Frustrated spin- 12 square lattice in the layered perovskite PbV O3

We report on the magnetic properties of the layered perovskite $\mathrm{Pb}\mathrm{V}{\mathrm{O}}_{3}$. The results of magnetic susceptibility and specific heat measurements as well as band-structure calculations consistently suggest that the $S=1∕2$ square lattice of vanadium atoms in $\mathrm{Pb}\mathrm{V}{\mathrm{O}}_{3}$ is strongly frustrated due to next-nearest-neighbor antiferromagnetic interactions. The ratio of next-nearest-neighbor $({J}_{2})$ to nearest-neighbor $({J}_{1})$ exchange integrals is estimated to be ${J}_{2}∕{J}_{1}\ensuremath{\approx}0.2--0.4$. Thus, $\mathrm{Pb}\mathrm{V}{\mathrm{O}}_{3}$ is within or close to the critical region of the ${J}_{1}\ensuremath{-}{J}_{2}$ frustrated square lattice. Supporting this, no sign of long-range magnetic ordering was found down to $1.8\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.