Frequency and field dependent dynamic properties of CoFe2-xAlxO4 ferrite nanoparticles

Aluminum doped CoFe2-xAlxO4 (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 Al3+ content. The saturation magnetization of samples decrease with increasing Al3+ 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 Al3+ content reduces the Gilbert damping parameter thus making CoFe2-xAlxO4 as an attractive material for high frequency applications. (C) 2015 Elsevier Ltd. All rights reserved.