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Magnetismus Poster: Do., 13:00–15:30 D-P229
Magnetic excitations in a Dy/Y superlattice investigated with
inelastic neutron scattering
Alexander Grünwald 1,2 , Helena Tartakovskaya 3 , Andrew Wildes 1 , Wolfgang
Schmidt 4,1 , Peter Link 5 , Roger Ward 6 , Andreas Schreyer 2
1 Institut Laue-Langevin, Grenoble, France – 2 GKSS-Forschungszentrum, Geesthacht,
Germany – 3 Institute of Magnetism, Kiev, Ukraine – 4 Forschungszentrum Jülich, Germany
– 5 TU München, Germany – 6 University of Oxford, United Kingdom
Modern thin film growth techniques allow enormous flexibility in the choice of sample
composition, making these materials of particular interest for the investigation of spin
dynamics in structures of reduced dimensionality. While techniques as Brillouin light
scattering and ferromagnetic resonance experiments are limited to specific regions in
reciprocal space, inelastic neutron scattering provides, in principle, access to the whole
Brillouin zone. We have shown that this technique can be used on multilayer samples
[1]. These measurements are difficult, however, due to the small sample mass in superlattice
structures. Rare earth elements are the best candidates for studying spin
wave excitations in multilayer structures, since they exhibit the largest magnetic moment,
and have the largest cross section for magnetic neutron scattering. Besides the
novelty of measuring spin waves in artificially modulated structures, the experiments
also provide new information on RKKY exchange coupling and its propagation across
non-magnetic spacer layers.
A new theory has been developed to describe the nature of the spin waves in a Dy/Y
multilayer. The theory predicts discrete energy levels for spin waves propagating along
the surface normal, with the number of discrete energy levels being derived from the
number of magnetic atomic planes in a bi-layer. In the limit of an infinite number
of atomic planes the dispersion of bulk Dy [2] is recovered. The new calculations
show significant dependence of the energy eigenvalues on interdiffusion and interfacial
roughness.
To compare with new calculations on spin wave excitation eigenvalues, we present inelastic
neutron scattering measurements of low energy magnetic excitations in a Dy/Y
superlattice. The experimental data of constant-q scans show in some regions of reciprocal
space double/multi-peak features, as predicted by the theory. Although measured
with high resolution, these peaks are broad in width, which might be due to interdiffusion
and roughness. However, these data give supporting evidence for the new theory
of spin wave excitations in constrained magnetic multilayer structures.
[1] A. Schreyer et al., J. Appl. Phys., 87 (2000) 5443
[2] R.M. Nicklow et al., Phys. Rev. Lett., 26 (1971) 140