We have examined the dependence of various properties of sputter-deposited amorphous GdCo, GdFe, and GdCoX (X=Mo,Cu,Au) films upon substrate bias and annealing. Particular interest was directed to changes in magnetization, anisotropy, composition, x-ray diffraction patterns, and Ar content of the films. In the case of the binary films, we applied substrate bias voltages to 400 V. We found that for the GdCo system, Ku rises with increasingly negative bias voltage to about Vb=-200 V. Further increases in V b cause Ku to decrease, so that Ku?0 for V b?-400 V. Furthermore, it was found that the Ar content of the films tends to correlate with Vb, reaching a maximum for Vb?-200 V. X-ray diffraction patterns of these films also appear to correlate with Ku but in a more subtle manner than has been suggested by other workers. The results for amorphous GdFe films were considerably different. In particular, it was found that Ku was large for Vb?0 but decreased rapidly with negative bias. The behavior of ternary GdCoX films was similar to that of the binary GdCo films, except that the x-ray diffraction patterns showed little dependence on Vb. On being annealed for 4 h at 200 °C, the binary films show no change in magnetization, composition, or x-ray diffraction profile, but do experience a decrease in Ku by about a factor of 2. The situation is similar for the GdCoCu and GdCoAu films except that the temperature dependence of the magnetization also changes dramatically. In contrast to these results, amorphous GdCoMo films undergo little or no change on annealing. Our results suggest that the incorporation of Ar into the films is closely related to the mechanism responsible for K u in these materials; however, there exist data which conflict with this interpretation, so that the origin of Ku remains in doubt. On the other hand, we have established the limits to the effects of Vb on the material's properties, and we present a comprehensive collection of empirical facts which will prove useful for preparing this class of materials with desired properties.