ACTA

Reentrant Metal-Insulator Transition in Ca_1-xEu_xB₆

V. Glushkov^a,b, M. Anisimov^a, R. Baybakov^c, S. Demishev^a,b, V. Filippov^d, K. Flachbart^e, A. Kuznetsov^c, N. Shitsevalova^d and N. Sluchanko^a
^aProkhorov General Physics Institute of RAS, Vavilov str. 38, Moscow 119991 Russia
^bMoscow Institute of Physics and Technology, Institutskii per. 9, Dolgoprudny, Moscow Region 141700 Russia
^cNational Research Nuclear University "MEPhI", Kashirskoe Shosse 31, Moscow 115409 Russia
^dFrantsevich Institute for Problems of Materials Science NAS, Krzhyzhanovsky str. 3, Kiev 03680 Ukraine
^eInstitute of Experimental Physics SAS, Watsonova 47, 040 01 Košice, Slovakia

Full Text PDF

Resistivity, Hall and Seebeck effects have been studied on single crystals of Ca_1-xEu_xB₆ (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(7 T)>10⁶ for x=0.63 at T < 10 K. Decreasing of Eu content in Ca_1-xEu_xB₆ below x* ≈ 0.6 restores the metallic ground state with moderate resistivity (ρ~1÷ 5 mΩ·cm) and CMR amplitude (ρ(0)/ρ(7 T) < 7). The second metal-insulator transition (MIT) in Ca_1-xEu_xB₆ 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-xEu_xB₆.

DOI: 10.12693/APhysPolA.126.294
PACS numbers: 71.30.+h, 72.15.Gd, 75.47.Gk