A correlation between specific heat and the ratioTK/TN in magnetic Kondo lattices

Besnus, M.J.; Braghta, A.; Hamdaoui, N.; Meyer, A.

doi:10.1016/0304-8853(92)90630-7

Cited by 80 publications

(45 citation statements)

References 12 publications

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“…Further, we observe that even at 6.5 K, which is above the T c , the magnetic entropy S mag ∼ 0.75R ln 2 which is considerably lower than that of R ln 2 expected for a magnetic doublet ground state. The reduced value of S mag together with moderately large value of γ suggests that the Kondo effect is weak but sizable in this compound and the RKKY interaction dominates leading to a magnetically ordered state below 5.1 K. The Kondo temperature T K can be estimated from the mean field theoretical universal plot of jump in specific heat ∆C mag vs. T K /T m obtained by Besnus et al 36 and Blanco et al 37 for Ce-based Kondo lattice systems. For the observed ∆C mag = 6.16 J/mol K at T c = 5.1 K for our compound we find T K /T c ≈ 0.83 from this universal plot.…”

Section: Resultsmentioning

confidence: 92%

Ferromagnetic ordering in CeIr2B2: Transport, magnetization, specific heat, and NMR studies

et al. 2012

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We present a complete characterization of ferromagnetic system CeIr2B2 using powder x-ray diffraction XRD, magnetic susceptibility χ(T ), isothermal magnetization M (H), specific heat C(T ), electrical resistivity ρ(T, H), and thermoelectric power S(T ) measurements. Furthermore 11 B NMR study was performed to probe the magnetism on a microscopic scale. Rietveld refinement of powder XRD data confirms that CeIr2B2 crystrallizes in CaRh2B2-type orthorhombic structure (space group fddd ). The χ(T ), C(T ) and ρ(T) data confirm bulk ferromagnetic ordering with Tc = 5.1 K. Ce ions in CeIr2B2 are in stable trivalent state. Our low-temperature C(T ) data measured down to 0.4 K yield Sommerfeld coefficient γ = 73(4) mJ/mol K 2 which is much smaller than the previously reported value of γ = 180 mJ/mol K 2 deduced from the specific heat measurement down to 2.5 K. For LaIr2B2 γ = 6(1) mJ/mol K 2 which implies the density of states at the Fermi level D(EF ) = 2.54 states/(eV f.u.) for both spin directions. The renormalization factor for quasi-particle density of states and hence for quasi-particle mass due to 4f correlations in CeIr2B2 is ≈ 12. The Kondo temperature TK ∼ 4 K is estimated from the jump in specific heat of CeIr2B2 at Tc. Both C(T ) and ρ(T ) data exhibit gapped-magnon behavior in magnetically ordered state with an energy gap Eg ∼ 3.5 K. The ρ data as a function of magnetic field H indicate a large negative magnetoresistance (MR) which is highest for T = 5 K. While at 5 K the negative MR keeps on increasing up to 10 T, at 2 K an upturn is observed near H = 3.5 T. On the other hand, the thermoelectric power data have small absolute values (S ∼ 7 µV/K) indicating a weak Kondo interaction. A shoulder in S(T ) at about 30 K followed by a minimum at ∼ 10 K is attributed to crystal electric field (CEF) effects and the onset of magnetic ordering. 11 B NMR line broadening provides strong evidence of ferromagnetic correlations below 40 K.

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Section: Resultsmentioning

confidence: 92%

Ferromagnetic ordering in CeIr2B2: Transport, magnetization, specific heat, and NMR studies

et al. 2012

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“…From the discussion above, we assume that the Kondo-impurity scale is 0.26 K or less. This scale is given by (2J N 0 )), where N 0 is the unrenormalized density of electronic states that we obtain from the Sommerfeld coefficient γ = 5 mJ mol We also can compare T K estimated above with a molecular field calculation for a spin-1/2 resonant level model [15]. With the experimentally observed specific heat jump ( C mag ∼ 5.2 J mol −1 K −2 ) at T N , this model gives a ratio of T K /T N ∼ 1, which is consistent with our previous estimates and the expectation of small Kondo and magnetic interaction energy scales.…”

Section: Resultsmentioning

confidence: 98%

Weak coupling magnetism in Ce₄Pt₁₂Sn₂₅: a small exchange limit in the Doniach phase diagram

