IN THE UNIAXIAL MAGNETIC THIN FILMS, FARADAY ROTATION OF TRANSMITTED LIGHT THROUGH THE ANTI-PARALLEL MAGNETIC DOMAINS HAS OPPOSITE SENSE, THUS LIGHT TRANSMITTED THROUGH A FILM CONTAINING STRIPE DOMAINS IS DIFFRACTED, AS BY A GRATING. THIS FILM IS CALLED MAGNETO-OPTIC PHASE DIFFRACTION GRATING. THIS KIND OF GRATING HAS AN ADVANTAGE WHICH ITS SPACING AND ORIENTATION OF DOMAINS CAN BE CONTROLLED BY APPROPRIATE MAGNETIC FIELD. THUS, IT HAS BEEN SUGGESTED THAT THIS FEATURE WOULD BE USEFUL IN LASER BEAM DEFLECTORS AND IN MODE CONVERTERS FOR THIN FILM OPTICS. THE DEFLECTION ANGLE AND EFFICIENCY ARE THE MOST IMPORTANT FACTORS. IN THIS PAPER, AFTER PRODUCING STRIPE DOMAINS IN (BIYTM)3(FEGA)5O12 THIN FILM AND FABRICATING MAGNETO-OPTIC PHASE DIFFRACTION GRATING, WIDTH OF DOMAINS, FARADAY ROTATION AND EFFICIENCY OF GRATING VERSUS APPLIED IN PLANE MAGNETIC FIELD, HAVE BEEN INVESTIGATED.