Search

Perforated steel plates are structural components widely employed in engineering. In several applications these panels are subjected to axial compressive load, being undesired the occurrence of buckling. The present work associates the computational modeling and the constructal design method to obtain geometries, which maximizes the mechanical behavior for these components. A numerical model was used to tackle with elastic and elasto-plastic buckling. Square and rectangular plates with centered elliptical cutouts were considered and several hole volume fractions and ratios between the ellipse axes (H 0/L 0) were taken into account. Stress limit improvements around 100% were achieved depending only on the cutout shape.

The occurrence of a maximum at a temperature T max in the resistivity of the dense Kondo compound CeNiAl4 and in (Ce1−xY x)NiAl4 alloys is investigated. T max ( ∝ T K , the Kondo temperature) first increases, goes through a maximum value and decreases with increase in x . This behaviour is qualitatively explained by considering the competing influence of volume changes and dilution (the Kondo-hole effect) on the Kondo system. Complementary magnetic susceptibility measurements corroborate these results.

Measurements of electrical resistivity are presented for polycrystalline alloys in the CePt 2 (Si 1− x Sn x ) 2 system. Results of X-ray diffraction indicate that the tetragonal region of the CePt 2 (Si 1− x Sn x ) 2 alloy system that is amenable for study only extends up to x =0.3. The resistivity maximum characteristic of a Kondo lattice is observed at a temperature T max =63 K for the parent compound CePt 2 Si 2 and shifts to lower temperatures with increase in Sn content. The compressible Kondo lattice model is applied to describe the results of T max in terms of the on-site Kondo exchange interaction J and the electron density of states at the Fermi level N ( E F ). A value of | JN ( E F )|=0.060±0.009 for the parent compound is obtained from the experimental results.

Electrical resistivity ρ(T) measurements on polycrystalline samples of the Ce (Pt1−xNix)2Si2 system exhibit dense Kondo behaviour for alloys with . The temperature at which a maximum appears in ρ(T) shifts from Tmax = 65 K for x = 0 to Tmax = 290 K for x = 0.6 as the system evolves towards the intermediate-valence regime for the CeNi2Si2 compound. At low temperatures the Ce (Pt1−xNix)2Si2 alloys show a Fermi liquid T2 contribution to ρ(T) below the coherence temperature Tcoh. It is observed that , with a transition that takes place from a dense Kondo regime of TK TCF (). TK () and TCF denote the Kondo and crystalline electric field splitting, EF and ER are the Fermi and the Abrikosov–Suhl resonance energies and j denotes the total angular momentum. An electronic Gruneisen parameter value of 19 has been obtained for the alloy system which is in reasonable agreement with Ω = 28 found from pressure studies on CePt2Si2. It is argued that volume effects are mainly responsible for the hybridization in the Ce (Pt1−xNix)2Si2 system and application of the compressible Kondo lattice model to Tmax data yields |JN(EF)| = 0.309 ± 0.008, where J is the on-site exchange interaction between conduction electrons and the localized 4f spin and N(EF) is the density of states at EF.

The influence of substituting Ce with La in the Kondo compound CeCu5In has been investigated using x-ray diffraction, specific heat (Cp), electrical resistivity (?(T)), magnetoresistivity?(MR) and thermoelectric power?(TEP) measurements. Cp of CeCu5In and the (Ce1?xLax)Cu5In alloys shows enhanced values at low temperatures. Between?10 and 20?K the equation Cp/T = ?conv+?T2 fits the data for all alloys with ?conv scaling linearly with Ce concentration. Below 10?K a pronounced upturn in Cp values occurs. Susceptibility data above 100?K follow the Curie?Weiss relation and give effective moment ?eff values in fair agreement with that of a Ce3+-ion. The ?(T) studies illustrate the evolution from Kondo lattice to single-ion Kondo behaviour with increase in La content in the (Ce1?xLax)Cu5In alloy series. MR measurements on Ce dilute alloys are interpreted within the single-ion Bethe ansatz description and values of the Kondo temperature TK are calculated. A compressible Kondo lattice model has been used to describe the decrease in TK and in Tm? (the temperature at which a maximum in ?(T) occurs for the coherent dense Kondo alloys) with decrease in Ce concentration for these alloys. The TEP is positive and shows a maximum at approximately 45?K for several investigated (Ce1?xLax)Cu5In alloys.

