Detection of emergent magnetic states at molecular interfaces by LE-μSR

The interfacial states that form due to orbital hybridisation and charge transfer at molecular interfaces can lead to fascinating magnetic properties. Several approaches to the characterisation of these surface states have been taken in the recent past such as SQUID magnetometry and XMCD. However, the resolution of these methods is often tested due to the confinement of these effects to interfaces. In this study, we use low energy muon spin rotation (LE-μSR) to probe such phenomena. Probing the transition oscillations between hyperfine energy levels of C₆₀ that has been interfaced with non-magnetic copper layers. We observe an increase in the transition frequency due to Zeeman splitting of the hyperfine tensor. We may eliminate this state through demagnetisation of the interface allowing us to attribute this observation to the emergent magnetic states at the CuC₆₀ interface. In a second system comprised of a metal oxide-C₆₀ interface. We have shown that optical gating of this photovoltaic device leads to increases in local fields at the interface due to a spin-dependent trapping of charge, thereby acting as a 'spin capacitor'. These measurements demonstrate the capability of the μSR technique for the characterisation of novel thin film molecular structures and devices.