Evolution of spin-wave excitations in ferromagnetic metallic manganites

TL;DR

This study uses neutron scattering to analyze spin-wave excitations in ferromagnetic manganites, revealing systematic behaviors of magnetic interactions that challenge existing theoretical models.

Contribution

It provides new experimental insights into how carrier concentration affects spin dynamics in manganites, highlighting limitations of current models.

Findings

Weak dependence of long wavelength spin dynamics on composition

Systematic variation of $J_4/J_1$ with carrier concentration

Prevailing models fail to explain observed behaviors

Abstract

Neutron scattering results are presented for spin-wave excitations of three ferromagnetic metallic $A_{1-x}A^{\prime}_{x}$MnO$_3$ manganites (where $A$ and $A^\prime$ are rare- and alkaline-earth ions), which when combined with previous work elucidate systematics of the interactions as a function of carrier concentration $x$, on-site disorder, and strength of the lattice distortion. The long wavelength spin dynamics show only a very weak dependence across the series. The ratio of fourth to first neighbor exchange ($J_4/J_1$) that controls the zone boundary magnon softening changes systematically with $x$, but does not depend on the other parameters. None of the prevailing models can account for these behaviors.