Magnetic properties of the S=12 honeycomb lattice antiferromagnet 2−Cl−3,6−F2−V

We successfully synthesized single crystals of the verdazyl radical $2\text{\ensuremath{-}}\mathrm{Cl}\text{\ensuremath{-}}3,6\text{\ensuremath{-}}{\mathrm{F}}₂\text{\ensuremath{-}}\mathrm{V}$ [=3-(2-chloro-3,6-difluorophenyl)-1,5-diphenylverdazyl], which is a rare model compound with an $S=\frac{1}{2}$ Heisenberg antiferromagnetic (HAF) honeycomb lattice. Ab initio molecular orbital calculations indicate two dominant AF interactions, forming a slightly distorted honeycomb lattice. We explain the magnetic susceptibility and the magnetization curve up to the saturation field based on the expected spin model using the quantum Monte Carlo method. In the low-temperature regions, we found a phase transition to an AF ordered state at about 0.77 K for the zero field and obtained the magnetic field-temperature phase diagram from the magnetic susceptibility and the specific heat for various magnetic fields. Through the analysis considering the effect of lattice distortion on magnetic behavior, we confirm that the lattice distortion of the present model is small enough that it does not affect the intrinsic behavior of the uniform $S=\frac{1}{2}$ HAF honeycomb lattice.