Koshihara Okimoto Lab.

Spin Crossover Fe Complexes
Spin Crossover Fe Complexes

A spin crossover complex is composed of transition metals (Fe, Zn, Mn, Cu, etc…) surrounded by anions that form a strong crystal field as shown in Fig. 1. We have investigated one of such examples, a Fe-complex ([Fe(2-pic)3]Cl2・EtOH) depicted in Fig. 2.

This complex is yellow at high temperature while dark red at low temperature, reflecting the spin-crossover transition between HS (eg2t2g4) and LS (t2g6) state at -150℃. (Fig.3)

The phase transition like this may be a similar phenomenon to that between water and ice at 0℃. However, phase transition of this complex also occurs by irradiation with light. A unique character in the phase transition of this complex is that a reversible photonic change beteween HS⇔LS can be realized by changing the wavelength of the excitation light. This phenomenon was discovered ten years ago, but we have been investigating the mechanism of the phase transition by light (i.e., photo induced phase transition).

"Magnetic Field Effect on the Dynamics of Photoinduced Spin State Phase Transition", Phys. Rev. B, 66 (2002) 073104. Y. Ogawa et al

Electronic and Structual Phase Transition Controlled by Photo-excitation and Magnetic Filed in Spin Crossover Complexモ, Mol. Cryst. Liq. Cryst., 379 (2002) 357-364.  Y. Ogawa et al