Iron moments, value

Table IX - Charge density pe(0) at the nucleus and Isomer Shift 6, Electric Field Gradient tensor, contact spin density p,(0), Magnetic Dipolar Field tensor, and net magnetic field Hjr at iron site in annite. Results are given for clusters containing only first, and first plus second coordination shells about iron. Principal values and directions of principal axes (in parentheses) are given for EFG and dipolar field. The 57Fe nuclear quadrupole moment is taken as 0.16 barn [91].

On the basis of the dipole moment values and viscosity measurements of the two forms of nitroglycerine, de Kreuk [20] considered that the difference between the two forms is produced by rotational isomerism. According to this hypothesis the labile and stable forms would correspond to cis- and /rans-isomers respectively. In a non-polar solvent the irons form predominates. In a polar solvent the content of the cis form increases and reaches a maximum in liquid nitroglycerine. 

The Curie temperature 7., spontaneous magnetization Af, at 4.2 and 300 K, theoretical moment for the rare earth ion R and value of the iron moment of the compound RFe,QSiC(, 5. 

Burzo and Ursu 1979). Some values thus obtained are listed in table 5. According to the peculiar environment, the iron moments may differ up to 23%. 

From the effective iron moments, the mean spin values, S, were computed according to the relation M jj(Fe) = gFe p( p + 1) (Burzo et al. 1985d). The 5p values thus determined are listed in table 6. These are somewhat greater than the spin values, S, obtained from the mean saturation iron moments. 

A measure of the localization of iron moments is given by the ratio r = SJS, between the number of spins deduced from the Curie constants and those obtained from saturation data (Burzo 1978a). In case of Fe, Co and Ni metals, the r values are 1.05, 1.34 and 1.46, respectively. The r values for iron moments in R2Fe,4B compounds are around 1.22 (table 6). These data do not suggest a great degree of itineracy. 

Arrese-Boggianq et al. (1977) have studied DyFes and again find a Dy hyperfine field close to the crystalline values and broadened by only about 1%, while in contrast the Fe field is broadened by 20% and is higher than that in the crystalline counterpart compound a result found also in DyNia, DyCos, and YFea with small amounts of Fe introduced as a Mossbauer probe. For example in amorphous DyFes, Hhf = 280 kOe and in crystalline DyFes, Hhf = 240 kOe leading to the conclusion that the net iron moment is increased from 1.6 to 1.9/u-B in going from the crystalline to the amorphous state. 

Finally, the use of simple valence bond theory has led recently to a significant discovery concerning the nature of metals. Many years ago one of us noticed, based on an analysis of the experimental values of the saturation ferromagnetic moment per atom of the metals of the iron group and their alloys, that for a substance to have metallic properties, 0.72 orbital per atom, the metallic orbital, must be available to permit the unsynchronized resonance that confers metallic properties on a substance.34 38 Using lithium as an example, unsynchronized resonance refers to such structures as follows. 

The values for the atomic saturation magnetization at the absolute zero, ferromagnetic metals iron, cobalt, and nickel are 2.22, 1.71, and 0.61 Bohr magnetons per atom, respectively.9 These numbers are the average numbers of unpaired electron spins in the metals (the approximation of the g factor to 2 found in gyromagnetic experiments shows that the orbital moment is nearly completely quenched, as in complex ions containing the transition elements). 

When the effective atomic number becomes a little greater than the value for iron, however, the stable atomic orbitals are occupied by one electron per orbital, and further electrons can enter this set of orbitals only by becoming paired accordingly, the magnetic moment begins to fall, as is indicated by the experimental data. The magnetic moment drops to the value 1.7 for cobalt and 0.6 for nickel, and to zero at a point 60 percent of the way between nickel and copper. 

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