Search

We present a revisiting analysis of thermal conductivity data in heavy fermion compounds. It is shown that the product WmagT, where Wmag is the magnetic part of the thermal resistivity taken as the difference between the inverse of the thermal conductivity of the Kondo compound and that of an equivalent non magnetic compound, is a good measurement of the strength of the Kondo interaction at sufficiently high temperatures with respect to the Kondo temperature and to the crystal-field splitting. In the considered temperature range, WmagT shows a log T dependence in a way similar to the magnetic part of the electrical resistivity. Such an analysis, which is analogous to the well known one for the electrical resistivity, has not been often used for the thermal conductivity. We present data for compounds with four anomalous Kondo rare earths Ce, Pr, Tm and Yb.

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.

We discuss multipole ordering in two cubic f-electron compounds. Field variation of the antiferroquadrupolar transition temperature TQ in PrPb3 is determined by the specific heat and the magnetization measurements. It is found that TQ(H) shows a pronounced increase for H∥〈100〉, which has been successfully explained by the antiferromagnetic interaction between the field-induced staggered moment in the O20(∝2Jz2−Jx2−Jy2) AFQ phase. From the analysis of the anisotropy in TQ(H), the importance of an octupolar interaction is pointed out. The new ordered state in CexLa1−xB6 (x

Antiferro-quadrupolar (AFQ) ordering in the cubic Γ 3 ground state system PrPb 3 has been studied by means of magnetization and specific heat measurements under magnetic fields H . Field variation of the AFQ transition temperature T Q (0.4 K at H =0) has been determined for the three crystallographic directions , and . The obtained T Q ( H ) is strongly anisotropic, with T Q ( H ) the largest (∼0.7 K at 6 T). The AFQ phase diagram and the magnetization behavior observed for H ∥ are well explained by a model that incorporates both antiferromagnetic and antiferroquadrupolar interactions. The interactions between field-induced staggered magnetic moments stabilize the AFQ order. This simple model, however, seriously fails to explain the observed anisotropy: T Q ( H )> T Q ( H )> T Q ( H ). Reconsidering the field-induced multipole moments in the AFQ phase, we propose that inclusion of a weak ferro-octupolar interaction between Γ 5 type octupole moments is importa...

We measured the specific heat, thermal expansion coefficient, magnetization, electrical resistivity, magnetoresistance and de Haas-van Alphen (dHvA) effect in PrSn 3 . The dense Kondo effect was confirmed from a negative magnetoresistance and the presence of heavy electrons with the cyclotron effective mass of 8–9 m 0 for the main Fermi surface. The magnetic phase diagram was also clarified by the high-field magnetization measurement.

We presented results of electrical resistivity, magnetoresistivity and Seebek effect measurements done in the paramagnetic state of an antiferromagnetically ordering intermetallic compound TmIn3. It was found that the magnetic part of the electrical resistivity showed maximum at 18 K and the lgT dependence in temperature range 20

The transverse ρ ⊥ and the longitudinal magnetoresistance ρ ‖ of a PrPb 3 single crystal was measured in the temperature range 2 T ρ ⊥ − ρ ‖ ) was compared with that theoretically predicted if the influence of the quadrupole scattering mechanism on magnetoresistivity is taken into consideration. The comparison shows that quadrupole scattering processes in PrPb 3 are essential.

Results of the linear thermal expansion coefficient α (T ) measurements for PrIn3, GdIn3 and LuIn3 are reported. These rare earth intermetallic compounds belong to a large family of RIn3 compounds which crystallize in AuCu3-type crystal structure. The measurements were made on monocrystalline samples in temperature range 5K ÷ 200 K. The compounds under investigation differ in their magnetic properties: PrIn3 is a typical example of a singlet ground-state paramagnet in which the interionic interactions are quenched by the crystalline electric field (CEF), whereas GdIn3 is the crystal-field free antiferromagnet in which the interionic RKKY interactions play essential role and cause the antiferromagnetic structure which is still unknown. The results of the measurements for LuIn3 served as a non-magnetic background for the separation of the contribution to α (T ) arising from the magnetic interaction. Theoretical considerations concerning the influence of CEF on the thermal expansion are remined. Pertinent Gruneisen parameters will be estimated in a forthcoming paper. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Results of the thermoelectric power (TEP) measurements done on monocrystalline samples of RESn 3 compounds (RE=La, Pr, Nd, and Gd) are presented for the temperature range of 5.5–300 K. It was found that the TEP is positive and weakly temperature dependent at temperatures T >100 K. For T 3 and the NdSn 3 compounds in the vicinity of 10 K.We argue that the Kondo and crystal field effects cause these anomalies. A shape of the TEP anomaly found for PrSn 3 resembles very much that observed in the electrical resistivity.

