  We study the spin ordering within the 3-leg ladders present in the oxyborate
Fe(3)O(2)BO(3) consisting of localized classical spins interacting with
conduction electrons (one electron per rung). We also consider the competition
with antiferromagnetic superexchange interactions to determine the magnetic
phase diagram. Beside a ferromagnetic phase we find (i) a phase with
ferromagnetic rungs ordered antiferromagnetically (ii) a zig-zag canted spin
ordering along the legs. We also determine the induced charge ordering within
the different phases and the interplay with lattice instability. Our model is
discussed in connection with the lattice dimerization transition observed in
this system, emphasizing on the role of the magnetic structure.

Strongly Correlated Electrons