M. Watanabe et al., MICROSTRUCTURE AND MAGNETIC-PROPERTIES OF HIGH-COERCIVE FE-PT ALLOY THIN-FILMS, Materials transactions, JIM, 37(3), 1996, pp. 489-493
We investigated microstructures and magnetic domain structures of sput
tered FePt alloy thin films in order to elucidate the origin of the hi
gh coercive force H-c. The FePt alloy thin films were prepared by RF s
puttering method on water-cooled glass substrates. Transmission electr
on microscopy (TEM) shows that the as-deposited film consists of an fc
c gamma phase with a grain size of 10 - 20 nm. Rippled domains were ob
served in the Lorentz micrographs. After annealing at 823 K,a steep in
crease in H-c up to similar to 800 kA/m and a decrease in resistivity
rho were observed. The TEM observation indicates that the annealed fil
m consists of an fct gamma(1) phase with a grain size of 20 - 80 nm. F
rom random patterns of grain size scale in the Lorentz micrograph it i
s suggested that the high H-c might be explained as being due to a rot
ation of magnetization for each grain with a single-domain state. The
H-c of the annealed samples increases with film thickness up to a thic
kness of 100 nm. From the thermomagnetic analysis (TMA), it is implied
that the order-disorder transformation occurs at T > 620 K; the T-c o
f the disordered gamma and ordered gamma(1) phases were evaluated to b
e 599 K and 739 K, respectively.