Synthesis of acicular Fe–Co nanoparticles and the effect of Al addition on their magneticproperties

Abstract

We have obtained Al(III)-protected Fe–Co metal nanoparticles with acicularshape by thermal reduction with hydrogen from Al(III)–Co(II)-codopedacicular goethite precursors prepared by oxidation with air of aFeSO4 solutioncontaining Al(NO3)3 andCo(NO3)3 precipitatedwith Na2CO3. These precursor particles were smaller ( nm in length) than those prepared by a previously reported procedure, resulting in smallermetal particles ( nm in length) suitable for high-density magnetic recording media in which higherbit-packing densities could be obtained. The location of Co and Al in the goethiteprecursors, as well as in the final metal particles, have been studied for a betterunderstanding of role that these elements play in the microstructural features and themagnetic properties of the final metal particles. It was found that the Al content in theparticle outer layers was enhanced during the reduction process, while cobaltdiffuses toward the inner part of iron nanoparticles forming an Fe–Co alloy. Theincorporation of cobalt helps to increase the magnetization saturation because itavoids corrosion and minimizes the growth of the iron crystals. The presence ofAl(III) in the particle outer layers of the precursors inhibited the growth of ironcrystals and preserved the acicular shape during the reduction process, whichhas a very favourable effect on the coercivity and the squareness of the metalsamples.