Andre Michael Strydom

Specific heat, susceptibility, magnetotransport and thermoelectric power of the Kondo alloys (Ce1-xLax)Cu5In

The influence of substituting Ce with La in the Kondo compound CeCu5In has been investigated using x-ray diffraction, specific heat (Cp), electrical resistivity (?(T)), magnetoresistivity?(MR) and thermoelectric power?(TEP) measurements. Cp of CeCu5In and the (Ce1?xLax)Cu5In alloys shows enhanced values at low temperatures. Between?10 and 20?K the equation Cp/T = ?conv+?T2 fits the data for all alloys with ?conv scaling linearly with Ce concentration. Below 10?K a pronounced upturn in Cp values occurs. Susceptibility data above 100?K follow the Curie?Weiss relation and give effective moment ?eff values in fair agreement with that of a Ce3+-ion. The ?(T) studies illustrate the evolution from Kondo lattice to single-ion Kondo behaviour with increase in La content in the (Ce1?xLax)Cu5In alloy series. MR measurements on Ce dilute alloys are interpreted within the single-ion Bethe ansatz description and values of the Kondo temperature TK are calculated. A compressible Kondo lattice model has been used to describe the decrease in TK and in Tm? (the temperature at which a maximum in ?(T) occurs for the coherent dense Kondo alloys) with decrease in Ce concentration for these alloys. The TEP is positive and shows a maximum at approximately 45?K for several investigated (Ce1?xLax)Cu5In alloys.

The effect of Th substitution and of magnetic field on Kondo semiconducting behaviour in U2Ru2Sn

Electrical resistivity, ρ(T), measurements on U2Ru2Sn show typical Kondo semiconducting behaviour, namely a ρ(T)~ln T behaviour at higher temperatures and an activation-like increase in ρ(T) below 20 K which indicates the opening of a small gap in the electronic density of states. The magnetic susceptibility, χ(T), of U2Ru2Sn has a maximum around 180 K which is characteristic of intermediate-valence behaviour. The χ(T) data for U2Ru2Sn have been fitted to the interconfigurational fluctuation model of Sales and Wohlleben giving a value of Tsf* = 155(2) K for the characteristic fluctuation temperature. Substituting as little as 5% Th for U leads to a ρ(T) variation reminiscent of that of a single-ion Kondo metal ρ(T) = ρ(0)[1-(π2/16)(T2/TK2)]. Values of TK = 79(1) and 113(1) K are respectively obtained for alloys with 5% and 10% Th substitution.

Gap closure in semiconducting APtSn cubic compounds (A = U, Th or Zr)

UPtSn is known as a semimetal with a bandgap in the electronic density of states. We report the results of measurements of the cubic lattice parameter a(T), coefficient of thermal expansion α(T), magnetic susceptibility χ(T), magnetization σ(T,B), specific heat C(T) and electrical resistivity ρ(T, B). We give arguments that this compound is antiferromagnetically ordered with T N = 35 K, although this is not confirmed by neutron diffraction. For carefully annealed samples of UPtSn we provide a phenomenological description of electron transport properties in terms of the fact that the temperature-dependent bandgap is closed at T = 0 K. Results of electrical measurements on the isostructural compounds ThPtSn and ZrPtSn provide evidence for bandgap formation in these two compounds as well.

Electronic and magnetic properties of Ce3Pd5Si

Abstract We present the results of exploratory measurements of the electrical resistivity ρ ( T ), magnetoresistivity MR, magnetic susceptibility χ ( T ), and specific heat C ( T ) on polycrystalline Ce 3 Pd 5 Si. The temperature variation of ρ ( T ) and of χ ( T ) from room temperature down to ∼10 K indicate largely normal-metal behaviour. Below 10 K ρ ( T ) decreases rapidly with lowering temperature and displays a knee at 3.5 K. χ ( T ) remains Curie–Weiss-like down to 100 K, with the paramagnetic Curie temperature of +12.7 K, and the effective magnetic moment of 2.37 μ B /mol Ce . At lower temperatures the inverse susceptibility χ −1 ( T ) reveals crystal field effects but no anomaly hinting that magnetic phase transition is seen down to 1.7 K. The MR is large and negative below 30 K. In C ( T ) there is an upturn towards very large values at low temperatures, and an anomaly is seen at 3.5 K, typical of magnetic ordering.

Magnetoresistivity of Ce(Pd0.6Rh0.4)2Si2

Abstract Magnetoresistivity isofield and isotherm measurements are presented for the alloy Ce(Pd0.6Rh0.4)2Si2 at low temperatures. The magnetoresistance MR is negative. The MR data are fitted to the Bethe-ansatz solution of the Coqblin–Schrieffer Hamiltonian for single-ion Kondo systems. This yields a Kondo temperature T K =9.2(1) K and an effective moment for the Kondo ion μK=0.087(1)μB.