Equiatomic CoPt and FePt alloy films were deposited by cosputtering at substrate temperatures between 25 and 640 °C. Those deposited at high temperatures (≥400 and ≥520 °C for FePt and CoPt, respectively) contained ordered intermetallic compounds with theL10crystal structure while those deposited at lower temperatures were chemically disordered. Deposition on single crystal [001] MgO and [0001] Al2O3resulted in [001] and [111] oriented films, respectively, for all deposition temperatures. Ordered alloys have out‐of‐plane magnetic easy axes and modified magneto‐optic Kerr rotation spectra relative to the disordered case. A difference in the Kerr rotation spectrum is observed between ordered, but not disordered, [001] and [111] films. ©1995 American Institute of Physics.