Rapid cooling and magnetic field-induced cooperative effect for the metastable quintet state in a spin crossover complex

Our study shows that metastable quintet state of spin crossover complex [Fe (dpp)(2)(NCS)(2)]. py (dpp=dipyrido[3,2-a:2',3'-c] phenazine, py=pyridine) at low temperatures may be realized by a rapid cooling. The relaxation from quintet state to singlet spin at low temperatures depends on the both of t ime and previous history of the sample. The U-shaped dents of the magnetic effective moment depending on the temperature after initial rapid zero-fiel d cooling indicate an obvious affection of magnetic field to the realizatio n of singlet state in the transition range. The observations for this sampl e are indeed consistent with the fact that cooperative effects play a very important role in the spin transition. (C) 1999 American Institute of Physi cs. [S0003-6951(99)00426-X].