Objective: We review the dynamical behavior of the charge transfer phase transition in aniron
mixed valence system, (CnH2n+1)4N[FeIIFeIII(dto)3] (dto = C2O2S2).
Background: In the case of assembled metal complex systems whose spin states are situated in the spin
crossover region, synergetic phenomena coupled with spin and charge have been expected. Based on this
viewpoint, we have developed a ferromagnetic organic-inorganic hybrid system, (CnH2n+1)4N[MIIFeIII(dto)3],
and discovered the charge transferphase transition (CTPT), where the thermally induced electron transfer between
FeII and FeIII occurs reversibly. However, the dynamics of the CTPT has not well been elucidated by
the measurements of magnetic susceptibility, EPR and 57Fe Mössbauer spectroscopy.
Methods: In order to investigate the dynamics of CTPT for (CnH2n+1)4N[MIIFeIII(dto)3], we performed muon spin relaxation
spectroscopy at Rutherford-Appleton Laboratory (UK) and the Paul Scherrer Institut (Switzerland), and dielectric
Results: From the analysis of muon spin relaxation, we revealed the hopping rate of electrons between the FeII and FeIII
sites at the CTPT. Moreover, we observed an anomalous enhancement of dielectric constant due to the valence fluctuation
at the CTPT. This anomaly has a tendency to be divergent as the measuring frequency is lowered to 1 Hz, which is quite
similar to the dielectric relaxation in relaxor ferroelectrics.
Conclusion: In a mixed-valence system, (CnH2n+1)4N[MIIFeIII(dto)3]], we have investigated the CTPT due to the synergetic
effect coupled with spin and charge, and revealed the valence fluctuation at the CTPT by means of muon spin relaxation
spectroscopy, and dielectric constant measurement techniques.