Bias-driven large power microwave emission from MgO-based tunnel   magnetoresistance devices
  Spin-momentum transfer between a spin-polarized current and a ferromagnetic layer can induce steady-state magnetization precession, and has recently been proposed as a working principle for ubiquitous radio-frequency devices for radar and telecommunication applications. However, to-date, the development of industrially attractive prototypes has been hampered by the inability to identify systems which can provide enough power. Here, we demonstrate that microwave signals with device-compatible output power levels can be generated from a single magnetic tunnel junction with a lateral size of 100 nm, seven orders of magnitude smaller than conventional radio-frequency oscillators. We find that in MgO magnetic tunnel junctions the perpendicular torque induced by the spin-polarized current on the local magnetization can reach 25% of the in-plane spin-torque term, while exhibiting a different bias-dependence. Both findings contrast with the results obtained on all-metallic structures - previously investigated -, reflecting the fundamentally different transport mechanisms in the two types of structures. 
Alina M. Deac, Akio Fukushima, Hitoshi Kubota, Hiroki Maehara,   Yoshishige Suzuki, Shinji Yuasa, Yoshinori Nagamine, Koji T...