Small single crystals of NbGe2 were grown by the hydrogen reduction of potassium-containing oxides. Measurements of electrical resistivity and superconductivity are given. © 1978.

Single crystals of CeCu2Si2 were grown from metal solvents and their magnetic properties were systematically varied by partial substitution of Cu by Sn or In. The susceptibility χ is anisotropic and at high temperatures it is dominated by the crystal field split 4f state. At low temperatures the magnetic moments are drastically reduced. This reduction, as well as the Curie-Weiss temperature, depend sensitively upon the chemical composition. The observed variations both in the magnetic and the resistance behavior point to a Kondo-like coupling between local moments and conduction electrons. The strength of this interaction varies as the Fermi level is shifted by chemical means.

To gain into the formation of the heavy Fermion state in CeCu2Si2 we have studied the relationship between the high temperature and low temperature physical properties. The single crystals are grown from metallic solvents, such as Sn, In or Ga. The low temperature susceptibility χ can be varied by factors of 5, and samples with smallest χ have the largest linear contribution γ to the specific heat. This "anticorrelation" of χ and γ is unexpected. The reduction of χ at low T is mainly due to a temperature independent antiferromagnetic molecular-field type interaction χ-1(T)=χ-10(T)+λ, and not due to interactions which become dominant below a characteristic temperature. Superconductivity occurs in small χ - large γ samples. © 1985.

Infrared reflectivity spectra of a La2CuO4+x single crystal have been studied over a spectral range of 50"5500 cm-1. Anisotropy of the spectra has been observed, indicating a strong anisotropy of the high-frequency conductivity of the crystal. New lines have been found in the optical-phonon excitation spectra. A classification of lattice optical vibrations has been proposed. Spectral reconstruction has been observed in the phonon region of 370 and 445 cm-1 at T0=220±5 K, which correlates with the antiferromagnetic transition. © 1989 The American Physical Society.

The results of a Raman scattering study of single crystal La2CuO4 are reported. Three Ag symmetry modes are observed, rather than the two predicted by group theory. Mode assignments are discussed. © 1988.

The ternary compound YbRh1.4Sn4.6 with the phase I structure (simple cubic) when subjected to a pressure of 40 kbar at 800°C is found to transform to phase III structure (f.c.c.) with the composition YbRh1.1Sn3. The latter compound has a lattice parameter of a = 13.735 A ̊ which suggests that the Yb is in an intermediate valence state. The temperature dependence of magnetic susceptibility suggests that the Yb is in a homogeneously mixed valence state in the pressure synthesized product. In the phase I structure YbRh1.1Sn4.6 is superconducting at 8.6°K, but in the phase III structure the compound YbRh1.1Sn3 is not superconducting down to 0.9°K. It is suggested that superconductivity and mixed valence are incompatible. © 1981.

We have used high energy inelastic neutron scattering to study the magnetic fluctuation spectrum of La2CuO4 in the energy and momentum ranges 30≤h{stroke};σ≤140 meV and |q|≤0.2 Å-1, respectively. Our results are consistent, within the experimental error, with conventional spin wave theory the low temperature spin wave velocity, being 850±30 meV Å-1. © 1990.

We present data on the magnetic and superconducting properties of rare earth osmium stannides. The compounds of Tb and Ho are superconducting only, those of Er and Tm are reentrant superconductors, and those of Gd and Dy appear to exhibit some type of short range magnetic order at low temperatures. © 1982.