Static susceptibility data

Figure 5.8 Static magnetic data for the Er(trensal) complex in the case of a powdered sample and an oriented single crystal measured in parallel or perpendicular direction to the C3 rotation axis, (a) Temperature dependence of the magnetic susceptibility...

Fig. 10.14 Measured static susceptibilities for Na and K solutions in NH3 and the calculated spin susceptibility of a set of independent electrons at 240 K (solid line). The diamagnetic contribution of the NH3 molecules has been eliminated from the measured total susceptibility by using the Wiedemann rule. Since the total susceptibility is quite small in concentrated solutions, the errors may be large. O represent data of Huster (1938) on Na solutions at 238 K represent K-NH3 data of Freed and Sugarman (1943) at the same temperature and + represent data of Suchannek et al. (1967) at room temperature for Na-NH3 solutions. From Cohen and Thompson (1968).

Fig. 4. The concentration dependence of various electronic properties of metal-ammonia solutions, (a) The ratio of electrical conductivity to the concentration of metal-equivalent conductance, as a function of metal concentration (240 K). [Data from Kraus (111).] (b) The molar spin (O) and static ( ) susceptibilities of sodium-ammonia solutions at 240 K. Data of Hutchison and Pastor (spin, Ref. 98) and Huster (static, Ref. 97), as given in Cohen and Thompson (37). The spin susceptibility is calculated at 240 K for an assembly of noninteracting electrons, including degeneracy when required (37).

Figure 49. Susceptibility spectra for propylene carbonate (Tg — 160 K) as measured by depolarized light scattering (top, data from Ref. 372) and dielectric spectroscopy (bottom, data from Ref. 9), each normalized by a temperature-independent static susceptibility. The full lines are fits from solutions of a two-component schematic MCT model. The dashed fines indicate a white noise spectrum. The dash—dotted line in the upper panel exhibits the asymptote of the critical spectrum. The dotted line shows the solution of the model at T — Tc with hopping terms being neglected. (From Ref. 380.)...

Data for 0-(BEDT-TTF)2I3 [20,98] are also included in Fig. 19. Ru is positive and falls sharply below 20 K. Fortune et al. [99] attribute this fall to the effect of a phase transition at 23 K (possibly a SDW) and suggest that the latter causes a reduction of about 50% in the electronic density of states. This is the reason put forward for the lower superconducting transition temperature (Tsc = 1.5 K) of the ambient pressure 0L phase compared with the pH phase, which is stable above 0.5 kbar and has Tsc = 8 K. However, in contrast to this, Bulaevskii [3] attributed the suppression of to the larger disorder, corresponding to a residual resistivity of about 170 pilcm, which is larger than for other (BEDT-TTF)2X superconductors. So more experiments are needed to verify the above hypothesis. Susceptibility anisotropy measurements may be useful in this respect, because they are more sensitive to the formation of a SDW than the static susceptibility of randomly oriented single crystals (Fig. 4, Section IV). 

One of the first applications of electron spin resonance (ESR) spectroscopy to catalysis was in a study of the chromia-alumina system, and during the last five years or so a number of publications have appeared dealing with this subject. The ESR spectra of supported chromia catalysts have been interpreted in terms of various chromium ion configurations or phases, each of which wiU be discussed below. It will be seen that these data substantiate many of the conclusions drawn from the magnetic susceptibility data described above, and, in addition, they provide a deeper insight into the molecular structure of chromia-alumina catalysts than can be obtained from static susceptibility measurements alone. This body of research serves as a very good illustration of the potential usefulness of ESR spectroscopy to the catalytic chemist, particularly when one considers that all of the data to be discussed below were obtained on poorly crystallized, high surface area powders, typical of practical catalysts. 

A thermally populated triplet excited state of the triclinic form of (KS03)2N02 has been detected by e.p.r. and static susceptibility measurements. The crystal structure of HK2NO6S2 has been redetermined from three-dimensional neutron-diffraction data. The reaction of SO2 with molybdate ions in aqueous solution... 

With these characteristics of relaxation in normal metals in mind, let us now consider the behavior of the dynamic, nonuniform susceptibility in a low-density metal approaching the critical region. It follows from the foregoing discussion that, within the Stoner model, the Korringa ratio T7 should decrease as the static enhancement increases. This can be tested directly with the NMR data for cesium. It is evident in Fig. 3.6 that the prediction of the Stoner model is not borne out—17 increases in the low-density region where the static susceptibility enhancement also increases. Thus, we are again led to the conclusion that the susceptibility enhancement in the low-density metal is of a fundamentally different character than that of the normal, dense metal near T . 

Most other work yield somewhat higher values of y (Berton et al. 1982, Barbara et al. 1981). Careful ac and dc susceptibility measurements were performed on the amorphous manganese aluminosilicate spin glass with 15 atom% Mn by Beauvillain et al. (1984b). The ac susceptibility data are fitted with a series expansion in even powers of an applied static field up to the fourth term in order to obtain Afni( )> resulting in y = 3.1 0.1 and jS = 1.4 0.1. 

The static susceptibility x iQfi F) derived from neutron scattering data may be in disagreement with the direct measurement of the static bulk susceptibility, which, by definition, corresponds to the Q=0 value, i.e., (0,0,r). Because of the form factor discussed earlier, part of the electron waveftmctions (the free-electron part) will contribute to the bulk susceptibility, but not to the neutron signal at finite Q (see Liu 1989 for a discussion of this point). In addition, there may be correlations between the localized part of the response function which cause oscillations in a fimction of Q. 

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