The magnetic properties of polycrystalline Tb(Co_{x}Ni_{1-x})_{2}B_{2}C (x=0.2,0.4,0.6,0.8) samples were probed by magnetization, specific heat, ac susceptibility, and resistivity techniques. For x{ eq}0.4, the obtained curves are consistent with the
features expected for the corresponding magnetic modes, namely k_{1}=(0.55,0,0) at x=0; k_{2}=([nicefrac] icefrac{1}{2}</LaTeX>,0,[nicefrac]<LaTeX> icefrac{1}{2}) at x= 0.2; k_{3}=(0,0,[nicefrac] icefrac{1}{3}) at x= 0.6, and k_{4}=(0,0,0) at x= 0.8 and 1. For x=0.4, even though the neutron diffraction indicates a k_{2} mode, but with a reduced magnetic moment, the magnetization, the ac susceptibility, and resistivity indicate two magnetic events; furthermore, deviation from Curie-Weiss behavior is observed below 150 K for this sample. These features, together with the evolution of both magnetic moment and critical temperature, are attributed to an interplay between competing magnetic couplings; for the particular x=0.4 case, additional factors such as crystalline electric field effects may be in operation.
