Study of the ferrodistorsive orbital ordering in NaNiO2 by neutron diffraction and submillimeter wave ESR
Grenoble High Magnetic Field Laboratory, CNRS and MPI-FKF, BP 166X, 38042 Grenoble, France
2 Laboratoire de Cristallographie, CNRS, BP 166X, 38042 Grenoble, France
Published online: 15 October 2000
NaNiO2 has been studied by neutron-powder diffraction, magnetic susceptibility and submillimeter wave ESR. The monoclinic structure at room temperature is characterised by a ferrodistorsive orbital ordering due to the Jahn-Teller (JT) effect of the Ni3+ ions in the low spin state. NaNiO2 undergoes a structural transition at around 480 K, above which the orbital ordering disappears. The high temperature phase is rhombohedral with the layered α-NaFeO2 structure ( space group). The magnetic susceptibility exhibits hysteresis and we observe a change of the Curie-Weiss law parameters above the JT transition. The anisotropy of the g-factor at 200 K can be attributed to the JT effect which favours the orbital occupation. Finally, the interplay between the magnetic and structural properties of NaNiO2 and LiNiO2 is discussed.
PACS: 71.70.Ej – Spin orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect / 61.12.-q – Neutron diffraction and scattering / 76.30.-v – Electron paramagnetic resonance and relaxation
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2000