Interfacial effects on the chiral domain walls in ultrathin PT/CO/ALOₓ heterostructures for the futuristic spintronics devices
Abstract
Heavy metal /ferromagnet/metal oxide heterostructures are important due to their immense prospects for establishing spin textures such as chiral domain walls which are the basic ingredient of low power and capacious next-generation spintronics devices. The in-depth study of several spin interactions and magnetic parameters within those material systems is essential for the realization of such textures in the material stack. For that purpose, as detailed in this thesis, we constructed a cost-effective and sensitive vibration sample magnetometer (VSM) for magnetization measurement and explored crucial magnetic interactions that are important for future spintronics devices. Our work mainly concentrates on exploring the interfacial effects on the Dzyaloshinskii-Moria interaction (DMI), depinning fields, and other magnetic parameters for efficient DW motion in thin films made of Pt/Co/AlOₓ trilayers. In the first part of this thesis, we develop a low-cost magnetization characterization instrument using a sound card and compared its sensitivity with a commercial lock-in amplifier. Secondly, we report the dependence of the domain wall depinning field, domain wall velocity including anisotropy direction, and magnetic properties on the oxidized aluminum thickness of perpendicularly magnetized asymmetric Pt/Co/AlOₓ trilayers. The low-temperature magneto-transport measurement technique is also adopted to investigate the amount of oxygen at the Co/AlOₓ interface. It is found that the tendency of variation of cobalt oxidation at the interface is also consistent with the modification of the depinning fields, coercive fields and surface roughness measured at room temperature. At the end, we adopt the methodology to study the impact of cobalt oxidation at the Co/AlOₓ interface in Pt/Co/AlOₓ trilayer structures on the DMI by varying the post-growth annealing time, Al thickness and substrate. To quantify DMI magneto-optical imaging of the asymmetric domain wall expansion, hysteresis loop shift, and spin-wave spectroscopy techniques are employed. We further correlated the Co oxidation with low-temperature Hall effect measurements and X-ray photoelectron spectroscopy. Our results emphasize the importance of full characterization of the magnetic films that could be used for MRAM technologies when subjected to the semiconductor temperature processing conditions, as the magnetic interactions are critical for device performance and can be highly sensitive to oxidation and other effects.
Collections
- OSU Dissertations [11222]