Rostislav Mikhaylovskiy
The antiferromagnetic materials appeal to spintronics and magnonics because of their very high terahertz (THz) frequencies of spin dynamics and unique functionalities in comparison to conventional ferromagnets. Due to the strong coupling of the propagating THz magnetic fields with magnons, the hybrid magnon-polariton modes are formed. The physics of the magnon-porations calls for an interdisciplinary approach at the merge of magnetism and photonics.
For instance, magnon-polaritons are shown to play a dominant role in propagation of terahertz (THz) waves through TmFeO3 orthoferrite, if the frequencies of the waves are in vicinity of the quasi-antiferromagnetic mode of spin resonance [1]. This leads to beating between magnon-polaritons due to the energy exchange between the higher and lower polariton branches formed in vicinity of the antiferromagnetic magnon frequency.
Polaritonic nature of spin modes in antiferromagnets has important implications for THz-driven spin control [2]. In DyFeO3 orthoferrite the lattice-mediated coupling of the electric fields produced by otherwise orthogonal magnon modes leads to internal resonance, when the frequencies of the modes are close to each other. This resonance results in a dramatic enhancement of spin oscillations excited by THz magnetic field.
[2] S. Baierl, M. Hohenleutner, T. Kampfrath, A. K. Zvezdin, A. V. Kimel, R. Huber, and R. V. Mikhaylovskiy. Nature Photonics 10, 715–718 (2016)