Materiaal exploratie voor geavanceerde MRAM

The continued scaling of memory devices requires energy-efficient technologies. Spin-orbit torque magnetic random-access memory (SOT-MRAM) offers fast and reliable switching using spin currents generated in a heavy metal, such as Pt, to manipulate the magnetization of an adjacent ferromagnet, like Co. However, low SOT efficiency necessitates high switching currents, limiting energy performance. In this work, ultrathin (few nanometers) metal-oxide interlayers are introduced in Pt/Co heterostructures to improve SOT efficiency. While oxides such as NiO at the interface have been reported to enhance SOT, the underlying mechanisms remain unclear, and systematic studies of structural and magnetic properties are lacking. In this thesis, the structural, magnetic, and spin-transport properties of Pt/oxide/Co systems were systematically investigated as a function of interlayer thickness and annealing temperature, using NiO, MgO, and CoOx as oxide interlayers. Atomic-scale interface structure and magnetic depth profiles were revealed by atom probe tomography and spallation-source-based polarized neutron reflectometry. Comparison across multiple oxides revealed the key interfacial properties governing SOT enhancement. The different interlayers induce distinct structural effects: NiO intermixes with Co upon annealing, MgO remains stable but enables Co diffusion toward Pt forming Pt-Co, and CoOx undergoes phase separation into Co-rich crystalline and O-rich disordered regions. Despite these differences, the Co magnetic properties are largely preserved, with perpendicular magnetic anisotropy observed after annealing, attributed to Pt-Co or Co-O hybridization. Annealing is essential to enhance these interfacial effects and maximize the SOT efficiency, which increases up to fourfold for intermediate oxide thicknesses (1.5-2 nm)), pointing toward oxygen-mediated interfacial effects as the unifying mechanism. Among the investigated oxides, MgO emerges as the most promising interlayer for device integration, combining high SOT efficiency at 400ºC annealing and 2nm thickness with compatibility with established MRAM processes. This systematic study shows how ultrathin metal-oxide interlayers impact interfacial chemistry, spin transport, and magnetic properties, and demonstrates that interfacial effects are the key mechanism enhancing spin-orbit torque efficiency, providing fundamental insight for designing next-generation, energy-efficient SOT-MRAM devices.