EXCHANGE FIELDS AND OPTICAL ZEEMAN EFFECT IN ERFEO3

The optical spectra of ErFeO3 with and without an external magnetic field along each of the three principal crystal axes are reported. The exchange splitting of Er3+ levels in zero applied field and the additional splittings due to the external field, at 77°K, are analyzed in terms of a two-sublattice model for the Er3+ ions. Values are derived for the g-tensor components and site-axis directions for the two lowest levels of Er3+ at E=0 and E=45.7 cm-1. Interactions with the Fe3+ spins are included by means of an effective field Heff=12 kOe at the Er3+ sites. The parameters derived from the optical spectra are used to calculate the sublattice magnetizations for Er3+. Assuming a contribution from the Fe3+ spins similar to that in YFeO3, a compensation point is predicted near the observed temperature T045°K. The magnetic dipolar contribution to Heff is shown to be small, and the exchange contribution lies nearly along the b axis. Above the spin-reorientation temperature T>Tr, the Fe3+-Er3+ exchange splitting becomes smaller than the optical linewidth. The optical data give Heff(T<Tr)Heff(T>Tr)>4, and this result is shown to be consistent with the value for Heff(T>Tr) obtained by other methods. It is suggested that either a model with more than two sublattices for the Fe3+ spins must apply for ErFeO3, or there must be significant antisymmetric exchange coupling between the Er3+ and Fe3+ ions. © 1969 The American Physical Society.