REENTRANCE IN THE MN(TETRACYANOETHYLENE)(X)CENTER-DOT-Y(CH2CL2) HIGH-T-C MOLECULE-BASED FERRIMAGNET

Results of static and dynamic magnetic studies of the compound Mn(TCNE )(x).y(CH2Cl2) (TCNE =tetracyanoethylene) are reported. Curie-Weiss an alysis of the high-temperature susceptibility data indicates a relativ ely strong exchange. The ac susceptibility, measured as a function of frequency and temperature, reveals frequency-independent peaks in both the in-phase and out-of-phase components of the susceptibility near 7 5 K. Additional peaks in both components, which are frequency dependen t, are observed near 10 K. Weak irreversibilities, including a remanen t moment and a bifurcation of the field-cooled (FC) and zero-field-coo led (ZFC) de magnetizations are observed below 75 K. These irreversibi lities become more pronounced below similar to 10 K. The presence of f requency dependence in the ac susceptibility and field dependence of t he FC/ZFC magnetizations near 10 K but not at 75 K strongly suggest re entrance. Static scaling analysis at the high-temperature transition a nd dynamic scaling analysis at the low-temperature transition provide clear evidence for ordering with a spontaneous moment at 75 K and as a spin glass below 10 K. Possible mechanisms for this behavior are disc ussed.