Reduction of critical current density for spin transfer magnetization switching in a spin-valve nano-pillar

Experimental results on the current induced magnetization switching of nano-patterned IrMn/CoFe/Cu/CoFe spin-valves are reported. The main emphasis is the increase of MR and the reduction of the critical current density through an improved fabrication process. A method using a batch-fabricated trilayer template is developed with the junction features defined by a platinum(Pt) stencil mask. Nano-pillars with the lateral dimensions (150times80 nm²) are fabricated by electron-beam lithography, including a wet etching to form a nanotemplate. A key to the improved fabrication process is the formation of the recessed part of the SiO₂ layer which helps to reduce the shadow effect during the deposition of the spin valve multilayers into the nanotemplate. Both the MR ratio and the critical current density are enhanced by the new improved fabrication process. The observed critical current density is 5.98times10⁶ A/cm², which is significantly smaller than the value of 1.16times10⁸ A/cm² observed in a similar device fabricated using a conventional fabrication process.