The effect of Ar pressure upon the structure, magnetic and magneto-optical properties was studied in Pt-3(Co1-chiNichi) (chi = 0.4) alloy films with a Curie temperature T-c of 200 degreesC. The experimental data indicated that 20 Pa was the most suitable Ar pressure for obtaining 100% remanence, high coercivity and the largest Kerr rotation angle theta (kappa) (0.435 degrees) during the blue-wave range. X-Ray studies showed that the < 111 > texture was not the source of perpendicular magnetic anisotropy in the studied films. Atomic force microscopy results showed that the average roughness of the films may greatly affect the saturated magnetization and, consequently, affect the shape anisotropy. The incremental inclination of H-c could be explained by the extended Kronmuller formula in the range of Ar pressures from 3 to 20 Pa.