Spin fluctuation-enhanced magnetic moments of terahertz phonons

Prof. Qi Zhang
Nanjing University, Nanjing, China


Phonons, the quasi-particles of lattice vibration, can carry momentum and angular momentum but commonly possess negligible magnetic moments. A large phonon magnetic moment enables the direct mutual control of magnetic orders and lattice motions, and could be applied to develop spin–phononic devices. Here, we report an experimental discovery of giant fluctuation-enhanced phonon magnetic moments (~0.68 Bohr magneton, ) in a polar antiferromagnet, Fe2Mo3O[1]. Combining magneto-Raman spectroscopy and inelastic neutron scattering measurements, we identified a pair of terahertz chiral phonons in this system which exhibit clear Zeeman splitting. When the spin order changes from antiferromagnetic to ferrimagnetic, the chiral phonon splitting suddenly increases, reaching an unprecedented 24% of the phonon frequency. We further observe a sixfold enhancement in the phonon magnetic moment near the Néel temperature, originating from the ferrimagnetic fluctuation. We will discuss the underlying mechanism for the large phonon magnetic moments in this system.