Fg Aliev

Narrow band in the intermetallic compounds MNiSn (M=Ti, Zr, Hf)

The presence of a narrow band below conduction band of nonmagnetic compounds MNiSn (M=Ti, Zr, Hf) is assumed to explain their low temperature properties such as the heat capacity, IR optics, electronics transport. A computation of the Seebeck coefficient supplies support for this assumption.

Electric and magnetic properties of the Kondo-lattice compound CeCu2Si2

Electric, magnetic, and thermoelectric properties of CexLa1−xCu2Si2 (0⩽x⩽1) compounds have been studied over a wide temperature interval 0.04 ⩽T⩽300 K in magnetic fieldsH⩽40 kOe. The paramagnetic-magnetic ordering transition temperatureTM is found to rise from ∼0.32 K for cerium concentrationx=0.2 to 1.6 K forx=0.6. A further increase inx from ∼0.8 to 1.0 leads to a decrease inTM. Simultaneously, the susceptibility kink is smeared out and atx≈1.0 it is transformed into temperature-independent enhanced Pauli paramagnetism. The magnetic phase diagram has been found to be similar to that proposed by Doniach for the one-dimensional Kondo-necklace model. The Kondo-lattice compound CeCu2Si2 exhibits a superconducting transition atTc⋍0.5 K. The variation of the magnetic properties of CexLa1−xCu2Si2 from magnetic ordering at 0.2≲x≲0.8 to the nonmagnetic superconducting state atx → 1.0 is caused by the crossover from the magnetic regimeTRKKY≫TK (in which the RKKY temperatureTRKKY exceeds the Kondo temperatureTK) to the nonmagnetic singlet ground state corresponding to the situation whenTK≫TRKKY. This crossover is accompanied by a sharp increase in the low-temperature Hall coefficientRH(T) in CexLa1−xCu2Si2 compounds atx → 1. At the same time, a minimum of the negative Seebeck coefficient with a high amplitude appears at 10<T<100 K. The anomalous low-temperature properties of Kondo lattices have been shown to be due to the rise of the narrow Abrikosov-Suhl resonance in the vicinity of the Fermi level εF as the temperature is lowered fromT≫TK toT≪TK. This resonance has a giant amplitude in concentrated Kondo systems and is responsible for the existence in CeCu2Si2 of heavy fermions with extremely low degeneracy temperatureT*F estimated to be 10 K from theRH versusT curve. Further increase of the Kondo coupling constantJ in CeCu2Si2 under pressure induces an increase in (1) the Hall coefficientRH(T=4.2 K), (2) the superconducting transition temperatureTc, (3) the derivative of the upper critical fielddHc2/dTc, and (4) the low-temperature Seebeck coefficientS(T), which have maximum values at the same pressurepK1≈3 kbar, corresponding to the Kondo-lattice state with the maximum amplitude of the Abrikosov-Suhl resonance in CeCu2Si2 atp=pKL. At higher pressuresp>pKL, a continuous transition from the Kondo lattice to the intermediate valence state is observed, which is accompanied by a complete smearing out of the resonance near the Fermi level. Therefore the Kondo lattices represent a new class of solids, which can be characterized as the link between stable magnetism of metals with a deep 4f level and unstable magnetism associated with fluctuating valence. This novel state can be described by a set of anomalous low-temperature properties related to the giant Abrikosov-Suhl resonance near the Fermi level.

Gap at Fermi level in some new d- and f-electron intermetallic compounds

Abstract Transport, thermal and optical properties of new classes of d- and f-electron intermetallic systems RNiSn (R = Ce, Ti, Zr, Hf) with a gap at the Fermi level are presented. The origin of the gap formation and possible zone scheme are discussed.

