Two-dimensional magnetism in α−CuV2O6

Several previous studies reported that a one-dimensional Heisenberg chain model is inadequate in describing the magnetic properties of the low-dimensional quantum antiferromagnet $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{CuV}}_{2}{\mathrm{O}}_{6}$, but the origin for this observation has remained unclear. We have reinvestigated the magnetic properties of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{CuV}}_{2}{\mathrm{O}}_{6}$ and found that our anisotropic magnetic susceptibility, neutron-powder diffraction, and electron paramagnetic spin-resonance measurements are in good agreement with extensive density-functional theory ($\mathrm{DFT}+U$) total energy calculations which indicate that the correct spin lattice model for $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{CuV}}_{2}{\mathrm{O}}_{6}$ is rather a $S=1/2$ 2D-Heisenberg antiferromagnetic lattice. The magnetic susceptibility data are well described by a rectangular Heisenberg antiferromagnet with anisotropy ratio $\ensuremath{\alpha}\ensuremath{\sim}$ 0.7 consistent with the DFT results. Quantum Monte Carlo simulations of the magnetic susceptibilities for a rectangular lattice Heisenberg antiferromagnet were performed in the anisotropy range 0.5 $\ensuremath{\le}\ensuremath{\alpha}\ensuremath{\le}$ 1.0. The results of the Quantum Monte Carlo calculations were cast into a Pad\'e approximant which was used to fit the temperature-dependent magnetic susceptibility data. Neutron-powder-diffraction measurements were used to conclusively solve the collinear antiferromagnetic structure of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{CuV}}_{2}{\mathrm{O}}_{6}$ below the N\'eel temperature of $\ensuremath{\sim}22.4$ K.