  We present a theory of the magnetic rare-earth nickel boride-carbides
(RENi$_2$B$_2$C, RE=Ho, Er, Tm). Large total angular momentum allows one to
employ semiclassical approximation and reduce the problem to the
four-positional clock model. The latter gives a proper phase diagram in
magnetic field-magnetic moment plane for varying directions of in-plane
magnetic field. The theory explains recent experimental observations.
  PACS: 74.72.Ny, 75.30.Cr, 75.30.Kz, 75.10.Dg
