Tunable microwave absorbers: divalent ion-doped soft magnetic ferrite/CNT composites with customizable electromagnetic properties

Abstract

This study investigated the influence of different metal cation substitutions in nickel–zinc ferrite composites on their magnetic and microwave absorption properties. Ni_0.4Zn_0.4Me_0.2Fe_1.94Cr_0.01O₄/CNT composites (Me = Mg, Co, Ni, Cu, and Zn) were synthesized via solid-phase reaction and ultrasonication, followed by comprehensive characterization of their microstructure, magnetic behavior, and microwave absorption performance. X-ray diffraction (XRD) analysis revealed cation-dependent variations in crystallite size. Scanning electron microscopy (SEM) demonstrated uniform dispersion of carbon nanotubes (CNTs) within the ferrite matrix, accompanied by robust interfacial bonding. Vibrating sample magnetometer (VSM) measurements indicated that Zn²⁺-doped samples exhibited the lowest saturation magnetization (61.53 emu g⁻¹), whereas their Co²⁺-doped counterparts achieved the highest value (75.97 emu g⁻¹). Vector network analyzer (VNA) results showed that Cu²⁺-doped composites attained a minimum reflection loss of −46.32 dB at 1.4 mm thickness, while Co²⁺-doped samples displayed the broadest effective absorption bandwidth (4.3 GHz) at 1.9 mm thickness.