Visible-Light-Induced Reversible Photomagnetism in Rubidium Manganese Hexacyanoferrate

The photoreversibility of a photoinduced phase transition was investigated in a rubidium manganese hexacyanoferrate, Rb0.88Mn[Fe(CN)6]0.96·0.5H2O. The present material shows a charge-transfer phase transition from the MnII−FeIII [high-temperature (HT)] phase to the MnIII−FeII [low-temperature (LT)] phase, and the LT phase shows ferromagnetism. Spectroscopic ellipsometry measurements of the dielectric constant suggest that the optical transitions in the LT and HT phases are a metal-to-metal charge transfer (FeII → MnIII) band at 420–540 nm and a ligand-to-metal charge transfer (CN– → FeIII) band of [FeIII(CN)6] at 410 nm, respectively. By irradiation with 532 nm light, the LT phase is transmitted to the photoinduced (PI) phase, which has a valence state similar to that of the HT phase, and photodemagnetization is observed. In contrast, irradiating the PI phase with 410 ± 30 nm light causes the reverse phase transition. Neutron powder diffraction measurement of an analogue compound, Rb0.58Mn[Fe(CN)6]0.86·2.3H2O, which does not show a charge-transfer phase transition and maintains the MnII−FeIII phase at a very low temperature, confirms that the PI phase is an antiferromagnet. Hence, the present visible-light-induced reversible photomagnetic effect is due to optical switching between the ferromagnetic LT phase and the antiferromagnetic PI phase.