Magnetic field induced quantum phase transition of the S = 1 2 antiferromagnet K 2 NaCrO 8

The magnetic properties of alkali-metal peroxychromate ${\text{K}}_{2}{\text{NaCrO}}_{8}$ are governed by the $S=1/2$ pentavalent chromium cation, ${\text{Cr}}^{5+}$. 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 ${T}_{N}=1.66\text{ }\text{K}$ in $H=0$. In the $T\ensuremath{\rightarrow}0$ limit, the magnetic field tuned antiferromagnetic to spin-polarized phase transition suggests a critical field ${\ensuremath{\mu}}_{\text{o}}{H}_{c}=7.270\text{ }\text{T}$ and a critical exponent $\ensuremath{\alpha}=0.481\ifmmode\pm\else\textpm\fi{}0.004$. The neutron data indicate the magnetic interactions may extend over intraplanar nearest-neighbor and interplanar next-nearest-neighbor spins.