Large Emission Power over 2 μW with High $Q$ Factor Obtained from Nanocontact Magnetic-Tunnel-Junction-Based Spin Torque Oscillator

We have developed a new type of nanocontact structure called a "sombrero-shaped" nano-contact for a spin torque oscillator (STO) based on magnetic tunnel junctions. This structure reduces the shunt current, which passes through the capping layer, and hence improves the magnetoresistance (MR) ratio to 46% compared with an MR ratio of 3% in conventional nano-contact structures. It also displays highly stable oscillation ($Q=350$) with high emission power over 2 μW. This is significant in the development of new spintronic devices such as nanosized microwave generators and highly sensitive nanoscale magnetic field sensors.