We have shown that FeCo alloy nanocomposites behave as superior magnetic materials, which were synthesized in Al₂O₃ matrices by sequential implantation of Fe and Co ions (1). In this contribution we report a formation of Fe-based binary alloy nanoparticles with immiscible elements of Cu or Au by implantation. Fe was implanted with mass-analyzed 100 keV ⁵⁷Fe. The total dose was in the range of 2 × 10¹⁷ ions/cm². The alloy formation was confirmed by conversion electron Mössbauer spectroscopy of ⁵⁷Fe probe, one of constituents in the co-implanted granules. GXRD and magnetization measurements were also used to characterize structural and magnetic properties. An additional tailoring of the granules was performed by KrF excimer laser irradiation with wavelength of 248 nm.

Our investigation shows that both bcc and fcc phase exist in FeCu alloys and the Fe granule’s size increases by alloying with implanted Cu, e.g., from ~4 nm in diameters to 5 nm in FeCu nanoparticles, and that internal magnetic field at iron sites decreases by the alloying due to magnetic dilution of Cu impurities. However, the change in the size and magnetization in Fe granules by Au alloying are suggested to be induced in opposite way from FeCu granules. Especially, Au impurities seem to cause an increase in the iron internal magnetic field. The result is consistent with the earlier observation on Au magnetic perturbation effect in bulk Fe by Vincze et al. Moreover, post implantation annealing with laser irradiation has been found to cause further changes in the physical properties of the alloy granules.

1) N.Hayashi et al, Nucl. Instru. Meth. B257 (2007) 25.

Nobuyuki Hayashi*, Kurume Institute of Technology, Japan
Isao Sakamoto, Hosei University, Japan
Kiyoshi Nomura, The University of Tokyo, Japan
Satoshi Iio, The University of Tokyo, 
Toshiaki Seino, The Japan Steel Works, Japan
Tanotsu Toriyama, Tokyo City University, 
Shigeo Honda, Shimane University, Japan

*presenting author