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The results of Hall-effect and resistance measurements on the substitutional solid solutions CeCu6-xAux with concentrations 0≼x≼0.3, corresponding to a wide neighborhood of the quantum critical point (QCP) at x=0.1, are presented. The measurements are made by rotation of the sample in a constant magnetic field of up to 70 kOe in a temperature interval of 1.8–300 K. For the classic heavy-fermion compound CeCu6 the temperature dependence of the Hall coefficient RH(T) exhibits a complex activational form with activation energies Ea1/kB≈110 K and Ea2/kB≈1.5 K in the temperature intervals 50–300 K and 3–10 K, respectively. It is shown that the anomalous behavior of the Hall effect can be explained in a spin-polaron approach, in which the values Ea1,2 can be associated to the binding energy of many-body and one can obtain estimates of the effective mass (meff1,2≈130–150m0) and localization radius (ap1,2*≈1.7 and 14 Å) of the charge carriers in CeCu6. For the compound CeCu5.9Au0.1, corresponding to the QCP, one observes correlated power-law behavior of the temperature dependence of the Hall coefficient RH(T)∼T-0.4 and magnetic susceptibility χ(T)∼T-0.4, as is characteristic of the regime of quantum critical behavior. For compounds in the immediate vicinity of the QCP an anomalous, even contribution RH2 to the angular dependence of the Hall voltage appears at temperatures below T*∼24 K and becomes stronger with increasing magnetic field. Different scenarios for passage through the QCP and their applicability for describing the Hall-effect anomalies in the substitutional solid solutions CeCu6-xAux are discussed. [ABSTRACT FROM AUTHOR]

The results of Hall-effect and resistance measurements on the substitutional solid solutions CeCu6-xAux with concentrations 0≼x≼0.3, corresponding to a wide neighborhood of the quantum critical point (QCP) at x=0.1, are presented. The measurements are made by rotation of the sample in a constant magnetic field of up to 70 kOe in a temperature interval of 1.8–300 K. For the classic heavy-fermion compound CeCu6 the temperature dependence of the Hall coefficient RH(T) exhibits a complex activational form with activation energies Ea1/kB≈110 K and Ea2/kB≈1.5 K in the temperature intervals 50–300 K and 3–10 K, respectively. It is shown that the anomalous behavior of the Hall effect can be explained in a spin-polaron approach, in which the values Ea1,2 can be associated to the binding energy of many-body and one can obtain estimates of the effective mass (meff1,2≈130–150m0) and localization radius (ap1,2*≈1.7 and 14 Å) of the charge carriers in CeCu6. For the compound CeCu5.9Au0.1, corresponding to the QCP, one observes correlated power-law behavior of the temperature dependence of the Hall coefficient RH(T)∼T-0.4 and magnetic susceptibility χ(T)∼T-0.4, as is characteristic of the regime of quantum critical behavior. For compounds in the immediate vicinity of the QCP an anomalous, even contribution RH2 to the angular dependence of the Hall voltage appears at temperatures below T*∼24 K and becomes stronger with increasing magnetic field. Different scenarios for passage through the QCP and their applicability for describing the Hall-effect anomalies in the substitutional solid solutions CeCu6-xAux are discussed. [ABSTRACT FROM AUTHOR]

The magnetic and transport characteristics of substitutional solid solutions of the Tm1− xYb xB12 rare earth dodecaborides have been investigated. The measurements performed in the wide temperature range 1.8−300 K on the high-quality single-crystalline samples make it possible to conclude that as x increases, antiferromagnetic instability develops with the quantum critical point ( T N = 0) near x = 0.3 and relevant dielectrization of the electron structure in the range 0 ≤ x ≤ 0.8 takes place. With the results of the thermoelectric measurements in Tm1− xYb xB12, the activation energy values and their dependence on x have been determined. [ABSTRACT FROM AUTHOR]

The magnetoresistance and magnetization of single-crystal samples of rare-earth dodecaborides RB12 (R = Ho, Er, Tm, Lu) have been measured at low temperatures (1.8–35 K) in a magnetic field of up to 70 kOe. The effect of positive magnetoresistance that obeys the Kohler’s rule Δρ/ρ = f(ρ(0, 300 K) H/ρ(0, T)) is observed for the nonmagnetic metal LuB12. In the magnetic dodecaborides HoB12, ErB12, and TmB12, three characteristic regimes of the magnetoresistance behavior have been revealed: the positive magnetoresistance effect similar to the case of LuB12 is observed at T > 25 K; in the range T N ≤ T ≤ 15 K, the magnetoresistance becomes negative and depends quadratically on the external magnetic field; and, finally, upon the transition to the antiferromagnetic phase ( T < T N), the positive magnetoresistance is again observed and its amplitude reaches 150% for HoB12. It has been shown that the observed anomalies of negative magnetoresistance in the paramagnetic phase can be explained within the Yosida model of conduction electron scattering by localized magnetic moments. The performed analysis confirms the formation of spin-polaron states in the 5 d band in the vicinity of rare-earth ions in paramagnetic and magnetically ordered phases of RB12 and makes it possible to reveal a number of specific features in the transformation of the magnetic structure of the compounds under investigation. [ABSTRACT FROM AUTHOR]

Within a wide temperature range of 1.8–300 K, the Hall effect in holmium dodecaboride is investigated. The measurements of the angular dependences of the Hall resistance ρH(φ, T, H) for HoB12 performed in a high magnetic field up to 80 kOe at helium and intermediate temperatures made it possible to separate the normal and anomalous contributions to the Hall effect. Analysis of the anomalous component behavior in the paramagnetic and Néel phases suggests the appearance of the 5 d-state magnetic polarization (the spin polaron effect) and makes it possible to compare the revealed features of the Hall coefficient RH( T, H) with the H-T magnetic phase diagram of HoB12. [ABSTRACT FROM AUTHOR]

Within a wide temperature range of 1.8–300 K, the Hall effect in holmium dodecaboride is investigated. The measurements of the angular dependences of the Hall resistance ρH(φ, T, H) for HoB12 performed in a high magnetic field up to 80 kOe at helium and intermediate temperatures made it possible to separate the normal and anomalous contributions to the Hall effect. Analysis of the anomalous component behavior in the paramagnetic and Néel phases suggests the appearance of the 5 d-state magnetic polarization (the spin polaron effect) and makes it possible to compare the revealed features of the Hall coefficient RH( T, H) with the H-T magnetic phase diagram of HoB12. [ABSTRACT FROM AUTHOR]

The concentration of carriers in LuB12 is evaluated theoretically by applying ab initio FP-LMTO calculations. Theoretical results are found to be in agreement with high-precision measurements of the Hall coefficient RH(T) carried out on single crystals of the rare-earth dodecaborides RB12 (R=Ho,Er,Tm,Lu) at temperatures 1.8–300 K. The nature of the antiferromagnetic ordering in RB12 is investigated within an RKKY-like model supplemented by comprehensive electronic structure calculations for paramagnetic, ferromagnetic, and antiferromagnetic phases. [ABSTRACT FROM AUTHOR]

The concentration of carriers in LuB12 is evaluated theoretically by applying ab initio FP-LMTO calculations. Theoretical results are found to be in agreement with high-precision measurements of the Hall coefficient RH(T) carried out on single crystals of the rare-earth dodecaborides RB12 (R=Ho,Er,Tm,Lu) at temperatures 1.8–300 K. The nature of the antiferromagnetic ordering in RB12 is investigated within an RKKY-like model supplemented by comprehensive electronic structure calculations for paramagnetic, ferromagnetic, and antiferromagnetic phases. [ABSTRACT FROM AUTHOR]