  The spin-orbit torque induced by a topological insulator (TI) is
theoretically examined for spin wave generation in a neighboring
antiferromagnetic thin film. The investigation is based on the micromagnetic
simulation of N\'{e}el vector dynamics and the analysis of transport properties
in the TI. The results clearly illustrate that propagating spin waves can be
achieved in the antiferromagnetic thin-film strip through localized excitation,
traveling over a long distance. The oscillation amplitude gradually decays due
to the non-zero damping as the N\'{e}el vector precesses around the magnetic
easy axis with a fixed frequency. The frequency is also found to be tunable via
the strength of the driving electrical current density. While both the bulk and
the surface states of the TI contribute to induce the effective torque, the
calculation indicates that the surface current plays a dominant role over the
bulk counterpart except in the heavily degenerate cases. Compared to the more
commonly applied heavy metals, the use of a TI can substantially reduce the
threshold current density to overcome the magnetic anisotropy, making it an
efficient choice for spin wave generation. The N\'{e}el vector dynamics in the
nano-oscillator geometry are examined as well.

Materials Science;Mesoscale and Nanoscale Physics