Spin dynamics of the charge-transfer phase transition of an iron mixed-valence complex observed using muon spin relaxation spectroscopy

Muon spin relaxation was performed to investigate the dynamic properties of electrons in the iron mixed-valence complex (n -C3 H7) 4 N [FeII FeIII (dto) 3] (dto= C2 O2 S2), which shows a charge-transfer phase transition around 120 K and a ferromagnetic transition at 7 K. The dynamic muon spin depolarization rate for (n -C3 H7) 4 N [FeII FeIII (dto) 3] in zero field exhibits an anomalous enhancement with thermal hysteresis between 60 and 140 K, which is due to the charge-transfer phase transition. The nature of the charge transfer is the oscillation of electrons between FeII and FeIII sites, producing a dynamically fluctuating internal field at the muon site with a frequency of about 0.1 MHz.