CRITICAL-DYNAMICS OF THE BODY-CENTERED-CUBIC CLASSICAL HEISENBERG-ANTIFERROMAGNET

We have used spin dynamics techniques to perform large-scale simulatio ns of the dynamic behavior of the LxLxL body-centered-cubic classical Heisenberg antiferromagnet with L less than or equal to 48 at a range of temperatures above and below as well as at the critical point T-c. The temporal evolutions of the spin configurations were determined num erically from coupled equations of motion for individual spins by a fo urth-order predictor-corrector method, with initial spin configuration s generated by Monte Carlo simulations. The neutron scattering functio n S(q,omega) was calculated from the space- and time-displaced spin-sp in correlation function. We used a previously developed dynamic finite -size scaling theory to extract the dynamic critical exponent z from S (q,omega) at T-c. Our results are in agreement with the theoretical pr ediction of z = 1.5 and with experimental results; however, we find th at the asymptotic regime was only entered at L approximate to 30. In t he analysis of the form of the transverse and longitudinal components of S(q,omega) we found that a central diffusion peak appears below T-c predominantly in the longitudinal component and remains present throu gh and above T-c. The transverse component of the spin-wave peak is Lo rentzian below T-c but for T greater than or equal to T-c is described best by a more complex functional form. Below T-c we see evidence of multiple spin-wave peaks in the longitudinal component.