Terahertz magnon excitations and switching in noncollinear antiferromagnets

We investigate how spatiotemporal spin polarized current can lead to terahertz frequency excitations in noncollinear antiferromagnets. By solving the Landau-Lifshitz-Gilbert equation numerically for noncollinear antiferromagnets, we show that the magnon frequency spectrum exhibits standing spin wave modes and depends on the thickness of ${\mathrm{Mn}}_{3}\mathrm{Ge}$ in heterostructure Fe|Au|${\mathrm{Mn}}_{3}\mathrm{Ge}$. Also, we analyze the switching process of the ground state as a function of a spin current. We show a switching phase diagram, which contains switching and nonswitching regions. Our work suggests noncollinear antiferromagnets as an efficient platform for terahertz magnonics and ultrafast memory devices.