Concurrent Terahertz Spin Excitations and Phase Shift Control in Fe₄Nb₂O₉: A Material for Synergizing Computation and...

Driven by escalating demands from emerging applications and inherent limitations of current technologies, terahertz (THz) science has surged as a cornerstone for 6G+ communication systems and magnonic computation. Phase shifters, essential for THz wave manipulation, drive communication advances, while magnons enable ultrafast, energy-efficient processing. Ideally, a multifunctional material co-hosting both would integrate these fields towards lab-on-a-chip applications; yet, no such experimental realization exists. Herein, a novel platform is presented to integrate intrinsic THz phase shifting and spin excitations within a single material system. Fe₄Nb₂O₉, selected as a model compound, demonstrates a remarkable intrinsic phase-shift of 304.7° at around 0.5 THz in the temperature range of 30-93 K. This gigantic effect either matches or surpasses the existing metasurface-based free-space THz phase shifters - with a correlated phase-frequency relationship across a wide sub-THz bandwidth (0.1 to 0.56 THz). The experimental results, corroborated by theoretical lattice vibration calculations, attribute the observed THz phase-shift to dielectric modulation in Fe₄Nb₂O₉. Complementing these findings, two distinct THz magnon excitations were detected above 0.56 THz in its antiferromagnetic phase. This unique coexistence of phase modulation and spin dynamics positions Fe₄Nb₂O₉ as a paradigmatic multifunctional material-a model compound for next-generation miniaturized THz communication and computation platforms.