Low-spin vs high-spin square planar Ni2+ ions in Sr2NiO2Cu2Se2-xSx.

This is a proposal for Rapid Access to WISH prior to the shutdown in mid 2021 to complete an investigation of the change in magnetic structures and a change in spin state of the Ni2+ ion in a highly distended octahedral coordination environment. Sr2NiO2Cu2Se2 is high spin with magnetic long range order and Sr2NiO2Cu2S2 is low-spin with a diamagnetic Ni2+ ion. Our measurements so far have captured the transition with x in the solid solution Sr2NiO2Cu2Se2-xSx but also show an evolution in the magnetic structure which we need to probe in more detail to complete the story for publication.