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Single crystals of ZrAs1.4Se0.5 (PbFCl type structure) were grown by chemical vapour transport. While their thermodynamic and transport properties are typical for ordinary metals, the electrical resistivity exhibits a shallow minimum at low temperatures. Application of strong magnetic fields does not influence this anomaly. The minimum of the resistivity in ZrAs1.4Se0.5 apparently originates from interaction between the conduction electrons and structural two-level systems. Significant disorder in the As-Se substructure is inferred from X-ray diffraction and electron microprobe studies.

We have grown single crystals of ThCoGa4 by the self-flux method. X-ray examination showed that it crystallizes in an orthorhombic structure of the Y NiAl4-type. Electron transport properties examination between 2 and 300 K allowed us to determine its phonon components to the electrical resistivities/thermoelectric powers, which at 300 K are equal (in µΩ cm /µV K−1) to 17.3/11.7, 40.6/1.9 and 35.0/2.7, along the a-, b-, and c-axes, respectively. Specific heat examination allowed us to estimate the Sommerfeld coefficient and Debye temperature, which are equal to 6.9 (± 0.3) mJ K−2 mol−1 and 288 K, respectively. ThCoGa4 was found to be a paramagnet with a nearly temperature independent susceptibility above 30 K, equal to about 6.7 × 10−5 emu mol−1.

We discuss recent low-temperature measurements on single-crystalline samples of the heavy fermion compounds YbRh2(Si1−xGex)2 (TK = 30 K) with x = 0 and 0.05 (nominal). Both show weak antiferromagnetic (AF) order at TN = 70 and 20 mK respectively. At the field-induced quantum critical point (QCP) that occurs at B = Bc ≈ 0.06 T (B ⊥ c) for the pure compound, non-Fermi-liquid properties are observed down to the lowest accessible temperatures (≈10 mK). These are caused by quantum critical AF fluctuations predominating over the competing ferromagnetic ones. At B = 0 and for TN < T < 0.3 K, both compounds show a magnetic susceptibility which follows a Curie–Weiss law with a surprisingly large effective moment of 1.4 μB, and a Sommerfeld coefficient of the electronic specific heat which deviates towards large values from the theoretically expected (− log T) dependence observed above T = 0.3 K. This observation is in striking contrast to the linear T dependence of the electrical resistivity found down to T ≈ 10 mK. It suggests a break up of the heavy fermion in the approach to the B = 0 QCP that occurs at a slightly larger Ge concentration.

The effect of pressure on the low-temperature states of the newly discovered clathrate Ba6Ge25 is investigated by means of measurements of the electrical resistivity. At ambient pressure, Ba6Ge25 undergoes a two-step structural phase transition between 230 and 180 K from metallic behaviour to a highresistivity state characterized by a mean free path of about 3 A. Interestingly, a Bardeen–Cooper–Schrieffer-like (BCS-like) superconducting transition occurs at TC ≈ 0.24 K fro mt he resulting ‘bad metal’. With increasing pressure, the structural phase transition is depressed but TC increases drastically. TC reaches am aximum value of 3.85 K at the critical pressure pC ≈ 2. 8G Pa, where the structural distortion is completely suppressed and the system exhibits metallic behaviour. Higher pressures lead to a slight decrease of TC.

We present a detailed pressure study of the electrical resistivity ρ(T) and the specific heat C(T) of the non-Fermi-liquid (NFL) compound YbRh2Si2 and of ρ(T) for a single crystal in which 5 at.% of Si is replaced by isoelectronic Ge. The magnetic phase diagram is deduced up to p ~ = 2.5 GPa. A comparison of the effects of the volume change introduced by doping and/or by hydrostatic pressure will be given. We show that the NFL behaviour observed in ρ(T) as well as the magnetic phase diagram are not influenced by the disorder introduced by alloying.

We present the results of magnetic susceptibility, magnetization, heat capacity, resistivity and magnetoresistance measurements for the low-dimensional Ce-based intermetallic compounds CePd5Ge3 and CePt5Ge3, which crystallize in the YNi5Si3-type structure. Magnetic order is manifested by a peak in both the magnetic susceptibility and the specific heat at 1.9 K and 1.1 K for CePd5Ge3 and CePt5Ge3, respectively. For CePt5Ge3 a significant tail in the specific heat from TN up to 5 K indicates pronounced antiferromagnetic short-range correlation of low-dimensional character above the 3D long-range order. Both compounds exhibit large negative magnetoresistance at low temperature.

