Spin dynamics in the axion insulator candidate EuIn2As2

Abstract

We report the investigation of spin dynamics in the antiferromagnetic metal ${\mathrm{EuIn}}_{2}{\mathrm{As}}_{2}$ with the Zintl phase by using time-resolved magneto-optical Kerr effect (TR-MOKE) and transient reflectivity spectroscopy. In TR-MOKE measurement, we observe a spin precession mode with a frequency of about 18 GHz below 1.4 T and a new emerging coherent acoustic phonon mode near 35 GHz at a higher field where the latter shows a field-independent behavior. With temperature increasing, the spin precession disappears above N\'eel temperature ${T}_{N}$, whereas the acoustic phonon persists up to 25 K due to existence of magnetic-field-induced polarized paramagnetism. In contrast, the quasiparticle dynamics of ${\mathrm{EuIn}}_{2}{\mathrm{As}}_{2}$ does not show dramatic change in the vicinity of ${T}_{N}$. By comparing the spin and quasiparticle dynamics, we attribute the appearance of an acoustic phonon in TR-MOKE to photoinduced transient perturbation of magneto-optical coefficient. Our paper provides an in-depth investigation on the dynamical magnetic properties and broadens the understanding of the ${\mathrm{EuIn}}_{2}{\mathrm{As}}_{2}$ system.