Magnetic Ordering in Copper Pyrazine Perchlorate, a S=1/2 2D Quantum Heisenberg Antiferromagnet

Copper pyrazine perchlorate, Cu(Pz)$_{2}$(ClO$_{4})_{2}$, consists of antiferromagnetic layers of Cu$^{2+}$ ions bridged by neutral pyrazine molecules. The exchange strength within the layers is J/k$_{B}$ = 17.5 K; excellent isolation between layers is provided by the bulky perchlorate ions. Specific heat studies and muon spin resonance measurements [1] show the ordering temperature to be 4.25 K, corresponding [2] to an interlayer/intralayer exchange ratio of 1 x 10$^{-3}$. The specific heat data show no characteristic anomaly at T$_{N}$, only a broad contribution attributable to the short-range order within the layers. This result is consistent with recent theoretical predictions [3]. The excellent isolation results in the observation of field-induced XY-behavior in the magnetic susceptibility, as predicted elsewhere [4]. 1. J. Manson \textit{et al}, unpublished results. 2. C. Yasuda \textit{et al}, \textit{Phys. Rev. Lett.} \textbf{94}, 217201 (2005). 3. P. Sengupta \textit{et al}, \textit{Phys. Rev. B}, \textbf{68}, 094423 (2003). 4. A. Cuccoli \textit{et al}, \textit{Phys. Rev. B}, \textbf{68}, 060402 (2003).