Results of electrical resistivity, magnetization and susceptibility measurements are reported for the pseudo-ternary alloys (Ce1−xGdx)Pt2Si2. The end-members of the alloy series are the non-magnetic Kondo lattice compound CePt2Si2 and the antiferromagnet GdPt2Si2. The resistivity results reveal a rapid evolution to Kondo behaviour beyond small Ce substitution in GdPt2Si2 (for 1 − x ≥ 0.2). Coherent Kondo scattering is observed for larger Ce substitution (1 − x ≥ 0.75). The low-temperature resistivity of CePt2Si2 in the coherent state is dominantly a T2 Fermi-liquid behaviour. The magnetization results suggest metamagnetic behaviour at Gd-rich concentrations. From the susceptibility results, the Gd and Ce moments seem to contribute independently to the magnetism of the alloy samples.

UPtSn is known as a semimetal with a bandgap in the electronic density of states. We report the results of measurements of the cubic lattice parameter a(T), coefficient of thermal expansion α(T), magnetic susceptibility χ(T), magnetization σ(T,B), specific heat C(T) and electrical resistivity ρ(T, B). We give arguments that this compound is antiferromagnetically ordered with T N = 35 K, although this is not confirmed by neutron diffraction. For carefully annealed samples of UPtSn we provide a phenomenological description of electron transport properties in terms of the fact that the temperature-dependent bandgap is closed at T = 0 K. Results of electrical measurements on the isostructural compounds ThPtSn and ZrPtSn provide evidence for bandgap formation in these two compounds as well.

We present results of transport, magnetic, and calorimetric measurements on two f-electron based compounds: U 2 Ru 2 Sn and Eu 8 Ga 16 Ge 30 . We show that U 2 Ru 2 Sn shares several properties with the strongly correlated semimetal CeNiSn. These analogies suggest that in U 2 Ru 2 Sn a narrow energy gap (or pseudogap) opens which is one order of magnitude larger than the one of CeNiSn. The two modifications of the clathrate Eu 8 Ga 16 Ge 30 behave as local-moment ferromagnetic metals with relatively low Curie temperatures and small charge-carrier concentrations. The thermal conductivity is low and glass-like, as expected for filled-cage' systems. If, by modification of the Ga-Ge cages, a 'Kondo insulating' ground state could be realized, a high thermoelectric figure of merit associated with the (pseudo)gap opening would be expected.

Electrical resistivity, ρ(T), measurements on U2Ru2Sn show typical Kondo semiconducting behaviour, namely a ρ(T)~ln T behaviour at higher temperatures and an activation-like increase in ρ(T) below 20 K which indicates the opening of a small gap in the electronic density of states. The magnetic susceptibility, χ(T), of U2Ru2Sn has a maximum around 180 K which is characteristic of intermediate-valence behaviour. The χ(T) data for U2Ru2Sn have been fitted to the interconfigurational fluctuation model of Sales and Wohlleben giving a value of Tsf* = 155(2) K for the characteristic fluctuation temperature. Substituting as little as 5% Th for U leads to a ρ(T) variation reminiscent of that of a single-ion Kondo metal ρ(T) = ρ(0)[1-(π2/16)(T2/TK2)]. Values of TK = 79(1) and 113(1) K are respectively obtained for alloys with 5% and 10% Th substitution.

