Abstract
The theory of s-d(f) direct and indirect exchange coupling in crystals involving the ions of d and f metals is generalized by taking into account variation of multiplicity of magnetoactive shells of these ions. The generalized exchange Hamiltonian are applied to the problems of electro- and superconductivity and those of magnetic order in metal crystals containing the magnetic ions. The excitations of ion multiplicity is shown to lead to the minimum of electroresistance at the temperature which exceeds the multiplicity excitation energy. The conditions are set at which the following decreasing of temperature results in appearance of the electroresistance maximum. It is shown that virtual multiplicity excitations of magnetic ions induce the repulsion of singlet pairs and thus prevent from the establishment of superconductivity at such electron coupling. Due to this effect the critical temperature of La decreases when Eu impurities are added. For triplet pairs the above-mentioned interaction can have the attraction nature. This ensures the real possibility of the nonphonon mechanism of superconductivity in three-dimensional crystals with high critical temperature of superconductivity. The effect of changes of multiplicity on appearance and character of long-range magnetic order in crystals with localized magnetic ions is considered.
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