Using RF-muSR to differentiate contributions to the LF relaxation in a conducting polymer

There are potentially many contributions to the muon spin relaxation in conducting polymers. Fast fluctuating intermittent hyperfine interaction with mobile carriers leads to a quasi-diamagnetic signal and produces a type of relaxation described by the Risch-Kehr model, which is valid when the fluctuations are significantly faster than the hyperfine frequency. On the other hand, there is usually also a repolarizing component present in the data, indicating the presence of additional quasi-static paramagnetic probe states, where the fluctuations are not significantly faster than the hyperfine frequency. In moderate LF there is considerable ambiguity about how the observed relaxation should be assigned to contributions from these two different types of state and this proposal aims to resolve this issue. We propose here to vary the LF over the region of interest and simultaneously use RF pulses applied to a coil wrapped around the sample, with RF frequency and pulse length chosen to provide 90-degree spin rotation of the diamagnetic component by the end of the pulse. This will allow us to measure the asymmetry and relaxation rate of the diamagnetic component independent of any relaxation contribution from the paramagnetic component. This diamagnetic relaxation can then be compared with the relaxation of the total signal when the RF is off, which includes any additional contributions from quasi-static repolarized paramagnetic states.