EFFECTS OF PRESSURE AND ISOTOPIC-SUBSTITUTION ON THE RAMAN-SPECTRUM OF ALPHA-FE2O3 - IDENTIFICATION OF 2-MAGNON SCATTERING

We report measurements of the effects of high pressure and O-isotope substitution on the Raman spectrum of +-Fe2O3. 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 Gr̈neisen parameters and isotope shifts of the first-order phonons are found to be comparable to the same quantities for the strong 1320-cm-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 cm-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 cm-1). © 1990 The American Physical Society.