Artificial Magnetic Systems in 2 and 3 Dimensions
Open Access
- Author:
- Kempinger, Susan
- Graduate Program:
- Physics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 17, 2019
- Committee Members:
- Nitin Samarth, Dissertation Advisor/Co-Advisor
Nitin Samarth, Committee Chair/Co-Chair
Vincent Henry Crespi, Committee Member
Zhiqiang Mao, Committee Member
Roman Engel-Herbert, Outside Member - Keywords:
- Artificial Magnetic Materials
Magneto-optics
Artificial Spin Ice
Magnetic Metamaterials - Abstract:
- Artificial magnetic materials are powerful platforms for investigating properties of magnetic systems, in addition to having potential applications of their own. These types of systems can be designed with control and understanding over the interaction strength, disorder, and other properties that is difficult in naturally occurring materials. There are many ways to probe the behavior of artificial magnetic systems, including magneto-optical measurements for systems based on two-dimensional films and bulk magnetometry measurements for more complex three-dimensional structures. In this dissertation, we present a collection of studies on artificial magnetic materials. First, we consider magnetic thin films patterned in the mesoscopic size regime from Pt/Co multilayers. We investigate the transition in these structures from continuous films that undergo domain wall nucleation and propagation to small dots that switch via seemingly instantaneous rotation. We find that as the feature size is decreased, so is the effective pinning field in the system. Qualitatively, the switching tends to increasingly favor the sample edges as the features are made smaller. The transition to single domain switching has an onset size of 2 μm and is complete by 500 nm. Next, we consider arrays of perpendicular artificial spin ice designed from Pt/Co multilayers patterned into the single domain regime. These arrays can be patterned with or without frustration, in a number of lattice spacings to tune the interaction strength. We pattern multiple physical samples with different levels of disorder and find that to understand the correlation in the arrays we must take into account both the interaction strength and disorder present. We also find that while the macrostate is reproducible from run to run on the same lattice, the microstate is stochastic. We believe this might be due to thermal fluctuations in the lattice. These studies were carried out on arrays in a weakly interacting regime. We then increase the coupling between islands using a soft magnetic underlayer and observe the effect this has on the correlations in demagnetized and hysteretic states. We find that the soft underlayer approximately doubles the interaction strength, but in hysteresis measurements on frustrated arrays this effect is somewhat dampened. Finally, we study a three dimensional artificial magnetic material called a magnetic metalattice. We first fabricate these systems from Ni and show that they are indeed nanoscale and fully interconnected magnetic systems. By annealing the samples we observe an exchange bias effect. We then fabricate similar systems from Pt and Pd. The nanoscale size regime of the samples leads to induced magnetism in the Pt and Pd. For Pt and some Pd samples, the observed effect is ferromagnetic. For other Pd samples, we also observe a superparamagnetic contribution to the magnetic signal. This could be due to incomplete infiltration or some more exotic effect.