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Brillouin light scattering: a powerful tool for magnonics research


The slow down in generation-over-generation improvement in CMOS based logic and storage devices has spurred recent exploration into magnonic devices, those based on propagating perturbations of magnetic order called magnons, or spin waves. These devices are of particular interest due to their chargeless, low-power operation, scalability to the nanoscale, and compatibility with existing CMOS technologies. By exploiting spin waves, information may be transferred and operated upon without electrical currents. Magnetic textures like Neel domain walls, chiral transitions between magnetic domains, or skyrmions, magnetic vortices, represent additional avenues in magnonics for data storage and logic devices. Magnonic crystals, artificial crystals made by modulating magnetic properties in a periodic fashion, are one example of magnonic devices that have seen recent interest. With applicability in logic and signal processing, study of how spin waves propagate through these crystals is a necessity in the pursuit of new crystal designs. Brillouin light scattering (BLS) spectroscopy, an inelastic light scattering technique, is a powerful tool in this pursuit, as it allows for the spatial and temporal mapping of spin wave propagation. In this thesis, we will discuss three studies of spin waves by BLS: a 1D magnonic crystal, a 2D magnonic crystal, and a study of the interfacial Dzyaloshinskii-Moriya interaction. First, time-resolved BLS was used to study the band gap formation in a 1D magnonic crystal. By mapping the propagation of spin wave pulses through the crystal, complex two dimensional interference patterns were observed. These patterns are ignored by the simple models used to understand the behavior of this crystal design, and we provide a model to calculate these patterns from the spin wave dispersion relation. The temporal development of interference that forms the basis for band gap formation in this system is also observed. Second, time-resolved BLS was used to study spin wave caustic beams in a 2D magnonic crystal. This crystal design represents a new regime in magnonic crystals, in which the patterning dimensions are much smaller than the spin wave wavelength and generate caustic beams. The formation of a narrow (3 MHz) wide rejection band is observed and the possible mechanisms, including edge effects and interference between caustic beams, are explored. Third, the temperature dependence of the interfacial Dzyaloshinskii-Moriya interaction (iDMI) is measured in a Pt/Co film for temperatures ranging from 15 K to room temperature. Previous studies have been reported for temperatures above room temperature and this study serves to test theory over a greater range of temperatures. The iDMI parameter was quantitatively measured by measuring the frequency difference for counter-propagating surface spin waves by BLS. These three studies demonstrate that BLS is a versatile and powerful tool in the field of magnonics.


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brillouin light scattering
spin waves
magnonic crystal


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