Effect of annealing on magnetic properties and domain structures of FePt thin films by rapid thermal annealing technique

Single-layered FePt films of 30 nm thick were annealed at temperature between 300 and 800 degrees C for 1-180 sec by a rapid thermal annealing (RTA) with a high heating rate of 100 degrees C/sec. It is found that both the grain size and magnetic domain size of the FePt film increase with increasing annealing temperature and annealing time. The FePt films exhibited soft magnetic properties and without domain images were observed by magnetic force microscope (MFM) when the films were post-annealed at below 500 degrees C for 180 sec. The in-plane coercivity (Hc(//)) and perpendicular coercivity (Hc(perpendicular to)) of FePt film increases significantly to 7.5 and 6.5 kOe respectively as annealing temperature increases to 600 degrees C. When the annealing temperature is increased to 700 degrees C, they are increased to 11.1 and 9.5 k0e, respectively, and the domain structure inclines to isolated domain. However, further increasing the annealing temperature to 800 degrees C, the Hc(//) and Hc(perpendicular to) values decrease to 9.8 and 8.9 kOe respectively due to largely increase the grain size of FePt and change the domain structure from isolation to continuity. On the other hand, in order to transform the FePt film from disordered gamma phase to the ordered L1(0) 0 phase, the annealing time of over 3 seconds is necessary when the film was post-annealed at 700 degrees C with a high heating rate of 100 degrees C/sec by RTA technique.