Effect of Y and Bi Substitution on Spin Reorientation and Optical Absorption in ErFeO3

The effects of Y and Bi substitutions on spin reorientation in ErFeO3 have been studied through optical absorption and magnetization measurements. Below the reorientation temperature Tr, optical absorption lines from low-lying Er3+ levels show splittings of several cm−1. The splittings decrease above Tr. With additions of Y or Bi, Tr decreases linearly from 102°K for ErFeO3. For crystals of Er1−xYxFeO3, 0≤x≤0.6, and Er1−xBixFeO3, 0≤x≤0.03, dTr/dx≃ −120° and −840°K, respectively. The internal energy for the Er3+ ions above and below Tr may be calculated from the optical data. The change in Er3+ energy at Tr in ErFeO3 is comparable with the energy required to move the Fe3+ spins from the a axis to the c axis in YFeO3. The behavior for substitutions of Y3+ may be understood as a simple dilution effect, whereas for Bi, having additional electrons outside the closed shell, the behavior is anomalous.