Controlling magnetic order and quantum disorder in molecule-based magnets

Metal-organic coordination polymers are materials in which transition metal ions are linked via organic molecules into chain or plane-like structures. Strong hydrogen bonds enable these units to form three-dimensional lattices, while the underlying anisotropy causes low-dimensional magnetism to evolve. Here the magnetic properties of a number of these compounds are investigated through high-field magnetization, heat capacity, and magnetic susceptibility measurements. It is shown that [Cu(pyz)H$_2$O(gly)$_2$]ClO$_4$ is a highly one-dimensional antiferromagnet, whilst the compounds [Cu(pyz)(gly)]ClO$_4$ and Cu(H$_2$O)VCF$_4$ are dimerized with a non-magnetic singlet ground state and behave as zero-dimensional disordered magnets at zero field. Furthermore, these two materials are shown to undergo a field-induced transition through a quantum critical point into an XY ordered phase, which in the case of [Cu(pyz)(gly)]ClO$_4$, is reminiscent of Bose-Einstein condensation of triplons.