  On the basis of first principles density functional theory electronic
structure calculations as well as classical spin analysis, we explored why the
magnetic oxide Li2CuO2, consisting of CuO2 ribbon chains made up of
edge-sharing CuO4 squares, does not exhibit a spiral-magnetic order. Our work
shows that, due to the next-nearest-neighbor interchain interactions, the
observed collinear magnetic structure becomes only slightly less stable than
the spin-spiral ground state, and many states become nearly degenerate in
energy with the observed collinear structure. This suggests that the collinear
magnetic structure of Li2CuO2 is a consequence of order-by-disorder induced by
next-nearest-neighbor interchain interactions.
