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We have performed elastic and inelastic neutron scattering experiments on single crystal samples of the coordination polymer compound CuF2(H2O)(2)(pyz) (pyz = pyrazine) to study the magnetic structure and excitations. The elastic neutron diffraction measurements indicate a collinear antiferromagnetic structure with moments oriented along the [0.7 0 1] real-space direction and an ordered moment of 0.60 +/- 0.03 mu(B)/Cu. This value is significantly smaller than the single-ion magnetic moment, reflecting the presence of strong quantum fluctuations. The spin wave dispersion from magnetic zone center to the zone boundary points (0.5 1.5 0) and (0.5 0 1.5) can be described by a two-dimensional Heisenberg model with a nearest-neighbor magnetic exchange constant J(2D) = 0.934 +/- 0.0025 meV. The interlayer interaction J(perp) in this compound is less than 1.5% of J(2D). The spin excitation energy at the (0.5 0.5 0.5) zone boundary point is reduced when compared to the (0.5 1 0.5) zone boundary point by similar to 10.3% +/- 1.4%. This zone boundary dispersion is consistent with quantum Monte Carlo and series expansion calculations for the S = 1/2 Heisenberg square lattice antiferromagnet, which include corrections for quantum fluctuations to linear spin wave theory.

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Physical Review B





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