Time-resolved thermal lens measurements of the thermo-optical properties of glasses at low temperature down to 20 K

In this work the time resolved thermal lens spectrometry was applied to measure the absolute values of the thermo-optical properties of low silica calcium aluminosilicate and soda lime glasses at low temperatures, in the range between 20 and 300 K. The thermal relaxation calorimetry was used as a complementary technique to determine the specific heat. The results showed a marked decrease of the thermal diffusivity with the temperature rise, with a dependence similar to that of the mean free path (similar to T-1) in the interval between 20 and 70 K, while in the range between 70 and 300 K the dependence was T-(0.33 +/- 0.02). The marked variation of the temperature coefficient of the optical path length change with the temperature rise was attributed to the increase in the coefficient of the electronic polarizability. The results also showed that for the aluminosilicate glass the excess in the specific heat correlated to the so-called boson peak occurred at about 17 K, higher than that of soda lime, which occurs at about 12 K. In conclusion, our results showed the ability of the time resolved thermal lens to determine the thermo-optical properties of glasses at low temperatures, bringing possibilities for experiments in a wide range of optical materials.712

Magnetic properties of the U(Ge1-xNix)(2) system

Magnetic results for the U(Ge1-xNix)(2) series of compounds with x=0.1, 0.2, 0.3, and 0.4 are reported. For xless than or equal to0.2 the system is ferromagnetic with T-c close to 52 K. For the remaining samples we found a spin-glass ground state with T-f around 30 K. The specific heat for the x=0.3 sample present an anomaly at 50 K, which does not seems to be of magnetic origin. We discuss the results in terms of the possible formation of the compound U2NiGe3. (C) 2003 American Institute of Physics.931037825782

Transition from Kondo to intermediate valence regime in (La1-x,Ce-x)Ni: an ESR study

We report on electron spin resonance (ESR) results for the series of compounds (La1-xCex)Ni doped with Gd. We show that from the Gd g-value and linewidth one can determine the concentration x(c) where the system goes from Kondo single impurity to Kondo lattice (and intermediate valence) regimes. The observed behaviour in both the g-value and the slope of the linewidth-T curves is explained using the indirect interaction between Gd and Ce moments. The calculation leads to the determination of the Ce-Gd exchange parameter J(Ce-Gd) = 4.8 meV and the Ce-conduction electron exchange parameter \J(f-s)\ = 19 meV, for x=1.10439763976

ELECTRON-SPIN-RESONANCE OF AU-YB THIN-FILMS - CRYSTAL-FIELD EFFECTS AND THE KONDO DILEMMA

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Effect of volume variation on the properties of the Kondo system (La1-xCex)(3)Al

We have measured the electrical resistivity and ac magnetic susceptibility (chi)(T) of (La1-xCex)(3)Al, for 0 less than or equal to x less than or equal to 1, and the electrical resistivity of (Ce1-zYz)(3)Al, for 0 less than or equal to z less than or equal to 0.1. The system was characterized using x-ray diffraction and metallography. From x-ray data we were able to determine the structure for all samples to be hexagonal and that the unit-cell volume decreases linearly in going from the La-rich side to the Ce-rich side. The results show that La3Al is a superconductor below 6.2 K a:nd that T-c decreases rapidly with the increase of the Ce concentration. For x > 0.04 we observed a minimum in the resistivity and a reduction of the effective magnetic moment of Ce due to a strong compensation promoted by the Kondo effect. Our results show that the Kondo temperature increases with Ce and Y concentration, according to the reduction of the unit-cell volume. We also show that the antiferromagnetic transition temperature goes through a maximum at z = 0.025, indicating that there is an interplay between superconductivity, antiferromagnetic ordering, and the Kondo effect. A diagram illustrating the evolution of the T-K and T-N is :presented. The electronic specific heat (gamma) increases with the Ce concentration showing a maximum around x approximate to 0.4. It was also possible to determine values for the rho J product and the relative variation of the exchange parameter.57105900590

Change of the Kondo regime in CePd2Al3 induced by chemical substitution: Verification of the Doniach diagram

We report on measurements of specific heat and resistivity for the series of compounds (La1 - xCex)Pd2Al3, for 0 less than or equal to x less than or equal to 1. The chemical substitution with La promotes an increase of the unit cell volume, which is responsible for the changes observed for the ground state of the system. The resistivity results show two distinct behaviors: the Kondo single impurity for low Cc concentration and the Kondo lattice regime for the other end. From the magnetic specific heat results we estimated the Kondo temperature (T-K) Our results show that T-K increases monotonously with Ce concentration but with a strong variation of the Neel temperature. We also estimated the s-f exchange parameter and density of states for the whole series of compounds. A Doniach type diagram is presented including the literature data obtained from pressure experiments. [S0163-1829(99)02313-9].59138738874

Unusual behavior of the Kondo temperature of La1-xYbxCu3Al2

Electrical-resistivity (rho), specific-heat (c), and magnetization (M) measurements were carried out for the series of compounds La1-xYbxCu3Al2(O less than or equal tox less than or equal to1). The resistivity results show two regions with a -1n T behavior, with different slopes that allows an estimation of the crystal-field (CF) splitting. Starting at x = 1, the susceptibility is reduced to x = 0.4, and this can be explained by the CF effect. Using the specific-heat and magnetic-susceptibility data, we were able to determine the Kondo temperature (T-K), the crystal-field splitting, and the Debye temperature (theta (D)) for the whole series. T-K was found to increase with the Yb concentration and with the corresponding unit-cell volume contraction. This behavior suggests the increase of the product \Jn(E-f)\ when the volume is reduced. This is the same trend found in Ce compounds, which is unusual for Yb compounds.6316art. no.16511

Temperature dependence of the Cr3+ site axial distortion in LiSrAlF6 and LiSrGaF6 single crystals

The electron spin resonance (ESR) of Cr3+ in LiSrAlF6 (LiSAF:Cr) and LiSrGaF6 (LiSGaF:Cr) single crystals has been measured in the temperature range between 270 and 470 K. The external magnetic field orientation dependence of the spectra is described by a spin Hamiltonian of axial symmetry for both compounds. The value of the zero-field splitting axial parameter (D) for LiSGaF:Cr decreases from 6.60 x 10(-2) cm(-1) to 5.60 x 10(-2) cm(-1), while for LiSAF:Cr it increases from 1.30 x 10(-2) cm(-1) to 1.60 x 10(-2) cm(-1) for increasing temperature. The larger values of D obtained for LiSGaF:Cr show that the distortion of the octahedral Cr site is greater in this compound, in agreement with x-ray diffraction results reported in the literature.13368435844

Study of the magnetic and calorimetric properties of (U1-xRx)Cu5Al (R = La and Y)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)We have investigated the magnetic and thermodynamic properties of the (U1-x)Cu5Al (R = La and Y) series. The results show a quick decrease of T-N for both La and Y substitutions. For the Y series with concentration between 0.3 <= x <= 0.4, the temperature dependence of the specific heat and magnetic susceptibility below 10 K are consistent with a non-Fermi-liquid regime. (C) 2009 Elsevier B.V. All rights reserved.4041931763178Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Faepex, Brazilian agenciesFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

ESR OF ND+3 IN TYPE-II SUPERCONDUCTORS

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