Charge–spin interconversion and its applications in magnetic sensing

Abstract

Charge–spin interconversion provides an effective way to generate spin current, spin–orbit torque, and unconventional magnetoresistance that is different from the magnetoresistance originated from spin-polarized current. A widely studied system that leads to all these phenomena is the ferromagnet/heavy metal bilayer, in which spin accumulation/current is generated through either the spin Hall effect in the heavy metal layer or Rashba–Edelstein effect at the ferromagnet/heavy metal interface. The subsequent interaction of the current-induced spins with the ferromagnet generates spin–orbit torque, and the inverse conversion of the backflow spin current to charge current in the heavy metal layer leads to different types of magnetoresistances. Many proof-of-concept devices and applications have been demonstrated based on the spin–orbit torque and magnetoresistance in the bilayer system, including non-volatile memory, logic, nano-oscillator, magnetic sensor, neuromorphic and scholastic computing, etc. In addition to the bilayer systems, recently there is also a growing interest in charge–spin interconversion in single-layer ferromagnets. In this Perspective, we first introduce the charge–spin interconversion in different systems based on phenomenological models, after which we show how the spin–orbit torque and spin Hall magnetoresistance in ferromagnet/heavy metal bilayers can be exploited for magnetic sensing applications. We also discuss charge–spin interconversion in single-layer ferromagnets via the anomalous Hall effect.