We report measurements of the effects of high pressure and O-isotope substitution on the Raman spectrum of α-${\mathrm{Fe}}_2$${\mathrm{O}}_3$. Spectra for the pressure effects were obtained from single crystals in a diamond-anvil cell; those for isotopic substitution from polycrystalline films grown in a controlled atmosphere. The Grüneisen parameters and isotope shifts of the first-order phonons are found to be comparable to the same quantities for the strong 1320-${\mathrm{cm}}^{\mathrm{-}1}$ line, consistent with its assignment by McCarty [Solid State Commun. 68, 799 (1988)] as a phonon overtone. We identify the two-magnon scattering as a weak and broad feature at ∼1525 ${\mathrm{cm}}^{\mathrm{-}1}$, showing a temperature dependence consistent with a magnetic origin. As expected, the magnon peak does not shift with isotopic substitution, and its frequency is in good agreement with that predicted by an Ising-model calculation (1540 ${\mathrm{cm}}^{\mathrm{-}1}$).

• Received 10 October 1989

DOI:https://doi.org/10.1103/PhysRevB.41.7822