Spin waves in the bilayer manganite La2−2xSr1+2xMn2O7, x=0.35

Abstract We report the measurements of low temperature spin waves in the bilayer colossal magnetoresistive manganite La 2−2 x Sr 1+2 x Mn 2 O 7 with hole doping x =0.35. The dispersion relations for acoustic and optic branches are reasonably well described by a Heisenberg Hamiltonian with nearest neighbour exchange only. The coupling constants are 2 SJ ∥ =9.3±0.1 meV and 2 SJ ⊥ =5.7±0.2 meV within and between planes respectively. The ratio J ⊥ / J ∥ =0.61 is larger than the corresponding value of ∼0.3 for x =0.4. This is explained by greater d 3 z 2−r 2 orbital occupancy as the hole doping is reduced. The acoustic spin wave damping is proportional to the spin wave energy in the long wavelength limit. The damping is much larger than expected from magnon–magnon or magnon–electron scattering.