Strongly correlated one-dimensional magnetic behavior of NiTa ₂O₆

The magnetic properties of NiTa₂O₆ were investigated by magnetic susceptibility, specific heat, electron paramagnetic resonance, neutron powder diffraction, and pulse field magnetization measurements. Accompanying ab initio DFT calculations of the spin-exchange constants complemented and supported our experimental findings that NiTa₂O₆ must be described as a quasi-1D Heisenberg S=1 spin chain system with a nearest-neighbor only antiferromagnetic spin-exchange interaction of 18.92(2) K. Interchain coupling is by about two orders of magnitude smaller. Electron paramagnetic resonance measurements on Mg1-xNixTa₂O₆ (x≈1%) polycrystalline samples enabled us to estimate the single-ion zero-field splitting of the S=1 states which amounts to less than 4% of the nearest-neighbor spin-exchange interaction. At 0 T NiTa₂O₆ undergoes long-range antiferromagnetic ordering at 10.3(1) K evidenced by a λ-type anomaly in the specific heat capacity. On application of a magnetic field the specific heat anomaly is smeared out. We confirmed the magnetic structure by neutron powder diffraction measurements and at 2.00(1) K refined a magnetic moment of 1.93(5) μB per Ni²⁺ ion. Additionally, we followed the magnetic order parameter as a function of temperature. Last, we found saturation of the magnetic moment at 55.5(5) T with a g factor of 2.14(1), with an additional high field phase above 12.8(1) T. The onset of the new high field phase is not greatly affected by temperature, but rather smears out as one approaches the long-range ordering temperature.