Electronic structure and magnetic symmetry in MnTiO3analyzed by second harmonic generation

Second harmonic generation (SHG) and linear absorbance spectra of MnTiO${}_{3}$ were measured and the 1.88, 2.41, 2.63, and 3.06 eV SHG features were identified as $d\ensuremath{-}d$ optical transitions from ${}^{6}{A}_{1g}$ to ${}^{4}{T}_{1g}{(}^{4}G)$, ${}^{4}{T}_{2g}{(}^{4}G)$, ${{}^{4}{E}_{g}$,${}^{4}{A}_{1g}{(}^{4}G)}$, and ${}^{4}{E}_{g}{(}^{4}D)$, respectively. These zero-phonon transitions were used to calculate the octahedral crystal field splitting energy (${\ensuremath{\Delta}}_{0}$) and the Racah parameters $B$ and $C$. The SHG spectra showed significant distinctions between the antiferromagnetic and the paramagnetic or spin-flop phases. The polarization dependence of the SHG in the spin-flop phase provided optical evidence that the spins canted from the $c$ axis toward the $a$ axis. These distinctions between the three magnetic phases could be useful for mapping 180${}^{\ensuremath{\circ}}$ antiferromagnetic domains in MnTiO${}_{3}$.