Preparation of Fe-Pt alloy particles by pulsed las...

Y. Ishikawa et al. / Chemical Physics Letters 428 (2006) 426–429 429
for stoichiometric alloying. The L1 0 phase was obtained
by heat treatment (above 773 K) of particles obtained by
laser ablation in hexane. The particles containing L1 0
phase exhibited low coercitivity compared with that of
bulk, due to a significant composition deviation from
Fe 50 Pt 50 .
Acknowledgement
Fig. 5. Hysteresis loops of the Fe–Pt alloy particles prepared in hexane for
as-prepared particles and those heat-treated at 873 K.
cles in water (Fig. 1b). However, heat treatment at 873 K
brought L1 2 phase disappearance and additional phase formation
close to L1 0 phase in the case of hexane. The additional
phase formation close to L1 0 phase was also
observed in the case of water after heat treatment at
873 K. These changes were possibly caused by the reduction
of Fe oxide species with consumption of L1 2 phase
[15]. Thus, the ablation in hexane was more effective than
that in water for preparing L1 0 phase, because the particles
obtained in hexane after heat treatment dominantly consisted
of L1 0 phase. This was probably due to the existence
of particles with Fe 38 Pt 62 composition, which was closer to
the 1:1 composition favorable for L1 0 phase formation.
Fig. 5 depicts the magnetic hysteresis loops of the particles
prepared in hexane for as-prepared particles and particles
that were heat-treated at 873 K, which was measured
at 5 K. The as-prepared particles showed no coercitivity,
while that of particles after heat treatment was 3500 Oe
at 5 K and 300 Oe at 300 K. This value was obviously
smaller than that of bulk and particles previously reported
in many papers [6–8,16–18], due to a significant composition
deviation from Fe 50 Pt 50 [6].
4. Conclusion
A mixture of Fe 23 Pt 77 and Fe 38 Pt 62 was obtained by
laser ablation of a FePt target in degassed hexane, and
Fe 26 Pt 74 was obtained in degassed deionized water. The
absence of oxygen in the liquid medium was important
The present work was supported by the Research Fellowships
of the Japan Society for the Promotion of Science
for Young Scientists. This study was partially supported by
the Industrial Technology Research Grant Program ’05
from the New Energy and Industrial Technology Development
Organization (NEDO) of Japan.
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