Spin Glass Statics and Dynamics in the Disordered Stacked Quantum Ferromagnet LiNiO2

We have performed time-of-flight neutron scattering measurements on polycrystalline LiNiO2 using the Disk Chopper Spectrometer at the NIST Center for Neutron Research. Similar measurements performed on its sister compound, NaNiO2, show a simple magnetic structure below Tn$\sim $22K consisting of ferromagnetic sheets of s=1/2 moments stacked in an antiferromagnetic (AF) fashion [1]. Our measurements on LiNiO2 illustrate the absence of magnetic order down to 1.7K. Further they provide direct evidence for a spin glass transition at 9K through a narrowing of the inelastic magnetic scattering on approaching Tg from above, along with a concomitant increase in the elastic magnetic scattering, indicative of frozen disordered moments. The inelastic magnetic scattering in LiNiO2 resembles that in NaNiO2 above Tn, suggesting that the low Q spin response is due to short-lived spin wave modes below the lowest Q AF ordering wavevector. This reinforces the picture that the simple stacked ferromagnetic ordered state displayed by NaNiO2 is precluded by mixing between the Li and Ni sublattices, which occurs in LiNiO2 at the 1-3{\%} level. [1] M.J. Lewis et al., PRB 72, 014408 (2005).