Microwave absorption studies of Cr-doped Co–U type hexaferrites over 2–18 GHz frequency range

• Cr3+ ions doping effect on EM properties of Ba4Co2Fe36O60Ba4Co2Fe36O60 hexaferrites was studied.
• Le-Bail refinement of XRD patterns was used to calculate lattice parameters a and c.
• M–H data shows decrease in Ms and increase in Hc with increasing Cr content.
• Complex permeability spectra observed the FMR peaks in all the prepared samples.
• Minimum reflection loss (RLmin) of −34.90 dB was observed in Ba4Co1.1Cr0.6Fe36O60Ba4Co1.1Cr0.6Fe36O60.

The effect of Cr3+ ions doping on the electromagnetic (EM) properties of polycrystalline U-type hexaferrite samples: Ba4Co2-3xCr2xFe36O60Ba4Co2-3xCr2xFe36O60 (0.0≤x≤0.60, in steps of 0.15) have been studied. The X-ray diffraction (XRD) studies confirmed the formation of single U-type hexaferrite phase in all the prepared samples. Le Bail refinement of XRD patterns was used to calculate the lattice parameters ‘a’ and ‘c’. The room temperature M–H studies indicate that the saturation magnetization (Ms) decreases and coercivity (Hc) increases with increasing Cr3+ ions concentration. The complex permittivity (ε*=ε′−iε″)ε*=ε′−iε″) and permeability (μ*=μ′−iμ″)μ*=μ′−iμ″) measurement were carried out using vector network analyser (VNA) over 2–18 GHz frequency range. The complex permeability (μ*=μ′−μ″)μ*=μ′−μ″) spectra clearly observed the ferromagnetic resonance (FMR) phenomenon in all the prepared samples. The maximum microwave absorption (MWA) of 99.97% (or minimum reflection loss RLmin=−34.90 dB) was observed for Ba4Co1.1Cr0.6Fe36O60Ba4Co1.1Cr0.6Fe36O60 sample at 8.2 GHz frequency with 1.7 mm absorber thickness. The RLmin peak was found to shift towards higher microwave (MW) frequency with increase in Cr3+ ions concentration.