Magnetic sextet

Figure 5.5 (bottom left) illustrates that a magnetic field removes all degeneration from the nuclear levels the ground state (spin 1/2) splits into two and the excited state (spin 3/2) splits into four levels. Two of the eight conceivable transitions between these levels are forbidden, and the spectrum consists of six lines, often called a sextuplet or magnetic sextet. Table 5.4 gives the relative intensities of the lines. 

The ferric oxide, hematite, used in the present work was a high purity powder reagent with a BET surface area of 27 m2/g 30 mg was employed in each run. Some measurements were made on hematite calcined in air to see the effects of sintering the surface on the chemical structure of the adsorbed metal ions. The hematite samples were checked by Mossbauer absorption and powder X-ray diffraction measurements. The Mossbauer absorption spectra consisted of a magnetic sextet with no superparamagnetic component due to fine particles ( ). 

Fig 3. The 4,1 K Mbssbauer spectra of horse spleen apoferritin loaded with iron at pH 6,4 as follows (A) with four Fe/molecule, (B) with four Fe/molecule after preloading with 150 Fe, Iron was added as Fe(II) in air and samples were frozen 3 min later. (A> The relaxation subspectrum, a, is due to solitary Fe(III) atoms (B) the magnetic sextet, e, is due to large Fe(III) clusters. Both samples show a central doublet due to small Fe(III) clusters and in B there is a second unresolved doublet due to Fellll) dimers. All the added iron is Fe(III) at 3 min. At 90 K the sextet, e, of spectrum B, collapses into a doublet, but the subspectrum, a, of spectrum A, is also seen at this temperature. Reproduced from Ref 69. 

For the chemical application of Mossbauer spectroscopy, it is not necessary to derive the magnetic splitting explicitly from the M5ssbauer spectrum in order to determine the magnetic flux density. As the separation of any two of the peaks in a magnetic sextet is also proportional to the magnetic flux density sensed by the corresponding nuclei, the basis of the determination of B is usually the separation of the two outermost peaks of the spectrum. 

A further development in the field of Mossbauer spectra fitting and analysis is expected regarding the explanation of applicability of either continuous distributions of quadrupole splitting and hyperfine field or a superposition of discrete quadrupole doublets and magnetic sextets with models of multidomain and multilayer structures of the ferritin iron core. In this case, application of Mossbauer spectroscopy with a high velocity resolution may be used because it leads to a lower instrumental error in the determination of hyperfine parameters (this allows small variations of hyperfine parameters to be distinguished) as well as to a more reliable fitting of complicated Mossbauer spectra (see reviews [32,34-39, 128]). 

NM were similar, yet not identical, to those obtained from ferritin. In the isolated NM, a magnetic sextet was observed at 90 K, indicating larger iron clusters than in ferritin [12]. The sextet observed at 4.2 K also showed a small quadrupole interaction that was not observed in ferritin (Table 16.1). In the spectra of the brain samples, no sextet was observed at 90 K and, therefore, only a small percentage of brain iron in whole tissues may be bound to neuromelanin [5]. However, as most of the iron in the brain is located in the glia and only a very small percentage of it is bound to neurons, iron in neurons may escape detection by MS measurements on whole tissues. This iron in neurons may be bound to neuromelanin or to another iron-storage compound different from ferritin. 

Sfo.sCao.sCoo.sfeo.sOs Sro.5Cao.sCoo,sFeo,s03 5 has an orthorhombic structure and its Mossbauer spectrum (either in EMS or in TMS mode) contains mostly magnetic sextets (Figs. 19.14 and 19.15) [IT]. 

The coexistence of the paramagnetic doubiet and the magnetic sextet in the emission Mossbauer spectra of Lao8Sro2Co03 5 was discussed as a coexistence of two different environments of the investigated transition metal ions below the transition temperature [36]. The Mossbauer spectra showed that below about 2I8 K, only a part of the single paramagnetic subspectrum converts into magnetic sextet the other part of the doublet (which diminishes with... 

The Mossbauer spectra of the as-milled samples at room temperature are shown in Fig. 21.13a and the relevant Mossbauer parameters are shown in Table 21.4. All the spectra show the presence of a hyperfine sextet and a quadrupole doublet. On fitting for discrete Lorentzians, the width of the magnetic sextets is seen to be large compared with the width of Fe inner peak (0.24 mm s ), indicating a distribution in the hyperfine fields. The spectra were therefore refitted using Windows program [40] for hyperfine field distribution (Fig. 21.13b). 

As shown in Fig. 25.14, the lackof direct correspondence between any Mossbauer component and the ferromagnetic component of the bulk ferromagnetism suggests that the latter in these garnets may arise not only from the rare doped magnetic iron ions but also from the crystal defects. While the MD/CF treatment increased the ferromagnetic moment in both samples, the magnetic sextets did not increase in the Mossbauer spectra in the case of x = 0.02, the sextets even shrink to their half. 

Fig. 4.25. Schematic Mossbauer spectra to demonstrate how asymmetric line-widths can arise in a magnetic sextet spectrum. The independent effects of the electric quadrupole interaction and the magnetic dipolar contribution to the hyperfine field are shown separately in (u) and (h) respectively and these effects are summed in (c). An equally probable site has a combined electric quadrupole interaction and magnetic dipolar contribution to the hyperfine field of opposite sign and this spectrum is shown in (d). Sites with both signs of interaction are present in the material and therefore (c) and (d) are added to give the spectrum shown in (e). Finally the distribution in magnitude as well as sign of the interactions is included in the spectrum shown in (/) which models the actual conditions in a real solid. It is seen that the resulting spectrum has linewidths Fj where F, >F4, r2

When the temperature is increasing, one observes a progressive collapse of the magnetic sextet into a single line which can be related to the evolution of the... 

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