Universality of Domain Growth in Antiferromagnets with Spin-Exchange Kinetics

We study phase ordering kinetics in symmetric and asymmetric binary mixtures, undergoing an order-disorder transition below the critical temperature. Microscopically, we model the kinetics via antiferromagnetic Ising model with Kawasaki spin-exchange kinetics. This conserves the composition while the order-parameter (staggered magnetization) is not conserved. The order-parameter correlation function and structure factor show dynamical scaling, and the scaling functions are independent of the mixture composition. The average domain size shows a power-law growth: $L_\sigma(t)\sim t^\alpha$. The asymptotic growth regime has $\alpha=1/2$, though there can be prolonged transients with $\alpha<1/2$ for asymmetric mixtures. Our unambiguous observation of the asymptotic universal regime is facilitated by using an accelerated Monte Carlo technique. We also obtain the coarse-grained free energy from the Hamiltonian, as a function of two order-parameters. The evolution of these order-parameters is modeled by using \textit{Model C} kinetics. Similar to the microscopic dynamics, the average domain size of the nonconserved order-parameter (staggered magnetization) field exhibits a power-law growth: $L_m(t)\sim t^{1/2}$ at later times, irrespective of the mean value of the conserved order-parameter (composition) field.

Prasenjit Das, Tanusri Saha-Dasgupta, Sanjay Puri · 2017