Softened Spin Waves in Films with Perpendicular Magnetic Anisotropy: Sombrero-Like Dispersion, Negative Reflection, Bi-, and Trireflection

Abstract: We theoretically investigate the effect of perpendicular magnetic anisotropy (PMA) on spin wave (SW) dynamics at low magnetic fields. PMA exerts an in-plane torque on magnetization, counteracting exchange, dipolar, and Zeeman torques, thereby significantly transforming SW dynamics. In ultrathin films, sombrero-like dispersion relation facilitates bireflection and negative reflection of SWs, while in thicker films we demonstrate anti-Larmor precession, cowboy-hat-like dispersion relation, and trireflection of SWs. These results open up new opportunities to explore wave phenomena beyond magnonics.