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Title: High-frequency dynamics in artificial spin ice
Author: Arroo, Daan Medard
ISNI:       0000 0004 9350 6368
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2019
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High-frequency techniques such as ferromagnetic resonance measurements are a sensitive probe of how internal magnetic fields are distributed in ferromagnetic samples and as such may be used to gain information about the magnetic state of complex systems. One class of such complex systems are artificial spin ice arrays, here frustrated interactions between nanoscale ferromagnetic islands lead to a highly degenerate energy landscape. In this thesis, it is explored how ferromagnetic resonance measurements might be used to read the magnetic state of artificial spin ice systems and conversely, whether controlling the magnetic state of such systems could be used as a way of tuning their high-frequency response for device applications. In order to assess the efeect on the high-frequency response of different microstates, a novel experimental technique is presented to prepare artificial spin ice systems in specific microstates and micromagnetic simulations are used to characterise the effect of microstate changes on ferromagnetic resonance measurements. The state-preparation technique allows an unusual phase of high-energy and low-entropy microstates that correspond to negative spin temperatures to be accessed. It is shown that ferromagnetic resonance measurements may be used to directly measure the spin temperature of artificial spin ice systems, including negative temperatures.
Supervisor: Branford, Will ; Cohen, Lesley Sponsor: Engineering and Physical Sciences Research Council ; Leverhulme Trust
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral