Spin transition with a very large thermal hysteresis in a molecular crystal: an EPR study of Fe(PM-PEA)(2)(NCS)(2)

Magnetic susceptibility and X- and Q-band EPR studies are reported for the Fe2+ spin transition compound (Fe(PM-PEA)(2)(NCS)(2)) in powder form. An ex ceptionally large thermal hysteresis loop, about 60 K, has been found by bo th techniques. The EPR studies have been carried out on compound doped with Mn2+ (0.1 parts per thousand of Mn/Fe). An original EPR spectra simulation program has been elaborated in order to yield data on the structural modif ications accompanying the spin transition. The fine structure parameters ob tained by simulations in the high-spin state of Fe2+, D = 460, E = 25, and in the low-spin state of this ion, D = 235, E = 20 (in 10(-4) cm(-1)) confi rm that the spin transition is accompanied by a crystalline phase transform ation. The Mn2+ EPR spectra in the spin transition region can be convincing ly fitted by linear combinations of the spectra observed in the high-spin a nd low-spin states of Fe2+, indicating that the spin transition occurs in d omains of like-spin ions. (C) 1999 Elsevier Science B.V, All rights reserve d.