Complete temperature study of the relaxation from HS to LS state in the mixed [Fe_xZn_{1-x}(Phen)_2(NCS)_2] systems (with x = 1, 0.73, 0.5, 0.32, 0.19 and 0.04)

The thermal and light-induced spin transitions in [FexZn1 x(Phen)2(NCS)2] (Phen = 1,10-phenantholine) have been investigated by magnetic susceptibility, photomagnetism and diffuse reflectivity measurements. These complexes display a thermal spin transition and undergo the light-induced excited spin state trapping (LIESST) effect at low temperatures. For each compound, the thermal spin transition temperature, T1/2, and the relaxation temperature of the photo-induced high-spin state, T(LIESST), have been systematically determined. It appears that T1/2 decreases with the metal dilution while T(LIESST) remains unchanged. This behaviour is discussed on the basis of the kinetic study performed by combining the use of SQUID magnetometer, up to the T(LIESST) value, and the dynamic diffuse reflectivity setup, from the T(LIESST) temperature up to the thermal spin transition.Transitions de phase photo-induites : vers la commutation ultra-rapide de matériaux moléculaire