The angular, temperature and magnetic field dependences of Hall resistance Н for the rare-earth dodecaboride solid solutions Tm 1-x Yb x B 12 have been studied in a wide vicinity of the quantum critical point (QCP) x C~0 .3. The measurements performed in the temperature range 1.9300 K on high quality single crystals allowed to find out for the first time in these fcc compounds both an appearance of the second harmonic contribution in Н at QCP and its' enhancement under the Tm to ytterbium substitution and/or with increase of external magnetic field. When the Yb concentration x increases a negative maximum of a significant amplitude was shown to appear on the temperature dependences of Hall coefficient R H (T) for the Tm 1-x Yb x B 12 compounds. Moreover, a complicated activation type behavior of the Hall coefficient is observed 2 at intermediate temperatures for x0.5 with activation energies E g~2 00K and E a~5 5-75K in combination with the sign inversion of R H (T) at low temperatures in the coherent regime. The density of states renormalization effects are analyzed within the variation of Yb concentration and the features of the charge transport in various regimes (charge gap formation, intra-gap manybody resonance and coherent regime) are discussed in detail in Tm 1-x Yb x B 12 solid solutions. PACS: 75.40.Cx, 72.15.Gd
In BCS-type superconductors Zr N B 12 (T C ≈ 6 K) and Lu N B 12 (T C ≈ 0.42 K) heat capacity C(T ) and magnetization measurements have been carried out on high quality single crystals with various boron isotopes (with N = 10, 11, and with natural composition of 10 B and 11 B). Parameters of the superconducting and normal states have been deduced from this study, allowing comparison between these two dodecaborides. It was shown that ZrB 12 is a type-II superconductor in which the Ginzburg-Landau parameter varies in the range κ = 0.8-1.12. A detailed analysis of specific heat in the normal state of R 10 B 12 , R 11 B 12 and R nat B 12 (where R = Zr, Lu) has revealed three Einstein type vibration modes of Zr 4+ -ions in ZrB 12 with characteristic energies θ E1 (Zr N B 12 ) ≈ 200 K and θ E2,3 (Zr N B 12 ) ≈ 450 K, N. Sluchanko ( ) •
Based on low temperature resistivity, heat capacity and magnetization investigations we show that the unusually strong suppression of superconductivity in LuxZr1−xB12 BSC-type superconductors in the range x<0.08 is caused by the emergence of static spin polarization in the vicinity of nonmagnetic lutetium impurities. The analysis of received results points to a formation of static magnetic moments with µ ef f ≈3µB per Lu-ion. The size of these spin polarized nanodomains was estimated to be about 5Å.
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