The electrical resistivities of the pseudo-ternary alloys (Ce1−xLax)TSi3 ( T = Rh, Ir; 0≤x≤1) are reported. The 4f-derived part of their resistivities, ρ4f, is found by subtracting the temperature-dependent part of the resistivity of LaTSi3. A maximum, characteristic of dense Kondo systems, is obtained in ρ4f at a temperature T max =105 K for CeRhSi3 and at 130 K for CeIrSi3. Tmax decreases for both compounds with increased La concentration, x. X-ray powder diffraction was used to measure the increase in tetragonal unit cell volume V for the (Ce1−xLax)TSi3 alloys with increase in x. The compressible Kondo model is applied to describe our results of Tmax(x) in terms of the on-site Kondo exchange interaction J and the electronic density of states N(EF) at the Fermi level. The experimental results yield |JN(EF)|x=0=0.072±0.016 for CeRhSi3 and 0.070±0.001 for CeIrSi3.

Previous studies on UPt samples indicated ferromagnetic ordering either at TC = 27 K or at TC = 19 K while in some samples there was evidence of the presence of both these transitions. These differences are thought to be associated with the presence of material of different crystal structure, viz. a monoclinic structure for the higher-TC material (H phase) and an orthorhombic structure for the lower-TC material (L phase). We have studied the crystal structure, magnetization, specific heat and transport properties of the solid solutions U1-xThxPt, including a pure UPt sample. We observed that the substitution of Th for U in UPt stabilizes the L phase for all compositions. Ferromagnetism is observed for 0≤x≤0.4 and there are indications of the presence of short-range magnetic order for x≥0.5, which vanishes slowly up to x≈1. At low temperatures in the magnetically ordered region the magnetic and electronic contributions to the specific heat C5f and electrical resistivity ρ5f are described by expressions that contain the magnon energy-gap Δ. These also include the γ5f(0)T and AT2 terms to describe the C5f and ρ5f temperature dependences respectively. For L-phase UPt, the low-temperature fitting (below 10 K) yields Δ = 19(1) K and γ5f(0) = 0.122(2) J K-2/mol U, while the higher-temperature one (above 10 K) yields Δ = 35(2) K and γ5f (hT) = 0.151(3) J K-2/mol U. With Th substitution Δ decreases, but the γ5f(0) value for both the magnetically ordered and non-ordered samples remains practically unchanged, being close to that of the higher-temperature value found for this compound. The magnetoresistance is negative and large in the ordered region and becomes slightly positive at low temperatures for the Th-rich alloys. The presence of the Kondo interaction is indicated in these alloys almost up to x≈1.

The temperature dependences of DC and AC magnetisation, electrical resistivity and magnetoresistivity of TbCu4Ag and DyCu4Ag are reported. In contrast to previous studies which indicate TbCu4Ag to be a simple antiferromagnet and DyCu4Ag to be a ferromagnet, our study indicates a more complicated behaviour for these materials. We observe three magnetic transitions for TbCu4Ag, viz. at TC=20 K, T1=11 K and T2=2.5 K. At temperatures T⩽ 10 K the magnetic isotherms show metamagnetic behaviour, while for T1⩽T⩽TC our results suggest canted antiferromagnetism. For DyCu4Ag magnetic transitions are observed at TC=19 K and in the vicinity of 5 K. Also for this material there is evidence suggesting a canted antiferromagnetic spin structure.

Measurements of X-ray diffraction (XRD), resistivity ( ρ ( T ) ), magnetic susceptibility ( χ ( T ) ) and magnetization ( σ ( μ 0 H ) ) are reported for the polycrystalline Ce ( Pt 1 - x Ir x ) 2 Si 2 alloy system. The unit cell volume derived from the XRD results deviates from Vegard's rule around x = 0.2 – 0.3 . χ ( T ) measurements show a Curie–Weiss behaviour at high temperatures for the x = 0, 0.1 and 0.2 alloys whereas the alloys with x ≥ 0.4 exhibit broad maxima in χ ( T ) at intermediate temperature (e.g. at 170 K for x = 0.4 ). The latter behaviour due to valence fluctuations as described by Sales and Wohlleben. ρ ( T ) data indicate Kondo lattice behaviour for x ≤ 0.2 and fluctuating valency for x ≥ 0.3 . σ ( μ 0 H ) data indicate metamagnetic behaviour for the x = 0.4 alloy.

