  The origin of chiral magnetic structures in ultrathin films of magnetic
metals is analyzed. It is shown that the Lifshitz-type invariant term in the
macroscopic thermodynamic potential can be derived from spin-orbit Rashba
Hamiltonian in two dimensional electron gas (2DEG). The former is the
prerequisite for existence of spin cycloid, skyrmions and other chiral
phenomena observed in thin films. The estimation of the period of spin cycloid
gives the value of an order of 10 nm that agrees well with the results of
scanning probe microscopy observation reported in the literature.
