title: Dispersionless Spin Waves and Underlying Field-Induced Magnetic Order in Gadolinium Gallium Garnet.
abstract: We report the results of neutron diffraction and inelastic neutron scattering on a powder sample of Gd_{3}Ga_{5}O_{12} at high magnetic fields. Analysis of the diffraction data shows that in high fields (B≳1.8 T) the spins are not fully aligned, but are canted slightly as a result of the dipolar interaction. The magnetic phase for fields ≲1.8 T is characterized by antiferromagnetic peaks at (210) and an incommensurate wave vector. The dominant contribution to inelastic scattering at large momentum transfers is from a band of almost dispersionless excitations. We show that these correspond to the spin waves localized on ten site rings, expected on the basis of nearest neighbor exchange interaction, and that the spectrum at high fields B≳1.8 T is well described by a spin wave theory.
authors.affiliation: Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom.
authors.forename: N
authors.initials: N
authors.lastname: d'Ambrumenil
authors.affiliation: Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom.
authors.forename: O A
authors.initials: OA
authors.lastname: Petrenko
authors.affiliation: Institut Laue-Langevin, 71 avenue des Martyrs, CS 20156, F-38042 Grenoble Cedex 9, France.
authors.forename: H
authors.initials: H
authors.lastname: Mutka
authors.affiliation: European Spallation Source ESS AB, Box 176, SE-221 Lund, Sweden Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, 2100 Copenhagen, Denmark.
authors.forename: P P
authors.initials: PP
authors.lastname: Deen