Evidence formagnetic phase separation in colossal magnetoresistance compound EuB5.99C0.01

TL;DR

This study provides experimental evidence for magnetic phase separation in EuB5.99C0.01, linking inhomogeneous carbon distribution to magnetic and transport properties, and explaining the compound's colossal magnetoresistance behavior.

Contribution

The paper presents direct experimental evidence of magnetic phase separation in EuB5.99C0.01 using multiple techniques, supporting theories of inhomogeneity-driven magnetoresistance.

Findings

Magnetic polarons influence transport near ferromagnetic transition.

Carbon-rich regions act as spacers preventing ferromagnetic cluster formation.

Small-angle neutron scattering confirms mixed magnetic structures.

Abstract

EuB5.99C0.01 is a low-carrier density ferromagnet that is believed to be intrinsically inhomogeneous due to fluctuations of carbon content. In accordance with our previous studies, electric trasport of EuB5.99C0.01 close above temperature of the bulk ferromagnetic (FM) ordering is governed by magnetic polarons. Carbon-rich regions are incompatible with FM phase and therefore they act as spacers preventing magnetic polarons to link, to form FM clusters, and eventually to percolate and establish a (homogoneous) bulk FM state in this compound, what consequently causes additional (magneto)resistance increase. Below the temperature of the bulk FM ordering, carbon-rich regions give rise to helimagnetic domains, which are responsible for an additional scattering term in the electrical resistivity. Unfortunately, there has not been provided any direct evidence for magnetic phase separation in EuB5.99C0.01 yet. Here reported results of electrical, heat capacity, Hall resistivity and small-angle neutron scattering studies bring evidence for formation of mixed magnetic structure, and provide consistent support for the previously proposed scenario of the magnetoresistance enhancement in EuB5.99C0.01.