Low-energy spin-wave excitations in amplitude-modulated magnetic structure of PrNi2Si2

J A Blanco,B Fåk,P Lejay,M Rotter,A Hiess,J Jensen,D Schmitt

doi:10.1088/1742-6596/663/1/012010

Abstract

Inelastic neutron scattering (INS) experiments and random phase approximation calculations have been used to investigate the low-energy spin-wave excitations in PrNi2Si2. The modulated magnitude of the ordered magnetic moments of Pr3+ ions implies that the associate, longitudinally polarized magnetic excitations are more intense and dispersive than the usual transverse spin waves. Within the random phase approximation the results are in good overall agreement with the predictions made by the model determined previously from the paramagnetic excitations. The most unusual observation is the well-defined amplitude mode detected close to the magnetic Bragg point existing simultaneously with the phason mode. At low energies, an extra mode is observed to hybridize with the magnetic phasons in the neighborhood of the magnetic Brillouin zone center. A magnetoelastic interaction between the magnetic excitations and the longitudinal phonons is able to explain part of the disturbances, but it is concluded that the extra mode must be of some other, unknown origin.

Highlights

In incommensurate magnetic structures, the only low–energy mode that is expected to be is the pseudo–Goldstone mode of broken translations, known as a phason [1]
The excitations observed in the ordered phase relate in a direct way to the excitations in the paramagnetic phase via the level diagram shown in Figure 1 [18]
The cc polarized paramagnetic excitations are the cooperative excitations deriving from the transition between the Γ(11) and Γ2 states at zero exchange field, and the longitudinal magnetic excitations in the ordered phase derive from the same transition at non-zero exchange fields

Summary

Introduction

The only low–energy mode that is expected to be is the pseudo–Goldstone mode of broken translations, known as a phason [1]. The modulated magnitude of the ordered magnetic moments of Pr3+ ions implies that the associate, longitudinally polarized magnetic excitations are more intense and dispersive than the usual transverse spin waves. The most unusual observation is the well–defined amplitude mode detected close to the magnetic Bragg point existing simultaneously with the phason mode.

Results

Conclusion