Spin-Wave Excitations in Two Dimensional Antiferromagnet of Stoichiometric La₂NiO₄

Abstract

Inelastic neutron magnetic scattering experiments were performed from the well characterized single crystal of La 2 NiO 4.00 ( T N =328 K) to study the spin-wave excitations in this system. The large energy gaps are observed at the two dimensional zone center, namely 15.7 meV for the out-of-plane mode, and 4.1 meV or 7.9 meV below or above 70 K for the in-plane mode respectively. Combined with the higher energy scans carried out by the spallation neutron source, the whole dispersion relation was determined, which follows a linear spin-wave model. It provides the microscopic parameters of nearest neighbor exchange interactions in plane, two anisotropy energies corresponding to the out-of-plane and in-plane modes, respectively, 28.7±0.7 meV, 1.26±0.12 meV and 0.10±0.02 meV at 10 K. The scattering intensities also nicely follow the linear spin-wave model at the lowest temperature. The results are discussed with the previous experiments on the spin dynamics of La 2 CuO 4 .