  We have synthesized R5Pb3 (R = Gd-Tm) compounds in polycrystalline form and
performed structural analysis, magnetization, and neutron scattering
measurements. For all R5Pb3 reported here the Weiss temperatures {\theta}W are
several times smaller than the ordering temperatures TORD, while the latter are
remarkably high (TORD up to 275 K for R = Gd) compared to other known R-M
binaries (M = Si, Ge, Sn and Sb). The magnetic order changes from ferromagnetic
in R = Gd, Tb to antiferromagnetic in R = Dy-Tm. Below TORD, the magnetization
measurements together with neutron powder diffraction show complex magnetic
behavior and reveal the existence of up to three additional phase transitions.
We believe this to be a result of crystal electric field effects responsible
for high magnetocrystalline anisotropy. The R5Pb3 magnetic unit cells for R =
Tb-Tm can be described with incommensurate magnetic wave vectors with spin
modulation either along the c axis in R = Tb, Er and Tm or within the ab-plane
in R = Dy and Ho.
