Non--Heisenberg Spin Dynamics of Double-Exchange Ferromagnets with Coulomb Repulsion

TL;DR

This paper investigates how Coulomb repulsion, Hund's rule, and superexchange interactions influence spinwave excitations in itinerant ferromagnets, revealing significant deviations from classical models and potential experimental relevance.

Contribution

It introduces a variational three-body calculation to analyze the complex interplay of interactions affecting spin dynamics in double-exchange ferromagnets.

Findings

Pronounced zone boundary softening observed in spinwave spectrum.

Strong deviations from Heisenberg spinwave dispersion.

Spin dynamics are highly sensitive to Coulomb and exchange interactions.

Abstract

With a variational three--body calculation we study the role of the interplay between the onsite Coulomb, Hund's rule, and superexchange interactions on the spinwave excitation spectrum of itinerant ferromagnets. We show that correlations between a Fermi sea electron--hole pair and a magnon result in a very pronounced zone boundary softening and strong deviations from the Heisenberg spinwave dispersion. We show that this spin dynamics depends sensitively on the Coulomb and exchange interactions and discuss its possible relevance to experiments in the manganites.