The effect of Sr 2 þ on the structure and magnetic properties of nanocrystalline cobalt ferrite

abstract We report the effect of Sr 2þ on the structure, morphology and magnetic properties of CoFe 2 O 4 synthesized by microwave-assisted combustion method. Results from X-ray diffraction and Mossbauerspectroscopy at 298 K suggest the formation of a mixed spinel Sr 2þ substituted CoFe 2 O 4 . However,secondary phases like CoO, SrCO 3 and SrFeO 2.96 were also observed. A decrease in the lattice parameterand particle size were observed with the addition of Sr 2þ . The crystallite size of ferrite phase rangedfrom 53 to 62 nm. Magnetic studies showed a gradual decrease in the saturation magnetization andremanence with the increase of Sr 2þ content, and an increasing value of the coercive field.& 2015 Elsevier B.V. All rights reserved. 1. IntroductionCoFe 2 O 4 is magnetic material with high coercivity field (H c ),moderate saturation magnetization ( M s ), excellent chemical stabilityand mechanical hardness [1–3], which makes it a potential candidatefor many technological applications such as magneto-hyperthermia,magnetic drug delivery, information storage among others [4–6].Theunit cell of spinel ferrite consists ofcubicclosedpackedarrangementof oxygen with 64 tetrahedral (A-site) and 32 octahedral (B-site)interstitial sites, being only 8 A- sites and 16 B-sites occupied by themetal cations. This large amount of empty sites allow the migrationof cations between interstitial sites during synthesis. Their physicaland chemical properties depend strongly on their composition,structure, shape and particle size, which are affected by the proces-sing method and thermal treatment [7]. The magnetic properties ofthese materials can be modified by replacing ions located at A and/orBsites[8,9]. The substitution with non-magnetic ions is particularlyinteresting. For example, Kumar and coworkers synthesized a mixedspinel La