Low Dimensional Magnetism in Cu(tn)Cl_(2) Mediated by Hydrogen Bonds

摘要

Electron paramagnetic resonance studies of Cu(tn)Cl_(2) (tn velence C_(3)H_(10)N_(2)) performed from 2 K to 20 K revealed quasi-tetragonal symmetry of the local Cu(II) surroundings leading to the stabilization of the d_(z~(2)) 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 J_(1)/k_(B) approx= -3 K is reflected in the magnetization, specific heat, and susceptibility data. The T~(2) dependence of the specific heat observed below 200 mK can be associated with a gapless character of spin excitation spectrum supporting Neel order in the ground state. The excellent low dimensionality is demonstrated by weak interlayer coupling J' approx= 10~(-3)J_(1) and no trace of long range order down to 60 mK.