  Single crystals of the title compounds were grown out of an AgGe-rich ternary
solution. Powder x-ray diffraction data confirmed the hexagonal AlNiZr-type
structure ($P\bar{6}2m$ space group), an ordered variant of the Fe$_2$P
structure type. Antiferromagnetic ordering can be inferred from magnetization,
resistance and specific heat measurements, with values of T$_N$ between 28.5 K
for TbAgGe, and 1.0 K for YbAgGe, which scale roughly with the de Gennes
factor. Anisotropic $M(H)$ measurements indicate one or more metamagnetic
transitions when the external field is applied along the c-axis (for R=Tb) or
perpendicular to it (R = Ho, Er, Tm), or even in both orientations as in the
case of DyAgGe. Furthermore, the extreme anisotropy of the magnetization in
TmAgGe, where magnetic moments lie in the $ab$-plane, provides the possibility
of studying the angular dependence of metamagnetism in hexagonal compounds with
the rare earth in orthorhombic point symmetry.
  YbAgGe has distinct properties from the rest of the series: an enhanced
electronic specific heat coefficient ($\gamma
\approx$(154.2$\pm$2.5)mJ/mol*K$^2$), and apparently small moment magnetic
ordering below 1.0 K. This compound appears to be close to a quantum critical
point.
