Fig. 3(a)e(f) show plane-view TEM images of the as-deposited
film and samples annealed at various temperatures. In Fig. 3(a),
the as-deposited FePt with fcc phase had an average grain size of
about 11.5 nm. After an annealing at 450 C, no distinct microstructural
variation was observed, as shown in Fig. 3 (b). With
increasing Ta to 500 C, the film started L10 ordered, but exhibited a
reduced grain size of about 5 nm(Fig. 3(c)). The reason for this grain
size reduction might be due to the nucleation of L10 phases, as
indicated by Fig. 3(d) where the weak spots represents the (001)L10 ordering domains with an average size of about 3 nmusing dark
field technique. With increasing Ta to 650 C, the sample was in the
fully ordered state with a coarsening average grain size of about
8 nm(Fig. 3(e) and (f)). When Ta was raised to 700 C, the average
grain of the film with PMA barely increases to about 9 nm
(Fig. 3(g)). For the films with the highest Ta, an extensive grain
growth with an average grain size of about 25 nmwas observed for
the FePt with perfect PMA, as shown in Fig. 3(h).
The dependence of in-plane residual stress (s) onTa is illustrated
in Fig. 4. For the as-deposited film, s was in tensile direction with a
magnitude of 0.93 GPa and almost remained for the sample after a
annealing of Ta ¼ 450 C, since no significant microstructural and
grain size alterations were observed. A minimum value of s was
found for the sample annealed at 500 C, which presumably results
from the nucleation of L10 ordering. The L10 ordering leads to a
volumetric expansion and atomic rearrangement [23,24], whichreleases the preformed tensile stress. A similar stress behavior was
also found in the FePt annealed using a conventional vacuum
furnace [17].With increasing Ta from 500 to 650 C, the s increases
from 0.73 to 1.65 GPa, while the average grain size increased from
about 5 to 8 nm, as shown in the inset of