Ordering and spin waves in NaNiO2: A stacked quantum ferromagnet

Neutron scattering measurements on powder NaNiO2 reveal magnetic Bragg peaks and spin waves characteristic of strongly correlated s=1∕2 magnetic moments arranged in ferromagnetic layers which are stacked antiferromagnetically. This structure lends itself to stacking sequence frustration in the presence of mixing between nickel and alkali metal sites, possibly providing a natural explanation for the enigmatic spin glass state of the isostructural compound, LiNiO2.