Magnetic tape offers potential capacities of 20 Mbits/cm2, while conventional readout heads are limited, particularly by the impossibility of integrating a large number of heads in a stack. A magneto-optical high resolution transducer, using thin garnet films, allows the exploration of the whole track width. These films, grown by liquid phase epitaxy, have to satisfy to some properties as : magnetization about 300 Gauss, high Faraday rotation and low uniaxial anisotropy (Ku). Films of YIG Bix Gay, YIG Bix (Ga, Al)y were grown from different melts composition. As grown films present high Faraday rotation but also high uniaxial anisotropy. Annealings at several temperatures are necessary to decrease Ku. For gadolinium garnet films doped with Bi and Pr, (Gd IG : Bi Pr Al), the required Faraday rotation and uniaxial anisotropy are obtained as grown, the presence of praseodymium decreasing the Ku.