One-dimensional quantum magnetism in the S=1/2 Mo(V) system, KMoOP₂O₇

We present a comprehensive experimental and ab initio study of the S = 1/2 Mo⁵⁺ system, KMoOP₂O₇ , and show that it realizes the S = 1/2 Heisenberg chain antiferromagnet model. Powder neutron diffraction reveals that KMoOP₂O₇ forms a magnetic network comprised of pairs of Mo⁵⁺ chains within its monoclinic P 2₁/n structure. Antiferromagnetic interactions within the Mo⁵⁺ chains are identified through magnetometry measurements and confirmed by analysis of the magnetic specific heat. The latter reveals a broad feature centered on T_N = 0.54 K, which we ascribe to the onset of long-range antiferromagnetic order. No magnetic Bragg scattering is observed in powder neutron-diffraction data collected at 0.05 K, however, which is consistent with a strongly suppressed ordered moment with an upper limit μ_ord < 0.15 μ_B . The one-dimensional character of the magnetic correlations in KMoOP₂O₇ is verified through analysis of inelastic neutron-scattering data, resulting in a model with J₂ ≈ 34 K and J₁ ≈ − 2 K for the intrachain and interchain exchange interactions, respectively. The origin of these experimental findings are addressed through density-functional theory calculations.