Spin transport and dynamics in van der Waals magnets and graphene devices

Doktorsavhandling, 2025

Magnetic materials that are only a few atoms thick, also known as van der Waals (vdW) or two dimensional (2D) magnets, are opening exciting opportunities in how we control and use the quantum property of spin in electronics. Unlike charge-based devices, which form the basis of today’s computers, spin-based electronics (or spintronics) promise entirely new ways of storing, controlling, and processing information.

This thesis explores Fe₅​GeTe₂​ (FGT), a vdW magnet with a high magnetic ordering temperature, along with its chemically tuned variants where some iron atoms are replaced with cobalt (CFGT) or nickel (NFGT). By measuring their magnetic responses at room temperature, we revealed how these materials behave dynamically and how their properties can be engineered through targeted doping. For instance, FGT and CFGT showed low magnetic damping, which is highly desirable for fast, energy-efficient devices, while NFGT offered greater thermal stability.

Building on these material insights, we created devices that combine vdW magnets with graphene, a single layer of carbon atoms known for its exceptional ability to carry and transport spins. These heterostructures demonstrated room temperature spin injection, transport, and detection, enabled by clean atomic interfaces. Importantly, we found that FGT has a canted magnetization and doping it with cobalt reorients the magnetization to in-plane. The ability to control the magnetic orientation is a key knob for designing future spintronic devices.

Beyond conventional spin valve behaviour, our experiments uncovered complex magnetic textures in FGT flakes with notches or constrictions. This swirling patterns of spins are usually detected by advanced microscopy techniques. As an alternative practical route, we detected these spin textures in graphene spin valves, proposing an all-electrical mechanism of detecting spin textures.

We also investigated Fe₃GaTe₂​, another vdW magnet, and found it to be a strong candidate for self-induced spin orbit torque devices, where electric currents can directly switch its magnetization. Its efficiency and robustness highlight its potential role in future memory technologies.

Taken together, these results show that Fe-based vdW magnets are not just model systems for studying fundamental spin physics, but also practical building blocks for 2D-based spintronic devices.