  Spin-flip excitations in a quantum Hall electron system at fixed filling
factor nu=2 are modelled and studied under conditions of a strong Coulomb
interaction when the `Landau level mixing' is a dominant factor determining the
excitation energy. The `one-exciton' approach used for the purely electronic
excitations in question allows us to describe the Stoner transition from the
unpolarized/paramgnet state to the polarized/ferromagnet one. The theoretical
results are compared with the available experimental data.
