1987 Volume 56 Issue 11 Pages 4027-4039
Critical properties of a Heisenberg antiferromagnet on a triangular lattice are investigated experimentally using a quasi-two-dimensional antiferromagnet VCl2 by means of neutron scattering. It is found that VCl2 shows characteristic critical behaviors of two and three dimensional models. A little above TN, the line shape of χ(Q) is found to be represented by the Ornstein-Zernike form (κ2+q2)−1. This suggests the existence of magnetic point defects which were predicted in the two dimensional model. The measured critical exponents are β=0.20±0.02, γ=1.05±0.03, and ν=0.62±0.05, in agreement with the theoretical work for three dimensional SO(3) systems. Successive phase transitions due to a small Ising anisotropy were found at TN1=35.88±0.01 K and TN2=35.80±0.01 K. The spin structure and the dispersion relation of the spin wave well below TN are also determined.
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