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Abnormal magnetic properties of the Ce24Co11 hexagonal phase
No full textThe lighter rare earth-cobalt and thorium-cobalt binary systems were revised on the rare earth or thorium side, by metallographic, electron microprobe and X-ray methods. In agreement with previous works, it is confirmed that, in these systems, the first intermetallic compound corresponds to the following stoichiometry: 3:1 for trivalent La, Pr and Nd; 7:3 for tetravalent Th; 24:11 for Ce. The electronic structure of Ce in the hexagonal (P63mc) Ce24Co11 phase was investigated via magnetic susceptibility measurements in the 4.2–1300 K temperature range. The results show that the Curie-Weiss law is not followed, no magnetic order occurs down to 4.2 K and a very small change in the thermal behaviour of the magnetic susceptibility appears above the melting point of the phase (750 K). The abnormally low values of the magnetic susceptibility of Ce24Co11 could be understood by assuming Co is a non-magnetic state and Ce in a temperature dependent mixed valence state
Thermodynamic properties of the CeSn3 mixed valence compound
No full textWe have measured on the CeSn3 compound, the expansion coefficient between 80 and 800 K at normal pressure, the isothermal compressibility in the 0–8 GPa pressure range at room temperature and the heat capacity at constant pressure in the 60–300 K temperature range. The experimental data were compared with those previously found for the isomorphous LaSn3 phase, assumed as a proper reference material for the study of the intermediate valency states in CeSn3. Both the thermal expansion (3α) and the isothermal compressibility (k) of CeSn3 show behaviours quite different from those of LaSn3: for instance, in the standard conditions, 3α is 55 × 10−6K−1for CeSn3 and 38 × 10−6K−1for LaSn3; k is 15 × 10−12 Pa−1 and 12 × 10−12 Pa−1 respectively for CeSn3 and LaSn3. The thermal behaviour of the molar specific heat at constant pressure of CeSn3 is similar to that of LaSn3 for temperatures lower than 50 K. In the 70–300 K temperature range, the heat capacity of CeSn3 is clearly higher than that of LaSn3, ΔCp being maximum near 150 K. The analysis of the calorimetric data show that the electronic coefficient γ of CeSn3 is temperature dependent: its value varies from 53 mJ K−2 mole−1 at low temperature 24 mJ K−2 mole−1 at 300 K
Thermodynamics and magnetic properties of LaPb3 and CePb3
No full textThermal expansion coefficient between 77 and 900 K, isothermal compressibility in the 0–8 GPa pressure range, magnetic susceptibility between 1.3 and 800 K and the heat capacity at constant pressure in the 20–300 K temperature range were determined for the LaPb3 and CePb3 compounds. Both the thermal expansion (3α) and the isothermal compressibility (kT) of the two phases show behaviours similar and free from singularities. In the standard conditions 3α is 53 × 10−6 K−1 for LaPb3 and 60 × 10−6 K−1 for CePb3; kT is 5.3 × 10−12 Pa−1 and 8.6 × 10−12 Pa−1 respectively for LaPb3 and CePb3. The magnetic susceptibility measurements show that in LaPb3 there is no evidence of a localized magnetic moment on the La atoms, and in CePb3 the magnetic moment localized on the Ce atoms is 2.32 μB, close to that one expected for Ce3+ ions. The thermal behaviours of the molar heat capacity at constant pressure and the calculated Cν+γT values, at high temperatures, are very similar for the two compounds. At low temperatures, an anomalous enhancement of the electronic contribution to the specific heat (γ) found for CePb3 is interpreted as an evidence of the possible occurrence, in the phase, of a Ce valence fluctuation at low temperatures
High temperature heat capacity of the LaSn3 and CeSn3 compounds
No full textThe high temperature heat capacities of LaSn3 compound and CeSn3 intermediate valence compound have been obtained from enthalpic contents measurements, using the technique of drop calorimetry in the 400–1200 K temperature range.
The heat capacity behaviour of CeSn3 has been compared with that of LaSn3 and the quantitative difference between the two trends is explained in terms of residual promotional energy of the 4ƒ electron of Ce to the conduction band
Magnetic susceptibility of intermediate valent CeRh and heavy fermion Ce24Co11 intermetallic compounds
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X-RAY IRRADIATION AS AN IMPROVEMENT TECHNIQUE FOR OXYGEN ORDERING AND ENRICHMENT OF YBa2Cu3O7-x SINGLE CRYSTALS
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