Magnetic hyperfine field, Mossbauer

Fig. 6.2 Theoretical Fe Mossbauer relaxation spectra for longitudinal relaxation with the indicated relaxation times and with a hyperline field that can assume the values 55 T. The symmetry direction of the axially symmetric EFG is assumed parallel to the magnetic hyperfine field. (Reprinted with permission from [9] copyright 1966 by the American Physical Society)...

Fig. 6.17 The average magnetic hyperfine field at low temperatures, obtained from Mossbauer spectra of coated and uncoated 8 nm particles of a-Fe203 (Fig. 6.16). The lines are linear fits to the data in accordance with (6.23) and (6.25). (Reprinted with permission from [77] copyright 2006 by the American Physical Society)...

Radioactive Ru is dilutely doped in Fe304. The value of the magnetic hyperfine field (at the Ru nucleus) obtained by TDPAC at 10 K (—16 T) is essentially in agreement with that derived from the Mossbauer spectrum at 5 K (14.5 T). The negative sign of means that the Ru ions... 

Fig. 7.5 Room temperature Mossbauer spectra and distributions of magnetic hyperfine fields for four goethites, decreasing in crystallinity from a to d (Murad, 1982a, with permission).

Fig. 17.3 Magnetic hyperfine field (left) and width of the outer lines of the sextets (right) obtained from Mossbauer spectra of ferritins, isolated from human spleen, limpet hemolymph and bacterial cells Pseudomonas aeruginosa) as a function of temperature (Webb St.Pierre, 1989 with permission).

In case of Fe, the resonant absorption of 14.4keV y-rays emitted by a radioactive Co source is measured. The spectra are determined by the hyperfine interactions (isomer shift, quadrupole sphtting, and magnetic hyperfine field) of the Mossbauer nucleus caused by the surrounding electron shell. 

Figure 6 Temperature dependence of the magnetic hyperfine field Shf(T) of a-Fe as a function of T/T with being the Curie Temperature. Note that Shf (T) is scaled with the value extrapolated to 0 K which is denoted as Shf (0). The dots represent Mossbauer data and the solid line represents saturation magnetization data. (Redrawn after Greenwood and Gibb. With kind permission from Springer Science Business Media)...

Figure 7 Mossbauer spectrum of nanometer-sized metallic iron particles in zeolite NaX obtained at T = 4.2K before (A) and after (B) subtraction of two Fe(ll) contributions with Si = 0.75 mm s and AEqi = 0.8 mm s (5% relative contribution) and S2 = 0.85 mm s and AEq2 = 1.85mms (6% relative contribution). The analysis of the magnetic hyperfine field distribution identifies metallic a-Fe-nanoparticles. (From Schiinemann, Winkler, Butzlaff and Trautwein. With kind permission from Springer Science Business Media)...

Figure 9 Mossbauer spectra of metallic iron nanoparticles in zeolite NaX taken at T = 77 K and different external fields (a). The analysis of the field dependence of the magnetic hyperfine field according to equation (21) yields a mean particle size of <7 = 2.1 0.1 nm (h). (Reprinted from Schimemann )...

Low-spin iron(III) ions have an electron hole in the t2g orbitals. Therefore, these centers have S = 1/2 and spin-orbit interaction contribntes considerably to the magnetic hyperfine field. Low-spin iron(III) componnds in solution always show a rather complicated magnetic Mossbauer pattern at temperatures around 4.2 K and low external fields, which means that the relaxation rate of these centers is lower than the nnclear precession rate of 10 s. Sometimes a magnetic sphtting is observed even at 77 K. Therefore, in order to pin down 8 and A g, it is advisory to measure between 100 and... 

Fe Mossbauer spectra of the mature teeth (Fig. 18) showed two components with different magnetic hyperfine field splitting values. Whereas the major component gave six-line magnetically split spectra characteristic of stoichiometric goethite (a-FeOOH) at all tempera-... 

Method 3 produces ca. 3 g of hematite. The sample prepared in 2 10 M HCl consists of subrounded crystals between 30-50 nm across (Fig. 10-1 c) with a surface area of around 30 m /g. In 10 M HCl the crystal size is around 150-200 nm (Fig. 10-1 d) and the surface area is only a few m /g. The X-ray peaks of the 0.002 M HCl product are somewhat broader than those of the material produced in 10 M HCl owing to the smaller crystal size. The Mossbauer spectrum at RT (Fig. 10-4) shows a sextet corresponding to a magnetic hyperfine field of 53.3 T. 

Measurements of the magnitude of the magnetic Hyperfine Field by Mossbauer spectroscopy revealed small values at small interatomic distances and much larger values at... 

Additionally, it was proposed that reaction 19 occurred only in the outermost 3-4 atomic layers of the magnetite crystallites. The MOssbauer spectrum of the catalyst in the reduced form agreed with this substitution. The spectral parameters of the tetrahedral cations were unaffected by the substitution, whereas the isomer shift and magnetic hyperfine field of the octahedral cations decreased. Also, the line width of the octahedral cations increased relative to an unsubstituted catalyst. Finally, the spectral area ratio of the iron cations in the tetrahedral to octahedral sublattices decreased. 

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