Magnetic behavior of amorphous Fe–Zr thin films sputtered at different Ar pressures

Amorphous Fe–Zr thin films with similar compositions exhibit a considerable change in their magnetic behaviors when they are sputtered at different Ar pressures. The change is well explained by a parameter – the SPM ratio – devised in this study, which is defined as the ratio of the magnetization due to the superparamagnetic behavior to the saturation magnetization. The change in the magnetic behavior of thin films with 40–70 at.% Fe depends on an increase in the SPM ratio, and it is more prominent at higher Fe contents; for example, the SPM ratio of a thin film with ∼60 at.% Fe increases from ∼0 to 0.69 with increasing Ar pressure from 2 to 10 mTorr. Subsequent annealing of the thin film fabricated at the Ar pressure of 10 mTorr at 150 °C leads to a 10-fold decrease in its SPM ratio from that in the as-deposited state. This decreased SPM ratio is, nevertheless, still higher than that of the thin film fabricated at the Ar pressure of 2 mTorr. These results indicate that the magnetic behaviors of amorphous Fe–Zr thin films are highly sensitive to the Ar pressure. Thus, it is crucial to take this parameter into account in the analysis of the magnetic behaviors of amorphous Fe–Zr thin films.