This paper reports the correlation between the composition of the functional Sr_0.5Ba_0.5Sm_0.02Fe_11.98O₁₉/x(Ni_0.8Zn_0.2Fe₂O₄) hard–soft nanocomposites (SrBaSmFe/x(NiZnFe) NCs), where 0.0 ≤ x ≤ 3.0, and their structural features, magnetic, and microwave properties. SrBaSmFe/x(NiZnFe) hard/soft ferrite NCs are produced using the one-pot citrate combustion method. According to the XRD analysis, all samples showed the co-existence of both SrBaSmFe and NiZnFe phases in different ratios. Magnetic properties are measured in a wide range of magnetic fields and temperatures (10 and 300 K) and correlated well with the composition of the investigated samples. The microwave properties (frequency dispersions of the magnetic permeability, and electrical permittivity) are discussed by using the co-axial method in the frequency range of 0.7–18 GHz. Non-linear dependences of the main microwave features were observed with varying of composition. The microwave behavior correlated well with the composite theory. These results could be used in practice for developing antenna materials.

Crystalline high-entropy single-phase products with a magnetoplumbite structure with grains in the μm range were obtained using solid-state sintering. The synthesis temperature was up to 1400 °C. The morphology, chemical composition, crystal structure, magnetic, and electrodynamic properties were studied and compared with pure barium hexaferrite BaFe₁₂O₁₉ matrix. The polysubstituted high-entropy single-phase product contains five doping elements at a high concentration level. According to the EDX data, the new compound has a formula of Ba(Fe₆Ga_1.25In_1.17Ti_1.21Cr_1.22Co_1.15)O₁₉. The calculated cell parameter values were a = 5.9253(5) Å, c = 23.5257(22) Å, and V = 715.32(9) ų. The increase in the unit cell for the substituted sample was expected due to the different ionic radius of Ti/In/Ga/Cr/Co compared with Fe³⁺. The electrodynamic measurements were performed. The dielectric and magnetic permeabilities were stable in the frequency range from 2 to 12 GHz. In this frequency range, the dielectric and magnetic losses were −0.2/0.2. Due to these electrodynamic parameters, this material can be used in the design of microwave strip devices.