Magneto-optical properties of PbTe and PbSe alloyed with paramagnetic ions Mn and Eu are reviewed. The k . p theory of the band structure of IV-VI compounds is presented, taking into account the narrow energy gaps and strong spin-orbit interactions in the materials. The exchange interaction between the paramagnetic ions and mobile carriers is included in the framework of the meanfield approximation. The experimental data of various authors on magnetization, interband magneto-optics. intraband magneto-optics and four-wave mixing are presented. All results are successfully described by the theory, treating the exchange integrals as adjustable parameters. It is shown that the exchange interaction is of particular importance for the valence bands. Differences between semimagnetic behaviours of Mn-based and Eu-based systems are emphasized as well as those between the IV-VI and Il-VI semimagnetic compounds.

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A microscopic tight-binding model of the spin-dependent coupling between efFective-mass electrons and localized spins in the IV-VI diluted magnetic semiconductors is proposed. Contributions from the direct Coulomb exchange as well as from the hybridization between band states and resonant levels associated with magnetic ions are taken into consideration. The exchange integrals are evaluated quantitatively and are shown to compare favorably with experimental values for both the Mnand the Eu-based compounds. Some peculiarities of IV-VI magnetic alloys, which may render the virtual-crystal approximation invalid, are noted and linked to the previously unexplained experimental results.

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