scholarly journals Thermoelectric Power of Gd4(Co-A)3 Compounds (A = Cu, Pt)

2012 ◽  
Vol 730-732 ◽  
pp. 159-163
Author(s):  
Teresa M. Seixas ◽  
Manuel A. Salgueiro da Silva ◽  
Hans F. Braun ◽  
Georg Eska
Keyword(s):  
Low Temperature ◽  
Thermoelectric Power ◽  
Phonon Scattering ◽  
Positive Maximum ◽  
Spin Disorder ◽  
Structure Changes ◽  
Power Measurements ◽  
Electron Band Structure ◽  
Electron Phonon Scattering

We report on a comparative study of thermoelectric power measurements (S(T)) in ferrimagnetic Gd4(Co1-xAx)3 compounds with A = Cu, Pt, in the temperature range 8 K – 300 K. Whereas in Gd4Co3S(T) is always negative, for x > 0 the substitution of Co for Cu/Pt gives rise to the appearance of a low temperature positive maximum in S(T) at around 30 K. Based on our previous study of Gd4(Co1-xCux)3 compounds, we argue that this maximum in S(T) originates from electron-magnon scattering and is sensitive to electron band structure changes resulting from the substitution of Co for Cu/Pt and the accompanying reduction in the ratio between the electron-magnon and the electron-phonon scattering strengths. The decreasing role of Co 3d electrons with the progressive substitution of Co for Cu/Pt, evidenced by a strong reduction in the spin disorder resistivity and the Co magnetic moment, is seen to be crucial for the existence of such low temperature maximum in S(T) for x > 0. It is seen that the substitution of Co for Pt leads to higher values of the amplitude and temperature of the positive maximum in S(T) than the substitution of Co for Cu.

The transport properties of the cubic alkaline earths Ca, Sr, and Ba

1978 ◽  
Vol 56 (1) ◽  
pp. 161-174 ◽  
Author(s):  
J. G. Cook ◽  
M. J. Laubitz
Keyword(s):  
Large Deviations ◽  
Transport Properties ◽  
Thermoelectric Power ◽  
Phonon Scattering ◽  
Thermal Resistivity ◽  
Elastic Electron ◽  
Phonon Drag ◽  
Alkaline Earths ◽  
Conductivity Function ◽  
Electron Phonon Scattering

The electrical resistivity (ρ), thermoelectric power(S), and thermal conductivity (κ) of two Sr samples and two Ba samples have been determined from 30 to 300 K. Large deviations from Matthiessen's rule (DMR) were observed. The estimated transport properties for ideally pure Sr and Ba indicate that these elements, like Ca, show large deviations from the Bloch–Gruneisen form for ρ(T) at all temperatures, large and positive diffusion thermopowers with a negative phonon-drag contribution, and large deviations from the Wiedemann–Franz relationship (DWFR). In these respects, they are much more like the transition metals than the monovalent metals.In the second, analytical, portion of the paper we study the DWFR in some detail. First, the effect of lattice conduction is estimated, and found to be large. Then, a function X(E) of the electron energy, closely related to the conventional conductivity function σ(E), is estimated from the ρ and S data now available for Ca, Sr, and Ba above 300 K, and used to compute S and the Lorenz function for elastic electron–phonon scattering below 300 K. Comparison with the experimental data indicates that the energy dependence of the electron parameters is responsible for the electronic DWFR, and effects the diffusion thermoelectric power. Such 'band effects' may also be seen in the thermal resistivity due to inelastic scattering in at least Sr. Regrettably, we are not able to explain the observed DMR.

Spin Disorder Resistivity and Electronic Specific Heat of Gd4(Co1-xCux)3 Compounds

2008 ◽  
Vol 587-588 ◽  
pp. 333-337
Author(s):  
T.M. Seixas ◽  
M.A. Salgueiro da Silva ◽  
O.F. de Lima ◽  
J. Lopez ◽  
Hans F. Braun ◽  
...  
Keyword(s):  
Specific Heat ◽  
Linear Dependence ◽  
Magnetic Moments ◽  
Spin Fluctuations ◽  
Electronic Specific Heat ◽  
Spin Disorder ◽  
Structure Changes ◽  
Thermal Disorder ◽  
Specific Heat Coefficient ◽  
Electron Band Structure

In this work, we present a study of the spin disorder resistivity ( ρm∞) and the electronic specific heat coefficient ( γ) in Gd4(Co1-xCux)3 compounds, with x = 0, 0.05, 0.10, 0.20, 0.30. The experimental results show a strongly non-linear dependence of ρm∞ on the de Gennes factor which, in similar intermetallic compounds, is usually attributed to the existence of spin fluctuations on the Co 3d bands and its amplification by the thermal disorder of the Gd magnetic moments through the Gd-Co exchange coupling. Using a novel combined analysis of ρm∞ and γ, we show, however, that only electron band structure changes are involved in the anomalous behaviour of ρm∞ and that a linear dependence of ρm∞ on the de Gennes factor is obtained when the variation of the effective mass is properly taken into account.

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