Temperature and applied magnetic field dependent magnetization measurements on 34 single crystalline samples of ( R , R ′ , R ″ … ) Ni 2 Ge 2 compounds ( R , R ′ , R ″ , etc. being primarily Gd–Lu, Y), were made. These measurements reveal that, despite extremes in local moment anisotropy, the average de Gennes parameter is a remarkably good predictor of the paramagnetic to antiferromagnetic ordering temperature. In addition, the pronounced metamagnetic phase transitions seen in the low temperature phase of TbNi 2 Ge 2 are found to be remarkably robust to high substitution levels of Gd and 25% substitutions of other heavy rare earths.