  Multiple spin density waves and related vortex-type magnetic structures in
the itinerant electron system with inversion symmetry have been investigated on
the basis of the Hubbard model and the generalized Hartree-Fock approximation
combined with the recursion method. Possible magnetic phase diagram on the fcc
lattice is presented in the space of the Coulomb interaction strength and the
electron occupation number. It is found that the 2Q multiple helical spin
density waves (SDW) with half-skyrmion half-antiskyrmion paired structure, the
3Q multiple helical SDW with 3 dimensional type vortex structure, the 4Q
multiple SDW with partially ordered state, and a new type of 12Q multiple SDW
showing both the half-skyrmion-type vortex structure and the partially ordered
state can be stabilized around the Stoner instability line. The stability of
their structures is explained on the basis of their electronic structures.
