Critical dynamics of the body-centered-cubic classical Heisenberg antiferromagnet

We have used spin dynamics techniques to perform large-scale simulations of the dynamic behavior of the L×{}L×{}L body-centered-cubic classical Heisenberg antiferromagnet with L{≤}48 at a range of temperatures above and below as well as at the critical point Tc. The temporal evolutions of the spin configurations were determined numerically from coupled equations of motion for individual spins by a fourth-order predictor-corrector method, with initial spin configurations generated by Monte Carlo simulations. The neutron scattering function S(q,{ω}) was calculated from the space- and time-displaced spin-spin correlation function. We used a previously developed dynamic finite-size scaling theory to extract the dynamic critical exponent z from S(q,{ω}) at Tc. Our results are in agreement with the theoretical prediction of z=1.5 and with experimental results; however, we find that the asymptotic regime was only entered at L{}30. In the analysis of the form of the transverse and longitudinal components of S(q,{ω}) we found that a central diffusion peak appears below Tc predominantly in the longitudinal component and remains present through and above Tc. The transverse component of the spin-wave peak is Lorentzian below Tc but for T{}Tc is described best by a more complex functional form. Below Tc we see evidence of multiple spin-wave peaks in the longitudinal component. {} 1996 The American Physical Society.