Magnetic properties and optical control of electrochemically prepared iron-chromium polycyanides

The magnetic properties and photo-magnetic effects of the electrochemically prepared metal polycyanide film, Fe_1.5^II[Cr^III(CN)₆]·7.5H₂O, were investigated. Magnetization measurements showed that it was a ferromagnet (parallel spin ordering) having a T_c = 21 K. The spontaneous magnetization decreased optically by the photoexcitation of the intervalence transfer (IT) band between Fe^II and Cr^III. This optically reduced magnetization persisted for a period of several days at 5 K after turning off the light. ⁵⁷Fe Moessbauer experiments showed that the spin state of iron did not change but the strength of a ferromagnetic interaction between Fe^II and Cr^III decreased after the irradiation, forming a paramagnetic metastable state. This metastable state returned to the original state above 40 K, showing that the magnetization of this compound can be controlled reversibly by the combination of optical and thermal methods.