Thus, until recently, the polar rock-salt surfaces were believed to be unstable and a mysterious class of surfaces. However, their technological importance is growing because of their interesting magnetic properties.
Large circles are oxygen atoms, and small circles are nickel.
The possible symmetry-compatible relaxations, and , are shown as arrows indicating a positive relaxation. For the thin film, the octopolar reconstruction was unable to reproduce the 32 non equivalent in-plane structure factors, regardless of the relaxations. Other models containing the two terminations over bulk-like layers are also able to reproduce the data, but they appeared unacceptable with respect to the growth process. From these studies it has become clear that the reconstruction mechanism proposed to stabilize polar rock-salt surfaces is correct but with a more complex surface chemistry than expected. A general instability due to the polarity can thus be ruled out.