The UCu5-xPdx heavy-fermion alloy system is known to exhibit non-Fermi-liquid (NFL) behaviour for compositions with x1. The magnetic properties associated with NFL behaviour of this system are the focus of this study. Results are presented on the temperature (1.7 T300 K) and magnetic field (0 B5 T) dependences of the magnetization M and susceptibility for polycrystalline UCu5-xPdx samples with x = 0.8, 0.9, 1.0 and 1.2. We emphasize the observed field dependence of at low temperatures and illustrate the instability of NFL properties against magnetic field. Our (T) data present a systematic power-law divergence for NFL UCu5-xPdx at low temperatures in the limit of small measuring fields. This is interpreted in terms of Griffiths-phase singularities near a quantum critical point which are treated in a model given by Castro Neto and co-workers that includes the effects of structural disorder and a generic RKKY-Kondo interplay (where RKKY Ruderman-Kittel-Kasuya-Yosida). For the extended range 1.7 T300 K, we find that (T) scales reasonably well with a theoretical expectation of Souletie and co-workers of NFL behaviour of Kondo systems. Finally, our M(T,B) data for magnetic fields up to 5 T and 1.7 T21 K are shown to conform to a NFL scaling relation that applies to T = 0 quantum critical systems. The above analyses support the role that magnetic interactions are thought to play in NFL UCu5-xPdx.

Inelastic neutron scattering with polarization analysis has been used to study the evolution of the magnetic response across the antiferromagnetic to paramagnetic transition in a single crystal of uranium dioxide ${(T}_{N}=30.8 \mathrm{K})$. The spin-wave dispersion curves have been determined at 16 K by measuring the spin-flip channel of the neutron cross section along the principal crystallographic directions. Evidence of magnon-phonon interactions along the $(0,0,\ensuremath{\xi})$ direction is given by the splitting of the lowest spin-wave branch, and by the Q dependence of the energy-integrated dynamic susceptibility. Above ${T}_{N},$ a magnetic inelastic response consisting of two dispersive peaks was observed between 3 and 10 meV. This signal was easily measurable even at 200 K, more than six times the N\'eel temperature, where spatial correlations between the uranium spins are essentially zero. We assume this result as evidence that in the time scale of our experiment the uranium triplet ground state is split into three singlets, due to a dynamical Jahn-Teller (JT) distortion of the oxygen cage which reduces the point symmetry at the uranium site. Since the position of the peaks and their dispersion are compatible to a $1\ensuremath{-}\mathbf{k}$ distortion along the $〈100〉$ direction, a picture emerges in which local, uncorrelated $1\ensuremath{-}\mathbf{k}$ dynamical JT distortions occur above ${T}_{N}$ along the three directions of the $〈100〉$ star; as ${T}_{N}$ is approached, a correlation builds up between the phases of the corresponding vibrations until, eventually, a static $3\ensuremath{-}\mathbf{k}$ structure is obtained below ${T}_{N}.$

Measurements of electrical resistivity ρ ( T ) , magnetoresistivity MR and magnetic susceptibility χ ( T ) are reported for the pseudo-ternary alloys ( Ce 1 - x Y x ) Pt 2 Si 2 . ρ ( T ) results reveal coherent Kondo scattering above 80% Ce concentration and a rapid evolution to single-ion Kondo scattering with an increase in Y concentration x. MR measurements on Ce alloys in the single-ion Kondo region are analyzed on the basis of calculations by Schlottmann for the Bethe-ansatz solution in the context of the Coqblin–Schrieffer model. The analysis yields values of the Kondo temperature T K and the effective moment of the Kondo ion μ K . χ ( T ) data above 120 K follow the Curie-Weiss relation for all the investigated concentrations and give effective moment values μ eff in close agreement with μ eff = 2.54 μ B expected for the Ce 3 + -ion.

