Average hyperfine field

The results of these modeling studies are shown in Figures 2 and 3> The value of ic (anisotropy constant) was chosen so that the average particle radius determined from the reduction in the average hyperfine field splitting due to collective magnetic excitations... 

McCammon et al. have studied fine nickel particles using Ni Mossbauer spectroscopy [22]. The measured average hyperfine field of 10 nm particles at 4.2 K was 7.7 T for nickel foil, it was found to be 7.5 T. Application of an external magnetic field of 6 T caused a reduction of the hyperfine splitting to 1.5 T as a consequence of the negative hyperfine field at Ni nuclei. 

Fig. 32. Average hyperfine fields in various Fe-base intermetallics versus the corresponding average Fe moments. The full line (which passes through the origin) corresponds to 14.8 T//ib. (After Van Noort e ...

Fig. 7. Concentration dependence of the average magnetic moments pVs. (circles) and pMn (squares) for (Fe,, Mn <)2Y alloys from the average transition metal moment and the average hyperfine field assuming hyperfine field and magnetic moment to be proportional (Besnus et al. 1982).

The extremely narrow ESR Une (Fig. 9.23a) could be made use of to measure the hyperfine coupling of the conduction electronen to the nuclear spins [35] due to the polarisation of the nuclear spins in the appUed magnetic field Bq, the average hyperfine field of aU the nuclear spins is superposed onto the applied field and leads to a smaller shift Avpsii of the ESR resonance frequency vesr in comparison to the ESR resonance frequency without hyperfine coupling or without nuclear-spin polarisation ... 

Fig. 94. Results from Mossbauer effect studies on the RSG system AuFe 16.8atom%. Top Average hyperfine field H T) at zero applied field Bottom Peak-intensity ratio versus temperature measured at = 20 kOe (see text) (from Lauer and Keune 1982).

These relationships were initially considered as promising complementary means to characterize goethite in natural samples. From the most probable hyperfine field Bp or better, the average hyperfine field Bav, either the A1... 

At very low temperatures the sextet of ferrihydrite exhibits broad lines with a rather symmetrical hneshape (Fig. 3.7). At 4 K the average hyperfine field amounts to between 46 and 50 T [67], with a small quadrupole shift 2s between —0.02 and —0.1 mm/s. The spectra are usually slightly asymmetric in which in particular the 6th line is less deep than the first one. This has been attributed to the presence of additional tetrahedral iron sites [68], although this is still in doubt and correlation effects between B in the distribution on the one hand, and A and/or d on the other hand, which are normally expected in largely disordered structures, may similarly produce such an asymmetry. 

In paramagnetic solids, an important consideration arises from the fact that the correlation time Tq of the ionic spin fluctuations is shorter than the characteristic nuclear precession time t in the effective hyperfine field of (18.9). Thus, Tc < T, or Tc > ASIh. Under this condition, the nuclear moment senses only the average hyperfine field which is proportional to the average value of the spin. 

At pH 2.5 the oxide surface is positively charged and ferric ions are present in dilute solution (lO moir ) as [Fe(OH2)f,] (70%), [Fe(OH)(OH2)5] + (20%), [Fe(OH)2(OH2)4] (3%) and [Fe2(OH)2(OH2)5] (6%). Mossbauer spectra of the suspension (Figure 9.3a), which exhibit a sexluplet, show that all adsorbed ferric ions interact magnetically with the substrate. The parameters of the adsorbed ions (isomeric shift, average hyperfine field) are very similar to those of solid hematite. Within the adsorbed layer, ferric ions occupy sites characteristic of the stmcture of hematite, and hence the layer is an extension of the crystalline network of the... 

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