Influence of Quasi - Bi - Stripe Charge Order on the Resistivity and Magnetism in a Bilayer Manganite

The charge ordering in the bilayer manganite system La 2−2x Sr 1+2x Mn 2 O 7 with 0.30 ≤ x ≤ 0.50 has been studied by neutron diffraction. The charge order is characterized by the propagation vector parallel to the [1 0 0] direction (MnO 2 direction), but the correlation length is short-ranged and extremely anisotropic, being ∼ 0.02a * and ∼ 0.2a * parallel and perpendicular to the modulation direction, respectively. The observed charge order can be viewed as a quasi-bi-stripe order, and accounts well for the x dependence of the resistivity. The quasi-bistripe order is stable within the ferromagnetic (FM) MnO 2 layers in the A-type antiferromagnetic order, but is instabilized by the 3 dimensional FM order. It has been recently demonstrated that an A-type antiferromagnetic (AFM) state in the 1