The results of electrical resistivity ρ(T) and magnetoresistivity MR(T, B) for K and T are reported for the (Ce1-xNdx)Cu6 alloy system. For small Nd substitutions in the heavy-fermion CeCu6 parent compound, the Kondo lattice is characterized through coherence effects in ρ(T) at low temperatures. The ρ(T) data above room temperature are used to resolve the electron-phonon scattering, and it is indicated that the single-ion Kondo interaction dominates both ρ(T) and MR(B) for a wide range of intermediate Ce concentrations. Based on this, the MR(B) data for different isotherms and alloy compositions are analysed according to the Bethe- ansatz description. We also discuss the observed deviations of our data from the preceding theoretical description due to the onset of magnetic order in alloys with high Nd content, and to phase coherence at low temperatures.

The electrical resistivities of the Kondo system are reported. It is observed that the resistivities of the alloy samples are reduced considerably as a result of annealing the samples. The results furthermore indicate the evolution from dense Kondo behaviour to single-ion incoherent Kondo scattering as x is increased. The resistivity in the dense Kondo regime shows a maximum which drops from K for to = 36 K for x = 0.2. Using the relationship where is the Kondo temperature, J is the exchange integral and is the density of states at the Fermi level , and the experimentally observed values of leads to .

Electrical resistivity results of Ce ( Pt 1 - x Ni x ) Ga and CePt ( Ga 1 - y Al y ) alloys show features at low temperature indicating antiferromagnetic ordering and Kondo behaviour. The variation of Neel temperature with alloy composition is interpreted in terms of a Doniach diagram and the possible existence of a quantum critical point is indicated. Magnetoresistance data are presented and analysed in terms of the Schlottmann formalism.

The effect of substitutions in the system has been investigated by means of electrical resistivity and magnetoresistivity measurements. The substitutions of Pd for Ru have been found to (i) suppress a Kondo behaviour at high temperatures, (ii) produce magnetic order and (iii) induce a Kondo-like minimum in the electrical resistivity at low temperatures. We analysed the low-temperature part of the electrical resistivity by considering electron scattering by impurities, by spin-wave excitations and originating from a Kondo effect. Samples with exhibit incoherent Kondo behaviour above about 100 K, while for the compositions a broad maximum appears in the resistivity around 150 - 180 K, presumably due to a combination of the Kondo and crystal-field effects. The magnetoresistivity results support the earlier proposal derived from the magnetic studies of the system in which a magnetic phase transition from paramagnetic to ferromagnetic and finally to an antiferromagnetic/ferrimagnetic state takes place. A marked difference was found in the magnetoresistivity data for the x = 0.2, 0.6 and 0.8 samples, reflecting a variety of magnetic structures which appear in these compounds.

X-ray and neutron diffraction, magnetic susceptibility, and magnetization measurements were performed on ${\mathrm{URu}}_{1\ensuremath{-}x}$Pd${}_{x}$Ga solid solutions $(x$ = 0.0--1.0). They crystallize in the hexagonal HoNiAl-type structure with space group $P6\ifmmode\bar\else\textasciimacron\fi{}2m$. The concentration dependence of the lattice parameters deviates from Vegard's law, showing anomalies at $x=0.2$ and 0.8. The magnetic phase diagram consists of three different concentration regions. Below $x=0.1$ the system is nonmagnetic down to 1.7 K. In the region 0.1$l$$xl0.8$ the magnetic state of these compositions at higher temperatures can be considered as a ferromagnetic state with a transition temperature ${T}_{C}$ that goes through its maximum value of 78.4 K at $x$=0.5. At lower temperatures this state seems to be more complex and requires further studies. For $x$\ensuremath{\geqslant}0.8 the magnetic state of the system also changes with temperature, but the magnetic ground state has been established as antiferromagnetic. The magnetic behavior of the ${\mathrm{URu}}_{1\ensuremath{-}x}$Pd${}_{x}$Ga solid solutions as other similar alloys is governed by a change in both the unit-cell volume and the number of $d$ and/or $\mathrm{sp}$ electrons in the system.

We present x-ray diffraction and electrical resistivity measurements on two series of compounds: (M = Al, Ga and Sn) and (T =Fe, Ni, Pd and Pt) with . The change in electrical resistivity with alloying is discussed in terms of the effect of this on the Kondo interaction and crystalline electric field splitting. These are influenced by two different mechanisms: the unit-cell volume and the number of conduction electrons of the systems.

