Magnetooptical effects of room temperature molecular-based magnetic films composed of vanadium hexacyanochromates

We electrochemically synthesized film-type vanadium hexacyanochromate-based magnets with high critical temperatures (T-c): K(0.31)(I)V(0.49)(II)V(III)0.51[Cr-III(CN)6](0.94).6.5H(2)O (1) (T-c = 310 K) and (K0.61V0.97VIII0.03)-V-I-V-II[Cr-III(CN)(6)](0.88). 7.2H(2)O(0.4)C(2)H(5)OH (2) (T-c = 345 K). The colors of these films were blue and dark blue. For film 1, the Faraday ellipticity (FE) spectra showed a weak negative peak (A) and a strong negative peak (B) around 550 nm (-640 deg cm(-1) at 50 K) and 660 nm (-2300 deg cm(-1) at 50 K), respectively. In the Faraday rotation (FR) spectra, two dispersive-shaped lines were observed at the same wavelength. Simulation of these spectra showed that the observed spectra can be classified as the paramagnetic type of Faraday effects. For film 2, the Faraday effect was observed even above room temperature. In its FE spectra, two negative peaks were observed around 530 nm (-850 deg cm(-1) at 50 K) and 660 nm (-300 deg cm(-1) at 50 K), respectively. These FE peak positions are close to the peak positions of A and B for film 1, suggesting that the origins of the Faraday effects of 1 and 2 are the same. Based on stoichiometric coefficients of the obtained films, A and B bands were assigned to the intervalence transfer (IT) bands of V-II-NC-Cr-III and Vm-NC-Crm, respectively. The present Faraday spectra in the ferromagnetic region are the first to be observed among molecular-based magnets.