Lee¹,

Kurita²,

Ho³

et al. 2010

J. Phys.: Condens. Matter

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Magnetic susceptibility, magnetization, specific heat, and electrical resistivity studies on single crystals of Ce 4 Pt 12 Sn 25 reveal an antiferromagnetic transition at T N = 0.19 K, which develops from a paramagnetic state with a very large specific heat coefficient (C/T ) of 14 J mol −1 K −2 -Ce just above T N . On the basis of its crystal structure and these measurements, we argue that a weak magnetic exchange interaction in Ce 4 Pt 12 Sn 25 is responsible for its low ordering temperature and a negligible Kondo-derived contribution to physical properties above T N . The anomalous enhancement of specific heat above T N is suggested to be related, in part, to weak geometric frustration of f -moments in this compound.

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“…Furthermore, the entropy recovery at 300 K is 15.67 J/mole K, which is close to Rln6 = 14.87 J/mole K, indicating that the overall CEF splitting is smaller than 300 K, in agreement with our INS study discussed in Sec. III F. We have made an estimate of the Kondo temperature T K of CeRhGe 3 using the method described by Besnus et al, 32 where in the mean-field approach, the jump in the heat capacity C mag of a Kondo system is related to T K /T N . The estimate of T K through this model agrees well with the experimental data on various Ce and Yb compounds.…”

Section: 31mentioning

confidence: 99%

Muon spin relaxation and neutron scattering investigations of the noncentrosymmetric heavy-fermion antiferromagnet CeRhGe3

et al. 2012

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The magnetic ground state of CeRhGe 3 has been investigated using magnetic susceptibility, heat capacity, neutron diffraction, muon spin relaxation (µSR), and inelastic neutron scattering (INS) techniques. Our µSR study clearly reveals the presence of two frequencies below T N2 = 7 K and three frequencies between 7 K and T N1 = 14.5 K, indicating long-range magnetic ordering of the Ce 3+ moment. The temperature dependence of the highest frequency follows a mean-field order parameter. Our powder neutron diffraction study at 1.5 K reveals the presence of magnetic Bragg peaks, indexed by the propagation vector k = (0, 0, 3/4) with the Ce 3+ magnetic moment ∼0.45(9) µ B along the c axis. INS studies at 18 K (i.e., above T N1 ) show the presence of two well-defined crystal-field (CEF) excitations at 7.5 and 18 meV. At 10 and 4.5 K, a very small increase has been observed in the CEF excitation energies. At 100 K, both CEF excitations broaden and a broad quasielastic component has also been observed. Further, the low-energy INS study reveals the presence of a nearly temperature-independent quasielastic linewidth between 16 and 60 K, which indicates a Kondo temperature T K = 12.6(3) K. The presence of well-defined CEF excitations in CeRhGe 3 suggests local moment magnetism and may explain the absence of pressure-induced superconductivity. Analyzing the INS data based on a CEF model, we have evaluated the CEF ground-state wave functions and ground-state moment. The observed small value of the ordered moment along the c axis, deduced from the neutron diffraction data, contrasts with the ab-plane moment direction predicted by the single-ion CEF anisotropy and indicates the presence of two-ion anisotropic magnetic exchange interactions, which govern the direction of the moment.

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A correlation between specific heat and the ratioTK/TN in magnetic Kondo lattices

Cited by 80 publications

References 12 publications

Ferromagnetic ordering in CeIr2B2: Transport, magnetization, specific heat, and NMR studies

Ferromagnetic ordering in CeIr2B2: Transport, magnetization, specific heat, and NMR studies

Weak coupling magnetism in Ce₄Pt₁₂Sn₂₅: a small exchange limit in the Doniach phase diagram

Muon spin relaxation and neutron scattering investigations of the noncentrosymmetric heavy-fermion antiferromagnet CeRhGe3

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A correlation between specific heat and the ratioTK/TN in magnetic Kondo lattices

Cited by 80 publications

References 12 publications

Ferromagnetic ordering in CeIr2B2: Transport, magnetization, specific heat, and NMR studies

Ferromagnetic ordering in CeIr2B2: Transport, magnetization, specific heat, and NMR studies

Weak coupling magnetism in Ce4Pt12Sn25: a small exchange limit in the Doniach phase diagram

Muon spin relaxation and neutron scattering investigations of the noncentrosymmetric heavy-fermion antiferromagnet CeRhGe3

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Weak coupling magnetism in Ce₄Pt₁₂Sn₂₅: a small exchange limit in the Doniach phase diagram