Abstract
The static and dynamic spin fluctuations in the spinS=1, two-dimensional (2D) square-lattice antiferromagnet La2NiO4 have been studied over a wide temperature range using neutron scattering techniques. The spin correlations in La2NiO4 exhibit a crossover from two- to three-dimensional (3D) behavior as the Neel temperature is approached from above. Critical slowing down of the low-energy spin fluctuations is also observed just aboveTN. The correlation length, ξ(T), and the static structure factor,S(0), have been measured and are compared with recent theoretical calculations for the quantum 2D Heisenberg antiferromagnet using microscopic parameters determined from previous spin-wave measurements. Good agreement for ξ(T) is found with the exact low-temperature result of Hasenfratz and Niedermeyer provided that 2πps is renormalized by ≈20% from the spin-wave value.
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