  Motivated by the unusual evolution of magnetic phases in stoichiometric and
Co-doped YbRh2Si2, we study Heisenberg models with competing ferromagnetic and
antiferromagnetic ordering combined with competing anisotropies in exchange
interactions and g factors. Utilizing large-scale classical Monte-Carlo
simulations, we analyze the ingredients required to obtain the characteristic
crossing point of uniform susceptibilities observed experimentally near the
ferromagnetic ordering of Yb(Rh0.73Co0.27)2Si2. The models possess
multicritical points, which we speculate to be relevant for the behavior of
clean as well as doped YbRh2Si2. We also make contact with experimental data on
YbNi4P2 where a similar susceptibility crossing has been observed.
