Thermally induced variable-range-hopping crossover and ferromagnetism in the layered cobalt oxide Sr2Y0.5Ca0.5Co2O7
Abstract
Temperature-dependent transport and magnetic measurements on Sr2Y0.5Ca0.5Co2O7 indicate that ferromagnetism appears along with a crossover between two forms of variable-range-hopping (VRH) conductivity on cooling. Efros-Shklovskii (ES)-type VRH conduction was found below approximately 30 K, transformed from Mott-type VRH at higher temperature. The magnitude of the Coulomb gap and the Mott-ES VRH crossover temperature are ~57 K and ~170 K, respectively. These are unusually large compared to those of nonmagnetic disordered materials. The peculiar electronic state for the ferromagnetic Coulomb gap is probably due to Coulomb correlations among d electrons in the disordered system.
- Publication:
-
Physical Review B
- Pub Date:
- February 2001
- DOI:
- Bibcode:
- 2001PhRvB..63f4401Y
- Keywords:
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- 75.50.Dd;
- 72.15.Rn;
- 81.40.Rs;
- Nonmetallic ferromagnetic materials;
- Localization effects;
- Electrical and magnetic properties