Small Angle Neutron Scattering Study of Sintering Behavior in Annealed FePt and FePtAu Nanoparticles

Shishou Kang1, Zigong Jia1, I. Zoto1, D. Reed1, David E. Nikles1, J. W. Harrell1, Gregory Thompson1, Gary Mankey1, Demure Krishnamurthy2, L. Porcar3

1Center for Materials for Information Technology, The University of Alabama
2Center for Neutron Scattering, Oak Ridge National Laboratory
3Center for Neutron Research, National Institute of Standards and Technology

Chemically synthesized FePt nanoparticles are one of the leading candidate materials for the next generation magnetic data storage media; however, high temperature annealing is required to obtain the desired high-anisotropy L10 phase. Additive Au or Ag can be very effective in reducing the required annealing temperature, but there is concern that these additives may promote particle sintering during the annealing process. In order to more thoroughly investigate this effect, we have done small angle neutron scattering (SANS) measurements on spin-coated 4-nm FePt and FePtAu nanoparticles [1]. Fig. 1 shows the SANS diffraction pattern from an annealed FePt Nan particle film. The diffraction ring is consistent with a self-assembled nanoparticle superlattice with hip symmetry. Annealed films show a broadening of the ring, which reflects the loss of the self-assembled pattern and aggregation and sintering of nanoparticles, and this process occurs at lower annealing temperatures for FePtAu than FePt. An important question remains to be answered: Can additive Au or Ag promote ordering if this sintering is prevented?

[1] S. Kang et al., JAP (to appear).