Observation of ultrafast propagation of magnon-polaritons

The field of magnonics has emerged as a promising candidate for beyond CMOS computing, by using collective magnetic excitations known as spin waves. However, one of the main limiting factors for applications is their low group velocities. Here, we overcome this limitation by utilizing ultrafast magnon–polaritons—hybrid quasiparticles arising from the coupling between spin waves and electromagnetic fields. We measured spatial and time evolution of the magnon-polaritons in bismuth- and gallium-substituted yttrium iron garnet films by using Brillouin light scattering and scanning transmission X-ray microscopy. We estimated magnon-polariton group velocities to exceed 100 μm/ns, three orders of magnitude faster than conventional spin waves. Notably, the magnon-polaritons have high initial amplitudes and long decay lengths, enabling ultrafast manipulation of the magnetization far away from the excitation source. These properties make magnon-polaritons promising candidates for high-speed information transfer in future computing architectures, potentially overcoming long-standing group delay bottlenecks in magnonic logic circuits.