Spin-slip behaviour in high-purity holmium single crystals is characterized by neutron diffraction and ultrasonic velocity and attenuation measurements as a function of temperature and of magnetic field applied along b, c, and a axes. Neutron diffraction measurements of intensity and turn angle give information on wave vector lock-in effects for various spin-slip structures in applied fields. These findings are supplemented with ultrasonic studies of the elastic constants and and corresponding attenuation coefficients and . Various phase diagrams are presented and results compared with experiments by other groups and with some theoretical predictions.

U 2 Ru 2 Sn has been classified as the first tetragonal U-based Kondo insulator. Here, we present measurements of the thermal conductivity κ and thermopower S of high-quality single-crystalline U 2 Ru 2 Sn along and perpendicular to the tetragonal c-axis, in the temperature range between 100 mK and 1 K, in zero field and in a magnetic field of 6 T. Below 400 mK, the phonon contribution to κ ( T ) shows a T 2 behaviour for both directions that can be attributed to phonons scattered by electrons. S ( T ) presents a linear behaviour in the whole temperature range. S is positive along the c-axis and negative perpendicular to the c-axis. Using a one-band model the effective mass m * is estimated to be 2 m 0 along and 16 m 0 perpendicular to the c-axis, where m 0 is the free-electron mass. This indicates that U 2 Ru 2 Sn has a highly anisotropic residual density of states within the pseudogap.

Resistivity measurements show Kondo-lattice behaviour for Ce 8 Pd 24 Al x alloys with 0.2 ⩽ x ⩽ 1.3 . At low temperatures magnetic susceptibility studies indicate antiferromagnetic ordering for alloys with 0.96 ⩽ x ⩽ 2 . Magnetoresistivity studies are interpreted in terms of the Schlottmann description for a Kondo impurity system.

We have analyzed the temperature dependence of the ac susceptibility, χ ac ( T ), of UCu x Ge y samples (0.800 ≤ x , y ≤ 1.00) applying various frequencies and magnetic field strengths up to 1 T. This was done in order to verify the reentrant ferromagnetic behaviour of UCu x Ge and the antiferromagnetic behaviour of UCuGe y previously observed by dc susceptibility experiments. Our χ ac results are discussed on the basis of existing theories.

Magnetoresistivity measurements of polycrystalline U2Rh2Sn in an applied magnetic field of 8.29 T reveal a sharp minimum at the antiferromagnetic transition temperature TN≊20 K. The thermoelectric power of U2Rh2Sn exhibits negative values for temperatures T⪯24 K. At T≊4 K, a large decrease in resistivity with lowering of temperature is observed for polycrystalline U2Fe2Sn. This anomaly originates from the occurrence of free tin on the grain boundaries of the sample giving a decrease in resistivity as a result of superconductivity.

The low-temperature magnetoresistance, ϱ( B ) ϱ(0) , of CePt2Sn2 as-cast and annealed samples has been measured. The results are interpreted in terms of Abrikosov's approach for calculating the resistivity of weakly spin-correlated Kondo-like systems. The exchange integral for the electron-impurity interaction was found to be J k B = 2.1 K .

Neutron diffraction measurements on high-purity Dy and Ho crystals indicate no discontinuity in the order parameter at TN, and no hysteresis in the value of TN within 0.05 K between consecutive cooling and heating runs. This finding is also reflected by the results of ultrasonic velocity and attenuation measurements, thus corroborating the continuous nature of the phase transition. Integrated neutron diffraction measurements near TN yield beta =0.38+or-0.02 for Dy and beta =0.39+or-0.02 for Ho in agreement with renormalization group predictions ( beta =0.39) of Mukamel, Krinsky and Bak. Neutron intensities in the paramagnetic region do not adhere to a conventional t+- gamma dependence over the complete temperature regime. A possible description for the region near TN with a 2D-planar spin model is indicated. The critical velocity change Delta nu 33 of Ho near TN is discussed.

