Critical Fields of the "Heavy-Fermion" Superconductor CeCu2Si2

FWN – Publicaties zonder aanstelling Universiteit Leide

Field-induced magnetic transitions in the quasi-two-dimensional heavy-fermion antiferromagnets Ce_{n}RhIn_{3n+2} (n=1 or 2)

We have measured the field-dependent heat capacity in the tetragonal antiferromagnets CeRhIn$_{5}$ and Ce$_{2}$RhIn$_{8}$, both of which have an enhanced value of the electronic specific heat coefficient $\gamma \sim 400$ mJ/mol-Ce K$^{2}$ above $T_{N}$. For $T<T_{N},$ the specific heat data at zero applied magnetic field are consistent with the existence of an anisotropic spin-density wave opening a gap in the Fermi surface for CeRhIn$_{5},$ while Ce$_{2}$RhIn$_{8}$ shows behavior consistent with a simple antiferromagnetic magnon. From these results, the magnetic structure, in a manner similar to the crystal structure, appears more two-dimensional in CeRhIn$_{5}$ than in Ce$_{2}$RhIn$_{8}$ where only about 12% of the Fermi surface remains ungapped relative to 92% for Ce$_{2}$RhIn$_{8}$. When $B||c,$ both compounds behave in a manner expected for heavy fermion systems as both $T_{N}$ and the electronic heat capacity decrease as field is applied. When the field is applied in the tetragonal basal plane ($B||a$), CeRhIn$_{5}$ and Ce$_{2}$RhIn$_{8}$ have very similar phase diagrams which contain both first- and second-order field-induced magnetic transitions .Comment: 15 pages, 4 figure

Thermodynamic properties of the periodic Anderson model:X-boson treatment

We study the specific dependence of the periodic Anderson Model (PAM) in the limit of $U=\infty$ employing the X-boson treatment in two fifferent regimes of the PAM: the heavy fermion Kondo (HF-K) and the heavy fermion local magnetic regime (HF-LMM). We obtain a multiple peak structure for the specific heat in agreement with experimental results as well as the increase of the electronic effective mass at low temperatures associated with the HF-K regime. The entropy per site at low T tends to zero in the HF-K regime, corresponding to a singlet ground state, and it tends to $k_{B}ln(2)$ in the HF-LMM, corresponding to a doublet ground state at each site. The linear coefficient $\gamma(T)=C_{v}/T$ of the specific heat qualitatively agrees with the experimental results obtained for differents materials in the two regimes considered here.Comment: 9 pages, 14 figure

Heat capacity studies of Ce and Rh site substitution in the heavy fermion antiferromagnet CeRhIn_5;: Short-range magnetic interactions and non-Fermi-liquid behavior

In heavy fermion materials superconductivity tends to appear when long range magnetic order is suppressed by chemical doping or applying pressure. Here we report heat capacity measurements on diluted alloyes of the heavy fermion superconductor CeRhIn_5;. Heat capacity measurements have been performed on CeRh_{1-y}Ir_{y}In_5; (y <= 0.10) and Ce_{1-x}La_{x}Rh_{1-y}Ir_{y}In_5; (x <= 0.50) in applied fields up to 90 kOe to study the affect of doping and magnetic field on the magnetic ground state. The magnetic phase diagram of CeRh_{0.9}Ir_{0.1}In_5; is consistent with the magnetic structure of CeRhIn_5; being unchanged by Ir doping. Doping of Ir in small concentrations is shown to slightly increase the antiferromagnetic transition temperature T_{N} (T_{N}=3.8 K in the undoped sample). La doping which causes disorder on the Ce sublattice is shown to lower T_{N} with no long range order observed above 0.34 K for Ce_{0.50}La_{0.50}RhIn_5;. Measurements on Ce_{0.50}La_{0.50}RhIn_5; show a coexistence of short range magnetic order and non-Fermi-liquid behavior. This dual nature of the Ce 4f-electrons is very similar to the observed results on CeRhIn_5; when long range magnetic order is suppressed at high pressure.Comment: 8 pages, 9 figure

SUPERCONDUCTING PROPERTIES OF (La, Nd )Sn3ALLOYS

Des mesures de la température de transition à l'état supraconducteur Tc en fonction de la concentration en Nd et le saut de la chaleur spécifique à Tc montrent que Nd se comporte dans LaSn3 comme un ion trivalent stable dont la dégénérescence est levée par le champ cristallin. comme on n'a pas détecté d'effet de mélange, les résultats confirment l'hypothèse que la diminution initiale relativement forte de Tc ne peut être expliquée par une interaction d'échange isotropique des spins.Measurements of the superconduction transition temperature Tc vs Nd concentration and the jump of the specific heat at Tc show that Nd in LaSn3 behaves as a stable crystal-field split trivalent ion. Since no hybridization effects have been found, the results support the assumption that the relatively large initial depression of Tc cannot be explained by isotropic spin exchange interaction

Schwere Fermionen und Kohaerenz in Kondo-Gittern: Spezifische Waerme niederenergetischer Anregungen in CER-Systemen

SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

CRYSTAL-FIELD EFFECTS IN (La, Nd)Sn3

Des mesures de chaleur spécifique et de la résistivité électrique des alliages (La, Nd)Sn3 à l'état normal sont présentées. En accord avec des résultats récents sur les propriétés supraconductrices, nos résultat confirment l'absence de l'effet Kondo et peuvent révéler les niveaux de champ cristallin de Nd3+ dans LaSn3We report measurements of the specific heat and the electrical resistivity of (La, Nd)Sn3 alloys in the normal state. In agreement with recent results on the superconducting properties our data confirm the absence of the Kondo effect and can reveal the crystal field scheme of Nd3+ in LaSn3