Temperature Dependence of Phonon Raman Scattering in FeBO3, InBO3, and VBO3: Evidence for a Magnetic Contribution to the Intensities

Abstract

The complete Raman spectra comprised of $4E_g$ and $1A_{1g}$ modes have been observed in four materials of calcite structure (point group $D_{3d}$) from 15 to 400 °K: ferromagnetic VB${\mathrm{O}}_3$ ($T_c=32.5\mathrm{}$ °K), antiferromagnetic FeB${\mathrm{O}}_2$ ($T_c=350\mathrm{}$ °K) and ${\mathrm{Fe}}_{0.9}$ ${\mathrm{Ga}}_{0.1}$B${\mathrm{O}}_3$ ($T_c=272\mathrm{}$ °K), and nonmagnetic InB${\mathrm{O}}_3$. The energies of the modes are similar in all samples, with approximate values of 930 ${\mathrm{cm}}^{-1\mathrm{}}$ ($A_{1g}$) and 1210, 650, 400, and 270 ${\mathrm{cm}}^{-1\mathrm{}}$ ($E_g$), and show no significant shift over the temperature range studied. Observed intensity variations with temperature of three lines in InB${\mathrm{O}}_3$ relative to the $A_{1g}$ symmetric mode are consistent with changes in phonon population with temperature. Large variations in intensity of lines relative to the $A_{1g}$ modes were observed in the region of $T_c$ which were qualitatively similar in all three magnetic materials. At high temperatures ($T>\mathrm{}6\mathrm{}{T}_c$) in VB${\mathrm{O}}_3$ the intensity changes with temperature were consistent with phonon population changes. The intensity changes in the magnetic crystals are attributed to a phonon-magnon interaction arising from an exchange coupling which depends on ion position. No scattering from magnons was observed in the borates, but the temperature dependence of a line in the spectrum of the structurally related (point group $D_{3d}$) transparent antiferromagnet Fe${\mathrm{F}}_3$ was characteristic of magnon scattering.