ИСТИНА

In our work we show that Mn or Cu atoms may be incorporated in the tetragonal-pyramidal polyhedra [LiAs5] of the LiFeAs structure instead of lithium. In the case of Li1-xMnxFeAs a continuous series of solid solutions (0 <x <1 ) is formed, and in the case of Li1-xCuxFeAs the maximum level of substitution x was found to be about 0.3. The study of the isothermal magnetization curves and the T-dependence of the magnetic susceptibility curves for Li1-xCuxFeAs samples (x≤0.3) showed that they exhibit paramagnetic properties. Treatment of the T-dependence of magnetic susceptibilities curves on the basis of the Curie-Weiss model allows us to conclude that the samples contain only diamagnetic Cu+ cations. Thus, the magnetic properties of Li1-xCuxFeAs samples can be described within the model of non-interacting magnetic moments, which may be impurity iron cations in the lithium positions. The features of the electronic and magnetic state of iron cations of the Li1-xTMxFeAs samples were studied by Mössbauer spectroscopy on 57Fe. The main spectral component over the entire temperature range is a slightly enlarged broadened, quadrupole doublet, which corresponds to the localisation of iron in a tetrahedral environment of arsenic atoms within conducting layers. In addition to the main component, the second signal is present in the spectra, which corresponds to the FeAs impurity. In contrast to TM=Cu, Li1-xMnxFeAs samples exhibited complex magnetic behavior and spontaneous magnetization observed up to room temperature. The authors would like to acknowledge the financial support by the Volkswagen Foundation and the Russian Foundation for Basic Research (grant # 15-03-99628).