Electrical transport properties of CaB$_6$

ORAL

Abstract

We report results from a systematic electron-transport study in a broad temperature range on twelve CaB$_6$ single crystals. None of the crystals were intentionally doped. The different carrier densities observed presumably arise from slight variations in the Ca:B stoichiometry. In these crystals, the variation of the electrical resistivity and of the Hall effect with temperature can be consistently explained by a variable charge state of intrinsic defects, most likely B-antisites (B atom replacing Ca atom). Our model is also consistent with the presence of a narrow, defect related, impurity band close to the Fermi level. Thus it may indicate the validity of defect-driven intrinsic ferromagnetism in alkaline-earth hexaborides. The magnetotransport measurements reveal that most of the samples we have studied are close to a metal-insulator transition at low temperatures. The magnetoresistance changes smoothly from negative---for weakly metallic samples---to positive values---for samples in a localized regime.

*We acknowledge support from grant MAT2012-38213-C02-01 of MEC, Spain and EP/I007210/1 from EPSRC, UK.

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Authors

  • Jolanta Stankiewicz

    • Instituto de Ciencia de Materiales de Arag\'on and Departamento de F\'isica de la Materia Condensada, CSIC--Universidad de Zaragoza, 50009-Zaragoza

  • Javier Ses\'e

    • Instituto de Nanociencia de Arag\'on and Departamento de F\'isica de la Materia Condensada, Universidad de Zaragoza, 50018-Zaragoza, Spain

  • Geetha Balakrishnan

    • Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK

  • Zachary Fisk

    • University of California at Irvine
    • Department of Physics and Astronomy, University of California, Irvine, CA 92697, USA
    • University of California, Irvine