Microstructure and high frequency electromagnetic parameters of the soft/soft (CoFe 2 O 4 ) x  : (Ni 0.4 Cu 0.2 Zn 0.4 Fe 2 O 4 ) y nanocomposites.

The soft/soft (CoFe 2 O 4 ) x  : (Ni 0.4 Cu 0.2 Zn 0.4 Fe 2 O 4 ) y (CFO x /NCZO y ) nanocomposites (NCs) based on spinel ferrites were produced by the sol-gel method with varying phase's ratio ( x  :  y = 0 : 1; 1 : 1; 2 : 1; 3 : 1; 1 : 3; 1 : 2 and 1 : 0). All NCs consisted of 2 single phases (initial spinels) without any impurities and the absence of chemical interaction between phases. Structural features were investigated and analyzed. The varying of the structural parameters was non-linear and correlated well with the lattice parameter for initial components. There were two maxima observed for all NCs on particle size distribution. It was demonstrated that an increase in the CFO content leads to an increase in the most probable size of the coarse fraction and a decrease in the most probable grain size of the fine fraction. An increase in the NCZO content leads to a decrease in the average size of both fine and coarse fractions. This is obviously due to the large number of defects in the NCZO crystal lattice. The high frequency electromagnetic parameters (real and imaginary parts of the permittivity and permeability, reflection losses) were analyzed in the range of 2-10 GHz. The increase of the energy losses with frequency increase was observed. The nature of the attenuation of the reflected energy associated with the electromagnetic absorption processes due to magnetic losses. Maximal values of the electromagnetic absorption were observed for CFO 2 /NCZO 1 (-18.9 dB). This correlates with the lattice parameters of the composites. The result of the electromagnetic characteristics opens broad perspectives for practical applications such kind of NCs for antenna technology (5G technology) and for electromagnetic absorbing coatings.