CeCu₃Al₂: Incoherent Kondo, or non-Fermi liquid?

A.M. Strydom 

CeCu₅ is a Kondo lattice in which antiferromagnetic ordering occurs at 3.9 K. Substituting Cu with Al to achieve CeCu₃Al₂ results in amplifying the Kondo interaction through addition of conduction electrons, and simultaneously driving the magnetic order down to beyond detection. We present results of specific heat and electrical resistivity that argue for the existence of non-Fermi-liquid behavior founded in a magnetic quantum critical point in CeCu₃Al₂.

Physica Status Solidi B 247, 713-716 (2010).

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Antiferromagnetic ordering and metamagnetism in PrCuSi - Evidence for a tricritical point 

A.M. Strydom

A variety of physical properties measured on the hexagonal rare-earth intermetallic compound PrCuSi are presented. We provide compelling evidence for antiferromagnetic ordering at T_N = 5.1 K in this compound, in contrast to the former claim of ferromagnetic ordering at 14 K. The antiferromagnetic order is, however, found to be unstable in applied magnetic fields, becoming ferromagnetic beyond a metamagnetic transition at a field of 0.7 T at 2 K. It is argued that the magnetism in PrCuSi has the ingredients of a tricritical phase transition at the intersection of paramagnetism, ferromagnetism, and antiferromagnetism. 

European Physical Journal B 74, 9-18 (2010).

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Quantum fluctuations and the magnetic ground state of Ce₃Pd₂₀Si₆

P.P. Deen, A.M. Strydom, S. Paschen, D.T. Adroja, W. Kockelmann, S. Rols 

The temperature and magnetic field dependence of neutron-scattering studies on the heavy fermion compound Ce₃Pd₂₀Si₆ are reported. Inelastic neutron scattering reveals two crystal-field excitations corresponding to the environments of the two distinct rare-earth locations within this cubic compound. Surprisingly, the ground states of the two individual Ce sites are inequivalent with the 4a site having a Γ₇ ground state, while the 8c site reveals a Γ₈ ground state. This is in contrast to the situation found in the analogous compound Ce₃Pd₂₀Ge₆, where the Γ₈ ground state is realized for both Ce sites. In addition, these results reveal an interaction between the 8c and 4a sites previously believed to be absent. The ground state was probed with uniaxial polarization analysis across the region in which field-induced quantum criticality has previously been determined. In zero applied magnetic field no long-range magnetic order could be determined. However, further evidence of field-induced quantum criticality is presented with the observation of diffuse scattering consistent with quantum fluctuations due to nearest-neighbor spin correlations between the two Ce sites.

Physical Review B 81, 064427 (2010). Highlighted as Editors’ Suggestion.

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Hysteretic behavior and magnetic ordering in CeRuSn

J.A. Mydosh, A.M. Strydom, M. Baenitz, B. Chevalier, W. Hermes, R. Pöttgen 

We report the thermodynamic and transport properties of the newly synthesized Ce-intermetallic compound CeRuSn. This ternary stannide possesses an unconventional structure with two Ce sites at room temperature which exhibit different valencies. Just below room temperature there are large thermal hysteretic effects in the magnetic susceptibility, in the specific heat, as well as in electronic and heat transport properties suggesting the formation of an incommensurate charge density wave modulation whose q vector changes as a function of temperature. Our measurements indicate that one site displays magnetic Ce³⁺ behavior while the other is a valence fluctuator. At 2.7 K antiferromagnetic long-range order occurs within one-half of the Ce sites, e.g., the magnetic entropy of the transition is 1/2Rln2. Below T_N a series of metamagnetic transitions takes place in rather small fields (~1–2 T), leaving a magnetically fluctuating background. Such behavior is unique among the many Ce–transition-metal compounds.

Physical Review B 83, 054411 (2011). Highlighted as Editors’ Suggestion.

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Specific heat and μSR study on the noncentrosymmetric superconductor LaRhSi₃

K.V. Anand, A.D. Hillier, D.T. Adroja, A.M. Strydom, H. Michor, K.A. McEwen, B.D. Rainford

We have investigated the superconducting properties of the noncentrosymmetric superconductor LaRhSi₃ by performing magnetization, specific heat, electrical resistivity, and muon spin relaxation (μSR) measurements. LaRhSi₃ crystallizes with the BaNiSn₃-type tetragonal structure (space group I4 mm), as confirmed through our neutron diffraction study. Magnetic susceptibility, electrical resistivity and specific heat data reveal a sharp and well-defined superconducting transition at T_c=2.16±0.08 K. The low-temperature specific heat data reveal that LaRhSi₃ is a weakly coupled bulk BCS superconductor and has an s-wave singlet ground state with an isotropic energy gap of ~0.3 meV, 2Δ₀/k_BT_c=3.24. The specific heat data measured in an applied magnetic field strongly indicate a type I behavior. Type I superconductivity in this compound is also inferred from the Ginzburg-Landau parameter, κ=0.25. Various superconducting parameters, including the electron-phonon coupling strength, penetration depth, and coherence length, characterize LaRhSi₃ as a moderate dirty-limit superconductor. A detailed study of the magnetic field-temperature (H-T) phase diagram is presented and from a consideration of the free energy, the thermodynamic critical field, H_c0, is estimated to be 17.1±0.1 mT, which is in very good agreement with that estimated from the transverse field μSR measurement that gives H_c0=17.2±0.1 mT. The transverse field μSR results are consistent with conventional type I superconductivity in this compound. Further, the zero field μSR results indicate that time-reversal symmetry is preserved when entering the superconducting state, also supporting a singlet pairing superconducting ground state in LaRhSi₃.

Physical Review B 83, 064522 (2011).

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