Reduction of a coercive field in the bilayers of CoGdTb/NiFe with perpendicular magnetic anisotropy

Abstract

We have investigated the magnetic properties of CoGdTb/NiFe bilayer with the variation of NiFe thickness (t(NiFe)). It was found that the composition of CoGdTb layer can be controlled by adjusting the Ar working pressure of the sputtering system. We used a CoGdTb/NiFe bilayer with the Co concentration of 82.2 at. %, which was deposited at an Ar working pressure of 3 mTorr, to investigate the bilayer coercivity. The deposition of NiFe (t(NiFe)=1.5 nm) on the CoGdTb layer caused the increase of the coercive field. It was found from the in-plane and out-of-plane hysteresis loops that the NiFe moments were aligned out of plane due to the strong coupling between NiFe and CoGdTb, leading to the increase of the coercive field. With the increase of the NiFe thickness (t(NiFe)=5 nm), the coercive field of CoGdTb decreased rapidly, which was likely to be caused by the in-plane component of NiFe moments. With further increase of the NiFe thickness (t(NiFe)=10 and 15 nm), no more reduction of the coercive field was observed although more portion of NiFe moments was in plane. We conjectured that the in-plane NiFe moments within the limited area near the interface between CoGdTb and NiFe contributed to the reduction of the coercive field of CoGdTb. (C) 2008 American Institute of Physics.