On the spin wave spectrum in a layered antiferromagnetic structure of the LaMnO3 compound

Theoretical expressions are obtained for the energy of spin waves in a layered antiferromagnetic structure ( A type) of the perovskite-like compound LaMnO 3 . The Heisenberg exchange interactions of the central spin moment of the trivalent manganese ion (spin S = 2) with its eighteen neighbors from five coordination shells and the single-ion magnetic anisotropy energy are taken into account. The analysis is performed using six parameters: five exchange integrals and one anisotropy constant. Three of these five integrals determine the interactions in the two-dimensional ferromagnetic planes and two integrals characterize the interplanar interaction. The expressions derived for the magnon energy are valid for any direction and any magnitude of the quasi-momentum in the first Brillouin zone. For the three principal crystallographic directions, the theoretical results are compared with the experimental data for the dispersion curves obtained from inelastic neutron scattering studies of the LaMnO 3 compound. It is shown that the in-plane ferromagnetic interaction can be more than sixteen times as great as the interplanar antiferromagnetic interaction. The conclusions drawn in this study are compared with the results obtained by other authors.