S-state ions

Sharma, R.R., Das, T.P., and Orbach, R. 1966. Zero-field splitting of S-state ions. I. Point-multipole model. Physical Review 149 257-269. 

Table XII gives representative results for the spin Hamiltonian parameters as determined for d5 ions in different crystal fields. This table is not a complete listing of ESR results on d5 ions, since such a list would be much larger, but is rather a selection of results for various types of crystalline fields. Several facts become evident when examining the results listed in this table. The g factors are always near the free spin value of 2.0023, as would be expected for an S state. The hyperfine constant is isotropic, as would also be expected for an S-state ion. The hyperfine constant also...

The small quadrupole splitting in the oxidized protein spectra imply that the electron density around the iron atoms is nearly spherical. A spherical charge density indicates that the iron is an S-state ion, although low-spin ferric atoms can have small quadrupole splittings 158). In addition, the oxidized protein spectra show a single quadrupole pair, which indicates that the environments for the two iron atoms are nearly identical. The isomer shift for this quadrupole pair is most consistent with that of ferric iron, although low-spin ferrous iron cannot be ruled out as possibility by the isomer shift value alone. 

Since gi arises from an S-state ion, spin-orbit interactions are not allowed to first order (163) and gi can therefore be assumed to be isotropic. It is assumed to be 2.019 in accord with the measurements of Title (166). With this assumption, the g-values for the ferrous iron can be derived using the above equation and the measured g-values for the proteins (Table 6). For spinach ferredoxin, these calculated values are g%x = 2.12, g%y — 2.07, and 221 = 2.00. 

Wichman, H. H. Nuclear and Magnetic Resonance Studies in S-State Ions Ph. D. Thesis, Lawrence Radiation Laboratory, Berkeley, California, 1965. 

From a magnetic point of view, Gd is the simplest of the lanthanide metals. Exchange favors FM, while all other heavy lanthanide metals initially show AFM order. The Curie temperature (7c = 293 K) is in a convenient temperature range. The Gd + ion has a half-filled 4f shell. It is thus an S state ion featuring pure (but very strong) spin magnetism. 

The magnetically induced electric quadrupolar interaction was recently observed in several cubic, ferromagnetically ordered intermetallic compounds at the nucleus of the rare-earth S-state ions Gd and Eu, despite the fact that the nuclei are residing on nominally cubic lattice sites e.g., nuclear quadrupole... 

Itoh et al. (1983) report that the perpendicular magnetic anisotropy in Gd-Fe films, when prepared by means of sputtering under low substrate bias voltage, is mainly stress determined. In alloys where the R component is a non-S state ion the... 

S-state ion. For fluorine ions at second nearest neighbour sites, the values of are (within experimental error) zero, and. 4pis close to A. For a review of other results for lanthanide ions in fluorite compounds, see Hayes (1974). 

The ferromagnetic moment in Gd is parallel to the c-axis from Tc (293 K) to 232 K, and below that starts moving away from that axis, reaching a maximum deviation of 65° near 180 K and then at still lower temperatures moving back to within 32° of the c-axis. This curious behavior is due to the temperature variation of the weak single-ion anisotropy constants for Gd. Since Gd is an S-state ion, there is no anisotropy to first order. However, higher order effects of the spin-orbit coupling can yield such anisotropy terms. 

Isotropic hyperfine interaction in EPR. Calculation of zero-field splitting of S-state ions. Point-multipole model. 

For those a-R-T films containing Gd or other S-state ions, usually the magnitude of the PMA is rather small if present at all. In such cases the structural anisotropy plus spin-orbit interactions involving the Gd- or T-subnetwork or dipole-dipole interactions... 

Table 4 lists the state energies, which are displayed in fig. 7 and symmetries in RBa2Cu307 of the trivalent rare-earth ions Pr-Tm (excluding Gd, which is an s-state ion, and Pm, which is not a stable isotope). The CEF parameters derived from these data are listed in table 5. 

Being an S-state ion, the Mn(II) g and A matrices can be considered to be isotropic in so far as simulation of spectra in amorphous materials is concerned, as their small anisotropies are smeared out in these samples. On the other hand, the hyperfme structure of its spectrum adds some complexity to the spectrum, which also reflects the effect of interaction with the environment, since the Mn(II) ion possesses an electronic spin larger than V2. 

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