Single crystal magnetic susceptibility of 1-D [PM·Cu(NO3)2·(H2O)2]n

Single crystal studies of the magnetic susceptibility of the chain compound [PM·Cu(NO3)2·(H2O)2]n (PM = pyrimidine) show that it is a good example of a uniform S = 1/2 antiferromagnetic Heisenberg chain, characterized by a single exchange parameter 12J|/kB = 36 K. The Cu g-tensor principal values are g = 2.34(2) and g⊥ = 2.05(2). In the low-T region a divergent contribution to the susceptibility (Curie tail) is observed that exhibits a pronounced anisotropy. This Curie tail cannot be reconciled assuming chain defects or impurities as its origin. It rather appears intrinsic to the chains and associated with the relative canting of the local g-tensors of neighbouring Cu ions and the Dzialoshinski-Moriya interaction. Our study constitutes evidence for a staggered contribution to the susceptibility which has been predicted theoretically recently.