Paramagnetic hyperfine spectra

It will be obvious that there are close similarities between the ordered magnetic and disordered paramagnetic hyperfine spectra. The hyperfine fields originate in similar ways, and the angular properties of the transitions... 

This phenomenon is appropriate to the paramagnetic hyperfine spectra of magnetically dilute iron phases, and contrasts with the magnetically concentrated rare-earth paramagnetic hyperfine spectra where the effective-field approximation holds. However, it is possible to revert to the former situation by magnetic dilution. This has been shown in erbium ethyl sulphate diluted with the corresponding yttrium salt [138]. The hyperfine tensor was already known from e.s.r. data to be less anisotropic than usual, and the spec-... 

DyaOa contains two distinct Dy sites, but these are not clearly distinguished in the MOssbauer spectrum. The paramagnetic hyperfine spectrum features only slight motional narrowing at 20 K, which implies an unusually long relaxation time [109]. 

The paramagnetic hyperfine spectrum at 4-2 K of ErCl3.6H20 has five well-resolved lines for th Er and Er. This is illustrated in Fig. 17.22 ... 

Fig. 17.23 The spectrum at 4-2 K of a sample of (Er2 Y97 6) (C2HsS04)3.9H20 showing the unequally spaced lines of the paramagnetic hyperfine spectrum caused by a breakdown of e effective-field approximation. [Ref. 138, Fig. 1]...

The paramagnetic hyperfine spectrum of Yb in YbCl3.6H20 at 4-2 K is a well-resolved quintet from the 0+ - 2+ 76-5-keV transition [187]. Comparison with the analogous °Yb data gave = 0-994(15)... 

R.C. Bray, F.M. Pick, and D. Samuel, Oxygen-17 hyperfine splitting in the electron paramagnetic resonance spectrum of enzymically generated superoxide. Eur. J. Biochem. 15, 352-355 (1970). 

Only brief details are available for anhydrous iron(III) sulphate it gives a paramagnetic spectrum at room temperature [111] with a chemical isomer shift of 0-39 mm s and a quadrupole splitting of 0-60 mm s" [9]. A sharp magnetic hyperfine spectrum is seen at 1-8 K with a field of 550 kG [98]. 

The orthochromite, DyCrOa, is paramagnetic above the Neel temperature of 2-16 K, but at 4-2 K a well-resolved magnetic hyperfine spectrum is seen because of a long paramagnetic relaxation time [107]. The parameters (Table... 

In paramagnetic substances, it is necessary to compare tr with tl If tr < < tl so that the orientation of the electronic spins fluctuates very rapidly, the internal magnetic field seen by the nucleus will average to zero and there will be no magnetic interactions. This appears to be the case with the ferrous hemoglobins and one observes unbroadened, nearly symmetric, quadrupole doublets. If on the other hand tr > > TL, magnetic hyperfine interactions can occur and one may expect line broadening and perhaps even a fully resolved hyperfine spectrum. 

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