Spin–orbit torque switching without an external field using interlayer exchange coupling

Abstract

Manipulation of the magnetization of a perpendicular ferromagnetic free layer by spin-orbit torque (SOT) is an attractive alternative to spin-transfer torque (STT) in oscillators and switches such as magnetic random-access memory (MRAM) where a high current is passed across an ultrathin tunnel barrier. A small symmetry-breaking bias field is usually needed for deterministic SOT switching but it is impractical to generate the field externally for spintronic applications. Here, we demonstrate robust zero-field SOT switching of a perpendicular CoFe free layer where the symmetry is broken by magnetic coupling to a second in-plane exchange-biased CoFe layer via a nonmagnetic Ru or Pt spacer. The preferred magnetic state of the free layer is determined by the current polarity and the sign of the interlayer exchange coupling (IEC). Our strategy offers a potentially scalable solution to realize bias-field-free switching that can lead to a generation of SOT devices, combining a high storage density and endurance with a low power consumption.

Antiferromagnetic spintronics

“…b Data for Fe 50 Rh 50 are for the specific antiferromagnetic-to-ferromagnetic transition. Fukami et al, 2016;Lau et al, 2016;Oh et al, 2016) (see Sec. III.D.4)].…”

“…However, ferromagnetic/ antiferromagnetic coupling increases the spin torque efficiency, making it an advantage for current-induced switching of the ferromagnet. Section III.D.4 focuses on the use of the multifunctionalities of antiferromagnets (spin Hall torques and exchange bias) to deterministically reverse the out-of-plane magnetization of a ferromagnet in zero applied magnetic field (Brink et al, 2016;Fukami et al, 2016;Lau et al, 2016;Oh et al, 2016;Sklenar et al, 2016). Note also that Ou et al (2016) further highlighted the importance and complexity of interfacial engineering (see also Sec.…”

“…Four groups (Brink et al, 2016;Fukami et al, 2016;Lau et al, 2016;Oh et al, 2016) simultaneously used the magnetic interactions between a ferromagnet with out-of-plane anisotropy (Co/Ni, CoFe and CoFe/Ni, Co/Pt, CoFeB) and an antiferromagnet (PtMn, IrMn) to create in-plane exchange bias and break the symmetry. Their results showed that the spin Hall torques, either directly from the antiferromagnet (Fukami et al, 2016;Oh et al, 2016) (see Fig.…”

“…Their results showed that the spin Hall torques, either directly from the antiferromagnet (Fukami et al, 2016;Oh et al, 2016) (see Fig. 41) or from an additional heavy metal (Brink et al, 2016;Lau et al, 2016) could then deterministically reverse the out-of-plane magnetization of the ferromagnet in zero applied magnetic field. In all these experiments, it was also confirmed that the dampinglike torque contribution prevails over the fieldlike torque contribution (see Sec.…”

Exploiting Spin-Orbit Torque Devices As Reconfigurable Logic for Circuit Obfuscation

“…Early research usually requires an external magnetic field to assist the switch- ing due to the induced SHE is not enough [20] [21]. But most recent research has shown that field-free magnetization reversal could be realized by spin-Hall effect and exchange bias when a perpendicularly magnetized Pt/Co/IrMn structure is introduced for ferromagnetic/anti-ferromagnetic interface [30][31] [32].…”