Magnetisation Texture Motion Driven by Spin Currents: Simulation and Measurement

This thesis contains the study results of magnetic texture motion induced by spin currents through both simulation analyses and experiments. The exploration into the force interactions between spin currents and magnetic textures furnishes a better understanding of the complex dynamical behaviour of these textures. More accurate predictability of magnetic texture responses within varied external conditions is crucial for applying magnetic texture as information carriers of spintronic devices.

Periodic heterostructures of ferromagnetic materials and heavy metals were fabricated via sputtering techniques. The samples presented pronounced Dzyaloshinskii-Moriya Interaction (DMI). This interaction helps the stabilization of magnetic textures. The initial step was characterizing the magnetic properties of the Ta/$\mathrm{[Pt/Co_{68}B_{32}/Ir]_{n}/Pt}$ system. These characterized magnetic parameters were used in subsequent micromagnetic simulations. The simulation results demonstrated the possibility of stabilizing skyrmions on our samples with an external magnetic field. More importantly, simulations found the different behaviours of skyrmion in varied widths and damping characteristics tracks. The result analysis revealed that the initial trajectory of the skyrmion is altered upon the balance between spin transfer torque from the transmitted spin wave, linear momentum transfer torque from the reflected spin wave and the repulsive forces from the sample edges.

The latter portion of this project is the experimental investigations of domain dynamics driven by spin currents from thermal gradients along the narrow tracks. Magnetic Force Microscopy (MFM) was used to look for the domain position before and after the heating application. An Oersted field due to the applied dc current must be accounted for the displacement of the domains. The effects of the Oersted field and thermal gradients were discussed. Ultimately, we observed the domain driven by a series of thermal gradients on the metal sample.In recent research, insulating materials, such as YIG, are widely used because they ensure that electric currents do not interfere with the magnetic texture movements or the pure spin current dynamics being studied. The results of our research can give the researchers more choices from designable magnetic heterostructures than traditional insulating magnetic materials.