Magneto-optical evidence of double exchange in a percolating lattice

Abstract

Substituting $Eu$ by $Ca$ in ferromagnetic $Eu{B}_6$ leads to a percolation limited magnetic ordering. We present and discuss magneto-optical data of the $E{u}_{1-x}C{a}_x{B}_6$ series, based on measurements of the reflectivity $R(\ddot{I}‰)$ from the far infrared up to the ultraviolet, as a function of temperature and magnetic field. Via the Kramers-Kronig transformation of $R(\ddot{I}‰)$ 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.

10 pages, 3 figures