We study the far-from-equilibrium properties of nanoscopic classical spin systems. In particular, we focus on the interplay between lattice vibrations and magnetic frustrations induced by surface effects in antiferromagnets. We use an extended Monte Carlo simulations which treats both the ionic degrees of freedom and spin variables on the same footing via a Heisenberg-Lennard-Jones Hamiltonian with a spin-lattice coupling. The interplay of the local ordered magnetic moments and the lattice dynamics provides, at zero temperature, a structural phase diagram characterizing the magnetic order in two different antiferromagnetic nanoclusters. At nonzero temperature, the competition between spins and the ionic vibrations considerably affects the magnetization of these systems. Next, we explore the dynamical response of the antiferromagnetic structures subjected to an initial ferromagnetic quench by solving the stochastic Landau-Lifshitz-Gilbert equation at finite temperature. The dynamics reveals a nontrivial structure-induced behavior in the spin relaxation with a concomitant memory of the initially applied ferromagnetic quench. These observations of long-lived nonthermal states could open new avenues in nanotechnology.

• Received 24 July 2018

DOI:https://doi.org/10.1103/PhysRevB.100.195431