Emergence of multiple quasi-ferromagnetic magnon modes induced by strong magnetoelastic coupling in $TmFeO_3$ single crystal

Abstract

We investigate the magnetization dynamics of $TmFeO_3$ single crystals across the spin-reorientation phase transition using broadband microwave absorption spectroscopy up to 87.5 GHz. Temperature- and magnetic-field-dependent antiferromagnetic resonance measurements reveal the characteristic softening of the quasi-ferromagnetic (q-FM) resonance mode at the $\Gamma_2\rightarrow\Gamma_{24}$ and $\Gamma_{24}\rightarrow\Gamma_4$ transition points. The finite magnon gap observed at the transition points reflects the strong magnetoelastic coupling. In addition to the uniform q-FM mode, multiple magnon modes appear in the intermediate $\Gamma_{24}$ phase, separated by approximately 0.5--2 GHz and exhibiting similar field and temperature dependence. These additional modes are attributed to nonuniform spin-wave excitations arising from the periodic magnetic domain structure present in the intermediate phase and their hybridization with acoustic phonons mediated by strong magnetoelastic coupling. Our results demonstrate that the spin-reorientation transition in $TmFeO_3$ provides a natural platform for generating multiple hybridized magnon modes, offering new opportunities for tunable magnonic excitations in rare-earth orthoferrites.