Neutron scattering and the critical behavior of the three-dimensional Ising antiferromagnet FeF2

Neutron scattering has been used to study a high-quality single crystal of the very anisotropic antiferromagnet FeF2 over the reduced temperature range 10/sup -4/<chemical bondtchemical bond<10/sup -1/. Analysis of the data by use of the Lorentzian scattering form of Ornstein and Zernike is shown to be inadequate, particularly for T<T/sub c/. The use of better theoretical scattering forms for chemical bondtchemical bond<10/sup -2/ yields power-law behavior with the exponents ν = 0.64 +- 0.01 and γ = 1.25 +- 0.02 and the amplitude ratios κ0+/κ0- = 0.53 +- 0.01 and κ0+/κ0- = 4.6 +- 0.2 for the inverse correlation length and staggered susceptibility, respectively. These results are in excellent agreement with the theory for the three-dimensional Ising model. Hence, the consistency between theory and neutron scattering in FeF2 is greatly improved over previous experiments