  The continuum limit of the tilted SU(2) spin model is shown to give rise to
the gauge Landau-Lifshitz equation which provides a unified description for
various spin orders. For a definite gauge, we find a double periodic solution,
where the conical spiral, in-plane spiral, helical, and ferromagnetic spin
orders become special cases, respectively. For another gauge, we obtain the
skyrmion-crystal solution. By simulating the influence of magnetic field and
temperature for our covariant model, we find a spontaneous formation of
skyrmion-fragment lattice and obtain a wider range of skyrmion-crystal phase in
comparison to the conventional Dzyaloshinsky-Moriya model.
