3. Results and discussion
Fig. 1(a) shows the x-ray diffraction spectra of the as-deposited
films and annealed films at various Ta (450e800 C). Note that intensity
axis for each pattern is plotted on a logarithmic scale and
shifted for clarity. For the as-deposited FePt film, it exhibited a
disordered fcc structure with (111) texture. After an annealing at
Ta ¼ 500 C, a very weak (001) diffraction peak was found, indicating
an emergence of L10 phase. The intensities of (001) and (002)
reflections enhanced as increasing RTA temperature, which were
even stronger than that of (111) reflection in the samples with
Ta 600 C. This evidences a crystallographic orientation alteration
from (111) to (001) plane. To further investigate the dependence of
Ta on evolution of preferred orientation, a semi-quantitative
parameter, Lotgering orientation factor (LOF) was adopted [18]. In
case of (001) preferred orientation in FePt, LOF is defined as
LOF ¼ (pp0)/(1p0), where p and p0 refer to S(00l)film/S(hkl)film
and S(00l)powder/S(hkl)powder, respectively. Accordingly, LOF ranges
from a certain negative value to 1. The negative value represents a
preferred orientation other than (001), 0 means a random orientated
state, and 1 refers to a prefect (001) texture. Dependence of
LOF on Ta is shown in Fig. 1(b). For the as-deposited film and
annealed film at 450 C, LOF values were 0.138, indicating a (111)
preferred orientation. With increasing Ta from 450 to 700 C, the
LOF value altered from negative value to unity, evidencing a significant
improvement of the (111) preferred orientation. The integrated
intensity ratio of the superlattice (001) and fundamental
(002) peaks was used to determine the ordering parameter of L10
phase (S) according to Warren's theory [19]. As illustrated in Fig. 1
(c), S value increased from 0 to greater than 0.9 as Ta was raised
from 450 to 600 C. No significant variation of S with increasing Ta
further was observed. It is worthy to note that the onset temperature
(500 C) for development of S and (001) texture was likely to
be the same; however, the progress of Swas more rapid than that of
(001) orientation. This result suggests that the L10 phase transformation
is one of key factors for (001) texture formation [11],
especially for determination of the onset annealing condition.
Furthermore, we also noticed that interference fringes in the vicinity of the Bragg peaks for the sample annealed at Ta ¼ 700 and
800 C, indicating the high coherence of lattice and surface flatness.
Out-of-plane and in-planeM-H loops of the rapid-annealed FePt
films at various temperatures are presented in