Asymmetric splitting of an antiferromagnetic resonance via quartic exchange interactions in multiferroic hexagonal HoMnO${}_3$

Abstract

The symmetric splitting of two spin-wave branches in an antiferromagnetic resonance (AFR) experiment has been an essential measurement of antiferromagnets for over half a century. In this work, circularly polarized time-domain THz spectroscopy experiments performed on the low symmetry multiferroic h-HoMnO${}_3$ reveal an AFR of the Mn sublattice to split asymmetrically in applied magnetic field, with an $\approx$ 50\% difference in $g$-factors between the high and low energy branches of this excitation. The temperature dependence of the $g$-factors, including a drastic renormalization at the Ho spin ordering temperature, reveals this asymmetry to unambiguously stem from Ho-Mn interactions. Theoretical calculations demonstrate the AFR asymmetry is not explained by conventional Ho-Mn exchange mechanisms alone and are only reproduced if quartic spin interactions are also included in the spin Hamiltonian. Our results provide a paradigm for the optical study of such novel interactions in hexagonal manganites and low symmetry antiferromagnets in general.

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Cited by in corpus (5)

• Renormalization of spin excitations in hexagonal HoMnO3 by magnon-phonon coupling
• Interplay between spin dynamics and crystal field in multiferroic compound HoMnO${}_3$
• A compact broadband terahertz range quarter-wave plate
• Efficient spin excitation via ultrafast damping-like torques in antiferromagnets
• Broadband Circular Polarization Time-Domain Terahertz Spectroscopy