Superconductivity in CeCu2Si2

Abstract Resistivity measurements of CeCu 2 Si 2 are carried out under pressures p up to 12 kbars. Unlike polycrystalline samples, no traces of superconductivity have been observed in CeCu 2 Si 2 at ambient pressure. When pressure is applied, CeCu 2 Si 2 monocrystals become superconducting with anomalously large ratio H c2 (0)/T c (0) = 34 K0e/K and with the derivative dH c2 /dT(T=T c ) = 140 K0e/K

The appearance of the many-body resonance at the Fermi level in Kondo-lattices

Abstract Studing transport and magnetic properties of solid solutions Ce x La 1−x Cu 2 Si 2 (0≤ x ≤ 1) and using for CeCu 2 Si 2 pressure p as an external parameter, we have observed the continious transition from Kondo-impurity regime ( x « 1 ) to Kondo lattice ( x ⋍ 1, p = 0, ν Ce ≈ 3+ ) and then through the intermediate valence state (x = 1, 0 ν Ce ν Ce ⋍ 4+ . We have found that all the anomal ous properties of Kondo-lattices (CeCu 2 Si 2 , CeAl 3 , CeAl 2 ) are caused by the appearance at the Fermi level of the many-body resonance of Abrikosov-Suhl type.

Transport and magnetic properties of intermetallic systems RNiM (R = U, Ce, Er, Ho, Tm, Yb, Sc, Ti, Zr, Hf; M = Sn, Sb)

Abstract Transport magnetic and calorimetric measurements of the CexLa1−xNiSn system show that in CeNiSn a narrow gap (ϵg ≈ 3 K) is formed in the vicinity of the Fermi level. This gap is related to the coherence of the Kondo screening in a regular Ce3+ lattice and is strongly suppressed by the Ce substitution by La. In other intermetallic RNiM systems (R = Ti, Zr, Hf; M = Sn) the effect of the ordered sublattice of the Ni atom vacancies on the temperature dependences of the Hall coefficient and lattice parameters are studied.

Gap formation in CeNiSn at low temperatures

Abstract Transport, thermoelectric, calorimetric properties and inelastic neutron spectra of the CeNiSn and solid solutions Ce1-xLaxNiSn (0

Thermal conductivity of the Bi2(Ca0.5Sr0.5)3Cu2Ox, Tl2Ba2Ca2Cu3Ox ceramics and ErBa2Cu3Ox single crystal

Abstract The maximum of thermal conductivity k(T) at T max =90 K in Tl 2 Ba 2 Ca 2 Cu 3 O x and two maxima at 80 K and 115 K in Bi 2 (Ca 0.5 Sr 0.5 ) 3 Cu 2 O x compounds are found. The superconducting critical temperatures of Tl-based oxide (T c =120K) and of the two phase Bi-based oxide (T c =80K and 110 K) are in a good agreement with temperatures below which the k(T) increase is observed. In the superconducting ErBa 2 Cu 3 O x samples the k(T) also begin to grow below T c determined from magnetic measurements.

Anisotropy of the upper critical field near Tc and the properties of URu2Si2 and UBe13 in the normal state

Simultaneous measurements of the electrical resistivity ρ Seebeck coefficientS, and thermal conductivity k of URu2Si2 and UBe13 are carried out. For URu2Si2 a strong anomaly in the k(T) dependence near the temperature of the antiferromagnetic transition was observed. The thermal conductivity of UBe13 exhibits only a small (about 30%) change of the derivativedk/dT near 8–9 K, which may be related to an increase of the characteristic length of antiferromagnetic correlations below this temperature. Studying STM spectra in the normal and magnetic phase of a URu2Si2 single crystal we observed that the magnetic gap, partially opened at the Fermi surface below the Néel temperature,TN=17.5 K, is strongly anisotropic: gapped states mainly correspond to the tetragonalab-plane. Anisotropy of the upper critical field nearTc(H<4kOe), studied for URu2Si2 and UBe13 single crystals, was found to be in a good correspondence with the character of the antiferromagnetic transition.

The quadrupolar Kondo ground state in

The transport, calorimetric and magnetic properties of have been investigated. For we have observed all low-temperature asymptotics predicted to date for the quadrupolar Kondo effect (QKE). Namely, this compound demonstrates a logarithmic increase of C/T where C is the specific heat, square-root temperature dependences of the resistivity and susceptibility, absence of magnetoresistivity as well as deviating to positive values of the non-linear susceptibility when temperature decreases. We have found that the Hall effect for the QKE is quenched in low magnetic fields. The anomalous properties of are compared with corresponding characteristics of and for x > 0.1.