Frequency and field dependent dynamic properties of CoFe 2−x Al x O 4 ferrite nanoparticles

Abstract Aluminum doped CoFe 2− x Al x O 4 (0 ≤ x ≤ 0.9) nanoparticles were synthesized via auto-combustion. Formation of single phase cubic spinel structure was confirmed by X-ray diffraction (XRD) analysis. XRD analysis suggests a linear decrease in lattice cell parameters and grain size (90–55 nm) with the increase in Al 3+ content. The saturation magnetization of samples decrease with increasing Al 3+ content due to magnetic dilution effect. A concomitant linear reduction in coercivity was also observed mainly due to decrease in magnetic anisotropy. Frequency and field dependent dynamic properties of nanoparticles were studied by ferromagnetic resonance (FMR) technique. The resonance frequency increases linearly with magnetic field for all nanoparticles. Magnetic field dependent experimental absorption data (S 21 vs. frequency) were compared with effective medium theory considering an effective demagnetization field and was observed to be in good agreement with each other. High Al 3+ content reduces the Gilbert damping parameter thus making CoFe 2− x Al x O 4 as an attractive material for high frequency applications.