Confined spin waves reveal an assembly of nanosize domains in ferromagnetic La(1-x)CaxMnO3 (x=0.17,0.2)

TL;DR

This study reveals that in ferromagnetic La$_{1-x}$Ca$_{x}$MnO$_3$ near the metal-insulator transition, spin-wave confinement indicates the presence of nanoscale orbital-ordered domains, shedding light on the precursor state of colossal magnetoresistance.

Contribution

The paper demonstrates that spin-wave measurements can identify nanoscale orbital-ordered domains in La$_{1-x}$Ca$_{x}$MnO$_3$, providing new insights into the material's magnetic and electronic phase behavior.

Findings

Presence of nearly q-independent energy levels indicating confined spin waves.

Domains are a few lattice spacings in size, with anisotropic magnetic coupling.

Domains are characterized as 'hole-poor' and orbital-ordered.

Abstract

We report a study of spin-waves in ferromagnetic La$_{1-x}$Ca$_{x}$MnO$_3$, at concentrations x=0.17 and x=0.2 very close to the metallic transition (x=0.225). Below T$_C$, in the quasi-metallic state (T=150K), nearly q-independent energy levels are observed. They are characteristic of standing spin waves confined into finite-size ferromagnetic domains, defined in {\bf a, b) plane for x=0.17 and in all q-directions for x=0.2. They allow an estimation of the domain size, a few lattice spacings, and of the magnetic coupling constants inside the domains. These constants, anisotropic, are typical of an orbital-ordered state, allowing to characterize the domains as "hole-poor". The precursor state of the CMR metallic phase appears, therefore, as an assembly of small orbital-ordered domains.