Transformation of the HoFe3(BO3)(4) absorption spectra at reorientation magnetic transitions and local properties in the excited F-5(5) states of the Ho3+ ion

Polarized absorption spectra of the ${}^{}{I}_8\to {}^{}{F}_5$ transition of the $H{o}^{3+}$ ion in the $\mathrm{HoF}{e}_3{\left(B{O}_3\right)}_4$ single crystal were measured at $T=2K$ as a function of magnetic field 0–60 kOe directed along the $a$, $b$, and $c$ axes of the crystal. The spin-reorientation transitions were observed in the field $H\parallel c$ at 5.35 kOe, in the field $H\parallel a$ at 10.25 kOe, and in the field $H\parallel b$ at 9.1 kOe. We also observed a small hysteresis of the transitions. We found that the optical properties of the crystal change as a function of the magnetic field orientation in the basal plane in spite of the nominally axial symmetry of the crystal. We found a number of specific local properties in the $H{o}^{3+}$ excited states. Nonequivalent positions of the $H{o}^{3+}$ ion appear in some excited states. It was shown that during one of the electron transitions the local symmetry changes not only in the excited state but in the ground state as well. We observed local metamagnetic transitions in some $H{o}^{3+}$ excited states. In some excited states, the $H{o}^{3+}$ ion is in the easy-plane state while the total crystal is in the easy-axis state and vice versa. This means that the magnetic moments of the $F{e}^{3+}$ and $H{o}^{3+}$ ions in these excited states of the $H{o}^{3+}$ ions are mutually perpendicular. Such phenomenon testifies to the existence of the antisymmetric Fe-Ho exchange interaction in the $H{o}^{3+}$ excited states.