Magnetic susceptibility and electron spin resonance of [(CH3)3NH]CuCl3· 2H2O

The low-temperature magnetic susceptibilities and electron spin resonance of single crystals of [${\left(\mathrm{C}{\mathrm{H}}_3\right)}_3$NH]Cu${\mathrm{Cl}}_3$ · 2${\mathrm{H}}_2$O are reported. The crystal orders magnetically at $T_c=0.157\mathrm{}\pm 0.003$ K. Above the transition the susceptibility can be fit to the high-temperature expansion for a two-dimensional ferromagnetic square Heisenberg lattice with $\frac{J}{k}=0.28\mathrm{}\pm 0.02$ K. Below $T_c$ the crystal exhibits behavior characteristic of weak antiferromagnetic coupling between the ferromagnetic layers.