3.
A semiquantitative model of circular magneto-optical effects in iron garnets is constructed within the concept of charge-transfer transitions and the existing qualitative notions. In the framework of the proposed model, the drastic enhancement of circular magneto-optical effects in
R3Fe
5O
12 iron garnets containing impurities of Bi
3+ or Pb
2+ ions is explained by the increase in the oxygen contribution to the spin-orbit coupling constant of the (FeO
6)
9? and (FeO
4)
5? complexes (the main magneto-optically active centers in iron garnets). This increase is associated with the covalent admixture of the Bi
3+ (or Pb
2+) 6
p orbitals (with a giant one-electron spin-orbit coupling constant) to the oxygen 2
p orbitals. The influence of the substitution does not reduce to an enhancement of the oxygen spin-orbit interaction alone but also leads to the appearance of the effective anisotropic tensor contributions to the spin-orbit interaction and circular magneto-optical effects. These contributions to the magneto-optical effects in garnets are estimated. The influence of an inhomogeneous bismuth distribution on the magneto-optical effects in Y
3?xBi
xFe
5O
12 garnets is investigated using computer simulation. Analysis of the available experimental data on the magneto-optical effects in garnets confirms the validity of the theoretical model proposed.
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