Dense Kondo Effect Research Articles

Samarium monoxide epitaxial thin film as a possible heavy-fermion compound

SmO (001) epitaxial thin films were grown on $\mathrm{YAl}{\mathrm{O}}_{3}$ (110) substrates by pulsed laser deposition method. X-ray photoemission spectroscopy indicated coexistence of $\mathrm{S}{\mathrm{m}}^{2+}$ and $\mathrm{S}{\mathrm{m}}^{3+}$, suggesting a valence fluctuating state. A SmO thin film showed a metallic conductionlike SmO polycrystal in a previous study. However, a SmO thin film showed nonmonotonical temperature dependence at low temperature in contrast with the polycrystal. A local resistivity minimum was observed at 16 K, probably caused by the dense Kondo effect, and the resistivity below 2 K was proportional to ${T}^{2}$. These features suggest the heavy-fermionic nature of SmO.

High Temperature Expansion for the Quadrupolar and the Octupolar Interactions

The moment method for high temperature expansion (HTE) is applied to the coexistent system of interactions of ( O y z , O z x , O x y ) quadrupole moments and of T x y z octupole moment, both of which are indispensable for discussing the properties in phase I and II of CeB 6 . The moments for HTE have been calculated up to fourth order exactly to give rise to the free energy and up to sixth order relevant to the susceptibility. The results are compared with those from the constant coupling approximation (CCA) to discuss the applicability of the CCA and HTE approximations. Comparison with the experimental results in phase I is also made to reveal the necessity of the interactions between the other moments to explain the properties of phase I, besides the dense Kondo effect being probably effective as well.

Combination of Dense Kondo Effect and RKKY Interaction in CeCuSb2, Investigated by NMR

A combination of the dense Kondo effect and Ruderman–Kittel–Kasuya–Yoshida interaction exhibited by an antiferromagnetic (AF) heavy-Fermion compound CeCuSb 2 ( T N =8 K) was investigated with the magnetic susceptibility χ and 63 Cu magnetic resonance measurements in the temperature range between 1.4 and 210 K. For temperatures above ∼25 K, characteristics of the localized 4 f spins are observed in the Curie–Weiss-type behavior of the Knight shift K and the strongly enhanced relaxation rate T 1 -1 . For the temperature below ∼25 K, the χ data tend toward a constant value, which is an indication of the onset of the heavy-Fermion state. The slope of the Knight shift versus susceptibility ( K -χ) plots decreases below ∼100 K, which is ascribed to the difference in the anisotropic hyperfine coupling to the crystal-field-split Γ 7 (ground state) and Γ 8 (excited state) wave functions of the Ce ions. The K -χ plots below ∼25 K exhibit another deviation from the linearity in opposite direction. We speculate that ...

Magnetic properties of the dense Kondo compound PrSn 3

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〉.

Systematic composition dependence in YbCu 5− xAu x from dense Kondo to antiferromagnetic system through quantum critical point around x=0.2–0.4

Temperature and magnetic field variations of the electric resistivitiy ( ρ) as well as temperature dependence of the magnetic susceptibility ( χ) are reported for the YbCu 5− x Au x system with the C15b-type structure. These results indicate a systematic composition dependence from dense Kondo to RKKY antiferromagnetic system via quantum critical point with x=0.2–0.4. The logarithmic temperature dependence of ρ was observed in the middle temperature range for all the compositions, implying that the incoherent Kondo scattering is dominant in this T-region. With decreasing temperature, the ρ tends to saturate, makes a maximum, then decreases toward the Fermi liquid ground state due to the coherent dense Kondo effect ( x<0.2), or toward the antiferromagnetic ground state due to the RKKY interaction (for x>0.4). The non-Fermi liquid behavior was observed around the quantum critical composition ( x=0.2–0.4).

Magnetic and Electrical Properties in a Dense Kondo Compound PrSn3

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.

Low-temperature specific heat of Ce xLa 1− xB 6

We have measured low-temperature specific heat of Ce x La 1− x B 6. No indication of long-range ordering was found in the specific heat of Ce x La 1− x B 6 ( x=0.6 and 0.5) within the limits of the accuracy of the measurements. On the other hand, a clear indication of long-range ordering (phase IV) was found in the case of Ce 0.65La 0.35B 6. The ground state of Ce x La 1− x B 6 in the low-temperature and low-field region would change from phase IV to a non-magnetic state at the critical Ce-concentration 0.6< x c<0.65 as a result of the competition between the intersite interactions and the dense Kondo effect.

