Crystal field effects in intermetallic compounds studied by inelastic neutron scattering  

Oleh:

Moze, O.

Jenis: Article from Books - Reference
Dalam koleksi: Handbook of Magnetic Materials Volume 11, page 493-624.
Topik: Neutron Scattering; Photoemission; Magnetization
Fulltext: MagnetcMaterials_11-4.pdf (2.43MB)

Isi artikel

The crystal field interaction in rare-earth intermetallic compounds is responsible for an enormous variety of magnetic phenomena. In such compounds, magnetism is partially due to the incompletely filled 4f shells. The wavefunctions of these electrons are known to be reasonably well localized. This implies that, to a good approximation, the rare-earth ions have a characteristic free ion behaviour, with the ground state obeying the Hund rules. The LS (spin-orbit coupling) therefore characterizes the ground state in terms of the total angular momentum J = L 4- S. The large spin-orbit coupling gives rise to separations between multiplets of more than 200 meV, with the notable exceptions of Sm 3+ and Eu 3+ ions (table 1). At temperatures of interest for most magnetic materials only the lowest multiplets will thus be populated. The electrostatic interaction experienced by these ions, arising from the presence of near neighbor ions and outer valence electrons is much smaller than the spin-orbit coupling, because of the minute spatial extent of the 4f electron wavefunctions. This CF (crystal field) interaction gives rise to splittings of the ground state multiplet of the order of 1-100 meV for lanthanide intermetallics. The consequences of such an interaction for the electronic structure and magnetism are well established and documented. The crystal field Hamiltonian is an important source of magneto-crystalline anisotropy, and can govern the existence of magnetic order. The 4f shells interact with the rest of the electrons in the system and consequently stabilize the magnetization and anisotropy. Given that the electronic properties of 4f ions are rather well understood, good estimates of the rare-earth ion contribution to the anisotropy depend crucially on the crystalline environment around the appropriate rare-earth ion.

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