Nature and mechanism of the photoinduced spin transition in[Fe(PM−BiA)2(NCS)2]

State of the art and opportunities in probing photoinduced phase transitions in molecular materials by conventional and picosecond X-ray diffraction

“…Therefore, the average molecular state probed by X-ray diffraction changes discontinuously from HS to LS states, and so does the crystalline volume. All the different phases have the same symmetry (Ichiyanagi et al, 2006) and the photoinduced HS states is very similar to what would be the high temperature HS phase at low temperature if no phase transition occurred.…”

“…mesoscopic regions consisting of molecules in HS state or regions of molecules in the LS state) around photoinduced phase transition is of growing interest nowadays, because of the key role it plays in the macroscopic state switching of the material. But such a phase separation in the time domain is one of these aspects, and so is the appearance of LightInduced Thermal Hysteresis (LITH), as in BIA1 for example, which was evidenced by photo-magnetic studies (Lé-tard et al, 2003, Ichiyanagi et al, 2006. As shown in Fig.…”

“…This phase separation process was described as indicative of an Avrami behavior (Huby et al, 2004). This was also investigated in the BIA1 compound (Ichiyanagi et al, 2006) and a detailed investigation of the Avrami behavior was carried out on another compound (Pillet et al, 2006). Since the spatial separation of the coexisting peaks is small, the intensity of a Bragg reflection (I int ), integrated by the software, is the sum of both peaks.…”

“…Out of equilibrium processes also occur under continuous or pulsed light irradiation, in particular the LIESST effect (Light-Induced Excited Spin-State Trapping) at low temperature. Only recently the LIESST effect has begun to be thoroughly investigated by X-ray diffraction (Gütlich et al, 2004;Huby et al, 2004;Ichiyanagi et al, 2006;Kusz et al, 2005;Marchevie et al, 2002;Niel et al, 2005;Thompson et al, 2004;Pillet et al, 2006;Trzop et al, 2007 . .…”

“…Below 78 K, the HS state can be generated under weak continuous laser excitation. This photoinduced phase transition was investigated by X-ray diffraction at different temperatures and resulting structures were compared to those of the LS and HS states at low and high temperature respectively (Ichiyanagi et al, 2006). The photoinduced HS state was generated from the LS state by a continuous laser excitation (808 nm) at 20 K, where complete transformation is easily reached, as shown by magnetic measurements (Létard et al, 2003).…”