New High Tc Molecule-Based Magnets - Magnetic Behavior of M(TCNE)2·x(CH2Cl2) (M ˭ Mn, Fe)

Abstract

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