Hyperfine field

NNS and NNS denote reference to Eu nuclei In the N planes and S planes, respectively. 

Hdip was obtained for the antiferromagnetic structures by a summation of (point) dipole contributions ( i = 7 iq) all Eu ions within a sphere of diameter = 40 lattice constants (a = 6.190 A). It is assumed that in the ferromagnetic and ferrimagnetic structures the demagnetization field is zero (polydomain crystallites), so that Hdip=Lorentz field (Vsjt M) +field contributions from within the Lorentz sphere. The sign + means H jp or Hthf has the same direction as the magnetic moment i or Mg of the Eu ion [3]. 

Hjhf = -292 kOe was derived from ESR of Eu isolated in SrSe, Kojima etal. [4]. More recent Eu NMR data on Eu0.99Sr0.01Se show that the intrinsic fields at Eu nuclei are equal in concentrated and diluted Eui. SrxSe, Hihara etal. [5]. Mossbauer studies on Eu0.99Sn0.01Se under pressure ( 37 kbar) revealed no pressure dependence of Hjhf, Moser et al. [6]. The value of -292 kOe was used throughout in calculating Hht for the different spin states. 

Values of Heff and Hhf (in kOe) in Antiferromagnetic (NNSS, NSNS) and Ferrimagnetic (NNS) Phases 

Based on Mossbauer measurements on Eu in single crystal powder of EuSe between 5.12 and 1.3 K, the effective magnetic field Hg f at the Eu nuclei in the paramagnetic phase near the Neel temperature (Tn = 4.6 K) increases due to formation of short range order (spin cluster) from I Heff 1 0 at 5.12 K to ca. 80 at about 4.40 K, when the phase disappeared. Heff of the 

---

The remainder of equation (38) describes the multiplet effect, and it can be seen that whether an individual line in the multiplet corresponds to emission or absor ption depends on the signs of the hyperfine coupling constants but is independent of Hq. The nature of the hyperfine field is such that the integral over the whole multiplet is zero if Ag = 0. 

Thus, the starting parameters for the computer-simulation of spectrum IB were chosen to agree with the value of hyperfine fields at 613 K as measured by Rlste and Tenzer, using neutron scattering measurements (36). In addition, the magnetic relaxation rate depends on temperature, as discussed in the Theory section of this paper. 

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... 

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)...

Mossbauer spectrum is then proportional to the average value of the hyperfine field which is given by... 

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... 

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. 

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... 

Apart from the already mentioned (Sect. 7.6.1) determination of the nuclear g-factors of W through Mossbauer measurements with tungsten diluted in an iron foil [225, 229] where a hyperfine field at the W site of 70.8 2.5 T was... 

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])...

---