Investigating thickness dependent perpendicular magnetic properties of ultrathin TbFeCo alloy films

Abstract

Ultrathin ferrimagnetic rare-earth transition-metal alloy films with perpendicular anisotropy are of great importance in developing spintronic devices. In this work, we investigate thickness dependent perpendicular magnetic properties of ultrathin Tb-rich TbFeCo films. The magnetic configuration, indicated by the sign of extraordinary Hall effect loops, was observed to change from Tb-rich to FeCo-rich state when TbFeCo film thickness reduces down to 7 nm. The compensation temperature Tcomp is shown to rise with increasing film thickness ranged from 7 to 42 nm. Nevertheless, for the 63 nm TbFeCo film a dip in thermomagnetic curve is earlier formed before the Tcomp is reached, which is revealed to be the competition between the temperature dependence of magnetization and film crystallization. For TbFeCo films with varying thickness the compensation thickness and the effective magnetization are derived from the fitting to be ∼10.4 nm and ∼208 emu/cm³, respectively. Compared with TbFeCo films, for TbFeCo(7 nm)/Ta (1.5 nm)/TbFeCo(63∼7 nm) structure the compensation thickness is found to be shifted by the thickness of bottom layer while the effective saturation magnetization keeps almost the same. Additionally, a perpendicular exchange coupling energy density of σ = ∼0.01 erg/cm² is achieved in the TbFeCo(7 nm)/Ta (1.5 nm)/TbFeCo(14 nm) structure with two-step switching. Our results provide some useful information for designing ultrathin TbFeCo-based spintronic devices.