Enhancement of spin-orbit torque efficiency in B2-CoGa(Pt)/L10-MnAl bilayers for high-density MRAM
Year: 2025
Type: article
Abstract: Magnetic random-access memory (MRAM) has emerged as a leading candidate for next-generation storage technology, offering high speed, high density, non-volatility, low power consumption, and radiation resistance. MRAM has evolved through three generations: field-driven toggle MRAM, spin-transfer torque (STT)-MRAM, and the experimental spin-orbit torque (SOT)-MRAM. The current commercial MRAM products primarily rely on STT-MRAM, which is based on Ta/CoFeB/MgO multilayers with the interfacial perpendicular magnetic anisotropy (PMA). However, STT-MRAM performance deteriorates at sub-10 nm size due to thermal instability. In contrast, the tetragonal Mn-based binary alloys exhibit stable bulk PMA and enhanced properties for sub-10 nm tunnel junction devices. Previous research has demonstrated the potential of these alloys for high-density MRAM, with magnetization switching achieved via SOT without the need for external magnetic fields. Among Mn-based binary alloys, L10-MnAl stands out due to its strong PMA, high spin polarization, and low magnetic damping, making it a promising material for next-generation MRAM. On the other side, the B2-CoGa alloy serves as both an ideal buffer layer and a spin current source for the epitaxial growth of PMA L10-MnAl thin films on GaAs substrates. Our study demonstrates that doping B2-CoGa with Pt significantly enhances the SOT efficiency in (CoGa)1−xPtx/L10-MnAl bilayers while preserving the excellent PMA properties of L10-MnAl. Experimental results show that Pt doping up to x = 0.1 keeps the PMA characteristics while simultaneously reducing the critical current density required for magnetization switching from 4.63×107 A/cm2 to 2.59×107 A/cm2. SOT efficiency increases from 0.042 to 0.080. This enhancement is attributed to the increased resistivity of the (CoGa)1−xPtx layer, which does not compromise its effective spin Hall conductivity. The optimized bilayer, with x = 0.075, supports magnetic tunnel junctions with lateral size as small as 8.09 nm, reducing power consumption by 37%. The SOT effect utilizes spin currents generated by phenomena such as the spin Hall effect to switch local magnetization in adjacent ferromagnetic layers. The damping-like SOT efficiency (ξDL), a crucial parameter for reducing device power consumption, is influenced by both spin Hall conductivity and resistivity of the material. The introduction of Pt impurities into (CoGa)1−xPtx bilayers optimizes this balance, significantly enhancing ξDL. Compared to traditional heavy metals used as buffer layers, the (CoGa)1−xPtx layer provides better lattice matching with Mn-based binary alloys, preserving their crystalline quality and PMA. This work systematically investigates the structural, magnetic, and SOT-driven magnetization switching properties of epitaxially grown (CoGa)1−xPtx/L10-MnAl bilayers, focusing on the dependence of magnetization switching on Pt concentration. Deterministic SOT-induced switching is achieved for x ≤ 0.1, with optimal PMA and SOT performance observed at x = 0.075. These results demonstrate the feasibility of incorporating Pt-doped CoGa layers into MRAM designs to enhance performance and scalability. This study provides valuable insights into improving SOT efficiency in Mn-based MRAM structures by incorporating Pt-doped CoGa buffer layers. These findings contribute to the development of high-density, high-performance MRAM devices with reduced power consumption.
DOI: 10.1360/tb-2024-1279
Authors: HongLi Sun, RongKun Han, DaHai Wei, JianHua Zhao
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W4407206211