image: a, Schematic of nonsymmorphic crystalline symmetry in SrIrO3. b, Schematic of bulk topological Dirac band and spin-momentum-locked surface state for charge-spin conversion. c, Comparison of SOT efficiencies between hexagonal SrIrO3 and other materials highlight its superior performance. d, Comparison of switching current density and power across varied materials, showcasing the ultra-low power consumption in devices based on hexagonal SrIrO3.
Credit: ©Science China Press
As artificial intelligence and big data technologies evolve rapidly, the demand for computing power and energy efficiency is skyrocketing. Spin-orbit torque (SOT) technology, which utilizes electron spin to manipulate magnetic moments, is a leading contender for next-generation high-speed, durable magnetic random-access memory (MRAM). However, current SOT devices face a major hurdle: they require high writing current densities, leading to excessive power consumption and heating issues. Finding new materials with high charge-to-spin conversion efficiency is critical to breaking this bottleneck.
Recently, a research team from the Ningbo Institute of Materials Technology and Engineering (NIMTE) of the Chinese Academy of Sciences (CAS) made a groundbreaking advancement in topological spintronics. They demonstrated a symmetry-enforced topological Dirac semimetal state in hexagonal oxide SrIrO3 and utilized its unique electronic structure to achieve record-breaking charge-spin conversion efficiency and ultra-low power magnetic switching. The related research findings have been published in the National Science Review under the title “Symmetry-enforced topological Dirac semimetal for giant spin–orbit torque with ultralow power dissipation.”
Rational Design Over Accidental Discovery
While topological semimetals have shown promise, most existing systems rely on accidental band inversions. Departing from this conventional trial-and-error paradigm, the team at NIMTE took a pioneering approach based on rational Crystal Symmetry Engineering.
By precisely controlling the substrate and growth orientation, the researchers stabilized SrIrO3 in a specific hexagonal phase. Theoretical analysis and experiments revealed that the intrinsic nonsymmorphic symmetry in this structure acts as a "guardian." It forces electron bands to cross at the boundary of the Brillouin zone, forming robust, symmetry-protected 3D topological Dirac points. Using in-situ angle-resolved photoemission spectroscopy (ARPES), the team directly observed these bulk Dirac cones and the coexisting spin-momentum locked surface states.
Record-Breaking Performance
The result of this rational symmetry design is exceptional device performance. Benefiting from the giant Berry curvature in the bulk and the synergy with surface states, hexagonal SrIrO3 exhibited a giant spin-orbital torque efficiency that is superior to most existing materials.
In prototype devices, the team achieved perpendicular magnetization switching at an ultra-low current density. This represents one of the lowest power dissipation levels reported to date, significantly outperforming mainstream heavy metals (such as Platinum and Tungsten) and other topological materials. This achievement effectively addresses the critical bottleneck of high energy consumption in spintronic devices.
Broad Impact
This research goes beyond the discovery of a single material. It successfully bridges the gap between abstract crystallographic symmetry and practical device performance. Unlike previous studies, this work establishes nonsymmorphic symmetry as a robust and universal criterion for screening and designing high-performance spintronic materials.
Consequently, this study provides a critical material platform and scientific foundation for the development of next-generation, ultra-low power spintronic devices, potentially accelerating the evolution of green computing technologies.
The paper’s corresponding authors include Prof. Zhiming Wang from NIMTE, Prof. Run-Wei Li from the Eastern Institute of Technology, Ningbo, and Prof. Milan Radovic from the Paul Scherrer Institute.