Current driven chiral domain wall motions in synthetic antiferromagnets with Co/Rh/Co

Abstract

Spin–orbit torque that originates from spin Hall effect and Dzyaloshinskii–Moriya interaction (DMI) can efficiently move chiral magnetic domain walls in perpendicularly magnetized wires. It has been shown that antiferromagnetically coupled composite domain walls across a ruthenium layer can be driven even faster by exchange coupling torque that is proportional to exchange coupling strength. Here, we report a current-driven motion of composite chiral domain walls in synthetic antiferromagnets with a rhodium spacer layer. It is found that the domain walls in the wire with a rhodium layer do not move as fast as that with a ruthenium layer although the exchange coupling in Co|Rh|Co is stronger than Co|Ru|Co, which is due to the formation of a large DMI at the Rh|Co interface. The Dzyaloshinskii–Moriya interaction at the Co/Rh interface has the same sign and comparable strength to the Pt|Co interface, thus negating the exchange coupling torque. The spin Hall effect from rhodium is found to be as small as ruthenium. Our findings show that rhodium can be used to tailor the DMI strengths in the current-driven motion of chiral domain walls in various magnetic nanostructures.

Domain wall motion at low current density in a synthetic antiferromagnet nanowire

“…In particular, very fast DW motion at several 100 m s −1 for high current drives of a few TA m −2 have been observed in these systems using a Ru spacer [12]. It has subsequently been shown that replacing the spacer material with Rh reduces the DW velocity [13], that DW velocity in a SAF can be controlled by means of iontronic gating [14], and that SAF nanowires can be connected to conventional FM wires and still transmit DWs [15]. A variety of effects related to curved tracks, disordered materials, and temperature fluctuations have been studied by means of micromagnetics [16].…”

Low Gilbert damping and high perpendicular magnetic anisotropy in an Ir-coupled L10-FePd-based synthetic antiferromagnet

“…However, the anti-ferromagnetic behavior—what is referred to as a synthetic antiferromagnet (SAF)—is of particular technological interest to spintronic applications as the building block of a fringe-field free reference layer for ultrahigh density spin-transfer-torque magnetic random access memory (STT-MRAM) cells 11 , 12 . Additionally, the SAF shows technological merit as the free layer for SAF magnetic tunnel junctions (MTJs) 20 , 28 , 29 and as domain wall and Skyrmion bubble devices 30 , 31 , in which case the IEC torques can generate faster magnetization switching, enable high domain wall velocities and stabilize Skyrmions at elevated temperature compared to ferromagnetic counterparts.…”

Sputter Gas Damage in Nanolayered Pt/Co/Ir-based Synthetic Antiferromagnets for Top-Pinned Magnetic Tunnel Junctions

“…Significant ongoing research efforts in spintronic applications are focused on the development and processing of synthetic antiferromagnets (SAFs), the trilayered FM1/NM/FM2 structure, where FM is a ferromagnet and NM is typically an ultrathin (<1 nm) nonmagnetic metal that typically includes Cr, Ru or Ir . The interlayer exchange coupling (IEC) across the NM layer shows an oscillatory and decaying behavior that can be ferromagnetic (FM) or anti-FM, − but the anti-FM behavior is of particular technological interest to spintronic applications as the building block of a fringe-field free reference layer for ultrahigh density spin-transfer-torque magnetic random access memory (STT-MRAM) cells. , Additionally, the SAF shows technological merit as the free layer for SAF magnetic tunnel junctions (MTJs) − and as domain wall and Skyrmion bubble devices, , in which case the IEC torques can generate faster magnetization switching, enable high domain wall velocities, and stabilize Skyrmions at elevated temperature compared to FM counterparts. Furthermore, SAFs are believed to deliver topological protection for energy efficient spin–orbit torque MRAM devices, including protection of chiral Neel-type domain walls in domain wall − and Skyrmion racetrack memory devices by potentially reducing or eliminating the deleterious Skyrmion Hall effect. , …”