Reentrance in the ${\mathrm{Mn}\left(\mathrm{tetracyanoethylene}\right)\mathrm{}}_x\cdot y\left({\mathrm{CH}}_2{\mathrm{Cl}}_2\right)$ high-$T_c$ molecule-based ferrimagnet

Results of static and dynamic magnetic studies of the compound ${\mathrm{Mn}\left(\mathrm{TCNE}\right)\mathrm{}}_x\cdot y\left({\mathrm{CH}}_2{\mathrm{Cl}}_2\right)$ (TCNE =tetracyanoethylene) are reported. Curie-Weiss analysis of the high-temperature susceptibility data indicates a relatively 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 75 K. Additional peaks in both components, which are frequency dependent, are observed near 10 K. Weak irreversibilities, including a remanent moment and a bifurcation of the field-cooled (FC) and zero-field-cooled (ZFC) dc magnetizations are observed below 75 K. These irreversibilities become more pronounced below $\sim 10\mathrm{K}.$ The presence of frequency dependence in the ac susceptibility and field dependence of the FC/ZFC magnetizations near 10 K but not at 75 K strongly suggest reentrance. Static scaling analysis at the high-temperature transition and 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 discussed.