Magnon spin transport in the van der Waals antiferromagnet Chromium Thiophosphate CrPS4

This thesis studies the manifestation of magnon spin transport in the van der Waals antiferromagnet Chromium thiophosphate (CrPS4). CrPS4 is a layered antiferromagnet with perpendicular magnetic anisotropy. Being a semiconductor and at low-temperature insulating, the electrons are localized. Therefore, information transport cannot happen via conduction, however, it can be realized by spin waves. These excitations of the magnetic order are quantized as magnons. To experimentally study magnon spin transport, devices are fabricated on exfoliated flakes of CrPS4 by depositing platinum strips in a nonlocal geometry. A charge current is sent through the platinum and is converted into a spin current orthogonal to the charge current via the spin Hall effect (SHE), which leads to a spin accumulation. This spin accumulation is used to inject magnon spins directly into the CrPS4. This magnon spin can be absorbed by another adjacent platinum contact, where it generates a charge voltage. This nonlocal voltage is the direct result of magnon spin injection by the first platinum contact. In this thesis, this direct “all-electrical” injection, detection, and transport of magnons is demonstrated for the first time in a van der Waals antiferromagnet. The role of the antiferromagnetic magnon modes on injection, detection, and transport of magnon spins is investigated. Furthermore, as a proof-of-principle application new magnon transistor geometries are proposed and demonstrated. Lastly, an outlook on a fully 2D van der Waals magnon transport device is discussed.