Spin-ordering and magnon collective modes for two-dimensional electron lattices in strong magnetic fields

We study the spin-ordering and the magnon collective modes of the two-dimensional Wigner crystal state at strong magnetic fields. Our work is based on the Hartree-Fock approximation for the ground state and the time-dependent Hartree-Fock approximation for the collective modes. We find that the ground state is ferromagnetic, i.e., that all spins are aligned at T=0 even when the electronic g factor is negligibly small. The magnon calculations show that the spin stiffness is much smaller in the crystal state than in fluid states which occur at nearby Landau-level filling factors.