  Bismuth substituted lutetium iron garnet (BLIG) films exhibit larger Faraday
rotation, and have a higher Curie temperature than yttrium iron garnet. We have
observed magnetic stripe domains and measured domain widths of 1.4 {\mu}{\mu}m
using Fourier domain polarization microscopy, Faraday rotation experiments
yield a coercive field of 5 Oe. These characterizations form the basis of
micromagnetic simulations that allow us to estimate and compare spin wave
excitations in BLIG films. We observed that these films support thermal magnons
with a precessional frequency of 7 GHz with a line width of 400 MHz. Further,
we studied the dependence of precessional frequency on the externally applied
magnetic field. Brillouin light scattering experiments and precession
frequencies predicted by simulations show similar trend with increasing field.
