Spectacular doping dependence of interlayer exchange and other results on spin waves in bilayer manganites - art. no. 217201

We report the measurement of spin waves in the bilayer colossal magnetoresi stive manganites La2-2xSr1+2xMn2O7 with x = 0.30, 0.35, and 0.40. For x = 0 .35 and 0.40 the entire acoustic and optic dispersion relations are well de scribed by those for a bilayer Heisenberg Hamiltonian with nearest-neighbor exchange only, which is explained together with the spin-wave lifetimes by the double exchange model. The in-plane exchange depends weakly on x, but that between the planes of a bilayer changes by a factor of 4, directly rev ealing a change from mixed d(3x2-r2) and d(x2-y2) orbital character to most ly d(x2-y2).