Magnons and acoustic phonons inY3−xBixFe5O12

Abstract

We use Brillouin light scattering (BLS) to study a series of single-crystal Bi-doped yttrium iron garnet ${\mathrm{Y}}_{3\ensuremath{-}x}{\mathrm{Bi}}_{x}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ (Bi-YIG) prepared with x= 0, 0.14, 0.36, 0.54, and 0.92. BLS shows that the optimal laser power should be as low as possible, $<~5 \mathrm{mW}.$ BLS manifests the Bi-concentration dependence of the magnetic and mechanic properties of Bi-YIG. Two bulk magnons are observed. One is the thermally excited magnon and another is the uniform magnetostatic mode. The stiffness constant ${D}_{\mathrm{ex}},$ the relative intensity and bandwidth (full width at half maximum) of the thermally excited bulk magnon all increase linearly with x, while $4\ensuremath{\pi}{M}_{s}$ is insensitive to doping. On the contrary, the scattering intensity and the sound velocity of the acoustic phonon decrease.