  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{\neq}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]\nicefrac{1}{2}</LaTeX>,0,[nicefrac]<LaTeX>\nicefrac{1}{2}) at
x= 0.2; k_{3}=(0,0,[nicefrac]\nicefrac{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.
