Temporal magnetic interfaces reveal damping-induced spin-wave amplification near the stripe-domain transition in ultrathin films with DMI

Abstract

Using micromagnetic simulations and analytical theory, we study temporal magnetic interfaces in ultrathin CoFeB films with perpendicular magnetic anisotropy and interfacial Dzyaloshinskii--Moriya interaction. We show that time refraction and reflection are governed by precession ellipticity, acting as a magnonic temporal impedance, while smooth field ramps suppress temporal reflections. Near the transition from a uniform state to stripe domains, the exceptional-point and critical fields delimit damping, slow-instability, and strong-instability regimes. In the slow-instability window, Gilbert damping counterintuitively drives spin-wave growth with a rate proportional to the damping parameter. Micromagnetic simulations confirm that a temporal-slab protocol exploiting this regime achieves up to 175-fold frequency-preserving amplitude amplification without continuous power injection. Energy analysis indicates that the field ramp stores energy in the metastable uniform state below the stripe-domain transition, later released into growing spin-wave excitations, consistent with the antimagnonic framework. These results establish temporal field modulation as a route to reconfigurable spin-wave gain.