Field-free spin–orbit-torque switching of perpendicular magnetization aided by uniaxial shape anisotropy

Abstract

It has been demonstrated that the switching of perpendicular magnetization can be achieved with spin orbit torque (SOT) at an ultrafast speed and low energy consumption. However, to make the switching deterministic, an undesirable magnetic field or unconventional device geometry is required to break the structure inverse symmetry. Here we propose a novel scheme for SOT-induced field-free deterministic switching of perpendicular magnetization. The proposed scheme can be implemented in a simple magnetic tunnel junction (MTJ) /heavy-metal system, without the need of complicated device structure. The perpendicularanisotropy MTJ is patterned into elliptical shape and misaligned with the axis of the heavy metal, so that the uniaxial shape anisotropy aids the magnetization switching. Furthermore, unlike the conventional switching scheme where the switched final magnetization state is dependent on the direction of the applied current, in our scheme the bipolar switching is implemented by choosing different current paths, which offers a new freedom for developing novel spintronics memories or logic devices. Through the macrospin simulation, we show that a wide operation window of the applied current pulse can be obtained in the proposed scheme. The precise control of pulse amplitude or pulse duration is not required. The influences of key parameters such as damping constant and field-like torque strength are discussed as well.

Multiferroic heterostructures for spintronics

“…Other manifestations of hybrid ME-SOT heterostructures have been explored to break critical symmetries and lift degeneracies in SOT switching [229][230][231][232]. For instance, SOT switching of a perpendicular magnetic anisotropy (PMA) magnet by the spin Hall effect of isotropic heavy metals is complicated by non-deterministic switching.…”

Magnetic Tunnel Junction Applications

“…When a current crosses the non-magnetic layer, spins are accumulated and a torque switching is generated over the magnetization of the ferromagnetic layer. A faster switching can occur using SOT with the elimination of the time-demanding precessional motion [28]. However, one disadvantage of SOT is that it requires bigger cell size than STT-based applications due to its three terminal structure, so it can be not compatible with high-density applications.…”

Nonvolatile Magnetic Memory Combined With AND/NAND Boolean Logic Gates Based on Geometry-Controlled Magnetization Switching

“…Because the spin orbit torque exerted on the electron spin in the FM layer was related to the current density of the NM layer, manipulation of the magnetization direction of the FM layer would be dependent on its position on the NM layer. It has been reported that specific patterning of both FM layer and NM layer could be utilized to control the magnetization state of the FM layer [Safeer 2016, Siddiqui 2020, Martinez 2016, Wang 2019]. Hence, the feasibility of applying such method in spinbased data storage has been confirmed.…”