Results of electrical resistance and magnetic susceptibility measurements on Ce2Bi, Ce2Sb, CeScGe, CeScSi and CeSb2 are presented. Ce2Bi and Ce2Sb have antiferromagnetic transitions at low temperatures, while CeSb2, CeScGe and CeScSi have ferromagnetic transitions, CeScGe having a Tc = 46 K. The data are analyzed with respect to the similarities of the two crystal structure groups that these materials fall into: CeSb2 having the LaSb2 structure and the other materials all having the La2Sb structure.

We present the results of electronic transport, magnetic susceptibility, and thermodynamic measurements on single crystals of the cubic compound Ce3Bi4Pt3. The susceptibility displays a broak peak centered at Tmax = 80K, which in Ce compounds is usually indicative of mixed valence and moderately heavy-electron behavior. Both the electronic transport properties and the low-temperature specific heat indicate that Ce3Bi4Pt4 is nonmetallic with a transport energy gap of roughly 35 K. We argue that this temperature is close to that scale over which coherence should develop in a periodic metallic system with Tmax = 80K. Resistivities typical of a Kondo-impurity system are realized when the compound is alloyed with moderate amounts of lanthanum. Further, lanthanum substitution increases the low-temperature specific heat to a value consistent with the single-ion energy scale determined from the magnetic susceptibility. © 1991.

Electrical resistivity ρ(T) and thermal expansion Δl/l were measured for the intermediate valence compound (IVC) YbCu2Si2 and its counterpart LuCu2Si2 between 4.2 K and 300 K. It was found that the thermal expansion coefficient α(T) has a negative minimum around 31 K (=Tmin) at atmospheric pressure and Tmin decreases with increasing pressure at the rate δTmin/δT = -0.45 K/kbar. © 1993.

Static-susceptibility and thermal-expansion measurements indicate that Ce3Bi4Pt3 is mixed-valent-like, whereas transport measurements reveal a gap of Δ=5 meV in the electronic excitation spectrum. We report the magnetic response of Ce3Bi4Pt3, at temperatures between 2 and 150 K, determined with incident neutron energies of 3.1, 17, and 69 meV. The isostructural, nonmagnetic reference compound La3Bi4Pt3 was also studied at the same temperatures and energies so that phonon contributions could be subtracted accurately. At 2 K, a gap Δm=12 meV is present in the magnetic excitation spectrum: the 3.1-, 17-, and 69-meV data consistently show that the magnetic intensity is zero for energy transfers less than 12 meV, rises sharply between 12 and 20 meV, and falls off smoothly beyond. Above 50 K, the gap in the spin-spin correlation function starts to fill. The neutron results reproduce the temperature dependence of the bulk susceptibility. The relationship between these and other measurements will be discussed. © 1991 The American Physical Society.

Inelastic neutron scattering from (Ce1-xLax)3Bi4Pt3, with x = 0, 0.1 and 0.25, shows that a gap in the spin excitation spectrum decreases monotonically with increasing x and remains well-defined even for x = 0.25. © 1994.

We present an analysis of transport data from Ce3Bi4Pt3 to deteermine the energy gap temperature dependence Eg(T). Eg(T) is a decreasing function of temperature. This result is consistent with the gap being a product of many-body correlations in which Eg(T) is scaled by the Kondo energy scale TK. © 1994.

The magnetoresistance (MR) of the narrow-gap Kondo insulator Ce3Bi4Pt3 and its non-magnetic analog La3Bi4Pt3 have been measured in magnetic fields to 10 T and in the temperature range 2-300 K. Ce3Bi4Pt3 exhibits a large negative MR component below 7 K. At higher temperatures this negative component progressively decreases and a positive contribution becomes evident. Above 75 K the MR is positive at all fields and saturates to a value of a few percent. The non-magnetic analog La3Bi4Pt3 exhibits the same positive magnetoresistance present in Ce3Bi4Pt3 as well as a conventional positive H2 term at low temperatures. We discuss potential mechanisms for both the common positive effect and the large negative MR present in Ce3Bi4Pt3. © 1993.

Doping studies are presented on three materials exhibiting hybridization gaps: Ce3Bi4Pt3, U3Sb4Pt3 and CeRhSb. In the case of trivalent La, Y, or Lu substituting for Ce or U, there is a suppression of the low temperature gap and an increase in the electronic specific heat, γ. In the case of tetravalent Th substitutions for U there is no change in γ and in the case of tetravalent Zr substitution for Ce in CeRhSb, there is an enhanced semiconductor-like behavior in the electrical resistance. These results are discussed in the light of a simple model of hybridization gapped systems. © 1992.

Resistivity measurements are reported on the cubic heavy-fermion compound YbBiPt at ambient and hydrostatic pressures to ≊19 kbar and in magnetic fields to 1 T. The phase transition at Tc=0.4 K is identified by a sharp rise in resistivity. That feature is used to build low-temperature H-T and P-T phase diagrams. The phase boundary in the H-T plane follows the weak-coupling BCS expression remarkably well from Tc to T c/4, while small hydrostatic pressure of ≊1 kbar suppresses the low-temperature phase entirely. These effects of hydrostatic pressure and magnetic field on the phase transition are consistent with an spin-density-wave (SDW) formation in a very heavy electron band at T=0.4 K. Outside of the SDW phase at low temperature, hydrostatic pressure increases the T2 coefficient of resistivity, signaling an increase in heavy-fermion correlations with hydrostatic pressure. The residual resistivity decreases with pressure, contrary to trends in other Yb heavy-fermion compounds.

We report measurements of the temperature dependence of the Bi209 nuclear quadrupole resonance frequency νQ, the Knight shift K, and the spin-lattice relaxation rate 1/T1 in the small-gap semiconductor Ce3Bi4Pt3 between 1.8 and 300 K. Corresponding measurements also are reported for the nonmagnetic metallic isomorph La3Bi4Pt3. The νQ data in the Ce compound show a characteristic departure from metallic-to-insulating behavior when the sample is cooled below TM=80 K, the temperature of the susceptibility maximum, attributable to a loss of low-frequency vibrational modes in the insulating state. The Knight shift has both isotropic and axial components; this anisotropy originates from the presence of Ce via a transferred hyperfine coupling between Ce 4f and conduction electrons. An s-f exchange constant 0.4 eV is found, consistent with hybridization in other rare-earth intermetallic compounds. A change in the scaling between the susceptibility and both the isotropic and axial Knight shifts at temperature TM provides evidence that hybridization between the Ce 4f orbitals and the conduction electrons is responsible for the gap structure. The temperature dependence of the 1/T1 data is consistent with a model electronic density of states possessing a temperature-independent gap δ of 180 K and a bandwidth of the order of 1600 K. The temperature dependence of 1/T1 can also be fit well with a temperature-dependent gap with δ(0) also 180 K. © 1994 The American Physical Society.