Preparation and Characterization of Magnetic Tunnel Junctions with Spin Transfer Torque

Current-perpendicular-to-plane (CPP) magnetic tunnel junctions (MgO-MTJ) have been prepared using electron beam lithography as well as argon ion beam etching. A tantalum hardmask was utilized for pattern transfer. The size of the elliptical nanopillars could be decreased down to 90nm x 150 nm while preserving a TMR ratio of 92.5 %. TEM images proof the absence of redepositions at the MgO layer edge and give an insight into the interface quality. Magnetization switching was performed using either static magnetic fields and/or dc current (spin torque). The nanopillars could be characterized at temperatures ranging from 5 K to 150 K and room temperature. The analysis of magnetization dynamics included single-shot time-resolved magnetoresistance measurements as well as dc current induced oscillations of the free-layer magnetization.