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 $\lambda \approx 5.15$. 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 $z=4-\epsilon/2$ and $\lambda = d$ (where $\epsilon = 6-d$). Indeed $\lambda$ is always equal to d for quenches to T_c whenever the order parameter is conserved.