  The recently reported coexistence of an oscillatory magnetic order with the
wave vector Q=0.241 \AA^{-1} and superconductivity in TmNi2B2C is analyzed
theoretically. It is shown that the oscillatory magnetic order and
superconductivity interact predominantly via the exchange interaction between
localized moments (LM's) and conduction electrons, while the electromagnetic
interaction between them is negligible. In the coexistence phase of the clean
TmNi2B2C the quasiparticle spectrum should have a line of zeros at the Fermi
surface, giving rise to the power law behavior of thermodynamic and transport
properties. Two scenarios of the origin of the oscillatory magnetic order in
TmNi2B2C are analyzed: a) due to superconductivity and b) independently on
superconductivity. Experiments in magnetic field are proposed in order to
choose between them.
