  Single crystals of RPtIn, $R~=$ Y, Gd - Lu were grown out of In-rich ternary
solution. Powder X-ray diffraction data on all of these compounds were
consistent with the hexagonal ZrNiAl-type structure (space group P $\bar{6}$ 2
m). The $R~=$ Tb and Tm members of the series appear to order
antiferromagnetically ($T_N~=$ 46.0 K, and 3.0 K respectively), whereas the
$R~=$ Gd, Dy - Er compounds have at least a ferromagnetic component of the
magnetization along the c-axis. The magnetic ordering temperatures of all of
these systems seem to scale well with the de Gennes factor dG, whereas the
curious switching from ferromagnetic to antiferromagnetic ordering across the
series is correlated with a change in anisotropy, such that, in the low
temperature paramagnetic state, $\chi_{ab} > \chi_c$ for the antiferromagnetic
compounds, and $\chi_c > \chi_{ab}$ for the rest. In order to characterize the
magnetic ordering across the RPtIn series, a three-dimensional model of the
magnetic moments in Fe$_2$P-type systems was developed, using the \textit{three
co-planar Ising-like systems model} previously introduced for the extremely
planar TbPtIn compound: given the orthorhombic point symmetry of the R sites,
we assumed the magnetic moments to be confined to six non-planar easy axes,
whose in-plane projections are rotate by $60^0$ with respect to each other.
Such a model is consistent with the reduced high-field magnetization values
observed for the RPtIn compounds, R$~=$ Tb - Tm, and qualitatively reproduces
the features of the angular dependent magnetization of Ho$_x$Y$_{1-x}$PtIn at
$H~=$ 55 kG.
