Spin correlations in charge-ordered La_5/3Sr_1/3NiO₄

Charge order of La_5/3Sr_1/3NiO₄ takes place in the NiO₂ layers and consists of parallel stripes of doped holes carrying spin S=1/2 in a background of Ni²⁺ ions carrying spin S=1. 

The contour plot, which was constructed from a 25 x 35 rectangular grid of points measured on IN8, shows the scattering intensity in the (h,k,0) plane at an energy transfer of 2.5 meV.
‘Hot spots’ at (h,k) = (1/3, 2/3), (2/3, 2/3), etc, derive from spin wave excitations of the S=1 spins, which are antiferromagnetically ordered. The diagonal lines of weak diffuse scattering indicate antiferromagnetic correla- tions along the charge stripes. This finding is important because charge stripe correlations also exist in the cuprate high-temperature superconductors, and it has been suggested that they could play an important role in the mechanism of superconductivity. The behaviour of the spin degrees of freedom in the stripes would be a crucial factor in the formation of a superconducting state.