Magnetophoretic study of photo-induced spin transition of single crystalline particles of cobalt-iron Prussian blue analogues

The photo-induced spin transition of crystalline microparticle of Co-Fe Prussian blue analog was investigated by means of magnetophoresis. An apparatus to observe the photo-induced spin transition of a single microcrystal in suspension was constructed, and the magnetophoretic velocities before and after the irradiation with 532 nm pulse laser were observed. The photo-induced spin transition from a low-spin state to a high-spin state of the microparticle was observed from the abrupt increase of the magnetophoretic velocity after the irradiation. The threshold value for spin transition was estimated to be lower than 10 mJ cm−2 by this method, more precisely than that reported from SQUID magnetometer measurements. Moreover, the magnetic susceptibility of an individual particle after irradiation was calculated from the magnetophoretic velocity change. The magnetic susceptibility values determined by the present method were highly scattered. This was caused not only by the experimental error resulting from Brownian motion but also by the difference in the spin transition probability for individual particles. The effect of size on the spin transition phenomena was discussed.