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Reentrant Metal-Insulator Transition in Ca_{1-x}Eu_{x}B_{6}

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Glushkov V., Anisimov M., Baybakov R., Demishev S., Filippov V., Flachbart K., Kuznetsov A., Shitsevalova N., Sluchanko N.

Resistivity, Hall and Seebeck effects have been studied on single crystals of Ca_{1-x}Eu_{x}B_{6} (0 ≤ x ≤ 1) at temperatures 2-300 K and in magnetic fields up to 8 T. An insulating ground state is found to be limited by narrow range of Eu doping 0.6 ≤ x ≤ 0.8. This region is characterized by an enhanced colossal magnetoresistance (CMR), which reaches values of ρ(0)/ρ(7T) > 10^{6} for x = 0.63 at T < 10 K. Decreasing of Eu content in Ca_{1-x}Eu_{x}B_{6} below x* ≈ 0.6 restores the metallic ground state with moderate resistivity (ρ ~ 1 ÷ 5 mΩ·cm) and CMR amplitude (ρ(0)/ρ(7T) < 7). The second metal-insulator transition (MIT) in Ca_{1-x}Eu_{x}B_{6} is observed beyond the whole conductivity region found earlier in the narrow range of Eu doping (0.7 ≤ x ≤ 0.8). The correlation between the enhanced CMR amplitude, the onset of positive diffusive thermopower and the elevation of anomalous Hall effect, determined for Eu content 0.6 ≤ x ≤ 0.85, favors the idea that a smooth change of band structure is the main factor governing the reentrant MIT in Ca_{1-x}Eu_{x}B_{6}.

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1 Acta Physica Polonica A

1 2014

1 Anisimov M.

1 Baybakov R.

1 Demishev S.

1 Filippov V.

1 Flachbart K.

1 Glushkov V.

1 Kuznetsov A.

1 Shitsevalova N.

1 Sluchanko N.

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Reentrant Metal-Insulator Transition in Ca_{1-x}Eu_{x}B_{6}