We have measured the de Haas-van Alphen effect of PrPb 3 whose antiferroquadrupolar ordering occurs at 0.4 K. Main Fermi surfaces consist of four closed ones, which are almost spherical. These Fermi surfaces are the same as those of a non- f reference compound LaPb 3 in topology, although the cyclotron effective masses are 2 to 6 times larger than those of LaPb 3 . The cyclotron effective masses are temperature-dependent, which starts gradually with decreasing the temperature below 1 K. A metamagnetic transition is also found to occur at about 70 kOe below 0.6 K through the magnetization, magnetostriction and AC susceptibility measurements. These phenomena are closely related to the antiferroquadrupolar ordering at 0.4 K.

Temperature dependence of resistivity for monocrystalline LaSn3, LaPb3, LuGa3, LuIn3 and LaIn3 was analyzed in the temperature range 4.2–300K. A good overall fit of their resistivities to a generalized Bloch—Gruneisen formula was observed in these temperatures. The phonon resistivity at the lowest used temperatures fulfill power law ϱph ∼ Tn with n equal to 3.86, 3.50, 3.22, 3.14 and 2.4 for the mentioned compounds, respectively. It was found also that n depends on free electron to real electron Fermi surface ratio.

Experimental results of thermal conductivity versus temperature for both PrSn 3 and the equivalent “non-magnetic” LaSn 3 are reported. The “magnetic” contribution to the thermal resistivity, W mag was separated and it was shown that the function W mag T has a log T behavior from roughly 15 up to 200 K, suggesting very strongly a presence of Kondo effect in PrSn 3 . Value for the s–f exchange integral, J has been deduced from the slope of that behavior and it was shown that such calculated J is in a good agreement with that obtained from the slope of the magnetic term of the electrical resistivity.

Results of the de Haas-van Alphen effect investigations are reported for the antiferromagnetically ordered compound GdIn 3 . For the first time data on the dHvA frequencies and their angular dependencies are shown for magnetic field higher than the metamagnetic transition field. The list of detected frequencies and related cyclotron masses is given. Among many Fermi surface branches observed, only the j, b and d correspond to theoretically predicted and experimentally observed branches for the nonmagnetic LaSn 3 . The metamagnetic transition taking place at 30 T in the GdIn 3 influences some branches of Fermi surface, mostly those in the (110) plane and close to the [111] direction. All effective masses found are lower than m 0 and close to those found for the LaSn 3 .

In order to investigate the influence of the 4f electrons on the scattering processes we measured resistivity of the NdPb3 in the temperature range 7-300 K. As a result, we could compare the experimentally determined magnetic contribution to the resistivity with the theoretically calculated ones for the exchange and quadrupolar scattering. The results may confirm that the direct Coulomb interactions between 4f and conduction electrons predominate.

The temperature dependence of the magnetic contribution to the resistivity was investigated in the paramagnetic phase of the REIn3 compounds where RE identical to Tb, Dy, Ho or Er. It was shown that the dependences for DyIn3, HoIn3 and ErIn3 behave in qualitative agreement with that calculated in the mean-field approximation assuming the crystal-field effect. The negative temperature coefficient of the magnetic resistivity found for TbIn3 corresponds to that for GdIn3 where the crystal field does not influence the resistivity. The anomalously large rise in the resistivity observed for ErIn3 at temperatures close to TN was attributed to the influence of the molecular field.

