Raman Spectroscopy and Photoluminescence of Vanadium Tetracyanoethylene*

Vanadium tetracyanoethylene (V[TCNE]_x≈2) is an organic-based ferrimagnet, with an ultra-low magnetic damping rate, comparable to yttrium iron garnet (YIG). Its mild growth conditions allow integration with a wide variety of processes. V[TCNE]_x≈2 is air sensitive, but its lifetime in ambient conditions can be extended to several weeks by encapsulating it with epoxy while preserving its low magnetic damping. However, its ageing mechanism is not well studied. Here we use confocal microscopy, microfocused Raman spectroscopy, and ferromagnetic resonance to study V[TCNE]_x≈2 and its ageing process. We identify Raman peaks in agreement with density functional theory calculations. These calculations, using the VASP code, help distinguish the frequency ranges for contributions from CN, CC and VN bonds. By comparing optical features with ferromagnetic resonance measurements, we monitor the V[TCNE]_x≈2 film as it ages. We find a correlation between a reduction in the effective magnetization 4πM_s-H_k and changes in Raman intensity as well as increases in the photoluminescence of the material. These results enable optical measurements that locally probe V[TCNE]_x≈2 film quality.