Structural and microwave absorption properties of Ni(1-x)Co(x)Fe2O4 (0.0 ≤ x ≤ 0.5) nanoferrites synthesized via co-precipitation route

Ni-Co nanoferrites show excellent magneto-dielectric properties and these materials can be used to miniaturize the size of the high frequency devices which is the order of the day. Nanocrystalline Ni-Co ferrites having general formula Ni1-xCoxFe2O4 (x=0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) were prepared by co-precipitation method. The structural morphology of the prepared samples was carried out using scanning electron microscopy. The results showed the spherical shaped nanoparticles varying in the range of 16-40 nm. The complex relative permittivity (epsilon(r)) and complex relative permeability (mu(r)) were measured using vector network analyzer for all the samples in the frequency range of 1 MHz to 3 GHz. The variation of complex relative permittivity (epsilon(r)) as a function of frequency is explained in accordance with Maxwell-Wagner model and Koop's phenomenological theory. The effect of frequency and cobalt concentration on permeability are reported. The reflectivity (R) of nanoferrites is also calculated. The value of minimum reflection loss (RL) is about -18 dB at 2.45 GHz with a thickness of 2.1 +/- 0.1 mm. The results indicate that Ni1-xCoxFe2O4 nanoparticles have excellent microwave absorbing properties and have a great potential for military use. (C) 2010 Elsevier B.V. All rights reserved.