Dense Kondo states in Pd-Ce intermetallic compounds under high pressure

The electrical resistivity of Pd-Ce intermetallic compounds, Pd 5Ce 3, Pd 4Ce, has been measured under high pressures up to 10 GPa. It is found that the resistivity increases with the external pressure for all these intermetallics. The increase is due to the dense Kondo effect. Intermetallics with a higher concentration of Ce have a greater ratio of the resistivity-increase to pressure. However, a high-pressure X-ray diffraction experiment showed that the compressibility of the intermetallics is the same. These results suggest that the influence of pressure on the dense Kondo effect depends not only upon the Ce concentration but also on the local environment of Ce.

External pressure enhancement of the dense Kondo effect in a PdCe intermetallic compound

In order to clarify the effect of external pressure on the dense Kondo state, we have measured the electrical resistivity of a PdCe intermetallic compound in the temperature range 77–300 K under several pressures up to 7 GPa. The changes in electrical resistivity and lattice volume with pressure have been also examined at room temperature. It was found that the resistivity ratio of PdCe at room temperature increases with pressure P gradually to R(P) R(P a) = 1.75 until it reaches 7.7 GPa, where P a is the ambient pressure, and then shows a rapid increase to 2.5 at about 8.5 GPa, while the lattice volume decreases monotonically with pressure over the whole range up to 9.5 GPa. The resistivity ratio R(T) R(T R) at low temperatures T increases significantly as the pressure is raised. These experimental results show that the dense Kondo effect in PdCe is strongly enhanced by external pressure.

The dense Kondo effect in ternary intermetallic compounds CeNiAl

The electrical resistivity, magnetic susceptibility and specific heat of CeNiAl 4 and CeNi 2Al 5 have been measured. It is found that the orthorhombic CeNiAl 4 is a new dense Kondo compound in a valence-fluctuation regime and is nonmagnetic above 1.6 K. A broad peak in the resistivity is observed at a fairly high temperature, around 130K, which reflects the coherence of the Kondo scattering. The orthorhombic CeNi 2Al 5 is also a new dense Kondo compound with a Néel temperature of 2.6 K. The maximum of the resistivity is observed at 4.0 K.

Magnetic specific heat of light rare earth Heusler compounds RInCu 2, (R [dbnd]La, Ce, Pr, Nd and Sm)

For the metallic compound LaInCu 2, the Debye temperature Θ D and the electronic specific heat coefficient γ are obtained, 183 K and 2.04 mJ/(mol K 2), respectively. Anomalous behaviour due to a dense Kondo effect is observed for CeInCu 2. PrInCu 2 is nonmagnetic down to 1.5 K. In PrInCu 2, a Schottky-type anomaly is observed. In the NdInCu 2 and SmInCu 2 compounds, antiferromagnetic phase transitions are observed at 2.0 and 3.7 K, respectively.

Intermediate valences of Ce and electrical resistivity changes of Pd-Ce intermetallic compounds

The changes in Ce valence and electrical resistivity have been studied for several intermetallic compounds of Pd-Ce. The Ce valence estimated from L3-XANES spectra varies smoothly with Ce concentration, with the exception of H-Pd5Ce. The extraordinarily low Ce valence of the H-Pd5Ce was interpreted in terms of the local configuration of Ce atoms in its crystal structure. The Ce valence of the Pd-Ce intermetallic compounds showed little variation with temperature. The resistivities of H-Pd5Ce and Pd3Ce have negative temperature coefficients below room temperature, suggesting that the dense Kondo effect becomes distinct in Pd-Ce alloys with the Ce valence close to 3.2.

Approximation to the Heavy Fermion State from the Dense Kondo Effect (25 Years of the Kondo Effect)

Approximation to the Heavy Fermion State from the Dense Kondo Effect (25 Years of the Kondo Effect)

Electrical Resistivity,Magnetization and Specific Heat Measurements on Stable Trivalent Compound Ce2Zn17

Experimental results of electrical resistivity, magnetization and specific heat on single crystal specimens of Ce 2 Zn 17 have been reported and analyzed by means of a single ion Hamiltonian model. There appeared a sharp peak in the specific heat due to a phase transition from paramagnetic to antiferromagnetic states. The antiferromagnetic state was characterized as a lower-dimensional Ising-type. It became clear that the crystal field had a substantial effect on the magnetic susceptibility and the electrical resistivity. There was no evidence of the dense Kondo effect for the electrical resistivity. These experimental results show that Ce 2 Zn 17 is a rare cerium compound with the stable valence.

γ-γ Perturbed angular correlation study of dense Kondo effect in Ce compounds

Abstract The relaxation of Ce 4f spins due to the Kondo effect was studied by γ - γ perturbed angular correlations of 140 Ce in (La-Ce)Si 2 , (La-Ce)Si 1.8 and (La-Ce)Al 2 . The deduced T K has a weak dependence on Ce concentration showing the single site character of the effect.