Terahertz absorption spectroscopy study of spin waves in orthoferrite ${\mathrm{YFeO}}_3$ in a magnetic field

We measured absorption of THz radiation in ${\mathrm{YFeO}}_3$ single crystals at a temperature of 3 K in the magnetic field up to 17 T applied in all three crystallographic directions. Two spin-wave modes were observed at the $\mathrm{\Gamma }$ point with energies 1.2 meV (9.8 ${\mathrm{cm}}^{-1}$) and 2.4 meV (19.3 ${\mathrm{cm}}^{-1}$) in zero field. From the magnetic-field dependence of mode energies, we have refined the previously proposed model [S. E. Hahn et al., Phys. Rev. B 89, 014420 (2014)] and quantified the parameters of Dzyaloshinskii-Moriya interactions and single-ion anisotropies.

Figure 1

Magnetic interactions in ${\mathrm{YFeO}}_3$. Magnetic Fe ions are blue and labeled 1 through 4; oxygen ions are red.

Figure 2

Magnetic-field dependence of SW absorption spectra of ${\mathrm{YFeO}}_3$ at 3 K. Panels (a), (b), and (c) correspond to the magnetic field H applied along crystallographic axes $a$, $b$, and $c$, respectively. The spectra are shifted vertically in proportion to the magnitude of the applied magnetic field, marked on the right side of the plot. In each panel, blue and red solid lines denote two orthogonal incident light polarizations, where the oscillating electric- and magnetic-field vectors E${}^{\omega }$ and H${}^{\omega }$ are aligned along different crystallographic axes. Dashed lines show the absorption peak positions obtained from the theoretical fit. The impurity peak position in zero field is marked with a star.

Figure 3

Magnetic-field dependence of the absorption peak positions (symbols) with the field applied along the three crystallographic axes and the theoretical fit result (solid lines). Dashed lines show the fit with the simplified model, where $D_c=0$.

Figure 4

Zero-field spectra measured in six different polarizations qualitatively showing the selection rules. The spectra are grouped according to the direction of the oscillating magnetic field H${}^{\omega }$. For each direction, only one mode is visible. The dashed lines show arbitrarily scaled theoretical spectra. The impurity mode is marked with a star.