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}.
We probed the evolution of the superconducting transition temperature T_c and the normal state parameters of Lu_xZr_{1-x}B_{12} solid solutions employing resistivity, heat capacity and magnetization measurements. In these studies of high-quality single crystals it was found that there are two types of samples with different magnetic characteristics. An unusually strong suppression of superconductivity in Lu_xZr_{1-x}B_{12} with a rate dT_c/dx=0.21 K/at.% of Lu was observed previously on the first "magnetic" set of crystals, and it was argued to be caused by the emergence of static spin polarization in the vicinity of non-magnetic lutetium ions. On the contrary, the second (current) set of "nonmagnetic" crystals demonstrates a conventional T_c(x) dependence with a rate dT_c/dx=0.12 K/at.% of Lu which is typical for BCS-type superconductors doped by nonmagnetic impurities. The reason for this difference is yet unclear. Moreover, the H-T phase diagram of the superconducting state of Lu_xZr_{1-x}B_{12} (0 ≤ x ≤ 1) solid solutions has been deduced from magnetization measurements.
The specific heat of high quality La^{N}B_{6} (N=10, 11, natural) single crystals is investigated in a wide range of temperatures 2 - 300 K. The obtained data allow to estimate correctly (i) the electronic γ· T term of specific heat (γ ≈ 2.4 mJ/(mol·K^{2})), (ii) the contribution from quasilocal vibrating mode of La^{3+} ions (Θ_{E} ≈ 150 - 152 K), (iii) the Debye-type term from rigid boron cages (Θ_{D} ≈ 1160± 40 K). Our data also suggest an additional defect-mode component (iv) which may be attributed to a contribution of 1.5% boron vacancies in LaB_{6}. The obtained results may be interpreted in terms of formation of two level systems, which appear when La^{3+} ions are displaced from their centrosymmetric positions in the cavities of rigid boron cages, apart from randomly distributed boron vacancies in the LaB_{6} matrix.
The Hall effect of GdB_{6} has been studied on high quality single crystals in the temperature range 2-150 K and in magnetic field of 1 T. The obtained data allow to detect anomalies in the antiferromagnetic (AF) phase including (i) a drastic enhancement of negative Hall coefficient below T_{N1} ≈ 15.5 K and (ii) the appearance of an anomalous Hall effect at T_{N2} ≈ 4.7 K. Possible scenarios of the AF ground state formation are discussed.
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