Low-energy spin-wave excitations in the bilayer manganite La1.2Sr1.8Mn2O7

Abstract

Inelastic neutron scattering experiments were performed on a single crystal of the bilayer manganite La1.2Sr1.8Mn2O7. Low-energy spin-wave excitations were observed along the c direction with a maximum energy of ∼ 0.5 meV at the zone boundary. The dispersion of these acoustic spin wave modes is modeled by a nearest-neighbor Heisenberg model with an interbilayer exchange interaction between neighboring spins in different bilayers of 0.048(1) meV and an anisotropy gap of Δ = 0.077(3) meV. These results confirm the two-dimensional nature of the spin correlations in the bilayer manganites, with a ratio of the in-plane to interbilayer interaction of ∼ 200. The temperature dependence of the energies and intensities of the spin wave excitations are in agreement with our earlier conclusion that the ferromagnetic transition is second order. © 2000 American Institute of Physics.