Raman and crystal field studies of Tb-O bonds inTbMn2O5

Abstract

We have studied the temperature dependence of $\mathrm{TbM}{\mathrm{n}}_{2}{\mathrm{O}}_{5}$ Raman-active phonons and its $\mathrm{T}{\mathrm{b}}^{3+}$ crystal field (CF) excitations. Interestingly, the Raman intensities of some phonons are significantly reduced below $\ensuremath{\sim}180\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Such behaviors are also observed in $\mathrm{HoM}{\mathrm{n}}_{2}{\mathrm{O}}_{5}$ and $\mathrm{YM}{\mathrm{n}}_{2}{\mathrm{O}}_{5}$ systems. A connection between the Raman intensities and the nearest-neighbor mean-square relative displacement ${\ensuremath{\sigma}}^{2}$ is established. Also, some of the $\mathrm{T}{\mathrm{b}}^{3+}$ and $\mathrm{H}{\mathrm{o}}^{3+}$ CF excitations become broader below $\ensuremath{\sim}180\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. These results are discussed in terms of the disorder induced by the Tb-O bond splitting.