  We report the structural and magnetic properties of RNi (R=Dy,
Tb$_{1/3}$Dy$_{1/3}$Ho$_{1/3}$, and
Gd$_{1/5}$Tb$_{1/5}$Dy$_{1/5}$Ho$_{1/5}$Er$_{1/5}$) to investigate the
high-entropy effect at the rare-earth site. The lattice parameters are almost
unchanged by the increase of configurational entropy, which is due to the
successive partial substitution of Dy by pair of rare earth elements located on
both sides of Dy in the periodic table. All compounds exhibit ferromagnetic
ground states. The replacement of Dy with Tb+Ho, which does not have magnetic
interactions in competition with Dy, does not affect the magnetic ordering
temperature. Although (Gd$_{1/5}$Tb$_{1/5}$Dy$_{1/5}$Ho$_{1/5}$Er$_{1/5}$)Ni
shows the Curie temperature close to that of DyNi, an additional magnetic
anomaly, which would be a spin reorientation, is observed probably due to the
introduction of competing magnetic interactions between R=Gd and Er compounds
and R=Tb, Dy, and Ho ones. We have also assessed the magnetocaloric effect, and
the configurational entropy dependence of the magnetic entropy change reflects
that of the temperature derivative of the magnetic susceptibility. Our analysis
suggests the possibility of enhancing magnetocaloric properties by designing
the anisotropy of rare-earth magnetic moments in the high-entropy state.
