Magnetic properties and domain structures of FeSiB thin films

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. (1 1 0) 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.