Low-temperature magnetoresistance ( MR ) and thermoelectric power ( S ) measurements are presented for antiferromagnetic U 2 Ni 2 Sn. Appreciable remanence in the MR behaviour is observed. S changes its sign at T N = 24 K from small positive values above T N to large negative values at 6 K where it shows a well resolved minimum.

UNiSn in the MgAgAs-type crystal structure is characterised by a simultaneous magnetic, metallic and crystallographic phase transition occurring at 43 K. Results of measurement of both the transverse and longitudinal sound velocities in polycrystalline UNiSn through this transition are presented and compared with theoretical predictions.

We present magnetic susceptibility, specific heat, electrical resistivity, magnetoresistance, Hall coefficient, thermal conductivity, thermoelectric power, and 119 Sn NMR data for U2Ru2Sn: Clear evidence is found for the formation of a gap in the electronic density of states at the Fermi level. Together with the disappearance of the local magnetic moments at low temperatures and the observation of enhanced effective masses this suggests to classify U2Ru2Sn as a Kondo insulator. r 2002 Elsevier Science B.V. All rights reserved.

Measurements are reported on the temperature dependence of the elastic constants of dilute Cr-Ru and Cr-Re alloy single crystals, containing respectively 0.3 at.% Ru, 0.5 at.% Ru, 0.3 at.% Re and 0.5 at.% Re. Neutron diffraction experiments were also performed on the two Cr-Ru crystals. Well defined anomalies were observed in all the elastic constants as well as in the integrated neutron intensities at the magnetic phase transitions of the alloys. The commensurate (C) spin density wave (SDW) to paramagnetic (P) and incommensurate (I). SDW to P transitions are second-order phase transitions, while the ISDW-CSDW and CSDW-ISDW transitions are of first order. A thermodynamic model describes the temperature dependence of the magnetic contributions ( Delta B) to the bulk modulus (B) reasonably well, but fails to give the observed relationship between Delta B and the magnetization.

A new uranium ternary compound UCu2Sn2 has been obtained, crystallizing with the primitive tetragonal structure of CaBe2Ge2-type (space group P4/nmm). The electrical resistivity versus temperature (ϱ(T)) depends on the annealing procedures. The ϱ(T) curve for the annealed sample exhibits anomalous behaviour with a gradual increase towards lower temperatures followed by a broad maximum below 110 K and steep decrease below approximately 20 K which may indicate Kondo-like behaviour.

Bulk magnetization measurements and elastic neutron scattering have been used to determine the critical exponents β, γ and δ for single-crystal USe. The magnetization behavior in the ferromagnetic region is significantly influenced by anisotropy. An anomalously low value of β = 0.246±0.010 is observed and this is discussed in terms of an axial next-nearest-neighbor Ising model.

Magnetic susceptibility X(T), electrical resistivity ρ(T) and magnetoresistivity of CePt 2 (Si 1-x Ge x ) 2 alloys (0 ≤ x < 1) are reported. For X(T) of these, the Curie-Weiss relationship is followed with effective moments in close agreement with μ eff = 2.54 μ B expected for Ce 3+ . A maximum in ρ(T) is observed at a temperature T max ∼ T K ∼ exp(-1/|JN(E F )|). From the decrease in T max with increasing x it is deduced that |JN(E F )| x=0 = 0.11 ± 0.02.

Both magnetoelastic and neutron-diffraction studies have been performed on Cr-Al single crystals containing 1.2, 1.9, and 2.6 at. % Al. These concentrations lie in a controversial region of the magnetic phase diagram. For the crystals containing 1.2 and 1.9 at. % Al the transition at the Neel point is from a paramagnetic to an incommensurate spin-density-wave (ISDW) state while it is from the paramagnetic to a commensurate (C) SDW state for Cr+2.6 at. % Al. All magnetic transitions are observed as second order phase changes within our experimental resolution

We present the results of an inelastic neutron scattering experiment with polarization analysis performed on a single crystal of UO2. A magnetic inelastic response is observed above TN in the energy region between 3 and 10 meV, at least up to 6.5TN. This result provides evidence of the fact that in the time scale of our experiment the uranium triplet ground state is split into three singlets because of a dynamical Jahn–Teller distortion of the oxygen cage, reducing the point symmetry at the uranium site. The position of the peaks and their dispersion are compatible with monoclinic 1-k distortions along the three directions of the 〈100〉 star. This suggests a picture in which as TN is approached, a correlation builds up between the phases of the corresponding vibrations until, eventually, a static 3-k distortion is obtained below TN.

