The magnetic properties of CrPt 3 L1 2 ferrimagnetic thin films have been studied. Films were produced by sputtering multilayers of Cr and Pt onto silicon nitride coated silicon substrates. The as-deposited films are nonmagnetic. An anneal at ϳ800°C results in ferrimagnetic behavior with a perpendicular easy-axis. X-ray diffraction and transmission electron microscopy ͑TEM͒ measurements show that ͑111͒ CrPt 3 is the only crystalline phase present after annealing. Rocking curves with a full width at half maximum as low as 1.8°indicate good crystallographic orientation. Magnetic properties of the films vary with composition, annealing temperature and time, layer thickness, and sputtering conditions. The films exhibit large coercivities, H c , that can be tuned in the range 1500-8000 Oe. Saturation magnetization, M s , is typically 150-200 emu/cc. Squarenesses, S, as high as 0.99 have been found. A uniaxial magnetic anisotropy constant, K u , of up to 8ϫ10 6 erg/cc was achieved. TEM micrographs show a 35 nm average grain size and complete interdiffusion of the Cr and Pt. Magneto-optical hysteresis loops at 632.8 nm wavelength reveal Kerr rotations of about 0.21°when the films are overcoated with a quarter-wavelength dielectric.