  The thermodynamic, magnetic, dielectric, and magnetoelectric properties of
HoFe$_3$(BO$_3$)$_4$ and Ho$_{0.5}$Nd$_{0.5}$Fe$_3$(BO$_3$)$_4$ are
investigated. Both compounds show a second order Ne\'{e}l transition above 30 K
and a first order spin reorientation transition below 10 K.
HoFe$_3$(BO$_3$)$_4$ develops a spontaneous electrical polarization below the
Ne\'{e}l temperature (T$_N$) which is diminished in external magnetic fields.
No magnetoelectric effect could be observed in HoFe$_3$(BO$_3$)$_4$. In
contrast, the solid solution Ho$_{0.5}$Nd$_{0.5}$Fe$_3$(BO$_3$)$_4$ exhibits
both, a spontaneous polarization below T$_N$ and a magnetoelectric effect at
higher fields that extends to high temperatures. The superposition of
spontaneous polarization, induced by the internal magnetic field in the ordered
state, and the magnetoelectric polarizations due to the external field results
in a complex behavior of the total polarization measured as a function of
temperature and field.
