Spin pumping measurements at interfaces between magnetic metal or insulator and organic semiconductors

Over the last 16 years, organic spintronics has developed into a striving field with exciting reports of extremely long spin diffusion lengths and spin relaxation times in organic semiconductors (OSCs). Easily processed and inexpensive, OSCs are a strong alternative to inorganic materials for use in spintronic applications. Spin currents have been detected in a wide range of materials, however, there is still uncertainty over the purity of the signals. This thesis covers three different ways of spin current detection and their challenges. First, the presence of spin current is explored using ferromagnetic resonance damp- ing. Linewidth broadening in a ferromagnetic alloy is measured due to spin current dissipation into the neighbouring material. We explore non-spin origins of linewidth broadening and attempt to detect spin dissipation into organic semiconductors. Secondly, spin transport through an organic semiconductor is explored with lateral spin valves. The injected spin current is detected non-locally via spin-to-charge conversion in the detector. The applicability of this measurement and its challenges with potential spurious effects are discussed. Through control experiments, an improved architecture is suggested, which removes the artefacts and improves signal-to-noise ratio. The biggest parasitic effect, anisotropic magnetoresistance (AMR), which arises from a change in resistance in ferromagnets during spin pumping, is studied at length using in-plane angular dependence measurements. Thirdly, spin conversion inside the semiconductor itself is explored when spin pumping from a ferrimagnetic insulator. The role of potential artefacts is explored in mimicking the spin pumping signal. The artefacts are removed using an updated device architecture; or quantified as some cannot be eliminated. Spin conversion is then studied through OSC thickness dependence, conductivity and temperature dependence measurements.

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2020

Author dc:creator

• Zadvorna, Olga

Advisor dc:contributor.advisor

• Sirringhaus, Henning

• spin pumping
• ferromagnetic resonance
• spin rectification
• spin current

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/a68c17d4-3935-45a6-a743-c7780b7224f0/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.62768

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/315654