Spectroscopic Observations of Antiferromagnetic Erbium Oxide

The far‐infrared and visible spectra of erbium oxide have been observed above and below the transition to the antiferromagnetic state at 3.4°K. Absorptions due to electronic transitions between levels of the ground‐state multiplet appear in the far‐infrared spectrum, they are split into several components below the Néel temperature. This structure can be interpreted in terms of transitions for ions on two inequivalent sites. The changes in the visible absorption spectrum, together with changes in phonon frequencies, are attributed to the presence of the exchange fields and a magnetostrictive expansion of the crystal lattice in the ordered state. This data and the results of crystal field calculations using the superposition model indicate a small value for g_z for C₂ site ions. Electron spin resonance spectroscopy and other methods give a much larger value for g_z. This discrepancy has not yet been resolved.