Frustrated Magnetism In Out-of-plane and In-plane Systems

Open Access
- Author:
- Grigas, Chris James
- Area of Honors:
- Physics
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Jorge Osvaldo Sofo, Thesis Supervisor
Dr. Richard Wallace Robinett, Thesis Honors Advisor
Peter E Schiffer, Faculty Reader - Keywords:
- solid state physics
magnetism
frustration
spin ice
artificial spin ice - Abstract:
- This thesis presents work related to the study of systems of frustrated nanomagnet arrays, or artificial spin ice, whose moments are oriented perpendicularly from the plane of the sample. It builds off of previous work by the same research group that has been done studying various other geometries of frustrated nanomagnet arrays. Frustration is a phenomenon found in real 3D materials like holmium stanate and holmium titanate which are called spin ices. Artificial spin ice is a useful model system for studying the behavior of these materials and provides several advantages over the real materials. Advanced lithographic techniques allow the specific interactions between the islands to be finely tuned and the length scale of the samples is such that they can be relatively easily imaged by techniques such as atomic force microscopy and magnetic force microscopy (AFM/MFM). This thesis explores the work that has been done on various lattice geometries with a particular emphasis on lattices whose constituent islands have their moments oriented perpendicularly to the plane of the sample. There are many parts to studying these materials; design of the islands, fabrication, demagnetization, and imaging. Of these steps this thesis places a particular emphasis on the techniques that are used to image the samples and extract meaningful data from them. Correlations in the orientation of islands in perpendicularly magnetized arrays, in kagome and honeycomb lattices, were computed for island pairs of differing distances. It is seen that the correlations between nearest-neighbor pairs of islands are strongest and then decay dramatically for higher order island pairs. Fitting this data to two different simulations shows that the correlations in perpendicularly magnetized arrays are dominated by nearest-neighbor interactions and, by analogy, the same conclusion holds for in-plane hexagonal arrays. The similarities between two very different realizations of spin ice suggest that the behavior of spin ice is independent of the particular geometry and material of the lattice, which could be further explored by studying different geometries. Demonstration of lattices with perpendicularly oriented moments opens up possibilities of using artificial spin ices to imprint a magnetic topology onto a thin film. This could have applications in diverse fields ranging from 2D electron gases to superconductors.