Magnetoelastic Dynamics in Nanomagnetic Metamaterials
5000 years ago cuneiform was imprinted on clay tablets in order to store information in Mesopotamia. The necessity to store information was due to the increasing complexity of civilizations which evolved after the Neolithic revolution. Today magnetic materials are used in order to imprint 0’s and 1’s into the spins of electrons. Again, this level of technological prowess is a reflection of our growing complexity as a civilization. Currently, we are in the throes of an information revolution, where individuals, businesses and governments alike store every possible bit of data obtainable. The demands of processing this data faster as well as addressing the massive amount of energy required to store it is going to be a major technological challenge of the ensuing decades. Being one of the dominant means of storing information, it is necessary to explore different methods of manipulating the spins in magnetic structures. Utilizing ultrafast laser pulses enables us to probe the magnetic system at unprecedentedly fast timescales and using the material’s elastic degree of freedom may enable more energy efficient control of the spins. At the very least a more thorough understanding of magnetoelastic interactions in condensed matter systems is important from a fundamental perspective.
In this thesis, Time Resolved Magneto-Optical Kerr Effect (TR-MOKE) Spectroscopy is used to characterize magnetic materials. This technique is used to measure the interlayer exchange coupling in magnetic multilayer structures. Additionally, a novel all-optical method to selectively manipulate spin dynamics in magnetic multilayers is introduced.
Next, the magnetoelastic coupling in nanomagnetic arrays is presented. The array acts as a metamaterial due to the dependence of the elastic and magnetic dynamics on the array geometry. Furthermore, the dynamics are modelled as a forced harmonic oscillator, where the elastic waves act as the driving term. Finally, the magnetoelastic coupling in an individual nanomagnet is explored, and is modeled as a pair of coupled harmonic oscillators. The hybridization between elastic and magnetic oscillations is observed for the first time, and the angular dependence between the relevant elastic and magnetic vectors is used to tune the system into the strong coupling regime.