Conserved Ordering Dynamics of Heisenberg Spins with Torque

Abstract

We show that a torque induced by the local molecular field drives the zero-temperature ordering dynamics of a conserved Heisenberg magnet to a new fixed point, characterised by exponents z=2 and $λ\approx 5.15$. Numerical solutions of the Langevin equation indicate that theories using a Gaussian closure are inconsistent even when the torque is absent. The torque is relevant even for quenches to T_c, with exponents $z=4-ε/2$ and $λ= d$ (where $ε= 6-d$). Indeed $λ$ is always equal to d for quenches to T_c whenever the order parameter is conserved.