Magnetic order in ferromagnetically coupled spin ladders

A model of coupled antiferromagnetic spin-1/2 Heisenberg ladders is studied with numerical techniques. In the case of ferromagnetic interladder coupling we find that the dynanic and static structure factor has a peak at (pi,pi/2) where the first (second) direction is along (transversal) to the ladders. In addition, we suggest that the intensity of this peak and the spin-spin correlation at the maximum distance along the ladder direction remain finite in the bulk limit for strong enough interladder coupling. We discuss the: relevance of these results for magnetic compounds containing ladders coupled in a trellis lattice and for the stripe scenario in high-T-c superconducting cuprates.