Tunable structural, magnetic, complex permittivity/permeability, and reflection loss parameters of Co2+ and Ni2+-Co-doped M-type strontium ferrites for microwave absorber applications

M-type hexaferrites SrCoyNiyFe12-2yO19 (y = 0.2, 0.4, 0.6) developed using the sol-gel method. The phase purity was investigated using X-ray diffraction (XRD) analysis. The formation of needle-shaped grain structures was observed from scanning electron microscopy (SEM). The various magnetic parameters viz-a-viz saturation magnetization (Ms), coercivity (Hc), remanence (Mr), and anisotropy field (Ha) were determined using hysteresis loops. The coercivity Hc decreased from 3955 to 3007 Oe, while an increment in saturation magnetization Ms\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${M}_{s}$$\end{document} from 72.01 to 105.77 emu/g was observed. Reflection loss v/s frequency graphs were used to investigate the absorption characteristics of the prepared compositions. The doping of Ni2+ and Co2+ has enhanced the absorption characteristics. The composition y = 0.4 (SCNF 2) had the highest RL of - 34.49 dB at a small thickness of 3.5 mm with an input impedance (Zin) of 366.07 Omega (Zreal = 365.97 Omega, Zimg = - 8.65 Omega). The composition SCNF 3 had the highest bandwidth of 0.84 GHz among all the compositions. The broad bandwidth, low thickness, and high absorption make the developed samples very suitable in the field of defense and commercial applications as microwave absorbers.