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Structural, magnetic and electronic properties of surface oxidised Fe nanoparticles

Janusz J. Przewoźnik 1Tolek Tyliszczak 2Damian Rybicki 1Jan Żukrowski 1Wojciech Szczerba 1Marcin Sikora 1Czesław Kapusta 1Helena Stepankova 3Rodrigo F. Pacheco 4David Serrate 4,5Ricardo M. Ibarra 4,5

1. AGH University of Science and Technology, Faculty of Physics and Applied Computer Science (AGH), Mickiewicza 30, Kraków 30-059, Poland
2. Lawrence Berkeley National Laboratory (LBNL), 1 Cyclotron Road, Berkeley, CA 94720, United States
3. Charles University, Faculty of Mathematics and Physics, Ke Karlovu 3, Prague 12116, Czech Republic
4. Universidad de Zaragoza-CSIC, Facultad de Ciencias, Pedro Cerbuna 12, Zaragoza 50009, Spain
5. Instituto de Nanociencia de Aragon, Universidad de Zaragoza (INA), Pedro Cerbuna 12, Zaragoza 50009, Spain


A combined XRD, Moessbauer, STXM and NMR study of surface oxidised, ball milled Fe nano-powders exhibiting magnetoresistive properties is presented. The XRD patterns show the peaks of bcc-Fe phase with linewidths increasing with increasing milling time. This is attributed to a decrease of the effective size of crystallites and increased strain due to accumulation of defects. Thermal treatment causes a reduction of the line-widths to their initial values from before milling. A similar effect is observed for the line-widths in the Moessbauer spectra, whereas other parameters, i.e. hyperfine field, quadrupole splitting and isomer shift remain unchanged. Scanning Transmission X-ray Microscopy (STXM) measurements provided the oxygen maps of the particles and, hence, the information on the distribution of oxides on particles surface. The O;K and Fe:L2,L3 near-edge absorption spectra (XANES) of selected areas of particle surface show differences between oxides in samples prepared under different conditions. The 57Fe spin echo NMR spectra consist of a dominant resonant line corresponding to bcc-Fe core and a much weaker resonance corresponding to the iron oxides in the surface layer of nanometric thickness. The resonant frequency of the main line of the oxide layer is slightly lower than that of the bulk magnetite. The effect can be attributed to the exchange coupling between the oxide layer and the bcc-Fe core of the particle and/or to the presence of strain in the oxide layer. A lack of the signals from oxides in the Moessbauer spectra can be attributed to a small thickness of the oxide layers and the related low probability for the recoiless absorption. The studies constitute a detailed investigation of the nature of the iron oxide surface layer and its interaction with the iron core in ball milled iron nanoparticles.


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Presentation: Oral at E-MRS Fall Meeting 2007, Acta Materialia Gold Medal Workshop, by Czesław Kapusta
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-21 23:57
Revised:   2009-06-07 00:44