EFFECT OF DIAMAGNETIC DILUTION ON THE S=1/2 SQUARE HEISENBERG-ANTIFERROMAGNET

Copper (II) formate tetrahydrate (CFTH) is a good example of a two-dimensional (2D) square Heisenberg antiferromagnet with S=1/2. Three-dimensional ordering, driven by weak inter-planar exchange, occurs at a temperature, T-N of 16.5 K. We have measured the de susceptibility of single crystals in which up to 11% of the CU2+ ions have been replaced by diamagnetic Zn2+ ions. T-N decreases linearly with dopant concentration, x, and the behaviour is very similar to that seen in La2CuO4 and in CFTH when studied by ESR spectroscopy. Our results also show an increase in the susceptibility below T-N as x increases due to the larger number of uncompensated moments in the diluted material.