Iron moment

Central ion No. of unpaired Compound elec-(Cp = [CbHs]") Irons Moment (Bohr magnetons) calc Moment (Bohr magnetons) exp Reference... 

The results obtained for the compounds of the series Rj Fe 4C confirmed the results on the isotypic R2Fej4B compounds, showing that the spontaneous volume magnetostriction extends to temperatures substantially above in this type of ternary compounds. This observation lends credence to the view that the local iron moments in iron-based metallic materials do not disappear above (Holden et al. 1984),... 

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. 

Y.-C. Yang et al. (1993) claim that carbon substitution increases both saturation magnetization and magnetocrystalline anisotropy. This conclusion is confirmed by other authors (see table 22). One can see that the silicide carbides of light rare earths exist with a different crystal structure of the BaCdi i -type (I4i/amd space group) in which the carbon atoms fill octahedral vacancies formed by four iron and two lanthanide atoms, with an occupancy of 25%. These compounds exhibit Curie temperatures which are lower than for corresponding the ThMni2-type phases they lie between 390 and 460 K. The mean iron moment amounts to about 1.4 Ub at low temperature (Le Roy et al. 1987). 

The magnetic properties of Fe-Al gismondine were studied the effective iron moments varied between 5.71 pe (14.6 % Fe) and 5.41 pe (22.7 % Fe) [08K1]. The magnetic data confirmed the substitution of A1 for Fe in gismondine framework. 

Data concerning the site dependence of the iron moments may be obtained by neutron diffraction measurements (Herbst et al. 1984, 1985, Herbst and Yelon 1986, Givord et al. 1985a) or may be estimated from Pe hyperfine fields. In table 5 we give a summary of the neutron diffraction measurements performed on R2pe,4B compounds (R = Y, Ce, Pr, Nd and Dy). Differences between magnetic moments of Nd and Pe reported by various authors in Nd2pOj4B compounds are shown. 

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%. 

The effect of substitution of Y or a non-magnetic rare earth by a magnetic one, on the iron magnetic contributions was analysed by Givord et al. (1985c). In Y2pei4B, small iron moments are evidenced in Fe2(4c) sites, Mp (4c) = 1.95/u.g. This site has four Y atoms as nearest neighbours as well as four Fe5(16k,) and... 

Fig. 13. The composition dependence of the mean iron moment in some R2Fe,.,B-based compounds.

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. 

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