Evolution of magnetic interactions in a pressure-induced Jahn-Teller driven magnetic dimensionality switch

Much of the research in molecular magnetism focusses on low-dimensional magnetic systems. Here we discuss the interesting possibility of controlling the magnetic dimensionality in a molecular magnet by driving the system through a quantum critical point using applied pressure. We present the results of muon-spin relaxation measurements and high-field magnetisation experiments on the coordination polymer CuF$_2$(H$_2$O)$_2$(pyrazine) in pressures up to 22.5 kbar that demonstrate a transition from a quasi-two-dimensional to a quasi-one-dimensional antiferromagnetic phase driven by a rotation of the Jahn-Teller axis at 9.1 kbar. Antiferromagnetic ordering is observed in both regimes. The dimensionality switch is accompanied by a halving of the primary magnetic exchange energy $J$ and a fivefold decrease in the ordering temperature $T_{\mathrm{N}}$. Density-functional theory calculations of the spin density and muon sites are used to complement the experimental data. Part of this work is published in S. Ghannadzadeh et al., Phys. Rev. B 87, 241102 (R).