Investigation of Magnetic Interactions in TbAlO3by Optical Spectroscopy

High-resolution optical absorption spectra of TbAl${\mathrm{O}}_3$ have been obtained between 1.4 and 4.2°K, at 20°K and at 77°K. For $T>\mathrm{}4\mathrm{}°$K, all absorption lines show a triplet structure which is interpreted as arising from an interaction of each Tb ion with only two nearest neighbors. Below $T=3.95\mathrm{}°$K, a temperature-dependent lineshift is observed giving a Néel temperature of $T_N=3.95\mathrm{}\pm 0.10°$K. Below the Néel temperature, the lineshift is proportional to ${(1-\frac{T}{T_N})}^{\beta }$ with $\beta =0.32\mathrm{}\pm 0.08$. After correction for dipolar interactions, we find for the interactions along the $c$ axis 2.4 ${\mathrm{cm}}^{-1\mathrm{}}$, and for those in the $a-b$ plane 1.0 ${\mathrm{cm}}^{-1\mathrm{}}$. The magnetic moment of the ground state is derived as (9.0±0.6) ${\mathrm{\mu }}_{\mathit{B}}$. The absorption spectra measured as a function of the external field show evidence for metamagnetic transitions, and a critical field of 8 kOe is derived.