Magnetic field induced quantum phase transition of the $S=1\mathrm{/}2$ antiferromagnet $K_{2}NaCr{O}_8$

The magnetic properties of alkali-metal peroxychromate K${}_2$NaCrO${}_8$ are governed by the $S=1\mathrm{/}2$ pentavalent chromium cation, Cr${}^{5+}$. Specific heat, magnetocalorimetry, ac magnetic susceptibility, torque magnetometry, and inelastic neutron scattering data have been acquired over a wide range of temperature, down to 60 mK, and magnetic field, up to 18 T. The magnetic interactions are quasi-two-dimensional prior to long-range ordering, where $T_N = 1.66$Kin$H = 0$\mathrm{.}Inthe$T \to 0$ limit, the magnetic field tuned antiferromagnetic-ferromagnetic phase transition suggests a critical field $H_c = 7.270$Tandacriticalexponent$\alpha = 0.481 \pm 0.004$. The neutron data indicate the magnetic interactions may extend over intra-planar nearest-neighbors and inter-planar next-nearest-neighbor spins.