Metal-organic frameworks (MOFs) can exhibit many interesting properties such as multiferroic behavior, dipolar glass, gas storage, and protonic conductivity. Here we report that dimethylammonium copper formate (DMACuF) [(CH${}_3$)${}_2$NH${}_2$]Cu(HCOO)${}_3$, a cation templated nonporous MOF with perovskite topology, exhibits strong one-dimensional (1D) antiferromagnetism with a Néel temperature, $T_N$, of 5.2 K. These conclusions are derived from detailed magnetic susceptibility, heat capacity, dielectric constant, and high-frequency electron paramagnetic resonance measurements as well as density functional theory (DFT) calculations. The magnetic susceptibility exhibits a broad maximum at ∼50 K, suggesting low-dimensional magnetism; heat capacity measurements show a Néel temperature of 5.2 K. The magnetization versus field data at 1.8 K shows a spin-flop transition at $H_{sf}$ ∼ 1.7 T. The ratio $T_N$/$J=6.5\times {10}^{-2}$, where $J$ is the near-neighbor exchange constant (77.4 K), and the small value (2 K) of the interchain coupling suggests that DMACuF is close to an ideal 1D magnet. In this three-dimensional crystal lattice, the 1D magnetic behavior is made possible by the Jahn-Teller distortion of the 3$d^9$ Cu${}^{2+}$ ions. Temperature dependence of the electron paramagnetic resonance field and the linewidth exhibits critical broadening for temperatures below 50 K, following a behavior quite characteristic of 1D spin systems. DFT calculations show that [(CH${}_3$)${}_2$NH${}_2$]Cu(HCOO)${}_3$ has a magnetic structure in which 1D antiferromagnetic chains parallel to the $c$ direction are weakly coupled ferromagnetically, supporting the thermomagnetic and EPR results. Dielectric measurements under applied magnetic fields of 0−7 T reveal a kink at the $T_N$, a clear indication of magnetostriction behavior.

• Received 25 July 2012

DOI:https://doi.org/10.1103/PhysRevB.87.224406