Korringa slope

J, exchange constant derived from the Korringa slope 5c, Overhauser relaxation rate (relaxation from electrons to ion)... 

A very different behavior of the ESR data has been obtained in the system Sci j Gd Hi.9 investigated by Venturini and Morosin (1977). They studied powdered samples at X-band frequencies in the temperature range 16isostructural phase transition. And indeed, measurements of the lattice constants revealed a low-temperature cell with a slightly smaller volume. 

ScPd definitely belong to this group. The Ag-values are positive and relatively large. The Korringa slopes are large. The alloys Sci- Gd Ag, Sci tGd Cu and Yi j GdiAg are even bottlenecked. The R values scatter around 0.2. 

Table 1 gives a survey of the experimental results (Seipler and Elschner 1977) and fig. 8 shows the Korringa slopes in several CsCl structures as a function of the electronic configuration. A comparison of these experimentally observed ESR systematics, with calculated energy bands and density of states by Kiibler (1978) revealed a remarkable agreement which is nicely documented in table 2 (after Seipler and Elschner 1977). 

Fig. 12. Korringa slopes for the Gd resonance as observed in Sci. Ce AljCGd) vs the cerium concentration jc. In this compound the valency of Ce can be changed continuously by varying the Ce content. Neutron scattering experiments and susceptibility measurements indicate an intermediate valence state of Ce for concentrations 0.05 <0.4 (Preusse et al. 1981).

Fig. 21. Korringa slopes (right scale) and g-values (left scale) of the Yb resonance absorption vs the covalency parameter as observed in YAs and in some yttrium antimonides. From Wienand et al. (1982).

Fig. 26, Korringa slopes characteristic for ESR experiments in monopnictides as a function of the lattice parameter. The squares with numbers indicate the results for mixed compounds (Urban et al. 1978).

The Gd-ESR in the metallic Prins has been reported Ity Davidov et al. (1977). The measurements were performed on powdered samples. The g-value, g = 2.40 0.01, is constant in the temperature range 1.4 < T < 4.2 K. The inferred exchange parameter J(Gd<- Pr) amounts to —1.6meV The linewidth increases linearly for T < lOK with a Korringa slope of 16 5G/K. At higher temperatures, AH rises nonlinearly, reaching values of 1.6kG at 30K. The rapid thermal broadening above lOK is attributed to fluctuations of the host Pr ions at the Gd-resonance frequency. The frequencies which are... 

Fig. 44. Temperature dependence of the Gd-ESR linewidth in Y j.CejAlj Gd. The solid lines were drawn to guide the eye. The dashed iines are extrapolations of the low-temperature Korringa slopes. From Coidea et al. (1987).

Fig. 47. Temperature dependence of the Gd-ESR linewidth in CeAljtGd. The dashed line is an extrapolation of the low-temperature Korringa slope. The open triangles represent the estimated contribution to the linewidth from spin fluctuations only. From Elschner and Schlott (1988).

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