Photoinduced Faraday effect in a cobalt-iron polycyanide film

We report on a photoinduced Faraday effect in an electrochemically synthesized cobalt-iron polycyanide film. When the Na0.36Co1.36[Fe(CN)(6)] .4.7H(2)O film was irradiated with light from a Xe lamp, the Faraday rotation (FR) and Faraday ellipticity (FE) effects emerge suddenly over the 400-800 nm spectral change. The FR angle changed from 0degrees to -800degrees cm(-1) at 530 nm although only 30% of the absorption coefficient changed (11x10(3)-->7.7x10(3) cm(-1)). After illumination, magnetic hysteresis loops were also observed in FR and FE spectra; The coercive field was 3 kOe. The present Faraday effect was caused by the photoinduced spin transition from the paramagnetic Co-III (S=0)-NC-Fe-II (S=0) phase to the ferromagnetic Co-II (S=3/2)-NC-Fe-III (S=1/2) phase. In addition, the observed transition in the Faraday spectra was assigned to the intervalence transfer band between Co-II and Fe-III through a cyano bridge. (C) 2002 American Institute of Physics.