Some results of thermal conductivity measurements on REIn3 (RETb, Dy, Tm, Lu) single crystals over the temperature range 4–80 K are reported. On the basis of experimental data, an extraction of the magnetic contribution to the thermal conductivity was performed. In the antiferromagnetic state the thermal conductivities of TbIn3 and DyIn3 are dominated by magnons. In the paramagnetic state the thermal conductivities of both compounds increase nearly linearly with increasing temperature. Contrary to other analogous compounds the temperature dependence of the thermal conductivity of TmIn3 is more complex. To separate the contribution resulting from the 4f electrons scattering from the total thermal conductivity in the studied compounds, the thermal conductivity of isomorphous and non-magnetic LuIn3 was measured.

Results of the thermoelectric power (TEP) measurements for REIn 3 compounds (RE = Gd, Tb, Dy, Ho, Er and Lu) are presented. A monotonic decrease of TEP with the De Gennes factor X = ( g − 1) 2 J ( J + 1) is found. Certain generalizations of previous theoretical considerations allow us to conclude that simple relations between total diffusive TEP and X govern the behaviour of normal rara earth compounds at sufficiently high temperatures.

We measured the specific heat, thermal expansion coefficient, magnetization, electrical resistivity, magnetoresistance and de Haas–van Alphen (dHvA) effect in PrSn 3 . The dense Kondo effect was confirmed from a negative magnetoresistance and the presence of heavy electrons with the cyclotron effective mass of 8–9 m 0 for the main Fermi surface. A magnetic anisotropy was found below T N , having an easy axis of 〈1 1 0〉.

Results of the thermoelectric power measurements carried out on monocrystalline REIn3 samples (RE=Gd, Tb, Dy, Ho, Er and Lu) in the temperature range 7–300 K are presented. The magnetic part of the thermoelectric power is determined in temperatures T ⪢ TN and T >TD using the Nordheim-Gorter rule. It is shown that this part is linearly dependent with temperature and with the same slop for the all investigated compounds. The values of magnetic parts taken at T = 295 K scales with de Gennes factor in the same way as the spin disorder resistivity does.

Quadrupolar ordering in the cubic compound PrPb3 has been studied by DC magnetization measurements at temperatures down to T∼50 mK in fields (H‖[1 0 0]) up to 8 T. The quadrupolar ordering temperature TQ(H), below which the magnetic susceptibility is enhanced, is found to increase in H from 0.4 K at H=0 to 0.6 K at H=5 T . On cooling below TQ(H), sharp metamagnetic transitions develop in the magnetization process at around 7 T. The resulting H–T phase diagram can be explained by incorporating magnetic interactions between the field-induced antiferromagnetic moments in the O02 type antiferro-quadrupolar phase.

The transverse and longitudinal magnetoresistances of LaIn3, CeIn3, PrIn3 and SmIn3 measured along the 〈1 0 0〉 direction in magnetic fields up to 32 T are presented. Field dependencies of the transverse magnetoresistance show, except SmIn3, a power-law character with the power exponents equal to 1.4, 1.35 and 1.4 for LaIn3, CeIn3 and PrIn3, respectively. For all the examined compounds the angular dependencies of the transverse magnetoresistance show a clear similarity.

The results of resistivity measurements of monocrystalline PrPb 3 , performed in the temperature range 0.03–2.5 K, are presented. The resistivity shows a large anomaly at 0.4 K which is associated with the Jahn-Teller-type phase transition. However, another anomaly in the resistivity, appearing at 0.8 K, was also observed. The source of this latter anomaly is unknown, but its shape suggests that an ordering process takes place at 0.8 K.

We report experimental results of resistivity measurements on PrPb 3 and LaPb 3 carried out in a temperature range of 7–300 K. A comparison of these data with theoretically calculated effects of scattering processes of exchange and quadrupolar type in PrPb 3 is presented. These studies show strong similarity of the temperature variation of the resistivity calculated for both kinds of scattering. Nevertheless, a dominant role of the quadrupoles in the scattering processes is established.