Hysteresis in the intensity of elastic neutron scattering from the incommensurate Bragg peak in the spiral phase of holmium is studied as temperature is cycled from above the Neel temperature, TN=132.2 K, to various low temperatures, T0. The nature of the hysteresis is different according to whether T0 TL, where TL approximately=100 K is the lock-in transition temperature at which the magnetic structure is supercommensurate.

The electronic structure (both valence band and $4f$ core level spectra) of the cubic monocompound UN in the paramagnetic state was studied by x-ray photoelectron spectroscopy. The experimental results are compared with the results of calculations employing full-potential local-orbital minimum-basis full relativistic method with the spin-orbit coupling included implicitly. The molar susceptibility of a single crystal of antiferromagnetic UN $({T}_{N}=51\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ is reported along three main crystallographic directions between 1.9 and $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The observed magnetic characteristics are in agreement with previous studies. The observed small anisotropy in the ordered region is discussed. Results of electronic structure, magnetoresistivity, thermoelectric power, and thermal conductivity as studied on single-crystalline specimens are given and discussed from the viewpoint of dual and spin-density-wave-like character of the $5f$ electrons.

The compound U2Ru2Sn is known to crystallize in the tetragonal U3Si2-type structure and is believed to be a weak paramagnet. We report electrical resistivity studies on this compound which seem to indicate semiconducting behaviour at low temperatures and hence a gap formation in this compound. This is evidenced from a sharp rise in the resistivity seen at low temperatures similar to that observed in the so-called Kondo insulators.

The temperature dependence of the resistivity, ϱ(T) and magnetoresistivity (T ≥ 1.5 K, B ≤ 8 T) of polycrystalline U2Pt2Sn are reported. ϱ(T) shows maxima at 12 K and 45 K and a minimum at 19 K. A minimum is observed in d ϱ(T) d T at the Neel temperature of 15 K. The magnetoresistance at low temperatures is negative and below TN it displays a step-like decrease in an applied field of about 2 T indicating the presence of a phase transition.

Resistivity ϱ ( T ) and magnetoresistivity results are reported for several U 1− x Th x Pd 2 Al 3 compounds and for U 0.3 Th 0.7 Pd 2 Ga 3 . Non-Fermi liquid behaviour is observed for U 0.4 Th 0.6 Pd 2 Al 3 as evidenced from a linear temperature dependence of ϱ ( T ) at low temperatures. Application of a magnetic field changes the resistivity to a ϱ = ϱ 0 − cT n dependence.

The resistivities ϱ(T) of U2Pt2In and UCu4Pd display NFL characteristics as indicated by linear ϱ(T) behaviour at low temperatures, but this linear relationship is broken down by applying at 7.5 T magnetic field. (U0.9Th0.1)2Pt2ln displays a knee at 19 K in its zero-field resistivity but the knee is smeared out by application of a magnetic field.

Measurements on the temperature dependence of resistivity (ϱ) of polycrystalline specimens of the heavy-fermion compound U 2 Pt 2 In and of thorium-substituted (U x Th 1 − x ) 2 Pt 2 In are reported. For U 2 Pt 2 In, a linear curve of ϱ ( T ) is observed for 15 K > T > 1.5 K, while the x = 0.9 alloy displays a knee at T = 20 K followed upon cooling by a quadratic decrease of ϱ ( T ).

Resistivity (ϱ) measurements on polycrystalline Ce x Nd 1− x Cu 6 indicate Kondo behaviour over the concentration range x = 0.2−0.95 as evidenced from fits of ϱ ( T ) = ϱ 0 + bT − c ln T , where bT characterizes the electron-phonon interaction.