[en] Full text: X- ray diffraction, Moessbauer spectroscopy, and the electrical and magnetic properties, were studied on a ferrite systems Ni_1-xCu_xFeMn0₄ (x=0-1) and Ni_0.8Cu_0.2Fe_2-yMn_yO₄ (y=0-1). All these samples were a cubic with partially inverse spinel structure, despite of the presence Jahn-Teller ions Mn³⁺ and Cu²⁺. Moessbauer spectra were measured at 20 - 628 K. The spectra were decomposed into only two Zeeman sextets due to the Fe ions in the oxidation state 3⁺ in the A and B sites. At room temperature the hyperfine field decreases with increasing Cu and Mn concentrations for both tow systems. Magnetic susceptibility (χ_m) measurements were performed in the range of 80-1033 K. Both Moessbauer spectroscopy and magnetic measurements agreement in the Curie temperature T_c decreases with increasing Cu. The conductivity and thermoelectric power of the ferrites were measured between 295 and 520 K. With increasing Cu in Ni_1-xCu_xFeMn0₄ and Ni_0.8Cu_0.2Fe_2-yMn_yO₄, the conductivity was increasing, while the activation energy of conduction decreases. All the samples, except for x = 0.4, and y=0, 0.25, are found to exhibit hole conduction. The temperature dependences of the thermoelectric power and conductivity are typical of the hopping conduction between Mn³⁺ and Mn⁴⁺ in B-sites. The results of electrical and magnetic measurements and Moessbauer data are used to determine the cation distribution in the ferrite systems Ni_1-xCu_xFeMn0₄ (x=0-1) and Ni_0.8Cu_0.2Fe_2-yMn_yO₄ (y=0-1)

[en] The role of quantum interference (QI) in spectra of the resonant Moessbauer scattering is investigated. As a mechanism ensuring the QI conditions, the radio-frequency (RF) mixing of the spin sublevels of the excited nuclear state is considered. It is shown that QI leads to a significant intensity redistribution of the elastic and Raman scattering.

[en] Results of structural, magnetic, and Mössbauer studies of quasi ordered alloys Fe₆₅Al_{35− x}M_x (M_x = Ga, B; x = 0, 5 at %) are presented. The magnetic state of examined structurally–single-phase alloys at low temperatures is interpreted from the viewpoint of magnetic phase separation. An explanation is proposed for the observed behavior of magnetic characteristics of Fe₆₅Al₃₅ and Fe₆₅Al₃₀Ga₅ in the framework of the model of two magnetic phases, a ferromagnetic-type one and a spin density wave. The boron-doped alloy Fe₆₅Al₃₀B₅ is shown to demonstrate behavior that is typical of materials with the ferromagnetic type of ordering.