[en] Carbon and Germanium resistors have been calibrated against a standard in the temperature range from 4K to 40K. From the data, values of temperature are obtained with 0,1% error (std deviation). These calibrations have been also checked against specific heat measurements. (author)

[en] The magnetic behaviour of 80 Ce-binary compounds is correlated with the minimum Ce-Ce spacing (D) in the lattice. Among the magnetically ordered compounds, three regions can be defined: I) with D smaller than the trivalent Ce diameter, where all the compounds order antiferromagnetically, with fractional entropy and large values of γ and θ_p. II) With 3.7amgstron < D < 4.1amgstron, which includes the ferromagnetic compounds, and III) with D > 4.1amgstron, where most of the compounds order antiferromagnetically with full entropy. The compounds which do not order magnetically (region IV) are distributed in two ranges of energy: < 10K for the heavy fermions and > 100K for the intermediate valent ones. Spin fluctuation effects are observed in the compounds with large D values and small volume contraction. (Author)

[en] A comparative study of the stability of a Shastry-Sutherland lattice (SSL) in Ce₂Pd₂Sn under different physical conditions is presented. Applied magnetic field suppresses the SSL of stoichiometric Ce₂Pd₂Sn in a magnetic critical point at T_cr(B) = 4.2K and B_cr = 0.13 T, whereas 25% of Ni does it at T_cr(Ni) = 3.4 K. Electronic concentration variation, driven by the increase of Pd (holes) concentration in Ce₂Pd_2+yIn_1-y, decreases the magnetic transition down to T_M = 2.8 K in the limit of the alloy solubility, i.e. y = 0.4. The existence of a M(B) plateau in SSL predicted by theory and the crossing of those isotherms, previously observed in the model compound SrCu₂(BO₃)₂ are analyzed.

[en] The absence of magnetic order in Rare Earth-based frustrated compounds allows to recognize the action of the third law of thermodynamics in the low temperature behavior of those systems. One of the most relevant findings is the appearance of a coincident specific heat $C_m/T{|}_{T\to 0}\approx 7\mathrm{J}/{\mathrm{molK}}^2$ ‘plateau’ in six Yb systems. This characteristic feature occurs after a systematic modification of the thermal trajectory of their entropies $S_m(T)$ in the range of a few hundred milikelvin degrees. Such behavior is explained by the formation of an entropy-bottleneck imposed by the third law constraint ($S_m{|}_{T\to 0}\ge 0$), that drives the system into alternative ground states. Based in these finding, three possible approaches to the $S_m{|}_{T\to 0}$ limit observed in real systems are analyzed in terms of the ${\partial }^2{S}_m/\partial T^2$ dependencies.

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No abstract available

[en] The fcc-Ce₃In compound is presented as the best available approximation to reproduce the main magnetic properties of γ-Ce at low temperatures, where such pure phase does not exist. The electronic specific heat shows a maximum at 18K and an anomaly at 2.2K, with an entropy of 0.8Rln at 32K. The susceptibility shows a broad maximum at 1.8K, while in the magnetization there are no trace of ordering up to 18 Tesla at 1.5 and 4.2K. The experimental results are interpreted as governed by a quadruplet crystal field ground state, which undergoes a quadrupolar transition at 18K. At lower temperatures a heavy fermion ground state developes with C_el/T = 500 mJ/Ceat.K² for T → 0 and χT/C_el = 0.ll emu K/J for T < 5K. (Author)

[en] CePd_1_-_xRh_x undergoes a continuous evolution from ferromagnetic order in CePd to an intermediate-valence (IV) ground state for CeRh. Close to the disappearance of magnetic order at x_c_r ∼ 0.87 unusual behavior of the ac susceptibility and the specific heat was observed. It was explained with a broad distribution of local Kondo temperatures T_K from below 2 K to above 50 K due to the disorder introduced by Pd-Rh exchange. The thermopower S is very sensitive to Kondo scattering even for diluted 4f systems. In Ce compounds a large positive maximum in S(T) is usually observed around T_K. We studied S(T) in CePd_1_-_xRh_x in order to evaluate the presence of Kondo scattering and the involved energy scales. Pure CeRh shows typical IV behavior with a large maximum at 220 K and small values at low T. Already 5 % Pd substitution leads to a strong enhancement of the low-T thermopower. Even larger values are found around x_c_r, while the high-T maximum shifts only moderately. Our results are in line with the existence of low (local) Kondo scales in the presence of IV behavior at high Rh content x > x_c_r. For lower Rh content a decreasing (average) Kondo scale is found.

[en] A recent investigation of the low temperature properties of the paramagnetic heavy fermion system CeRuSi revealed an anomalous decrease of the coefficient C/T below 6 K, indicating a second low energy scale well below the Kondo temperature of about 50 K. We started an investigation of this unusual behavior using the local probe ²⁹Si-NMR. Here a preliminary ²⁹Si field sweep NMR study in the temperature 4.2-200 K is reported. ²⁹Si-NMR powder spectra obtained at 72.9 MHz could be simulated and shift components ²⁹K_ab(T) and ²⁹K_c(T) were determined. The shift along the basal plane ²⁹K_ab(T) shows the expected behavior with a Curie-Weiss dependence at high T merging in a constant value below 15 K. In contrast the shift along the tetragonal axis reveals an anomalous T dependence below 15 K where ²⁹K_c(T) drops by a factor of 2, confirming the presence of a further low T energy scale. We suspect this drop to be related to the anomalous decrease of C/T below 6 K and discuss possible mechanism.