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Disordered one-dimensional XYZ Heisenberg ferromagnets with substitutional impurities are studied. The substitutional spins give rise to a random distribution of the exchange couplings. By introducing a new transformation for spin operators, the XYZ Heisenberg Hamiltonian can be exactly diagonalized and expressed by Bose operators. Being restricted by the spin wave approximation, the Hamiltonian obtained is shown to be similar to the Anderson Hamiltonian for electronic systems. We have shown that the magnon localization should be destroyed at the middle of the band due to the effects of commensurability of the magnon wavelength and lattice constant. The magnon density of states and the localization length are shown to have singularities at the middle of the band irrespective of the strength of disorder. The middle of the magnon band can be reached not only by changing the magnon energy but also by varying the external magnetic field which facilitates the observation of the phenomenon.

Effects of correlation in weakly disordered systems on the density of electronic states (DOS) and the conductivity are examined in the framework of the mean field approach. As a result of the approximation, the electronic energy spectrum is changed from a free electron energy spectrum to a Hartree exchange term added energy spectrum form. Coulomb interaction is shown to give a correction to the DOS, which reduces the electronic states. Calculations of the conductivity show that, although Coulomb interaction evaluated by the mean field theory decreases the Drude conductivity, it acts as a dephasing factor for the quantum localization correction to the conductivity.