Raman light scattering by low-energy electronic excitations of ion Tb3+

The Raman scattering spectrum in a KTb(WO4)2 crystal is investigated in the frequency range 3-950 cm-1 at temperatures 5, 80, and 300 K. The symmetry of all 36 vibrational excitations predicted by group-theoretical analysis is determined. The temperature behavior of the scattering spectra indicates that there is no phase transition in the temperature interval studied. Low-energy electronic transitions are found between the levels of the ground-state multiplet 7F6 of Tb3+ split in a crystal field with symmetry C2. It is determined that the first excited electronic quasi doublet consists of two singlet levels with different symmetry and is separated by a quite high (∼75 cm-1) energy from the ground-state quasi doublet. The behavior of all experimentally observed levels in external magnetic fields H perpendicular C2 and H|| C2 is investigated. The results confirm that a virtually pure case of Ising anisotropy is realized at low temperatures and the magnet studied in the present work can be regarded as a system of two-level magnetic ions