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)center dot 0.5H(2)O. The present material shows a charge-transfer phase transition from the Mn-II-Fe-III [high-temperature (HT)] phase to the Mn-III-Fe-II [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 (Fe-II -> Mn-III band at 420 - 540 nm and a ligand-to-metal charge transfer (CN--> Fe-III) band of [Fe-III(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)center dot 2.3H(2)O, which does not show a charge-transfer phase transition and maintains the Mn-II - Fe-III. 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.