Spin-Torque Microwave Detectors

Abstract

It is known that the spin-transfer torque (STT) effect provides a new method of manipulation of magnetization in nano-scale devices. According to the STT effect, bias DC current traversing magnetic multilayers can transfer angular magnetic moments from one layer to another, which can give rise to microwave dynamics of magnetization in the layer. However, it is clear that an inverse effect is also possible. This inverse effect leads to the so-called spin-torque diode effect, first originally observed experimentally in 2005. The spin-torque diode effect is a rectification effect of the input microwave current in a magnetoresistive junction. In this case, the resonance oscillations of the junction resistance can mix with the oscillations of the input microwave current and produce a large enough output DC voltage across the junction. The devices which utilize this effect are called the spin-torque microwave detectors (STMD). In this chapter, we review the general properties of STMDs and consider the performance of a STMD in two different dynamic regimes of detector operation: in the well-known traditional in-plane regime of STMD operation and in the recently discovered novel out-of-plane regime of STMD operation. We analyze the performance of a STMD and consider the typical applications for such detectors in both regimes.