The REMe3 intermetallics crystallise with the fee, AuCu3 type of crystal structure. There are few series of compounds among them. The most numerous are REPb3, REln3 and REGa3 In the two last decades these systems have attracted a great deal of interest because of their salient feature such as valence fluctuation, superconductivity, magnetic moment formation, crystal field effects or multiaxial magnetic structures. The electronic structure of this family of compounds has been recently intensively studied by investigation of the de Haas-van Alphen effect and similarities in topology of their Fermi surface has been found [1].

We present measurements of the thermal conductivity of both PrSn3 and LaSn3 compounds. We deduce the “magnetic thermal resistivity” Wmag of PrSn3 and show that WmagT exhibits a Log T behavior characteristic of the Kondo effect. The theoretical analysis of the thermal conductivity measurements offers a new method to study the Kondo effect, especially in the case of a praseodymium compound.

We have investigated thermoelectric power of some uranium arsenochalcogenides (UAsS and UAs 1− x Se 1+ x ) and dipnictides (UP 2 , UP 1.7 As 0.3 and UAs 2 ) that crystallise in tetragonal structure and order ferro- and antiferro-magnetically, respectively. The thermoelectric power, S ( T ), is strongly anisotropic for all examined systems. While S ( T ) along c -axis displays a complex behaviour for all the compounds, a broad peak of S ( T ) along a -axis around 60 K has been observed only for the arsenochalcogenides. We ascribe it to be of a Kondo origin. A dependence of the peak behaviour on x is discussed in the frame of the multi-channel Kondo model.

We measured the electrical resistivity, magnetoresistance and de Haas–van Alphen effect in PrSn3. The Kondo effect was confirmed from a negative magnetoresistance and the presence of heavy electrons with the cyclotron effective mass m ∗ C =7.43–9.3 m 0 .

Both, the magnetisation and the magnetoresistivity of a GdIn 3 single crystal have been investigated at 4.2 K in magnetic fields up to 40 T. The magnetisation shows an almost linear dependence on the applied field and reaches a value of only 3.4 μ B /Gd-atom at the highest applied field strength. The magnetoresistance shows a saturation-type of dependence on the field. Both quantities investigated display a distinct anomaly at about 30 T in their field dependencies. A possible origin of this field-induced anomaly will be discussed.

We have observed the de Haas–van Alphen (dHvA) oscillations in SmPb 3 , GdPb 3 , EuPb 3 and YbPb 3 . Detected dHvA branches are discussed on the basis of the result of the FLAPW band calculation.

The temperature dependences of the thermopower of six REIn 3 compounds (RE  La, Pr, Gd, Dy, Er and Lu) were measured in the temperature range up to 1000 K. The observed changes in the slopes of the temperature versus thermopower curves for all the investigated compounds are interpreted as originating from a special shape of the density of states (DOS) near the Fermi energy, E F .

The electrical resistivity of the antiferromagnetic compound GdIn3 was investigated in both the paramagnetic range and the critical region. An increase of the magnetic resistivity with lowering of the temperature was attributed to spin fluctuations. The critical index λ was found to be 0.56 in the region 2 × 10−4

We report the results of resistivity and thermoelectric power measurements of TbIn3 and DyIn3 in temperature range 5K–300K. Both the results are consistent with our previously reported data of the REIn3 compounds with other heavy RE elements and confirm a similarity in electronic properties of the heavy REIn3 compounds.

We report results of the resistivity measurements of HoIn3 and ErIn3 in temperature range 4.2–300 K. A comparison of these data with that for the nonmagnetic LuIn3 indicates a big similarity of these three temperature dependences of the resistivity. An appearance of the spin disorder resistivity for the HoIn3 and ErIn3 is noticed. The resistivity results confirm the existence of an anomaly observed before for the HoIn3 in the ordered phase.

Resistivity of TmGa 3 over paramagnetic range up to 300 K was measured. The magnetic contribution to the resistivity separated exhibits very anomalous behaviour manifested by a pronounced maximum around 30 K. This maximum was interpreted as resulting from the covalent interactions of the crystal field split 4f state with conduction electrons leading to a Kondo — like anomaly of the resistivity. Other possibilities of this anomaly existence have been also discussed.

