Simulation of the Magnetization Dynamics of a Single-Domain BiFeO₃ Nanoisland

The switching dynamics of a single-domain BiFeO₃ nanoscale nanoisland is investigated by studying the dynamics of polarization and Neel vector. We use the Landau-Khalatnikov (LK) equation to describe the evolution of the ferroelectric polarization, and we implement the Landau-Lifshitz-Gilbert (LLG) equations to model the dynamics of spins in two sublattices and the time evolution of the antiferromagnetic order (Neel vector) in a G-type antiferromagnet. Our model can calculate the weak magnetization more accurately compared to previous works on the antiferromagnet using the Neel vector as the order parameter and weak magnetization are often neglected. This work also theoretically demonstrates that the rotation of the magnetic hard-axis, which follows the polarization reversal, can reverse the Neel vector while the weak magnetization remains unchanged. The simulation results are consistent with the ab initio calculations, where the Neel vector rotates during polarization rotation, and also match our calculation of the dynamics of the order parameter using Landau-Ginzburg theory. We also find that the switching time of the Neel vector is a strong function of the polarization switching time and can be as short as 30ps if the polarization can switch faster. However, the Neel vector does not reverse if the polarization switches in less than 30ps.