Application of magneto-optic materials of garnet single crystal films in ring laser gyroscopes, bias frequency properties of the garnet magnetic mirror and comparison of the garnet magnetic mirror with the metal magnetic mirror are sammarized. Growth technlogy and magneto-optic preperties of single crystal films of (BiPrGdYb)3(FeAl)5O12, and experimental results in a ring laser gyroscope of bias frequency of the garnet magnetic mirror are reported.