Terahertz optical activity near crystal field transitions of Tm3+ ions in magnetoelectric alumoborates

Abstract

Crystal field (CF) excitations in the ground multiplet ${}^3{H}_6$ of Tm${}^{3+}$ ions were investigated using terahertz transmission spectra of magnetoelectric TmAl${}_3$(BO${}_3$)${}_4$ and Tm${}_{0.05}$Yb${}_{0.1}$Y${}_{0.85}$Al${}_3$(BO${}_3$)${}_4$. These excitations were identified as mainly magnetic dipole transitions from the ground singlet A${}_1$ to the next excited doublet E, split by the crystal field of the D${}_3$ symmetry. The fine structure of the modes was resolved at low temperatures. It manifested differently in lightly doped and in pure Tm borates, consistent with different distortions of the local crystal field with the D${}_3$ symmetry. Strong natural optical activity was observed near the CF transitions resulting in a polarization plane rotation up to 25 degrees. The optical activity is quantitatively described by contributions of magnetic and electric dipole transitions to dynamic magnetoelectric susceptibility and taking into account the classification of local distortions.

10 pages, 6 figures

References in corpus (6)

• Giant Magnetoelectric Effect in HoAl_3(BO_3)_4
• Magnetoelectric Effect and Spontaneous Polarization in HoFe${}_3$(BO${}_3$)${}_4$ and Ho${}_{0.5}$Nd${}_{0.5}$Fe${}_3$(BO${}_3$)${}_4$
• Magnetoelectricity and Magnetostriction due to the Rare Earth Moment in TmAl${}_3$(BO${}_3$)${}_4$
• Sign change of polarization rotation under either time or space inversion in magnetoelectric YbAl3(BO3)4
• Magnetoelectric spectroscopy of spin excitations in LiCoPO4
• Optical activity of oriented molecular systems in terms of the magnetoelectric tensor of gyrotropy