Phase control of a coherent magnon excitation in a van der Waals antiferromagnet

Magnon excitations in antiferromagnets have recently become the focus of both fundamental studies in magnetism, as well as the effort to establish new platforms for next-generation spintronic devices. While magnons are characterized by an amplitude, frequency, and phase, control over only the first two properties has been widely demonstrated. Complete control of the phase has remained elusive, imposing limitations on the manipulation of magnons for further applications. Here, we report a phase controlled coherent magnon excitation in a van der Waals antiferromagnet NiPS_3 using an optical pump-probe measurement. The presence of both linearly and circularly polarized pump-induced excitations enables full phase control with the pump helicity. The ability to control the initial phase of the magnon excitation has promise for both fundamental studies, such as the creation of a transient phase grating, as well as in spintronic applications in spin-wave phased arrays and spin-based terahertz technology.