Amorphous gadolinium-cobalt films with uniaxial magnetic anisotropy perpendicular to the film plane have been made by rf bias sputtering. Film composition has been controlled by selection of source target composition and by adjusting a negative dc bias voltage applied to the films during deposition. For bias voltages in the range studied, cobalt content increased by .25 percent per volt. Perpendicular anisotropy was observed for atomic fraction of cobalt in the range .75 to .85, and for bias voltage in the range -5 to -1 volts dc. Uniformity in composition, thickness, and magnetic properties were observed across the surface of the films.