Spectroscopic and Microscopic Insights into the Phase Evolution in Ag, Ni, Cu-Doped Strontium Hexaferrites: Correlating Magnetic and Dielectric Properties

This study provides comprehensive insights into the phase evolution of Ag, Ni, and Cu-doped strontium hexaferrites (SrFe _12-xM _xO ₁₉, M = Ag, Ni, Cu, x = 0.00 to 0.12), synthesized through the co-precipitation method. X-ray diffraction (XRD) confirmed the primary M-type hexagonal structure (P63/mmc, JCPDS card no: 33-1340), while secondary phases appeared at higher doping concentrations, indicating slight deviations from phase purity yet retaining the hexagonal structure. In Ag-doped samples (x ≥ 0.06), secondary phases of AgFe₂O₄ (JCPDS 74-1913) and α-Fe₂O₃ (JCPDS 33-0664) were detected, reducing magnetic coercivity and saturation, making them ideal for high-frequency EMI shielding. Ni-doped samples (x ≥ 0.06) showed the formation of NiFe₂O₄ (JCPDS 54-0964) and α-Fe₂O₃, enhancing dielectric stability, thus suiting them for capacitors and energy storage applications. Cu-doped samples (x ≥ 0.06) displayed the emergence of CuFe₂O₄ (JCPDS 34-0425) and α-Fe₂O₃, which improved magnetic anisotropy and microwave absorption potential. Crystallite sizes decreased across all compositions, with Ag-doped samples shrinking from 48 nm to 32 nm, Ni-doped from 50 nm to 37 nm, and Cu-doped from 49 nm to 35 nm. Grain size followed this trend, decreasing from 1.737 µm to 1.350 µm for Ag-doped samples, while Ni-doped samples reached a minimum of 663.25 nm at x = 0.06, and Cu-doped samples showed reductions from 2.876 µm to 1.654 µm. Magnetic properties revealed shifts in saturation magnetization, remanence magnetization, and coercivity across all doping levels. In Ag-doped samples, Ms dropped from 68.42 emu/g to 46.89 emu/g, and Hc decreased from 5,714.10 Oe to 4,215.89 Oe. Ni-doped samples saw a reduction in Ms from 67.56 emu/g to 46.89 emu/g, and Hc from 5,914.25 Oe to 3,673.88 Oe.