Magnetic field induced quantum phase transition of the S= 1 2 antiferromagnet K₂ NaCrO₈

The magnetic properties of alkali-metal peroxychromate K₂ NaCrO₈ are governed by the S=1/2 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-K in H=0. In the T→0 limit, the magnetic field tuned antiferromagnetic to spin-polarized phase transition suggests a critical field μ_o H_c =7.270-T and a critical exponent α=0.481±0.004. The neutron data indicate the magnetic interactions may extend over intraplanar nearest-neighbor and interplanar next-nearest-neighbor spins.