Stevens factor rare earth

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. 

Table 1. Stevens multiplicative factors associated with equivalent operators for the ground states of rare earth ions and the calculated Hartree-Fock radial integrals (r > in atomic units of length...

The quantities 6 are the Stevens factors (a, fir, y, for n = 2, 4 and 6, respectively), (rn) are Hartree-Fock radial integrals and A are crystal-field potentials. The quantities O are Stevens operators and Hm in the last term of eq. (11) represents the molecular-field acting on the rare earth moment. 

As can be seen from table 33.6 there is generally a rather marked difference between the effective Z4 values derived for the nitrides compared with those for the remaining pnictides. As Yuan (1977) pointed out this difference is due to the extremely small Ln-Ln distances in the nitrides which are virtually the same as in the trivalent metals. In the nitrides, therefore, the 12 nearest Ln neighbors will have a nonnegligible influence on the crystal-field potential as they will alter the form of the f-electron cloud and hence the Stevens factors p and y which were calculated for free rare earth ions. 

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