system. In this approach, spin configurations are nodes of a network, and the way that disorder re-wires the network gives an elegant way to describe its effects. Disorder dramatically increases the reversibility of dynamics by allowing transitions that are forbidden in the perfect system. (Phys. Rev. Lett. 107 217204; arXiv:1112.2069)

Selected grants and prizes

•  Finalist, Student presentation award, MMM conference 2011.
• Special commendation, UWA prizes for higher degree by research achievements, 2011.
• Australian Research Network for Advanced Materials Travel Grant, 2009.
• Hackett Postgraduate Scholarship, 2008-2011.
• Maslen Physics Prize, 2007.
• Jean Rogerson Honours Studentship, 2007.