Evidence of anisotropic magnetic polarons in la$_{0.94}$Sr$_{0.06}$MnO$_3$ by neutron scattering and comparison with Ca-doped manganites

TL;DR

This study uses neutron scattering to reveal anisotropic magnetic polarons in La$_{0.94}$Sr$_{0.06}$MnO$_3$, showing small-scale electronic segregation and comparing these features with Ca-doped manganites.

Contribution

It provides new insights into the anisotropic shape and growth behavior of magnetic polarons in Sr-doped manganites, and compares these with Ca-doped counterparts.

Findings

Magnetic polarons are platelike and anisotropic.

Polaron size is approximately 17 Å with inter-polaron distance around 38 Å.

Growth of magnetic polarons is faster in Sr-doped samples.

Abstract

Elastic and inelastic neutron scattering experiments have been performed in a La$_{0.94}$Sr$_{0.06}$MnO$_3$ untwinned crystal, which exhibits an antiferromagnetic canted magnetic structure with ferromagnetic layers. The elastic small q scattering exhibits a modulation with an anisotropic q-dependence. It can be pictured by ferromagnetic inhomogeneities or polarons with a platelike shape, the largest size ($\approx17\AA$) and largest inter-polaron distance ($\approx$ 38$\AA$) being within the ferromagnetic layers. Comparison with observations performed on Ca-doped samples, which show the growth of the magnetic polarons with doping, suggests that this growth is faster for the Sr than for the Ca substitution. Below the gap of the spin wave branch typical of the AF layered magnetic structure, an additional spin wave branch reveals a ferromagnetic and isotropic coupling, already found in Ca-doped samples. Its q-dependent intensity, very anisotropic, closely reflects the ferromagnetic correlations found for the static clusters. All these results agree with a two-phase electronic segregation occurring on a very small scale, although some characteristics of a canted state are also observed suggesting a weakly inhomogeneous state.