Chiral Domain Wall Injector Driven by Spin–Orbit Torques

Abstract

Memory and logic devices that encode information in magnetic domains rely on the controlled injection of domain walls to reach their full potential. In this work, we exploit the chiral coupling induced by the Dzyaloshinskii-Moriya interaction between in-plane and out-of-plane magnetized regions of a Pt/Co/AlO x trilayer in combination with current-driven spin-orbit torques to control the injection of domain walls into magnetic conduits. We demonstrate that the current-induced domain nucleation is strongly inhibited for magnetic configurations stabilized by the chiral coupling and promoted for those that have the opposite chirality. These configurations allow for 1 arXiv:2003.11805v1 [cond-mat.mes-hall] 26 Mar 2020 efficient domain wall injection using current densities of the order of 4×10 11 Am −2 , which are lower than those used in other injection schemes. Furthermore, by setting the orientation of the in-plane magnetization using an external field, we demonstrate the use of a chiral domain wall injector to create a controlled sequence of alternating domains in a racetrack structure driven by a steady stream of unipolar current pulses. Main TextThe nucleation of magnetic domains underpins magnetization reversal processes and, consequently, the functioning of most types of magnetic storage devices. Domain wall (DW) racetrack memory and logic devices, in particular, require reliable control over domain nucleation and current-induced DW propagation in order to work efficiently. 1-3 The problem of domain nucleation was first addressed by modifying the magnetic anisotropy of the nucleation sites using altered shapes 4-6 or ion irradiation of magnetic structures, 7-12 which favor magnetization reversal at specific locations. These methods are commonly used in field-induced domain nucleation and DW propagation studies. [13][14][15][16] Current-induced domain nucleation techniques based on the Oersted field produced by a narrow write line, 17 spin-transfer torque switching using magnetic tunnel junctions 18 and using magnetization boundaries where the magnetization of the two adjacent regions are orthogonally aligned 19 have been shown to mitigate the shortcomings of field nucleation. These methods offer faster and more localized domain nucleation at the cost of higher device complexity.A significant leap forward in magnetic writing was made with the advent of spin-orbit torques (SOTs), 20-24 which emerge at ferromagnet/heavy metal interfaces. 25 Ever since the

Asymmetric depinning of chiral domain walls in ferromagnetic trilayers

“…A variety of device concepts based on domain wall (DW) motion has been proposed for memory and logic operations [4][5][6]. Many of these proposals rely on unidirectional DW motion along a racetrack, which can be easily achieved by current-induced spin torques [7][8][9][10][11][12][13][14][15][16], rather than externally applied magnetic fields [3].…”

Field- and Current-Driven Magnetic Domain-Wall Inverter and Diode

“…This interaction favors the orthogonal alignment of adjacent magnetic moments with a fixed chirality, as expressed by the Hamiltonian H DMI = −D(m 1 × m 2 ), where D and m i (i = 1 or 2) represent the DMI vector and two neighboring magnetic moments, respectively [30,31]. In competition with the exchange interaction, magnetic anisotropy, and dipolar interaction, the DMI favors the formation of noncollinear spin textures, such as chiral Néel domain walls [10][11][12][32][33][34][35], spin helices, cycloids, and skyrmions [36][37][38][39]. Here, we exploit the lateral chiral coupling promoted by the DMI in combination with patterning of the magnetic anisotropy of a Pt/Co/Al trilayer to achieve control over the preferred magnetic configurations of consecutive regions of a racetrack with IP and OOP magnetization.…”

“…As a result of the DMI arising from the Pt/Co interface, the left-handed configurations down-right (⊗→) and up-left ( ←) are energetically favored over the right-handed configurations ⊗← and → in adjacent OOP-IP regions. By patterning the magnetic anisotropy with high-resolution lithography, we are able to create chirally coupled nanomagnetic systems with extended OOP-IP structures that can be used for fabricating artificial spin ices [40], lateral synthetic antiferromagnets, synthetic skyrmions, and fieldfree memory elements [22], as well as current-driven DW injectors [33] and DW logic circuits [23,24].…”

Engineering of Intrinsic Chiral Torques in Magnetic Thin Films Based on the Dzyaloshinskii-Moriya Interaction

“…Indeed, in recent work performed on DMI-coupled systems, a number of phenomena arising from the lateral coupling have been demonstrated, such as lateral exchange bias between adjacent regions of the same magnetic layer, two-dimensional synthetic antiferromagnets, and fieldfree switching of coupled nanomagnets by spin-orbit torques [28]. Moreover, the intralayer DMI can be used to nucleate and define the position of magnetic domain walls (DW) [29,30] and realize all-electrical DW logic circuits [10,26,31,32].…”

“…In order to observe the spontaneous effect of chiral coupling in such basic elements, the anisotropy has to be low-enough so that the effective magnetic field can overcome the associated energy barrier. This approach has been used to form spontaneous chiral magnetic textures such as skyrmions and polar vortices, as well as DW injectors, inverters or logic devices [10,26,29,31,32].…”