B. Buschinger

Magnetic properties of new CeTMg compounds (T Ni, Pd)

Abstract We present results of the first investigation of ternary Ce-compounds containing a transition metal and Mg. The structure, resistivity and susceptibility of Ce 2 Ni 2 Mg, CeNi 4 Mg and CePdMg are reported and discussed. These compounds crystallise in the same structure as their respective In-homologues and show very similar structural parameters, but weaker strength of the Ce-4f-hybridization.

Crystallographic and physical properties of new ternary R2T3X9 (R=La, Ce, U, T=Rh, Ir, X=Al, Ga) compounds

Abstract Ternary compounds with the stoichiometry R 2 T 3 X 9 (R=La, Ce, U, T=Rh, Ir, X=Al, Ga) were synthesized for the first time and were found to crystallize in the orthorhombic Y 2 Co 3 Ga 9 -type structure. Preliminary measurements of the resistivity, the susceptibility, the specific heat, and the Seebeck coefficient revealed a rather unconventional behavior for the Ce-compounds, which exhibit characteristics of both intermediate valent and of heavy fermion compounds. The U counterparts were found to order antiferromagnetically at temperatures below 40 K.

Preparation and low temperature properties of FeSi-type RuSi

We have reinvestigated the metallographic RuSi phase diagram and could establish the transition temperature from the low temperature FeSi-type to the high temperature CsCl-type structure for stoichiometric samples. Magnetic and transport properties of the low temperature modification in the temperature range 1.5 K<T<300 K are presented and discussed. FeSi-type RuSi is found to be semiconducting but still in the extrinsic regime at room temperature. Below 100 K, an additional gap opens and at temperatures <40 K variable-range hopping conduction sets in as the dominant transport mechanism. In contrast, resistivity measurements on CsCl-type RuSi show simple metallic behavior.

Transport and magnetic properties of new ternary Ce2T3X9-compounds (T = Rh, Ir, X = Al, Ga)

Abstract Measurements of thermoelectric power, electrical resistivity, and magnetic susceptibility on new Ce 2 T 3 X 9 -compounds (T=Rh, Ir; X=Al, Ga) are presented. These compounds crystallize in the orthorhombic Y 2 Co 3 Ga 9 -structure. The transport data show for each compound two characteristic anomalies, around 100 K and around 20 K, respectively. In contrast to many Ce-systems, where such anomalies can be ascribed to crystalline-field and Kondo effects, respectively, for these systems the temperature dependence of the susceptibility and the specific heat suggest an intermediate valent Ce-state which shows additional low energy interactions.

RuSi: metal-semiconductor transition by change of structure

Abstract RuSi has long been known to form in two modifications, i.e. CsCl-type at high temperatures, and FeSi-type at low temperatures. The transition temperature has recently been determined as 1300°C for stoichiometric material, but is strongly dependent on the exact stoichiometry. We have evaluated the structures of both phases under applied pressure of up to 40 GPa. No evidence for a pressure-induced transition was found. The bulk moduli of CsCl- and FeSi-type RuSi were determined as (215 ± 15) GPa and (255 ± 15) GPa, respectively. Transport and optical properties of both modifications have been investigated. Obviously, the CsCl-modification is metallic, whilst the FeSi-modification is a narrow-gap semiconductor with a gap of 0.2=0.3 eV.

Yb2Ni2Al: A prototypical Yb-based heavy-fermion system

Abstract We have investigated the properties of Yb2Ni2Al by means of resistivity, susceptibility and specific heat measurements. Our results suggest that it is the first magnetically non-ordered Yb heavy-fermion system with a low characteristic energy and clear coherence effects in the resistivity. A logarithmic temperature dependence of C/T indicates that it is close to the transition to a magnetic ordered ground state. We further found a simple systematic for composition dependence of the Yb-valence in binary and ternary YbTAl compounds (T: Ni, Pd, Pt).

The optical properties of RuSi: Kondo insulator or conventional semiconductor?

Abstract We have investigated the electrodynamic response of single-phase RuSi in its low and high temperature phases. While the high-temperature phase (CsCl-type) is a simple metal, the low-temperature phase (FeSi-type) is a semiconductor which shows at room temperature a narrow gap of approximately 0.4 eV, while an even smaller gap of approximately 20 meV appears in the optical spectra below 100 K. Extrinsic-like inclusions, due to deviations from the ideal stoichiometry in the RuSi-matrix, lead to a remaining low frequency spectral weight of metallic nature in the FeSi-type RuSi.

The zero-gap Ce3Au3Sb4-x system: a transport, thermodynamic and optical study

Abstract We report our resistivity, thermoelectric power and optical investigations on the Ce3Au3Sb4−x narrow-gap insulator. The resistivity for x=0.12 and 0.17 is characterized by a semiconducting-like behaviour at low temperatures, which contrasts with the metallic-like temperature dependence of the thermoelectric power. This apparent contradiction can be reconciled by a so-called “zero-gap” scenario, as supported by the optical investigation.

Magnetic order in Zr-doped CeNiSn

The effects of Zr doping on the low-temperature properties of CeNiSn were studied by means of measurements of the thermoelectric power, the electrical resistivity, the magnetic susceptibility and the specific heat. Even Zr concentrations as small as 3% were found to dramatically increase the low-temperature metallic character in this otherwise gapped material and to stabilize antiferromagnetic ordering below 5 K.

MAGNETIC PROPERTIES OF CEXLA1-XCU2.05SI2

We investigated magnetic properties of CexLa1−xCu2.05Si2 for 0.01⩽x⩽1, between 2 and 340 K, using the Faraday and the torque method. For x<0.1, magnetic response is found to be given by the single-ion contribution χion(T), which relates to the Kondo susceptibility of the 4f1 multiplet split by the tetragonal crystal field (CF). For x⩾0.1 the susceptibility is given by χCe-mol(x,T)=χion(T)/(1+λ(x)χion(T)), where λ(x) is the x-dependent constant, probably due to Ce–Ce interactions. The anisotropy has a maximum at about 50 K and remains finite for T→0 for all x, reflecting a strong CF influence.