Stevens factor compounds

According to a two-sublattice mean field model, the EMD of inter-metallic compounds is determined by the competition between the EMDs of the rare earth sublattice and the transition metal sublattice. In the Th2Zn]7-type crystal lattice, the Sm sublattice prefers c-axis anisotropy to others because of the positive Stevens factor (aj) of Sm, and the Fe sublattice contributes to the c-plane anisotropy. Both Co and carbon in Sm2(Fe1 xCox)17C>. help to enhance the contribution of the Sm sublattice dominant to the EMD, but the effect of carbon is larger than that of Co. 

Second-order Stevens factor for different R elements and preferred magnetization direction observed in various R2Fe14B and R2Co17 compounds. (After Buschow et al. 

Estimated values of anisotropy fields in RjCoj B compound are 0.6 T for R = La and 7.5 T for R = Pr (Buschow et al. 1985c). The cobalt sublattice anisotropy favours an easy magnetization direction perpendicular to c-axis, whereas the crystal field induced anisotropy of the 4f sublattice corresponds to the second order Stevens factor Uj of R component. 

It does not depend on steric factors.1 For example, Curry and Stevens have shown that compounds such as 1 may open to give products whose bulky group is found in the inside position ... 

Nair, R.S., J.H. Sherman, M.W. Stevens, and F.R. Johannsen. 1995. Selecting a more realistic uncertainty factor Reducing compounding effects of multiple uncertainties. Hum. Ecol. Risk Assess. 1 576-589. 

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