Magnetic lanthanide sublattice

The reduced magnetic moment of the lanthanide sublattice m = Jz)IJ can then be calculated as... 

On the other hand, the magnetic properties of the lanthanide sublattice are governed by 4f electrons in the inner orbitals. The 4f electrons have little effect on the band structure of the crystals, since their narrow width, 0.1ey means their interaction with the neighboring atoms is weak. 

Since some properties of each sublattice, ei ecially the anisotropy of the lanthanide sublattice, as experimentally established, govern the behavior of the whole crystal of the magnet, the magnetic properties of the lanthanide sublattice will affect the sublattice of the transition metals, i.e., interactions between sublattices exist. The 4f electrons, however, have almost no direct bonds with the 3d electrons of the transition-metal sublattice, so the anisotropy of the 4f electrons initially transfers to the outer orbitals of 6s, 5d and/or 6p electrons of the lanthanide atoms, and these in turn interact with 4s and/or 4d electrons of the transition-metal sublattice, which is composed of and/or spd bands with the transition metal s 3d electrons. The interactions between the 4f and 3d electrons, therefore, are indirect. Figure la schematically shows the band structure in the lanthanide-transition-metal compounds. 

Oesterreicher (1973) has by neutron diffraction and other techniques studied the effect of replacing Al in RAI2 compounds by Fe or Co. He finds that on initial substitution, the bulk moment decreases which is partly explicable in terms of an antiparallel transition metal ion moment, but appears also to be due to magnetic disorder produced on the lanthanide sublattice. The microscopic reasons for this are not yet completely clear. 

Fig. 15.10. Lanthanide sublattice magnetic moment in RFej compounds (Taken from Rhyne, unpublished).

Spin freezing conditions exist for the 2a site (if occupied by magnetic lanthanide or actinide ions) as well. It is believed (Gal et al. 1990) that this behavior of the lanthanide or actinide sublattice is an outcome of conflicting RKKY interactions between the antiferromagnetically coupled (Fe) moments on the 8f site and the ferromagnetic (An) moments on the 2a sites. 

The rare-earth permanent magnets were bom by combining the high magnetization of the transition-metal sublattice with the high crystalline anisotropy of the lanthanide... 

The discussion in this subsection will be based on the band structure of the lanthanide-transition-metal compounds as shown schematically in figs. la,b. If we think about the effect of the anisotropy of the inner 4f electrons of flie lanthanides (Sm or Nd) on the Fe sublattices, the 4f electrons should initially transfer their characteristics to 5d, 6s and 6p band electrons of the lanthanide atom, which in turn will transfer the information to 4s, 4p and 3d electrons of the Fe atoms, finally affecting the magnetic properties, for example the crystalline anisotropy, of the entire crystal. 

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