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Title

Synthesis and characterization of Fe-B nanoparticles for potential magnetic applications

AuthorsGaliana, Beatriz ; Oprea, Bodgan; Huttel, Yves ; Ballesteros Pérez, Carmen Inés
Issue Date2014
CitationMRS Spring Meeting & Exhibit (2014)
AbstractResearch in nanoparticles (NPs) has become a hot topic in the last decades. In the case of magnetic nanoparticles, they can be used in a wide range of potential applications in medicine or high-density data storage among others (1,2). To design magnetic nanoparticles for a specific application is required to control size, composition and distribution and to be able to modify their magnetic properties. The Fe-B system is especially attractive due to its ability to tailor its magnetic behavior with continuous composition variations (3,4). In fact, magnetization measurements in Fe1minus;x Bx glasses indicate that the saturation magnetic moment depends on their composition (5). The present work analyzes Fe-B nanoparticles (NPs) of different sizes formed in a single process by gas aggregation from Fe80B20 targets. Crystal structure studies were carried out by electron diffraction pattern simulation, using Fast Fourier Transform (FFT) of the high resolution transmission electron microscopy (HTEM) images. Compositional information was achieved by means of Z- contrast scanning transmission electron microscopy (STEM), Energy Dispersive X-Ray (EDX) and energy-filtered TEM (EFTEM). The experimental data reveal that all NPs, regardless their size, are covered by a less than 3 nm thick amorphous Fe-B alloy. Conversely, the crystal structure and chemical composition of the NPs core depend on their size. More concretely, NPs with a diameter above 30 nm are monocrystalline and are identified as tetragonal Fe3B (I 4), NPs with a diameter ranging from 20 to 30 nm are not monocrystalline showing amorphous areas together with different phases -orthorhombic FeB (pnma) and tetragonal Fe3B (I 4)-, and finally, NPs with a diameter below 20 nm are fully amorphous. The variety of crystal structures measured in Fe-B nanoparticles can be explained as different stages of amorphous Fe80B20 crystallization being an indicative of the important role of thermal diffusion in the cooling process. It is expected that the external amorphous layer gets cold easily, as well as the core of small nanoparticles not permitting the full rearrangement of the atoms, whereas the core of large NPs is cooled down more slowly favouring its crystallization. Thanks to the observed size dependence of the structure and composition of the Fe-B nanoparticles it can be inferred that their magnetic properties could be mass selected, opening new possibilities in the development of Fe-B applications.
DescriptionPoster presented at the 2014 MRS Spring Meeting & Exhibit that was held in San Francisco (CA, United States) on April 21-25th, 2014. The poster was presented at Symposium VV: Magnetic Nanomaterials and Nanostructures, VV4: Poster Session: Preparation of Nanostructured Magnetic Materials and Their Applications. VV4.14.
URIhttp://hdl.handle.net/10261/182509
Appears in Collections:(ICMM) Comunicaciones congresos
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