Interlayer exchange coupled composite free layer for CoFeB/MgO based perpendicular magnetic tunnel junctions

Abstract

We have investigated the effect of Ta insertion thickness on perpendicular magnetic anisotropy (PMA) in [Co/Pt multi-layers]/Ta/CoFeB (Hard/Soft) composite free layer. For insertions less than 0.6 nm thick, the ferromagnetic exchange was strong enough to switch the two layers together. The exchange turned from ferromagnetic to anti-ferromagnetic in nature for Ta insertion thickness above 0.7 nm. We observed increase in PMA with increasing Ta insertion thickness. It was noticed that this increase in PMA was caused by the enhancement of CoFeB/MgO interface anisotropy. The interface anisotropy increased by more than 0.9 erg/cm2 as the Ta insertion thickness increased from 0 nm to 0.5 nm. The Hk value for the composite free layer with 0.5 nm thick Ta insertion is around 11 kOe leading to a high thermal stability factor, estimated around 152 for 20 nm nano-dots. © 2013 AIP Publishing LLC.