Local structure of LiNiO2 studied by neutron diffraction

J.-H. Chung (1) , Th. Proffen (2) , S. Shamoto (3) , A. M. Ghorayeb (4) , Laurence Croguennec (5) , W. Tian (6) , B. C. Sales (6, 7) , R. Jin (6) , D. Mandrus (6) , T. Egami (8, 6, 7)

1 University of Pennsylvania
2 LANL - Los Alamos National Laboratory
3 Japan Atomic Energy Agency
4 L2MP - Laboratoire matériaux et microélectronique de Provence
5 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux
6 Department of Physics and Astronomy [Knoxville]
7 ORNL - Oak Ridge National Laboratory [Oak Ridge]
8 Department of Materials Science and Engineering [Knoxville]

The nature of the magnetic state of LiNiO2 has been controversial. In this compound Ni spins (S = 1/2) form a triangular lattice with the possibility of magnetic frustration, but the exact state of spin correlation has not yet been known in spite of the extensive research work. A factor that complicates understanding of the magnetic state is the orbital state of Ni3+ which is a Jahn-Teller (JT) ion. While there is no signature of long-range Jahn-Teller distortion, local JT distortion has been suspected. We have performed neutron diffraction and atomic pair-density function analyses up to unprecedented large distances to discover a number of unusual features, such as anomalous peak broadening, local JT distortion, sharp oxygen-oxygen distance correlations, and inverted temperature dependence of medium range correlation. These observations are best explained by local orbital ordering of Ni3+ ions into three sublattices. This orbital ordering, however, cannot develop into long-range order because of the strain field it generates, and domains of about 10 nm in size are formed. Domains are susceptible to random pinning by impurities (site disorder) resulting in the loss of structural long-range order. We suggest that this local orbital ordering is the basis for the complex magnetic properties observed in this compound.

Mots clés: Zeeman and Stark splitting; Jahn-Teller effect; Neutron diffraction; Strongly correlated electron systems; Heavy fermions; Spin-orbit coupling

Domaines: Matériaux

J.-H. Chung, Th. Proffen, S. Shamoto, A. M. Ghorayeb, Laurence Croguennec, et al.. Local structure of LiNiO2 studied by neutron diffraction. Physical Review B: Condensed Matter and Materials Physics (1998-2015), 2005, 71 (6), 064410 (11 p.). ⟨10.1103/PhysRevB.71.064410⟩. ⟨hal-00022199⟩