Multilevel remanence states have potential applications in ultra-high-density storage and neuromorphic computing. Continuous tailoring of the multilevel remanence states by spin-orbit torque (SOT) is reported in perpendicularly magnetized Pt/Co/IrMn heterostructures. Double-biased hysteresis loops with only one remanence state can be tuned from the positively or negatively single-biased loops by SOT controlled sign of the exchange-bias field. The remanence states associated with the heights of the sub-loops are continually changed by tuning the ratio of the positively and negatively oriented ferromagnetic domains. The multilevel storage cells are demonstrated by reading the remanent Hall resistance through changing the sign and/or the magnitude of current pulse. The synaptic plasticity behaviors for neuromorphic computing are also simulated by varying the remanent Hall resistance under the consecutive current pulses. This work demonstrates that SOT is an effective method to tailor the remanence states in the double-biased heavy metal/ ferromagnetic/antiferromagnetic system. The multilevel-stable remanence states driven by SOT show potential applications in future multilevel memories and neuromorphic computing devices.

Increasing spin Hall angle of heavy metals has attracted considerable attention due to their potential applications in spintronic technology. Here, we demonstrate that the spin Hall angle could be enhanced dramatically in the Ta/[Pt/Ru]n/Pt/Co/Ta multilayers. The spin Hall angle reaches a maximum value of 0.28 when n = 5 from the loop-shift method with a relative low resistivity of approximately 48 μΩ cm. Meanwhile a minimum critical switching current density approximately 3.2 × 106 A/cm2 under an in-plane bias magnetic field around 5% of the perpendicular anisotropy field was obtained for the sample with n = 5 in current-induced magnetization switching experiment. We find that the extrinsic spin Hall mechanism changes from the spin skew scattering when n < 2 to spin side-jump mechanism when n > 2. This work provides an effective way in increasing spin Hall angle for low-power consumption spintronics devices.

The interfacial Dzyaloshinskii–Moriya interaction (DMI) in ferromagnetic/non‐magnetic‐metal bilayers is essential to stabilize chiral spin textures for potential applications. Recent works reveal that the interlayer DMI is beneficial to designing 3D chiral spin textures that possess fundamental importance and the associated technological promises. Here, the interlayer DM constants are determined quantitatively in synthetic ferromagnetic/antiferromagnetic Pt/Co/Pt/Ru/Pt/Co/Ta structures. The results demonstrate that the interlayer DMI shows uniaxial anisotropic characteristics. The first‐principles calculations elucidate that the anisotropic interlayer DMI is induced by the in‐plane symmetry breaking along two high symmetric directions, which favors the magnetization of adjacent ferromagnetic layers canting in different directions. The anisotropic interlayer DMI is also confirmed by spin‐orbit torque driven asymmetric magnetization switching. Moreover, the interlayer DMI can be tuned by the Ru‐layer‐thickness and beneficial to designing 3D spin textures for future spintronic devices.

Current induced spin–orbit torque (SOT) in heavy metals with strong spin–orbit coupling strength has attracted considerable attention due to its potential applications in spintronic technology. Pt, as one of the mostly used heavy metals in SOT-based spintronic devices, shows large spin Hall angle (θSH) with its single phase and alloy counterparts. In this work, the in-plane crystallographic orientations related θSH of epitaxial Pt(111) layer is reported in MgO(111)/Pt(111)/Co/Ta heterostructures with strong perpendicular magnetic anisotropy. The θSH shows a quite large difference with values, respectively, around 0.083 and 0.057 when the current applied along the [11¯0] and [112¯] crystallographic directions of Pt(111) by the damping-like SOT efficiency using the harmonic Hall voltage measurement technique. The critical switching current densities also show large difference between these two orthogonal crystallographic orientations with the trend of that the larger SOT efficiency leads to the smaller critical switching current density. It independently confirms the generation of different damping-like SOT efficiency when current along [11¯0] and [112¯] directions of Pt(111). Moreover, a perpendicularly magnetized Pt/Co/Ta reference heterostructures with Pt having polycrystalline phase shows tiny variation of damping-like SOT efficiency in in-plane two orthogonal directions, which also indirectly indicates the crystallographic orientations related θSH in epitaxial Pt(111) layers. This study indicates that the θSH of epitaxial Pt is a crystallographic orientations related parameter.

We found that the exposure of a Co/Pt bilayer to air will result in a trace amount of oxidation at the Co/Pt interface, while the Pt layer is immune to oxidation. The appearance of CoOx results in a negative spin Hall magnetoresistance and unconventional spin–orbit torques (SOTs), which are observed through temperature-dependent transport and spin-torque ferromagnetic resonance measurements. These results can be understood by considering CoOx as an individual magnetic layer between Pt and Co, with two important characteristics: (1) its magnetization is aligned in the plane that is perpendicular to the magnetization of Co and (2) the spin transparency of CoOx increases with increasing temperature. These results help us understand the features of spin transport at the interface when oxidation occurs and further indicate that trace amounts of oxidation can be a highly effective method to control SOT in magnetic heterostructures.