Micromagnetic study of hotspot and thermal effects on spin-transfer switching in magnetic tunnel junctions

The hotspot and current self-heating effects on the spin-transfer-induced magnetization switching are investigated for low resistance magnetic tunnel junctions. Two kinds of spin torque theories, one for ohmic-like conduction from randomly distributed hotspots and the other for tunnel conduction from an insulator barrier, are combined together in this study by using a parallel resistor model. We find that the spin torque amplitude is locally enhanced in the hotspot region due to the large current density, which leads to a strong reduction of the current switching threshold (Jc), in a way that the enhanced spin torque induces the local magnetization near the hotspot switching first, and then drives the switching spreading through the whole free layer. The current self-heating effect is also studied; the free layer temperature increases only a few degrees at an applied current close to Jc ∼1× 107 A cm2, which results in a slight decrease in Jc for the low resistance junctions with hotspots.