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-C3H7)(4)N[(FeFeIII)-Fe-II(dto)(3)] (dto=C2O2S2), 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-C3H7)(4)N[(FeFeIII)-Fe-II(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 Fe-II and Fe-III sites, producing a dynamically fluctuating internal field at the muon site with a frequency of about 0.1 MHz.