Optical and magnetic properties of the photo-induced state in the coordination network Na2Co4[Fe(CN)6]3.3·14H2O

Abstract

The study of the metastable state, obtained by light irradiation of Na₂Co₄[Fe(CN)₆]_3.3·14H₂O is reported using reflectivity and magnetic measurements. This compound is characterized by a charge transfer phenomenon occurring between a high-temperature phase (HT phase) formed by paramagnetic Co^II–Fe^III pairs and a low-temperature phase (LT phase) formed by diamagnetic Co^III–Fe^II pairs with the occurrence of a thermal-induced hysteresis loop. A metastable phase can be also formed at low temperature by irradiation following a photo-induced charge transfer between the LT phase and the photo-induced phase (PI phase) formed by Co^II–Fe^III pairs. The phenomenon corresponds to the well-known light-induced excited spin state trapping (LIESST) effect. The study of the dynamics in the PI phase showed that the relaxation curves follow monoexponential decays. This is in apparent contradiction with the presence of a thermal hysteresis loop. The thermodynamic parameters that govern the relaxation have been determined. The accuracy of these parameters has been checked by simulating the experimental T(LIESST) curve.