The new sputtering technique was developed in which film deposition and ion bombardments were performed alternately and independently. By the technique, amorphous Gd-Co films were prepared with various thickness of the periodically deposited layers (td). It was confirmed that ion bombardments by applying the bias of V change the composition within only about two atomic layers near the surface. The films with the compositional modulation of amplitude of a few at.% were synthesized in the range of tdlarger than about 0.6 nm. A large anisotropy perpendicular to the film plane appeared abruptly at tdlarger than 2.0 nm and the anisotropy decreased as tdincreased. The results obtained may be interpreted qualitatively by the improved pair-ordering model.