We report on the basis of Cu-NQR measurements that superconductivity (SC) and antiferromagnetism (AF) coexist on a microscopic level in CeCu_{2}(Si_{1-x}Ge_{x})_{2}, once a tiny amount of 1%Ge (x = 0.01) is substituted for Si. This coexistence arises because Ge substitution expands the unit-cell volume in nearly homogeneous CeCu2Si2 where the SC coexists with slowly fluctuating magnetic waves. We propose that the underlying exotic phases of SC and AF in either nearly homogeneous or slightly Ge substituted CeCu2Si2 are accountable based on the SO(5) theory that unifies the SC and AF. We suggest that the mechanism of the SC and AF is common in CeCu2Si2.

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.

We present results of low-temperature calorimetric and resistive measurements on the isostructural heavy-fermion compounds and . `Non-Fermi-liquid' effects are established which suggest the nearness of an antiferromagnetic quantum critical point (QCP) in both systems. The observed deviations from the properties of a Landau Fermi liquid (FL) may be related to anomalous energy dependences of both the quasiparticle mass and the quasiparticle - quasiparticle scattering cross section. For , a moderately heavy FL can be recovered by application of moderate values of either magnetic field or hydrostatic pressure. For p = 1.7 GPa a novel, non-superconducting, phase transition has been discovered at .

We have performed inelastic neutron scattering (INS) experiments to study the spin dynamics and search for crystalline-electric-field (CEF) excitations in the antiferromagnetic heavy-fermion superconductor . The low-energy-transfer spectra are predominantly characterized by a quasielastic Lorentzian (weighted by the detailed balance factor) with a residual line width of approximately 5 meV. For uranium-based intermetallics, this is an unusually small line width and is one of the rare examples of 5f-electron systems whose residual line width corresponds to the macroscopically estimated Kondo lattice temperature. However, significant deviations from this fit suggest additional inelastic contributions that persist up to T = 150 K, i.e. . This additional scattering may be attributed to the presence of CEF excitations or intersite magnetic correlations. A survey of the scattering within the whole accessible momentum - energy space provides further evidence for the existence of these inelastic magnetic intensities. We find a surprisingly good agreement between the excitation energies of our neutron scattering spectra and a CEF-level scheme proposed on the basis of magnetic susceptibility and specific heat measurements.

We studied the pressure dependence of the Néel temperature and the superconducting critical temperature of the heavy-fermion superconductor UPd₂Al₃ at pressures up to 13.6 GPa by means of resistivity measurements. The pressure variation of the normal state resistivity is dominated by a large shift of the resistivity maximum to higher temperatures. The Néel temperature decreases with increasing pressure, while the onset of the superconducting state is almost invariant with pressure up to 6.5 GPa. At higher pressures a decrease of Tc has been observed.

We report inelastic neutron scattering (INS) measurements on the polycrystalline oP60-type clathrate BaGe_5, whose crystal structure is related to the type-I clathrate Ba8Ge_(43□3) and to the cP124-clathrate Ba_6Ge_(25). Our results show that BaGe_5 exhibits a similar phonon density of states (PDOS) in the energy range 0–40 meV with respect to Ba8Ge_(43□3). The low-energy region of the PDOS spectrum (0–10 meV) consists of two peaks at 4.1 and 6.2 meV likely related to Ba-weighted modes. Compared to Ba8Ge_(43□3), the low-energy region of the phonon spectrum of BaGe_5 shows a more complex structure, likely reflecting the presence of three distinct crystallographic sites for Ba. The specific heat data of BaGe_5, reexamined in light of the INS results, indicate that the Ba-weighted modes dominate the low-temperature behavior of C_p.

