LATTICE-DIMENSIONALITY AND SPIN-DIMENSIONALITY CROSSOVERS IN A LINEAR-CHAIN-MOLECULE-BASED FERRIMAGNET WITH WEAK SPIN ANISOTROPY

[MnOEPI[HCBD], a member of the metalloporphyrin family of donor-accept or molecule-based magnets, consists of isolated ferrimagnetic chains o f alternating S=2, [MnOEP], and s=1/2, [HCBD] units (OEP=octaethylporp hyrinato and HCBD=hexacyanobutadiene). Analysis of the exchange pathwa ys reveals an exchange along one interchain axis (J(inter)) almost 3 o rders of magnitude weaker than the intrachain exchange (J(intra)) and a negligible exchange along the other interchain axis. From the suscep tibility and magnetization data we determine J(intra) and J(inter) to be antiferromagnetic with values of -172 K and -0.4 K, respectively. A t 19.6 K, the system undergoes both lattice and spin dimensionality cr ossovers in which the ferrimagnetic chains couple antiferromagneticall y as two-dimensional Ising sheets.