Figure 4: The frustration scenario in La_2−xSr_xCoO₄.

(a) Neutron-scattering intensities for (H±H0) scans of La_2−xSr_xCoO₄ for different x showing a continuous peak broadening below half doping. (b) The peak width for different x as a function of incommensurability Δε=ε−1/4. (c) The AFM structure in an ideal CBCO state. (d) Schematic drawing of our frustration scenario. The introduction of an additional electron (Co²⁺ ion) into the AFM matrix of the ideal CBCO half-doped compound induces strong frustration because of a strong nn-exchange coupling J compared with the existing exchange couplings J′ within the undistorted AFM matrix. Thus, effectively, one additional FM exchange interaction is introduced into each AFM sublattice of the ideal CBCO spin structure (blue dotted/dashed line). To release frustration, the formation of a chiral or non-collinear magnetic structure appears likely (the change of the spin directions is emphasized by the colour change). Intensity error bars are statistical error bars calculated by the square root of intensity. Other error bars are s.d. obtained from Lorentzian peak fits.