Thickness and substrate effects on the perpendicular magnetic properties of ultra-thin TbFeCo films

Rare-earth transition metal ultra-thin TbFeCo amorphous films in the thickness range from 3.5 to 35 nm are radio frequency (RF)-sputtered based on a composition target method. Perpendicular magnetic anisotropy (PMA) is found to be strongly related to the thickness of sputtered TbFeCo film in this thickness range. No PMA can be observed in the 3.5 nm film, which may be too short to form local intrinsic single ion anisotropy. Strong PMA develops with the increasing film thickness. A critical compensation thickness of similar to 14 nm is found, where both the largest coercivity and lowest saturation magnetization are demonstrated. Across this critical thickness the change in polarity of the EHE loops is observed, corresponding to a transition from a FeCo-dominant to a Tb-dominant configuration. Additionally, the magnetic properties of the alloy films are shown to be significantly affected by the substrates used for deposition, which can be mainly attributed to preferential oxidization of the rare-earth Tb element in the films at the interfaces between the film and the substrates. Our results provide a simple method to manipulate magnetic properties of ultra-thin TbFeCo alloy films for the applications in spintronic devices.