Alterations in the magnetic and electrodynamic properties of hard-soft Sr_0.5Ba_0.5Eu_0.01Fe₁₂O₁₉/Ni_xCu_yZn_wFe₂O₄ nanocomposites

Hard/soft (H/S) Sr_0.5Ba_0.5Eu_0.01Fe₁₂O₁₉/Ni_xCu_yZn_wFe₂O₄ nanocomposites (NCs) were produced via a one-pot sol–gel auto-combustion procedure. Phase and surface analyses were performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HR-TEM). Magnetization measurements for H/S NCs with different x, y, and w ratios were investigated at two different temperatures (300 and 10 K). The M−H curves were not smooth for the different H/S NCs, revealing that the exchange interaction was incomplete. The derivative of the magnetization (dM/dH versus H) exhibited two separate peaks, confirming the non-coupled H/S mixtures. Maximum saturation magnetization (M_s) values of 93.9 and 63.1 emu/g were obtained at 10 and 300 K, respectively, for the H/S Sr_0.5Ba_0.5Eu_0.01Fe_11.99O₁₉/Ni_0.3Cu_0.3Zn_0.4Fe₂O₄ NC, which contained the highest content of Zn and the same contents of Ni and Cu within the soft magnetic phase. The calculated squareness ratios (SQR = M_r/M_s) were less than 0.5, indicating incomplete exchange coupling. The coercive field (H_c) of the produced NCs reached a maximum value of approximately 2485 Oe at 300 K and 2331 Oe at 10 K with a decrease in the M_s values to 56.9 emu/g at 300 K and 78.5 emu/g at 10 K for the H/S Sr_0.5Ba_0.5Eu_0.01Fe_11.99O₁₉/Ni_0.8Cu_0.1Zn_0.1Fe₂O₄ NC, which contained lower fractions of Zn and Cu and the highest fraction of Ni. The reflection/transmission-based waveguide approach was employed to investigate the electrodynamic properties of the H/S NC samples within a frequency band of 7–18 GHz. The reflection and transmission coefficients (S₁₁/S₂₁) were measured using a vector network analyzer (VNA) for the sample placed inside a waveguide. The frequency dispersions of the magnetic permeability and electric permittivity were calculated.