Spin-wave excitations in the ferromagnetic-metallic and in the charge, orbital and spin ordered states in Nd$_{1-x}$Sr$_{x}$MnO$_{3}$ with x$\approx$0.5

TL;DR

This study investigates spin-wave excitations in Nd$_{1-x}$Sr$_{x}$MnO$_{3}$ with x≈0.5, revealing anisotropic magnetic interactions in both ferromagnetic metallic and charge-ordered insulating states through neutron scattering.

Contribution

It provides a detailed comparison of magnetic excitations in different phases of Nd$_{1-x}$Sr$_{x}$MnO$_{3}$, confirming theoretical models for charge and orbital ordering and magnetic interactions.

Findings

Anisotropic spin-wave stiffness in the antiferromagnetic state.

Perfect description of dispersion by linear spin-wave theory in the charge-ordered phase.

Similar magnon dispersion in ferromagnetic metallic state explained by a Heisenberg model.

Abstract

Inelastic neutron scattering experiments have been performed on single crystals of Nd$_{1-x}$Sr$_{x}$MnO$_{3}$ with x$\approx$0.5. Colossal magnetoresistance (CMR) in the manganites arises from the interplay between a ferromagnetic metallic and antiferromagnetic charge and orbital ordered insulating state. Therefore, it appears important to compare these phases concerning their underlying magnetic interaction parameters. Our investigations of the spin-wave disperion in the AFM ordered state of Nd$_{0.5}$Sr$_{0.5}$MnO$_{3}$ exhibits a strongly anisotropic stiffness. The sign of the anisotropy is characteristic for the site-centered model for charge and orbital ordering in half-doped manganites. Within this model, linear spin-wave theory yields a perfect description of the experimental dispersion. Furthermore, magnetic excitations in the ferromagnetic metallic state of Nd$_{1-x}$Sr$_{x}$MnO$_{3}$ with x=0.49 and x=0.50 exhibit nearly the same magnon dispersion which can be described with a Heisenberg model including nearest-neighbor interactions.