Effect of the stray field profile on the switching characteristics of the free layer in a perpendicular magnetic tunnel junction

Abstract

We show that the magnetic tunnel junction's coercivity (Hc) and anisotropy field (Hk) are linked to the stray field. This is shown by deliberately breaking the antiparallel configuration in the synthetic antiferromagnetic (SAF) reference layer to obtain changes to the stray field. Experimentally, Hc is larger in the low-Ho magnetic configuration with a normal SAF than in the high-Ho configuration with parallel-aligned SAF layers. Simulations reveal that the Hc reduction comes from the magnetization of the free layer tilting in-plane at the edge, which in turn is due to the large in-plane component of the stray field. Fitting the switching field distribution into the thermal activation model, we also show a close relationship between the thermal stability of the bi-stable switching, the anisotropy field (Hk), and the stray field. While it is possible to reduce Ho to zero with careful choice of the thickness of the SAF reference layers, the stray field at the edge cannot be fully eliminated.