Spin-Torque Diodes: From Fundamental Research to Applications

Among a rich variety of emerging spintronic devices, spin-torque diodes (STDs) are among the most interesting, from both a fundamental and an applied perspective. The spin-torque diode effect occurs when a microwave alternating electric current injected into a magnetic tunneling junction (MTJ) is rectified due to the simultaneous actions of tunneling magnetoresistance and spin-transfer torque. While the sensitivity of STDs observed in the initial research is rather modest (about 1.4 mV mW(-1)), after only a few years researchers have increased it to 200 kV W(-1)and demonstrated rectification at nanowatt input powers, which radically exceeds the capabilities of mainstream Schottky diodes. This impressive progress is based on a deep understanding of the complex STD physics and on recent advances in MTJ fabrication technology. Herein, the experimental pathways toward increasing the sensitivity and extending the frequency range of STDs and theoretical works aimed at explaining the complex nonlinear dynamics are analysed, and a wide variety of possible STD applications are discussed.