Polycrystalline samples of the type-I clathrate Ba(8)Ni(x)Ge(46-x-y)□(y) were synthesized for 0.2 ⩽ x ⩽ 3.5 by melt quenching and for 3.5x ⩽ 6.0 by melting with subsequent annealing at 700 °C. The maximum Ni content in the clathrate framework at this temperature was found to be x ≈ 4.2 atoms per unit cell. Thermoelectric and thermodynamic properties of the type-I clathrate were investigated from 300 to 700 K by means of electrical resistivity, thermopower, thermal conductivity and specific heat measurements. As the Ni content increases, the electronic properties gradually evolve from a metallic character (x3.5) towards a highly doped semiconducting state (x ⩾ 3.5). Below x ≈ 4.0 transport is dominated by electrons, while further addition of Ni (x ≈ 4.2) switches the electrical conduction to p-type. Maximum value of the dimensionless thermoelectric figure of merit ZT ≈ 0.2 was achieved at 500 K and 650 K for x ≈ 2.0 and x ≈ 3.8, respectively.

We have performed a series of magnetic aging experiments on single crystals of Dy0.5Sr0.5MnO3. The results demonstrate striking memory and chaos-like effects in this insulating half-doped perovskite manganite and suggest the existence of strong magnetic relaxation mechanisms of a clustered magnetic state. The spin-glass-like state established below a temperature Tsg ≈ 34 K originates from quenched disorder arising due to the ionic-radii mismatch at the rare earth site. However, deviations from the typical behavior seen in canonical spin glass materials are observed which indicate that the glassy magnetic properties are due to cooperative and frustrated dynamics in a heterogeneous or clustered magnetic state. In particular, the microscopic spin flip time obtained from dynamical scaling near the spin glass freezing temperature is four orders of magnitude larger than microscopic times found in atomic spin glasses. The magnetic viscosity deduced from the time dependence of the zero-field-cooled magnetization exhibits a peak at a temperature T < Tsg and displays a marked dependence on waiting time in zero field. (Some figures in this article are in colour only in the electronic version)

Single crystals of Pr0.68Pb0.32MnO3 have been investigated by scanning tunneling microscopy over a broad temperature range. In this material, a distinct separation of the ferromagnetic and the metal–insulator transition temperature, TC≈210 K and TMI≈255 K, respectively, was observed. Spectroscopic tunneling studies revealed that even on a local scale the system switches from predominantly metallic to insulating within a narrow temperature range around TMI. Inhomogeneities of the zero-bias conductance with small patches of metallic clusters on a length scale of 2–3 nm, however, were only observed within the temperature range TC

Low-temperature results of the thermodynamic and transport properties of polycrystalline Ce3Rh4Sn13 are presented. The study of the ground-state properties reveals that Kondo interactions become important below 2 K, as evidenced by a large Sommerfeld coefficient and high magnetic resistivity. At 1 K the specific heat exhibits a broad peak that is attributed to short-range magnetic order. Support is given by ac susceptibility measurements. The resistivity and the susceptibility around 80 K are dominated by effects due to the crystal electric field splitting of the Ce3+ multiplet. Additionally, clear indications for local vibrations of Sn(2) atoms within the cage-like structure are deduced from an Einstein term in the specific heat. The crystal structure is known to form two atomic cages: one in which the Ce atoms are located; the other containing the Sn(2) atoms. Although strong correlations at low T are present in this system, the thermopower is found to be surprisingly small.

The magnetic properties of URh0.7Ru0.3Ge were investigated by means of ac susceptibility, dc magnetization, specific heat and electrical resistivity measurements. We observed a maximum of the ac susceptibility at Tmax = 2.9 K and its frequency dependence, but no spontaneous magnetization at 2 K. An alternative scenario for the observed feature, for example, spin-glass freezing, is not confirmed by dc field dependences of the ac susceptibility and dc magnetization. The data from specific heat and electrical resistivity studies down to 2 K do not suggest long-range magnetic ordering, and point to spin-fluctuation behaviour of the alloy. We have estimated a spin-fluctuation temperature of ~27 K and Stoner enhancement factor of ~490. The experimental data are discussed in the framework of spin-fluctuation theories.

We report an electron spin resonance (ESR) study in single crystals of the new heavy-fermion metal YbIr 2 Si 2 whose spin dynamics is characterized by a Kondo energy scale T K ≃ 40 K and which acquires a Landau Fermi-liquid state below 0.2 K. The ESR spectra are observed well below T K and show typical properties of a Yb 3+ resonance. This enables the direct observation of the spin dynamics and static magnetic properties of YbIr 2 Si 2 below the Kondo temperature.