Spin-wave softening and Hund's coupling in ferromagnetic manganites

TL;DR

This paper demonstrates that finite Hund's coupling causes spin-wave softening in ferromagnetic manganites, providing an analytical spectrum correction that explains experimental observations.

Contribution

It offers an analytical derivation showing Hund's coupling as the key factor for spin-wave softening in manganites, extending the understanding of magnetic excitations.

Findings

Finite Hund's coupling leads to spin-wave softening.

Analytical spectrum derived for JH  t  JH, explaining experimental data.

Correction term accounts for zone boundary softening.

Abstract

Using one-orbital model of hole-doped manganites, we show with the help of Holstein-Primakov transformation that finite Hund's coupling is responsible for the spin-wave softening in the ferromagnetic $B$-phase manganites. We obtain an analytical result for the spin-wave spectrum for $\JH\gg t$. In the limit of infinte Hund's coupling, the spectrum is the conventional nearest-neighbor Heisenberg ferromagnetic spin-wave. The $o(t/\JH)$-order correction is negative and thus accounts for the softening near the zone boundary.