Spin fluctuation temperature

However, the intra-atomic Coulomb interaction Uf.f affects the dynamics of f spin and f charge in different ways while the spin fluctuation propagator x(q, co) is enhanced by a factor (1 - U fX°(q, co)) which may exhibit a phase transition as Uy is increased, the charge fluctuation propagator C(q, co) is depressed by a factor (1 -H UffC°(q, co)) In the case of light actinide materials no evidence of charge fluctuation has been found. Most of the theoretical effort for the concentrated case (by opposition to the dilute one-impurity limit) has been done within the Fermi hquid theory Main practical results are a T term in electrical resistivity, scaled to order T/T f where T f is the characteristic spin fluctuation temperature (which is of the order - Tp/S where S is the Stoner enhancement factor (S = 1/1 — IN((iF)) and Tp A/ks is the Fermi temperature of the narrow band). 

Figure 8. The spin-fluctuation temperature, Tsf, of UPt3 as a function of the pressure-induced relative change in the c/a ratio a comparison is made with the shift in Tsf by the relative change in the c/a ratio induced by substituting Pt by Pd and Th in U( Pt,Pd)3, respectively data from ref.[35].

Although we shall include the CeSi, compounds with x > 1.9 within the nonmagnetic systems (region IV), the borderline as a function of x is not unequivocal. Specific heat measurements performed under a magnetic field in the x = 1.85 and 1.9 compounds shows the occurrence of a hump at about 3.5 K, with a very low associated entropy, which is mainly gained in the spin-fluctuation temperature region (Dhar et al. 1987). Similar behaviour was observed in CeSnj (Ikeda and Gschneidner... 

ICF interconfiguration fluctuation 7 sf magnetic spin-fluctuation temperature... 

SF magnetic spin fluctuation temperature A exp experimental magnetic moment... 

In the event that the amount of hybridization is too strong for the exchange hamiltonian to be an adequate starting point for a theoretical description of the Kondo-like anomalies in the physical properties, the characteristic temperature is often identified with a spin fluctuation temperature T,f which has the obvious definition Tsf = h/keTsf. In this view, Tjt, rather than Tk, is a boundary which separates high temperature (compared to Tsf) magnetic behavior from low temperature nonmagnetic behavior. 

Indeed, an earlier investigation of the ThCe system revealed that the depression of TJT with n followed a modified exponential relation of the form T o/Tcd = exp[-An/(l-Dn)], while the depression of ACIACo with TJTc conformed to the linear BCS law of corresponding states (Huber and Maple, 1970). The modified exponential relation for TJT vs n was derived theoretically by Kaiser (1970) for matrix-impurity systems in which the impurities contribute localized d or f states which are nonmagnetic in the sense of the Friedel-Anderson model (i.e., ttAIU > 1) A and D can be related to the Friedel-Anderson parameters Ni Ep) and U which characterize the localized d or f state. On the basis of thermoelectric power measurements. Cooper and Rizzuto (1973) have suggested that the characteristic spin fluctuation temperature of the ThCe system is of the order of 10 K. Measurements of the lattice constant as a function of relative Th-Ce composition indicate that the valence of Ce is 3.25 in the ThCe system up to 20at.% Ce (Harris and Raynor, 1%4). 

To maybe considered as Kondo temperature Tk, spin fluctuation temperature Tsf, and so forth. F(T, V) relates the two strongly temperature-dependent quantities Xy and Cy but is relatively weakly dependent on temperature. Taking into account this fact and that for real solids F is often roughly constant over a wide range of temperatures, F has often been referred to as "the Griineisen constant." But in some solids such as HF... 

The paramagnons change the physical properties of the system in much the same way as damped phonons do. The scale on which these changes occur is determined by a characteristic temperature, the spin-fluctuation temperature , given by... 

Hrebik and Coles (1977) determined a spin-fluctuation temperature of 150 K. From the coefficient A (40 x 10" iQcm/K ) in the relation p = Po + AT we estimated the spin-fluctuation temperature to be 27 K. It would be interesting to investigate whether in the temperature variation of the thermopower a minimum in the low-temperature region exists, as in spin-fluctuation systems hke UAlj, YC02, LUC02, etc. 

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