The metal-insulator transition of the ferromagnetic La7/8Sr1/8MnO3 probed by spin waves: a 2D stripe superstructure

TL;DR

This study investigates the spin wave behavior in La7/8Sr1/8MnO3 across the metal-insulator transition, revealing a 2D stripe superstructure and charge segregation associated with domain ordering.

Contribution

It provides new insights into the 2D stripe superstructure and domain ordering during the metal-insulator transition in ferromagnetic manganites.

Findings

Observation of propagating spin waves up to q=0.25

Detection of four dispersionless levels beyond this q-range

Identification of a 2D stripe superstructure associated with charge segregation

Abstract

We report a study of spin waves in hole-doped ferromagnetic La7/8Sr1/8MnO3, in the metallic state (165K) below TC (181K) and through the puzzling metal-insulator transition which occurs at TO'O''=159K. They reveal very unusual excitations. Propagating spin waves are observed in the small q-range up to q=0.25 (lambda=4a), and, beyond, four dispersionless levels. Both types of excitations have a quasi two-dimensional (2D) character. The transition is revealed by a folding of the dispersed magnon branch at q=1/8. In the metallic state, the dispersionless levels reveal ferromagnetic domains with 4 lattice spacings for their size along a and b. They lead to a picture of charge segregation with hole-poor domains surrounded with hole-rich paths. Within this description, the transition appears as the ordering of domains, which can be interpreted in terms of a 2D superstructure of orthogonal stripes.