Hyperfine field, magnetic

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)...

For fiB 2KV, there is only one energy minimum, i.e. there is no energy barrier between different magnetization directions [57], and the fluctuations of the magnetic hyperfine field can therefore be considered fast compared to Tm- The induced magnetic hyperfine field is then proportional to the induced magnetization. Using... 

The magnetic hyperfine field of iron atoms is usually opposite to the magnetization, and therefore... 

Fig. 6.15 Induced magnetic hyperfine fields, estimated from the spectra in Fig. 6.14, as a function of the reciprocal applied magnetic field. The full lines are linear fits in accordance with (6.20). The dotted line is a fit to the Langevin function. (Reprinted with permission from [58] copyright 1985 by the American Chemical Society)...

Numerous experimental studies have shown that the magnetic hyperfine field of magnetic nanoparticles varies linearly with temperature at low temperatures, in accordance with (6.23). This is in contrast to bulk materials for which the decrease in the hyperfine field with increasing temperature in accordance with spin wave... 

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)...

The magnirnde and sign of the magnetic hyperfine field in the nickel spinel compounds NrFe204 (Fig. 7.8), NiCr204 (Fig. 7.9), NiFeo.3Cr1.7O4, NiRh204, and... 

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... 

Steiner et al. have measured the magnetic hyperfine field of and in iron... 

Fig. 7.50 Magnetic hyperfine field //hf in Ni-W-alloys at the W-site as a function (a) of the tungsten concentration and (b) of the average magnetic moment (from [238])...

Since natural Au consists solely of Au, the interface-selective enrichment technique cannot be applied in Au studies. The absorber thickness for Au is required to be large and therefore multilayered samples of Au layers/3r/ metal layers have to be prepared. The spectra for Au/Fe with varying Au-layer thickness are shown in Fig. 7.83 [437]. The results were interpreted as follows large magnetic hyperfine fields at Au sites exist only within two monolayers at the interface region, which are supposed to be induced by direct coupling with anti-ferromagnetically oriented Fe 3d atoms. 

The spin state of a paramagnetic system with total spin S wiU lift its (25 + l)-fold degeneracy under the influence of ligand fields (zero-field interaction) and applied fields (Zeeman interaction). The magnetic hyperfine field sensed by the iron nuclei is different for the 25 + 1 spin states in magnitude and direction. Therefore, the absorption pattern of a particular iron nucleus for the incoming synchrotron radiation and consequently, the coherently scattered forward radiation depends on how the electronic states are occupied at a certain temperature. 

Mineral Colour Most intense X-ray lines IR bands (cm 1) Magnetic hyperfine field (T) ... 

The magnetic hyperfine field (Bhf) decreases as structural Al increases. This is to be expected because the diamagnetic Al does not contribute to the magnetic field. Since, however, Bhf (T) is also reduced as the crystal size decreases (even at 4 K), both Al substitution and crystal size (here represented by mean coherence length perpendicular to (111), MCLm, in nm) must be combined to account for the variation of Bhf satisfactorily, (Schwertmann Murad, 1983) i.e. 

Fig. 3.9 Effect of Al-substitution in synthetic hematites on (Left) the unit cell edge length a of hematites synthesized at various temperatures (Stanjek Schwertmann, 1992, with permission), and (Right) the magnetic hyperfine field Bhf of hematites formed at 70 °C and 1000°C dotted lines indicate 95% confidence limits (Murad Schwertmann 1986 with permission).

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).

Morris et al. (1991) obtained hematite of very small particle size ( 10 nm), termed nanophase by slow thermal decomposition in air of tri-Ee -acetato-hy-droxy-nitrate. XRD shows only two broad lines as in a 2-line ferrihydrite, but the magnetic hyperfine field at 4.2 K of 50.4 T appears to be more in agreement with poorly crystalline hematite. Well-crystalline hematite and Al-hematite were produced by decomposing Ee-Al-oxinates at 700 °C (da Costa et al. 2001). 

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).

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