We report magneto-optical recording with 62 dB CNR (carrier-to-noise ratio) at 488 nm for quadrilayer structures comprising polycrystalline CoxPt1-x (x = 0.28) alloy films deposited on ungrooved, silicon nitride -coated glass discs, held at 300°C, by UHV evaporation. The key parameter controlling magnetic anisotropy of the films is substrate temperature during deposition. Polycrystalline films grown on amorphous silicon nitride have a large coercivity and full perpendicular remanance when grown at 300°C. Synchrotron X-ray diffraction data for polycrystalline films grown at 300 and 600°C confirm the presence of short-range compositional order, to the CoPt3-L12 phase in both cases. Such ordering can introduce an anisotropy in the distribution of Co-Co pairs in the alloy and is a possible source of the magnetic anisotropy.