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.
Highlights
In addition to the bilayer systems, recently there is 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
In addition to fundamental studies, these MRs can be used to realize novel devices such as memory[112] and sensors.[95]. Another interesting application of charge–spin interconversion is in terahertz (THz) generation, where a transient spinpolarized current is converted to a transverse charge current via either inverse spin Hall effect (ISHE),[113–117] inverse Rashba–Edelstein effect (IREE),[109,118,119] or anomalous Hall effect (AHE),[120,121] thereby emitting the THz waves
The results suggest that anomalous Hall magnetoresistance (AHMR) exist in FM with large spin–orbit interaction (SOI) and it can be described by the phenomenological model described in Sec
Summary
The last 30 years have witnessed several fundamental discoveries and technological breakthroughs in magnetism and spintronics,[1,2,3] the giant magnetoresistance (GMR) effect,[4,5] magnetic tunnel junction (MTJ),[6,7,8,9] spin-transfer torque (STT),[10,11,12] and most recently, the spin–orbit torque (SOT).[13,14,15,16,17,18,19,20] The SOT, when applied to memory and three-terminal devices, has the potential to overcome the limitations of STT as it allows us to separate the write and read current paths and, promises high endurance, fast speed, and low power. In addition to fundamental studies, these MRs can be used to realize novel devices such as memory[112] and sensors.[95] Another interesting application of charge–spin interconversion is in terahertz (THz) generation, where a transient spinpolarized current is converted to a transverse charge current via either ISHE,[113–117] IREE,[109,118,119] or anomalous Hall effect (AHE),[120,121] thereby emitting the THz waves. Several excellent reviews have already been published on this subject covering materials, physics, and applications.[122–130] In this Perspective, we will first present a phenomenological model on charge–spin interconversion in both bilayer and single-layer systems and focus on the applications of SOT in magnetic field sensors. We will provide a perspective view on how to further improve the performance of SOT-enabled magnetic field sensor by introducing alternative designs, such as the three-terminal magnetic field sensor and charge–spin interconversion in single-layer FM
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