Hyperfine-interaction parameters

However, when it comes to the simulation of NFS spectra fi om a polycrystalline paramagnetic system exposed to a magnetic field, it turns out that this is not a straightforward task, especially if no information is available from conventional Mossbauer studies. Our eyes are much better adjusted to energy-domain spectra and much less to their Fourier transform therefore, a first guess of spin-Hamiltonian and hyperfine-interaction parameters is facilitated by recording conventional Mossbauer spectra. 

One must beware of confusions in nomenclature. Owen and Thornley (11) use a and instead of A and y. Hubbard and Marshall (26) used to denote / and this convention has been followed in some neutron diffraction studies. Use of A to denote fractional spin transfers however, can lead to confusion with the hyperfine interaction parameters determined experimentally by magnetic resonance. 

Alternatively, Fe-M6ssbauer spectroscopy is an extremely powerful technique for spin-transition studies on iron(II) compounds. The different iron(II) spin states are unambiguously identified on the basis of the hyperfine interaction parameters allowing us to evaluate directly Whs-... 

ENDOR measurements of the transferred hyperfine interaction parameters A, (all in MHz) for the nearest fluorine neighbours of two divalent lanthanide ions substituting for Ca in CaFj. The measurements on Eu are by Baker and Hurrell (1963), and on Tm by Bessent and Hayes (1965). Hyperfine constants for the two europium isotopes are given in table 3 for Tm the ENDOR measurements of Bessent and Hayes give g = ( + )3.443(2), A = (-)l 101.376(4)MHz, for the single stable isotope of mass 169 I =2). 

Nuclear hyperfine interaction parameters for the lanthanide metals in degrees Kelvin. (Conversion factor - 1 MHz = 0.047994 mK) Note The signs are given for those cases only where the sign can be unambiguously determined. 

Even at 4 K the nuclear contribution dominates the heat capacity of holmium by about 85%. Thus Krusius et al. (1969) in measurements below 0.6 K were essentially looking at Cn only, and obtained the hyperfine interaction parameters given in table 5.2. These parameters agree fairly well with those of van Kempen et al. (1964), whose Cn results showed considerably more scatter, although Krusius et al. (1969) felt that the fit to their own results was not as good as for the other lanthanides they have measured. The results of NMR (Mackenzie et al. 1974) give slightly lower parameter values. 

TABLE 12.1 Hyperfine Interaction Parameters Obtained from Zero-Field Conventional Fe Mossbauer Parameters Fe NFS Spectra Compared with the ... 

Both NFS and Mossbauer results on oxidized Pf DI4C Fd are very similar with the Mossbauer data on oxidized 4Fe Fd from 6. stearothermophilus [52]. Here, four iron sites were used to fit the Mossbauer data. The obtained quadrupole splittings at4.2 K were - -1.50, -H. 20, -H. 10, and -1-0.66 mm s. The corresponding isomer shifts were 0.42,0.43,0.42, and 0.42 mm s . The asymmetry parameter r] of the first two sites was 0.7, and of the second two sites was 0.9. The similarity of the hyperfine interaction parameters of these two oxidize ferredoxins indicates that the [4Fe-4S] " clusters in these two proteins are very similar in structural and electronic environments. 

EuRu2Si2 and EuRu2Ge2 are antiferromagnets with the Neel temperatures of 78 K and 63 K, respectively (Felner and Nowik 1984, 1985). The values of the hyperfine interactions parameters for EuRu2Ge2 indicate, that at 4.1 K the Eu spins are in the basal plane. Due to low magnetic anisotropy, small fields are sufficient to saturate the magnetization (Felner and Nowik 1985). 

Fig. 1.8 Mossbauer spectrum obtained from Nd2Fei4B at room temperature. Spectrum consists of six different sextets that correspond to Fe at six different atomic sites. Hyperfine interaction parameters like l/hf> relative aria contribution can be determined from the...

By the observation of quantum beat Q, one can determine the details on the nuclear levels, from which the hyperfine interaction parameters are evaluated precisely. 

Poppl A, Kevan L. 1996. A practical strategy for determination of proton hyperfine interaction parameters in paramagnetic transition metal ion complexes by two-dimensional HYSCORE electron spin resonance spectroscopy in disordered systems. J Phys Chem 100 3387-3394. 

More then 99.5% of all applications of Mossbauer spectroscopy are connected with hyperfine interaction parameters and structure factor determinations. An example of a sophisticated application is the study of the low temperature properties of magnetic impurities in metals that have an antiferromagnetic exchange interaction (Kondo effect). In order to study the very low temperature behaviour of a Kondo system, Mossbauer spectroscopy was used on two typical Kondo systems, Fe Qu and Fe Au. The first system (Fe Qu) showed expected Kondo-type properties - an extra polarization in the electron gas due to the correlations produced by the Kondo effect. The Fe Au system, on the other hand, exhibited quite unexpected and striking results incompatible with those for Fe Cu. In brief, in Fe Au the temperature dependence of the susceptibility differed for T > 10 K from that for T < 10 K, yielding... 

Figure 11 The histograms of iron content S in different phases of different subiayers (sampie i) as function of the iower border of the subiayers. The sampie is an iron fiim about - 50 nm thick, sputtered on the beryiiium disk 10 mm thick. 1 sextet of a-Fe 2, broadened sextet with smaiier magnetic spiitting than in a-Fe 3, asymmetric strongiy broadened sextet associated with hyperfine interaction parameters for a-FeOOH 4, the doubiet.

Fig. 1 Comparison of the CAS and uncontracted PCFI convergence patterns of the electric quadrupole hyperfine interaction parameter as a function of the size ( niax) orbital active set...

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