Advances in electronics are hindered by energy dissipation from Joule losses associated with charge transport. In contrast, the processing of information based on spin waves propagation (magnons) in magnetic materials is free from such losses. For magnonic devices, materials with ultralow magnetic damping are required as magnon waveguides to ensure long propagation lengths of magnons. Ferrimagnetic Y3Fe5O12 garnets (YIG) exhibit the lowest magnetic damping of all known materials. However, the lowest damping constant YIG materials require epitaxial growth on single crystal substrates of Gd3Ga5O12 at elevated temperatures, hindering their CMOS integration in electronic devices. In the search for alternative material systems, polycrystalline ferromagnetic Co25Fe75 alloy films and ferrimagnetic spinel ferrites, such as MgAl0.5Fe1.5O4 (MAFO), have emerged as potential candidates. The magnetic damping in these materials is comparable, although it is at least one order of magnitude higher than YIG’s. However, Co25Fe75 alloy thin film growth is CMOS compatible, and its magnon diffusion length is 20x longer than in MAFO. In addition, MAFO requires epitaxial growth on lattice-matched MgAl2O4 substrates. The work in this dissertation focuses on growth and characterization of Co1-xFex ferromagnetic binary alloy thin films and is considered as a material of choice for practical magnonic applications.

 

In this project, a narrow composition range of Co1-xFex alloy thin films around 25 % Co have been fabricated and characterized to reveal unique trends in the Gilbert damping as the Co composition in the alloy is changed. Microstructural analysis using STEM, revealed that Cu interdiffusion takes place from Cu buffer layer into magnetic layer of Co36Fe64. This interdiffusion was found to be up to 7x higher at grain boundaries than in the bulk of the thin film. The presence of Cu in the thin film and at the grain boundaries negatively influences magnetic damping, as Cu modifies the magnetic exchange interactions of spins in the thin film, in particular at grain boundaries which is important for efficient magnon propagation. It is noted that Co25Fe75 epitaxially grown on single crystal MgO yielded magnetic damping parameters of 7.1 × 10-4 [https://doi.org/10.1038/s41467-017-00332-x]. We ascribe this improvement to the stronger ionic bonding in MgO vs metallic bonding in Cu, thereby preventing interdiffusion of either Mg or Oxygen into the CoFe thin film.

 

In addition, in this work, COMSOL optical modeling was conducted to investigate the generation of opto-magnetic fields driven by fs laser pulses in 30 nm diameter magneto-plasmonic resonators consisting of Au as plasmonic material and Co25Fe75. These nanopillars are employed as magnon injection sources into CoFe waveguide thin films. An enhancement of the electric field at the waveguide interface generates ultrafast optomagnetic fields. Additionally, a prototype design of magneto-plasmonic device is proposed that provides dynamic magnon amplification and propagation re-configurability employing arrays of magneto plasmonic resonators independently addressed by fs laser pulses.