The resistivity, thermopower and thermal conductivity were measured on single crystals of CeCu2Si2 and CeNi2Ge2 between 60mK and 300 K. All transport anomalies associated with the unstable 4f-shell in Ce are strongly anisotropic in these noncubic systems.

The RECU2Si2(RE=Rare Earth) series shows pronounced anomalies of the lattice parameters. In those stable valent compounds with 4f orbital angular momentumL≠0 thec/a ratio shows an anomalous temperature dependence due to crystal field effects. The compounds with unstable valence (RE=Ce, Eu, Yb) show less or no such effects but on the other hand show anomalies of the volume which are temperature dependent. Using these volume anomalies of the unstable valent systems and the measured bulk moduli of the reference compounds we have extracted the valence as function of temperature.

Single crystals of CeNi2Ge2 and CeCu2Si2 were grown by combining two methods: growth from the melt and the Bridgman method. The dimensions of the plate-like single crystals are in the millimetre range. Both compounds probably melt congruently and the CeCu2Si2 compound shows almost equal lattice parameters for different stoichiometries.

We report the thermopower for the REIn 3 compounds in temperature range between 5 K and 300 K. We show that differences in thermopower observed for compounds containing either light or heavy RE element can be interpreted in terms of differences in topology of their Fermi surface. Beyond the well known anomalies observed in low temperatures the presence of an additional crystal field effect is suggested.

Results of the experimentally found temperature dependence of the magnetic resistivity for PrIn 3 are compared with theoretical data for two possible scattering mechanisms. A good quantitative agreement between theory and experiment is observed at low temperature region in the case of the pure crystal field effected exchange scattering.

The experimentally determined magnetic contributions to the total resistivity of NdIn 3 and NdSn 3 compounds have been compared with those calculated in the first Born approximation. For NdSn 3 the satisfactory agreement between theory and experiment was obtained. In the case of NdIn 3 the coincidence was worse and therefore it was not possible to judge unmistakably about the specific CEF level sequence.

Temperature dependences for four nonmagnetic compounds of the type (La, Lu) Me3 are measured and compared with those calculated according to Gruneisen-Bloch formula. The results show that the lanthanum compounds exhibit more clearly and character of the electrical resistivity than the lutetium ones. Additionally the LaSn3 shows a poor similarity to the simple metal. Ein Vergleich der gemessenen mit den aus der Gruneisen-Bloch-Relation berechneten Werten des Widerstandes wird fur vier nichtmagnetische Verbindungen des Typs (La, Lu)Mc3 durchgefuhrt. Die Ergebnisse weisen darauf hin, das die Lanthanum-Verbindungen einen ausgepragteren d-Charakter des elektrischen Widerstandes als die Lutetium-Verbindungen haben. Die LaSn3-Verbindung weist nur geringe Ahnlichkeit zum einfachen Metall auf.

The effects of 4f electrons on the electric properties of RESn/sub 3/ compounds were examined (RE denotes La, Ce, Pr, or Nd). Results of conductivity measurements performed on single crystals along the STA001! direction at 2 to 300 deg K by dc methods are prcsented graphically and analyzed. (JRD)

The results of electrical resistivity measurements on single crystals of UAsY type compounds in the temperature range from 4.2 to 650 K and in an electric field perpendicular to the [001] axis are presented and discussed. [Russian text ignored].

Electrical resistivity derivative of NdSn 3 , NdIn 3 , SmSn 3 and SmIn 3 has been investigated in the vicinity of Neel temperature. Results were compared with available specific heat data, and a quite satisfactory agreement was observed. Both results indicate the existence of additional phase transitions close to T N . A notable influence of inner strains on the value of the resistivity derivative was observed.

Neutron inelastic scattering experiments have been performed on polycrystalline PrSn 3 to obtain information on the crystal field level structure. The measurements yield the crystal field parameters W = 0.158 ± 0.005 meV and x = 0.80 ± 0.03 which correspond to a Γ 5 ground state with an overall splitting of 74K. The importance of including exchange fluctuations in the data analysis is demonstrated.