Low Dimensional Magnetism in Cu(tn)Cl2 Mediated by Hydrogen Bonds.

Electron paramagnetic resonance studies of Cu(tn)Cl2 (tn = C3H10N2) performed from 2 K to 20 K revealed quasi-tetragonal symmetry of the local Cu(II) surroundings leading to the stabilization of the dz2 electronic ground state. Consequently, despite the presence of much stronger covalent bonds coupling Cu(II) ions into isolated covalent ladders, the magnetic system is determined by the geometry of hydrogen bonds serving as exchange paths that form a triangular lattice with a spatial anisotropy. The low dimensional character of magnetic correlations with effective intralayer interaction J1/kB ≈ -3 K is reflected in the magnetization, specific heat, and susceptibility data. The T2 dependence of the specific heat observed below 200 mK. can be associated with a gapless character of spin excitation spectrum supporting Néel order in the ground state. The excellent low dimensionality is demonstrated by weak interlayer coupling J′ ≈ 10-3 J1 and no trace of long range order down to 60 mK. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]