in Pulsed High Magnetic Fields*

Antiferromagnetic materials are promising for spintronic applications due to faster spin dynamics than ferromagnets. YFeO₃ is a canted antiferromagnet that supports quasi-antiferromagnetic and quasi-ferromagnetic magnon modes in the terahertz (THz) frequency range. Here, we investigate magnon polaritons arising from coupling between THz photons and the quasi-ferromagnetic magnon mode as a function of magnetic field up to 30 T applied along the c-axis using single-shot THz time-domain spectroscopy. We observe a peak splitting whose magnitude increases with the applied magnetic field. We developed a microscopic theoretical model that explains the data without any fitting parameters. The thickness dependence of the splitting at a given magnetic field shows a smooth crossover from a magnon regime to a magnon-polariton regime.