SECTION 7.4. INTERSUBLATTICE COUPLING IN ALLOYS OF RARE EARTHS AND 3d METALS 73between the 3d and 4f spins which is always antiparallel. For more details, the reader is
referred to the paper of Brooks and Johansson (1993).
Before closing this section, it is good to recall that the coupling scheme presented above
is one between the spin moments. The itinerant model describes the 3d moments exclusively
as spin moments, as mentioned already at the end of the previous section. We have seen in
Section 7.2 that the 4f moments are composed of a spin moment and an orbital moment.
For the heavy rare earths, we have J = L + S, meaning that the total 4f moment is also
coupled antiparallel to the 3d moment. By contrast, we have J = L – S for the light rare
earths (see, for instance, Table 2.2.1). Consequently, the total 4f moment couples parallel to
the 3d moment. In the two-sublattice model described in Section 4.4, with a negative spin-
spin coupling for both cases, this different coupling behavior is taken
account of by the different signs of the intersublattice-molecular-field constant
in Eq. (4.4.9). It arises from the different signs of being negative for the light rare
earths but positive for the heavy rare earths (see Table 2.2.1).References
Brooks, M. S. S. and Johansson, B. (1993) in K. H. J. Buschow (Ed.) Handbook of Magnetic Materials, Amsterdam:
North Holland Publ. Co., Vol. 7 , p. 139.
Franse, J. J. M. and Radwanski, R. J. (1993) in K. H. J. Buschow (Ed.) Handbook of Magnetic Materials
Amsterdam: North Holland Publ. Co., Vol. 7, p. 307.
Friedel, J. (1969) in J. Ziman (Ed.) The Physics of Metals, Cambridge: Cambridge University Press, Vol. 1 , p. 340.
Heine, V. (1967) Phys. Rev., 153, 637.
Pauling, L. (1938) Phys. Rev., 54, 899.
Slater, J. C. (1937) J. Appl. Phys., 8, 385.
Stoner, E. C. (1946) Rep. Progr. Phys., 9, 43.