New high Tc molecule-based magnets -: Magnetic behavior of M(TCNE)2•x(CH2Cl2) (M = Mn, Fe)

We report and review studies of new partially crystalline members of the high-T-c molecule-based magnets family, M(TCNE)(2). x(CH2Cl2), (M = Fe, Mn, TCNE = tetracyanoethylene). Remanent magnetization revealed high critical temperatures, T-c = 97 K for M = Fe and 75 K for M = Mn. Hysteresis curves for the Fe compound, for 5 less than or equal to T less than or equal to 80 K, have a spin-flop shape, indicating ferrimagnetic behavior. Field-cooled and zero-field-cooled magnetization reveals magnetic irreversibilities below T-c for both compounds. Static and dynamic scaling analyses of the de magnetization and ac susceptibility for M = Mn show a transition to a 3D ferrimagnetic state at T-c = 75 K, followed by a reentrant transition, to a spin glass state at T-g = 2.5 K. For M = Fe static scaling analyses are consistent with a high-T transition to a correlated sperimagnet, while below similar to 20 K there is a crossover to sperimagnetic behavior.