Abstract All-electrical driven magnetization switching attracts much attention in next-generation spintronic memory and logic devices, particularly in magnetic random-access memory (MRAM) based on the spin–orbit torque (SOT), i.e. SOT-MRAM, due to its advantages of low power consumption, fast write/read speed, and improved endurance, etc. For conventional SOT-driven switching of the magnet with perpendicular magnetic anisotropy, an external assisted magnetic field is necessary to break the inversion symmetry of the magnet, which not only induces the additional power consumption but also makes the circuit more complicated. Over the last decade, significant effort has been devoted to field-free magnetization manipulation by using SOT. In this review, we introduce the basic concepts of SOT. After that, we mainly focus on several approaches to realize the field-free deterministic SOT switching of the perpendicular magnet. The mechanisms mainly include mirror symmetry breaking, chiral symmetry breaking, exchange bias, and interlayer exchange coupling. Furthermore, we show the recent progress in the study of SOT with unconventional origin and symmetry. The final section is devoted to the industrial-level approach for potential applications of field-free SOT switching in SOT-MRAM technology.
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Field-free current-induced magnetization switching in GdFeCo: A competition between spin–orbit torques and Oersted fields
Switching of perpendicular magnetization via spin–orbit torque (SOT) is of particular interest in the development of non-volatile magnetic random access memory (MRAM) devices. We studied current-induced magnetization switching of Ir/GdFeCo/Cu/Pt heterostructures in a Hall cross geometry as a function of the in-plane applied magnetic field. Remarkably, magnetization switching is observed at zero applied field. This is shown to result from the competition between SOT, the Oersted field generated by the charge current, and the material's coercivity. Our results show a means of achieving zero-field switching that can impact the design of future spintronics devices, such as SOT-MRAM.
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- Award ID(s):
- 2105114
- NSF-PAR ID:
- 10352021
- Date Published:
- Journal Name:
- Journal of Applied Physics
- Volume:
- 132
- Issue:
- 8
- ISSN:
- 0021-8979
- Page Range / eLocation ID:
- 083903
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Giant spin-orbit torque (SOT) from topological insulators (TIs) provides an energy efficient writing method for magnetic memory, which, however, is still premature for practical applications due to the challenge of the integration with magnetic tunnel junctions (MTJs). Here, we demonstrate a functional TI-MTJ device that could become the core element of the future energy-efficient spintronic devices, such as SOT-based magnetic random-access memory (SOT-MRAM). The state-of-the-art tunneling magnetoresistance (TMR) ratio of 102% and the ultralow switching current density of 1.2 × 105 A cm−2have been simultaneously achieved in the TI-MTJ device at room temperature, laying down the foundation for TI-driven SOT-MRAM. The charge-spin conversion efficiency
θ SHin TIs is quantified by both the SOT-induced shift of the magnetic switching field (θ SH = 1.59) and the SOT-induced ferromagnetic resonance (ST-FMR) (θ SH = 1.02), which is one order of magnitude larger than that in conventional heavy metals. These results inspire a revolution of SOT-MRAM from classical to quantum materials, with great potential to further reduce the energy consumption. -
The emergence of embedded magnetic random-access memory (MRAM) and its integration in mainstream semiconductor manufacturing technology have created an unprecedented opportunity for engineering computing systems with improved performance, energy efficiency, lower cost, and unconventional computing capabilities. While the initial interest in the existing generation of MRAM—which is based on the spin-transfer torque (STT) effect in ferromagnetic tunnel junctions—was driven by its nonvolatile data retention and lower cost of integration compared to embedded Flash (eFlash), the focus of MRAM research and development efforts is increasingly shifting toward alternative write mechanisms (beyond STT) and new materials (beyond ferromagnets) in recent years. This has been driven by the need for better speed vs density and speed vs endurance trade-offs to make MRAM applicable to a wider range of memory markets, as well as to utilize the potential of MRAM in various unconventional computing architectures that utilize the physics of nanoscale magnets. In this Perspective, we offer an overview of spin–orbit torque (SOT) as one of these beyond-STT write mechanisms for the MRAM devices. We discuss, specifically, the progress in developing SOT-MRAM devices with perpendicular magnetization. Starting from basic symmetry considerations, we discuss the requirement for an in-plane bias magnetic field which has hindered progress in developing practical SOT-MRAM devices. We then discuss several approaches based on structural, magnetic, and chiral symmetry-breaking that have been explored to overcome this limitation and realize bias-field-free SOT-MRAM devices with perpendicular magnetization. We also review the corresponding material- and device-level challenges in each case. We then present a perspective of the potential of these devices for computing and security applications beyond their use in the conventional memory hierarchy.more » « less
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Abstract Magnetization dynamics induced by spin–orbit torques in a heavy‐metal/ferromagnet can potentially be used to design low‐power spintronics and logic devices. Recent computations have suggested that a strain‐mediated spin–orbit torque (SOT) switching in magnetoelectric (ME) heterostructures is fast, energy‐efficient, and permits a deterministic 180° magnetization switching. However, its experimental realization has remained elusive. Here, the coexistence of the strain‐mediated ME coupling and the SOT in a CoFeB/Pt/ferroelectric hybrid structure is shown experimentally. The voltage‐induced strain only slightly modifies the efficiency of SOT generation, but it gives rise to an effective magnetic anisotropy and rotates the magnetic easy axis which eliminates the incubation delay in current‐induced magnetization switching. The phase field simulations show that the electric‐field‐induced effective magnetic anisotropy field can reduce the switching time approximately by a factor of three for SOT in‐plane magnetization switching. It is anticipated that such strain‐mediated ME‐SOT hybrid structures may enable field‐free, ultrafast magnetization switching.
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Abstract This article discusses the current state of development, open research opportunities, and application perspectives of electric‐field‐controlled magnetic tunnel junctions that use the voltage‐controlled magnetic anisotropy effect to control their magnetization. The integration of embedded magnetic random‐access memory (MRAM) into mainstream semiconductor foundry manufacturing opens new possibilities for the development of energy‐efficient, high‐performance, and intelligent computing systems. The current generation of MRAM, which uses the current‐controlled spin‐transfer torque (STT) effect to write information, has gained traction due to its nonvolatile data retention and lower integration cost compared to embedded Flash. However, scaling MRAM to high bit densities will likely require a transition from current‐controlled to voltage‐controlled operation. In this perspective, an overview of voltage‐controlled magnetic anisotropy (VCMA) as a promising beyond‐STT write mechanism for MRAM devices is provided and recent advancements in developing VCMA‐MRAM devices with perpendicular magnetization are highlighted. Starting from the fundamental mechanisms, the key remaining challenges of VCMA‐MRAM, such as increasing the VCMA coefficient, controlling the write error rate, and achieving field‐free VCMA switching are discussed. Then potential solutions are discussed and open research questions are highlighted. Lastly, prospective applications of voltage‐controlled magnetic tunnel junctions (VC‐MTJs) in security applications, extending beyond their traditional role as memory devices are explored.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1063/5.0091944
