We have synthesized the series of compounds RMIn5 and R2MIn8 in single crystal form, where R=Sm or Gd and M=Rh or Ir. These materials form in tetragonal derivatives of the Cu3Au structure RIn3. Measurements of magnetic susceptibility, electrical resistivity, and low-temperature heat capacity are reported. These compounds order antiferromagnetically at low temperature (TN < 45 K) and their low-temperature magnetic properties remain nearly unaltered compared to their SmIn3 and GdIn3 cubic relatives. The present data are compared to the magnetic properties of the isostructural (Ce, Nd) (Rh, Ir)In5 and (Ce, Nd)2(Rh, Ir)In8 compounds, and the validity of de Gennes scaling as a function of rare earth in a given structure is discussed. © 2001 The American Physical Society.

We present measurements of the complete elastic constants of single-crystal FeSi using resonant ultrasound spectroscopy (RUS). FeSi is a narrow-gap (0.05 eV) semiconductor whose physical properties are similar to a class of compounds known as hybridization gap semiconductors or Kondo insulators. The narrow gap is reflected in the temperature dependence of the elastic moduli. © 1994.

We have performed a photoemission study of YbInCu4, which undergoes a first-order phase transition at Tν ≃ 40 K between the low-temperature intermediate-valence state and the high-temperature local-moment state. The Yb 4f photoemission peak (Kondo peak) just below the Fermi level, which probably originates from the subsurface region of the YbInCu4 samples but tracks the valence transition in the bulk YbInCu4, has been studied above and below Tν. It has been found that the 4f photoemission peak is shifted from ∼ - 35 meV at 75 K to -40 meV at 7 K. By analyzing the 4f peak position and the Yb valence in the two phases using the Anderson impurity model, we find that the bare 4f level, which is located close to the Fermi level, is shifted downward and the hybridization strength decreases in going from the high-temperature to low-temperature phases. © 2001 Published by Elsevier Science Ltd.

This work reports on the phase diagram study of the dense Kondo system CeB6 by means of magnetization (M) and transverse magnetoresistance (MR) measurements in magnetic fields (B) to 1ST, in the temperature (T) range from 1.8 to 40 K. The zero field resistivity displays Kondo behavior in the paramagnetic P-phase, while two discontinuities at low T were observed at TQ ≈3.5 K and TN ≈ 2.3 K, the boundaries of the antiferro-quadrupolar (AFQ), and antiferromagnetic (AF) phases, respectively. The isothermal transverse MR is large and negative at low T, and it shows a distinct feature when the P-AFQ line of the B-T phase diagram is crossed. Similarly, the M vs. B curves at low temperatures show upward discontinuities at the phase boundary. Both the features in MR and M at the P-AFQ line correlate well in T, revealing the gradual increase of the T for the onset of AFQ ordering with B. No evidence for reentrant behavior could be observed in fields to 1ST. © 2001 Published by Elsevier Science B.V.

We report neutron-scattering experiments for (Formula presented) that were performed in the time-of-flight mode at a neutron spallation source. Two independent methods were used to determine the nonmagnetic scattering and both gave comparable results for the magnetic scattering. The magnetic scattering was measured at temperatures (Formula presented) and 60 K, below and above the temperature of the valence transition (Formula presented) Our key result is that the spin dynamics in the mixed valent phase are well described over a broad range of energy transfer (Formula presented) and incident energies (Formula presented) by a Lorentzian power spectrum, centered at (Formula presented) and with halfwidth (Formula presented) The magnetic susceptibility derived from the fits is within 20% of the value measured for the dc susceptibility. The peak energy is in good agreement with the Kondo temperature derived from thermodynamic studies but the Lorentzian line shape fits the data significantly better (Formula presented) than the line shape expected for a Kondo impurity (Formula presented) In addition we report results for (Formula presented) For this compound, the scattering is inelastic at low temperature (at 10 K (Formula presented) and (Formula presented)) but is quasielastic at higher temperature where (Formula presented) and 13.2 meV at 150 and 300 K, respectively. This increase in linewidth is contrary to the 50% decrease in linewidth predicted by the Anderson impurity model for this temperature range, and is also smaller than the factor of four increase in characteristic energy suggested by application of the impurity model to the magnetic susceptibility. © 1999 The American Physical Society.

We have used high pulsed magnetic fields to 50 T to observe de Haas - van Alphen oscillations in the tetragonal antiferromagnet CeRhIn5, which has an enhanced value of the electronic specific heat coefficient γ≥420 mJ/mol K2. For T

We have measured the momentum and energy dependence of the spin fluctuations in the low-temperature mixed-valent state and the high-temperature integral-valent state of (Formula presented), using flux-grown single crystals and a triple axis spectrometer. The magnetic scattering can be fit with a Lorentzian power spectrum, with positions and halfwidths equal (Formula presented)=2.3 meV and (Formula presented)=1.8 meV in the high-temperature state at 50 K and (Formula presented)=40.2 meV and (Formula presented)=12.3 meV in the low-temperature state at 20 K. Within the experimental uncertainties, the line shape as a function of energy transfer (i.e., the power spectrum) does not depend on momentum transfer Q. The static susceptibility χ(Q) is no more than 10% larger at the zone boundary than at zone center for the [1,0,0] direction. The results compare reasonably well to the predictions of the Anderson impurity model and to earlier measurements on polycrystalline samples. © 1997 The American Physical Society.

La2Li0.5Cu0.5O4 has been investigated by electron diffraction and high resolution electron microscopy at room temperature. Ordering between Li and Cu cations is nearly perfect within the (a, c) plane but there is disorder between Cu and Li cations along the b axis. The detection of weak reflections which violate the C centering of the Cmmm space group (initially proposed [1] for this compound), indicates that the crystal symmetry allows lattice distortions. The evolution of the structure as a function of the temperature may lead to the determination of whether the low energy singlet-triplet excitation, found in NMR/NQR studies, is coupled with lattice distortions. © 1998 Elsevier Science Ltd. All rights reserved.

We have measured the thermal expansion of the Kondo insulator SmB6 from 5 to 80 K using a sensitive capacitance dilatometer. There is a pronounced negative anomaly in the linear expansion coefficient α, of electronic origin, which achieves a local minimum of -5×10-6 K-1 at 45 K. We interpret this anomaly as a Schottky-like contribution arising from transitions across a semiconducting energy gap Eg140 K. Although there are several energy scales in the problem, a Grüneisen analysis indicates that the thermodynamics is driven by a single energy, which we identify as the gap energy. © 1994 The American Physical Society.