Abstract
Spin orbit interactions are rapidly emerging as the key for enabling efficient current-controlled spintronic devices. Much work has focused on the role of spin-orbit coupling at heavy metal/ferromagnet interfaces in generating current-induced spin-orbit torques. However, the strong influence of the spin-orbit-derived Dzyaloshinskii-Moriya interaction (DMI) on spin textures in these materials is now becoming apparent. Recent reports suggest DMI-stabilized homochiral domain walls (DWs) can be driven with high efficiency by spin torque from the spin Hall effect. However, the influence of the DMI on the current-induced magnetization switching has not been explored nor is yet well-understood, due in part to the difficulty of disentangling spin torques and spin textures in nano-sized confined samples. Here we study the magnetization reversal of perpendicular magnetized ultrathin dots, and show that the switching mechanism is strongly influenced by the DMI, which promotes a universal chiral non-uniform reversal, even for small samples at the nanoscale. We show that ultrafast current-induced and field-induced magnetization switching consists on local magnetization reversal with domain wall nucleation followed by its propagation along the sample. These findings, not seen in conventional materials, provide essential insights for understanding and exploiting chiral magnetism for emerging spintronics applications.
Highlights
Spin orbit interactions are rapidly emerging as the key for enabling efficient current-controlled spintronic devices
We focus on current-induced magnetization switching (CIMS) of a ultrathin Pt/Co/AlO with in-plane dimensions two orders of magnitude below (≈100 nm). These dimensions should be amenable for the uniform magnetization description, our study indicates that the Dzyaloshinskii-Moriya interaction (DMI) is essential to describe the CIMS at these dimensions, which occurs through chiral asymmetric domain walls (DWs) nucleation and propagation
The CIMS can be described as or ↓) determines the direction (inward→s or follows: (i) outwards) otfhethieniltoicaal loiunt--polfa-npela→nme magnetization direction at the edges imposed by the DMI also imposes specific boundary conditions (DMI-BCs). (ii) The longitudinal field B supports the longitudinal in-plane magnetization component at one of the two lateral edges, and acts against it at the opposite one. (iii) For the favored lateral →edge, the l→ocal magnetization reversal is triggered at the corner where the out-of-plane torque τ z due to H SH and B opposes to the initial out-of-plane magnetization component
Summary
Spin orbit interactions are rapidly emerging as the key for enabling efficient current-controlled spintronic devices. Understanding and controlling the current-induced magnetization dynamics in high perpendicular magnetocristaline anisotropy heterostructures consisting of a heavy-metal (HM), a ferromagnet (FM) and an oxide (HM/FM/O) or asymmetric HM1/FM/HM2 stacks, is nowadays the focus of active research[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16] Apart from their interest for promising spintronics applications, these systems are attracting growing attention from a fundamental point of view due to the rich physics involved in the current-induced magnetization switching (CIMS)[1,2,3,4,5] and in the current-induced domain wall motion (CIDWM)[7,8,9,10,11]. The SL-SOT due to the SHE is physically distinct from other torques STTs and Rashba-SOTs: it is independent of P because it arises from the spin current generated in the HM, rather than the spin polarization of the charge current in the FM
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