Muon spin relaxation studies of iron(II) spin crossover complexes

A series of model iron(II) spin crossover complexes have been investigated by temperature dependent muon spin relaxation (μSR) techniques at ISIS, UK. The thermally induced spin crossover in these materials could be monitored by following the initial asymmetry parameter, a0, in zero-field. We established that the behavior of a0 correlates well with the shape of the spin crossover curve derived from magnetic susceptibility measurements, whether hysteretic, smooth, or abrupt. In addition, the longitudinal field dependence of a0 not only provides information on the nature of the muonic species but also on their interactions and respective localization in the crystal lattice. Useful insights to the electronic structure and dynamic phenomena of these model spin crossover complexes can be derived.