Sector type targets were used to fabricate a series of alloys by planar magnetron sputtering with an rf mode. From the binary Co–M system (M: Al, Si, Ti, Cr, Fe, Ni, Cu, Zr, Nb, Mo, Ag, Ta, and W) rf sputtering yield ratios were compared with dc sputtering yields by Laegreid and Wehner. It was found that rf planar magnetron sputtering was well predicted by dc plasma discharge data. The relation of the rf peak-to-peak voltage and Ar ion energy is discussed. Cosputtering of dissimilar elements caused cross contamination on the target surface and it was attributed to the seeding effect. The application to a ternary system Co–Nb–Zr known as an amorphous soft magnetic material was quite successful and suggests sector target to be a convenient way for searching new materials.