Influence of Quasi-Bi-Stripe Charge Order on Resistivity and Magnetism in the Bilayer Manganite La2-2xSr1+2xMn2O7

The charge ordering in the bilayer manganite system La₂₋₂ₓSr₁₊₂ₓMn₂O₇ 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 (MnO₂ 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) MnO₂ layers in the A-type antiferromagnetic order, but is instabilized by the 3 dimensional FM order.