  Neutron-diffraction experiments have been carried out on U(Pt1-xPdx)3 single
crystals (x<= 0.05). The small-moment antiferromagnetic order (SMAF) reported
for pure UPt3 is robust upon doping and persists till at least x= 0.005. The
ordered moment grows from 0.018(2) mB/U-atom for pure UPt3 to 0.048(8)
mB/U-atom for x= 0.005. The Neel temperature, TN, is approximately 6 K and does
not vary with Pd contents. The order parameter for the SMAF has an unusual
quasi-linear temperature variation. For x>= 0.01 a large moment
antiferromagnetic phase (LMAF) is found. For this phase at optimum doping (x=
0.05) TN attains a maximum value of 5.8 K and the ordered moment equals 0.63(5)
mB/U-atom. TN(x) for the LMAF follows a Doniach-type phase diagram. We infer
that the antiferromagnetic instability in U(Pt1-xPdx)3 is located in the range
0.5-1 at.% Pd.
