Permanent lanthanides

Among the rare-earths, samarium is the most commonly used because it provides the best permanent-magnet property. Other rare-earth elements are sometimes employed in combination with samarium to meet special requirements. The compounds SmCos and Sm2Coi7 are the most important magnetic materials among the cobalt-lanthanide alloys. 

The trigonal planar complexes of the MX3 type, whether of the lanthanide or of the transition metal series, have a particular significance. In an amendment to the crystal field intensity theory, designed to accommodate the hypersensitive f—f transitions, the addition of the first-rank spherical harmonics, Yim to the ligand field was proposed in order to form, with the dipole operator, an effective quadrupole operator within the 4f shell i). Crystal field potentials of the Yim form are restricted, however, to metal complexes with a permanent dipole moment, that is, to the site symmetries Cpv and their subgroups ), and the proposal does not account for the relatively large oscillator strengths of the quadrupole-allowed d—d or f—f transitions of... 

The uses of lanthanide compounds are diverse and are expanding due to modern technological advances. In 2000, the principal applications for the rare earths were glass polishing and ceramics, 39% automotive catalytic converters, 22% permanent magnets, 16% petroleum refining catalysts,... 

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... 

We present a summary of the resulting compounds containing a third elements, and their simplified characteristics as the materials for permanent magnets, in table 1. We also show, in fig. lb, a schematic representation of the band structure of lanthanide-transition-metal alloys containing a third element. 

The crystal structures of Sm-Co and Sm-Fe-X (X=N, C) compounds of the lanthanide permanent magnets are based on the CaCus structure. SmCos has this structure, and the... 

Experimental studies of the band structure in lanthanide permanent magnets, therefore, must be continued, and should help to solve the complex interactions of the 3d and 4f electrons through other bands. A clearer imderstanding of the physics of lanthanide magnets should be achieved by these studies. 

As a conclusion of the above-mentioned discussions, clearly more work needs to be done in the future concerning the origin of the anisotropy in lanthanide permanent magnets during HDDR processing. 

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