Eur. Phys. J. B 27, 287-297 (2002)
https://doi.org/10.1140/epjb/e2002-00157-2

Quantum spin dynamics of the bilayer ferromagnet La_1.2Sr_1.8Mn₂O₇

¹ Max–Planck–Institut für Physik komplexer Systeme, Nöthnitzer Str. 38, 01187 Dresden, Germany
² Institut Laue-Langevin, BP 156, 38042 Grenoble Cedex 9, France
³ Institut für Theoretische Physik III, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany
⁴ Max-Planck-Institut für Chemische Physik fester Stoffe, Nöthnitzer Str. 40, 01187 Dresden, Germany

Corresponding author: ^a shannon@mpipks-dresden.mpg.de

Received: 15 January 2002
Published online: 6 June 2002

Abstract

We construct a theory of spin wave excitations in the bilayer manganite La_1.2Sr_1.8Mn₂O₇ based on the simplest possible double–exchange model, but including leading quantum corrections to the spin wave dispersion and damping. Comparison is made with recent inelastic neutron scattering experiments. We find that quantum effects account for some part of the measured damping of spin waves, but cannot by themselves explain the observed softening of spin waves at the zone boundary. Furthermore a doping dependence of the total spin wave dispersion and the optical spin wave gap is predicted.