The temperature variation of the magnetic susceptibility of the compounds LiNiO2 and NaNiO2 has been measured. Contrary to a previous report by Hirakawa and co-workers (1985), which claimed that these materials were antiferromagnetically coupled, and so could potentially possess quantum liquid ground states, the authors' data suggest that these materials behave as weakly coupled 2D Ising ferromagnets. They show that this conclusion is in fact support by much of the data in the previous report.
The layered oxides LiCoO2, LiNiO2, NaCoO2 and NaNiO2 have been studied by XPS, UPS and EELS. The interpretation of data is somewhat hampered by surface segregation, especially for the Na compounds. However, all these materials are shown by photoemission to possess a very narrow d band, in contrast to the perovskite oxides LaMO3, and EELS reveals the presence of local, ligand-field-type excitations for LiCoO2. The authors argue that this is a consequence of the layered nature of these oxides. PES also shows satellites in both core and valence regions; the valence satellite intensity appears to correlate more with ligand ionizations, rather than metal ionizations. They interpret these results in terms of semi-empirical band calculations, and an impurity model.
High resolution electron energy loss spectra have been measured for a variety of first-row transition metal oxides for loss energies of up to 5 eV. The features observed are qualitatively consistent with the electronic properties of these materials (i.e., a highly damped plasmon for metals, and local d-d excitations for insulators), with the notable exception of CuO. Quantitatively, however, the intensities of the d-d transitions are an order of magnitude greater than expected from optical dipole strengths, and the authors evaluate possible explanations for this.
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