Smooth Fe78Si10B12 thin films were prepared by r.f. sputtering with the very slow deposition rate of 0.59 nm/min. The as-deposited films were not fully amorphous, instead α-Fe(Si) nanocrystallites were found to be embedded in the amorphous matrix. The saturation magnetostriction λs of the as-deposited film is about 6.5×10-6. After annealing at 540 °C for 1 h in an ultrahigh vacuum (4.5×10-5 Pa), the fraction of α-Fe(Si) crystalline phase largely increased, and correspondingly the λs decreased to 4.5×10-7. Ripple domain structures were observed in the as-deposited film, while dense stripe domains were observed in the annealed sample, characterized by a very narrow domain width of 80 nm. (110) texture and island-like configuration of α-Fe(Si) nanocrystallites formed by the annealing treatment are responsible for the perpendicular anisotropy. For the as-deposited film, the magnetization curves increased linearly with the increase of the magnetic field, and showed the very small hysteresis. On the other hand, the annealed sample clearly showed a very steep jump near the origin, which is due to the switch process of the dense stripe domain.
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