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Phys. Rev. Lett. 96, 016403 (2006) [4 pages]

Magneto-Optical Evidence of Double Exchange in a Percolating Lattice

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G. Caimi1, A. Perucchi1, L. Degiorgi1, H. R. Ott1, V. M. Pereira2,3, A. H. Castro Neto2, A. D. Bianchi4,5, and Z. Fisk6
1Laboratorium für Festkörperphysik, ETH Zürich, CH-8093 Zürich, Switzerland
2Department of Physics, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, USA
3CFP and Departamento de Física, Faculdade de Ciências Universidade de Porto, 4169-007 Porto, Portugal
4National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306, USA
5Hochfeldlabor Dresden, Forschungszentrum Rossendort, Postfach 510119, D-01314 Dresden, Germany
6Department of Physics, University of California, Davis, California 95616, USA

Received 6 October 2005; published 5 January 2006

Substituting Eu by Ca in ferromagnetic EuB6 leads to a percolation limited magnetic ordering. We present and discuss magneto-optical data of the Eu1-xCaxB6 series, based on measurements of the reflectivity R(ω) from the far infrared up to the ultraviolet, as a function of temperature and magnetic field. Via the Kramers-Kronig transformation of R(ω) 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.

© 2006 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevLett.96.016403
DOI:
10.1103/PhysRevLett.96.016403
PACS:
71.30.+h, 75.47.Gk, 78.20.−e
 
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