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

2004; IOP Publishing; Volume: 15; Issue: 4 Linguagem: Inglês

10.1088/0957-4484/15/4/013

1361-6528

Raúl Pozas, Manuel Ocaña, M. P. Morales, Pedro Tartaj, Nuria O. Núñez, Carlos J. Serna,

Magnetic properties of thin films

We have obtained Al(III)-protected Fe–Co metal nanoparticles with acicular shape by thermal reduction with hydrogen from Al(III)–Co(II)-codoped acicular goethite precursors prepared by oxidation with air of a FeSO4 solution containing Al(NO3)3 and Co(NO3)3 precipitated with Na2CO3. These precursor particles were smaller ( nm in length) than those prepared by a previously reported procedure, resulting in smaller metal particles ( nm in length) suitable for high-density magnetic recording media in which higher bit-packing densities could be obtained. The location of Co and Al in the goethite precursors, as well as in the final metal particles, have been studied for a better understanding of role that these elements play in the microstructural features and the magnetic properties of the final metal particles. It was found that the Al content in the particle outer layers was enhanced during the reduction process, while cobalt diffuses toward the inner part of iron nanoparticles forming an Fe–Co alloy. The incorporation of cobalt helps to increase the magnetization saturation because it avoids corrosion and minimizes the growth of the iron crystals. The presence of Al(III) in the particle outer layers of the precursors inhibited the growth of iron crystals and preserved the acicular shape during the reduction process, which has a very favourable effect on the coercivity and the squareness of the metal samples.