  Theoretical model for magnetic ordering in the heavy-fermion metal URu2Si2 is
suggested. The 17.5K transition in this material is ascribed to formation of a
spin-density wave, which develops due to a partial nesting between electron and
hole parts of the Fermi surface and has a negligibly small form-factor.
Staggered field in the SDW state induces tiny antiferromagnetic order in the
subsystem of localized singlet-singlet levels. Unlike the other models our
scenario is based on coexistence of two orderings with the same
antiferromagnetic dipole symmetry.The topology of the pressure phase diagram
for such a two order parameter model is studied in the framework of the Landau
theory. The field dependences of the staggered magnetization and the magnon gap
are derived from the microscopic theory and found to be in good quantitative
agreement with experiment.
