Magneto-optical evidence of double exchange in a percolating lattice

TL;DR

This study uses magneto-optical measurements to investigate how substituting calcium for europium in EuB6 affects its magnetic and electronic properties, revealing a transition from metallic to insulating behavior driven by double exchange mechanisms.

Contribution

It provides experimental magneto-optical evidence supporting the role of double exchange in the magnetic and electronic phase transition of EuB6 with calcium substitution.

Findings

Spectral weight change in the Drude component correlates with magnetic field.

Evidence of a crossover from ferromagnetic metal to Anderson insulator.

Magneto-optical data supports double exchange model in EuB6-Ca system.

Abstract

Substituting $Eu$ by $Ca$ in ferromagnetic $EuB_6$ leads to a percolation limited magnetic ordering. We present and discuss magneto-optical data of the $Eu_{1-x}Ca_{x}B_6$ series, based on measurements of the reflectivity $R(\omega)$ from the far infrared up to the ultraviolet, as a function of temperature and magnetic field. Via the Kramers-Kronig transformation of $R(\omega)$ we extract the complete absorption spectra of samples with different values of $x$. The change of the spectral weight in the Drude component by increasing the magnetic field agrees with a scenario based on the double exchange model, and suggests a crossover from a ferromagnetic metal to a ferromagnetic Anderson insulator upon increasing $Ca$-content at low temperatures.