MAGNETIC SPECIFIC-HEAT ANALYSIS OF CU(C2H8N2)(2)NI(CN)(4) - A QUASI-2-DIMENSIONAL HEISENBERG-ANTIFERROMAGNET

The specific heat of Cu(C2H8N2)Ni(CN)(4) measured in the temperature r ange from 80 mK to 2 K revealed significant deviations from the assume d one-dimensional (1D) magnetic behaviour. The behaviour of short rang e correlations was described by a S=1/2 quadratic Heisenberg antiferro magnetic model with the exchange constant J/k = -180 mk. Intrachain co valent bonds are completed by bifurcated hydrogen bonds of the N-H...N (C)...H-N type connecting adjacent chains and creating a 2D net of exc hange paths. The origin of the lambda-like anomaly in the specific hea t observed at 128 +/- 2 mk was ascribed to the 2D-3D crossover in magn etic lattice dimensionality activated by the interlayer dipolar intera ction.