Aging effects on amorphous Tb–transition-metal films prepared by diode and magnetron sputtering

Abstract

We have studied and compared the aging characteristics of the amorphous Tb(FeCo) films from both dc getter diode and magnetron sputtering. No protecting layer such as SiO2 or Al2O3 was put on the films. Fresh films of 1.0-μm thickness from diode sputtering showed a perpendicular anisotropy and well-behaved magnetic properties using a vibrating sample magnetometer and an automatic torque magnetometer. We noticed a decrease in perpendicular anisotropy when the films were exposed to the air. However, this aging phenomenon was not observed in films of the same thickness prepared by magnetron sputtering even after seven months’ exposure to the air. The reasons for the difference are due to two distinct reaction mechanisms: bulk reaction in diode-sputtered films and surface reaction in magnetron-sputtered films. A variation of the microstructure is believed to attribute to this. The surface reaction was studied in thinner magnetron-sputtered films of 10 and 25 nm, where the surface-to-bulk ratio is larger. A decrease in perpendicular anisotropy with aging was observed in these thinner films.