Room-temperature perpendicular magnetization switching through giant spin-orbit torque from sputtered BixSe(1-x) topological insulator material (1703.03822v1)

Abstract: The spin-orbit torque (SOT) arising from materials with large spin-orbit coupling promises a path for ultra-low power and fast magnetic-based storage and computational devices. We investigated the SOT from magnetron-sputtered BixSe(1-x) thin films in BixSe(1-x)/CoFeB heterostructures by using a dc planar Hall method. Remarkably, the spin Hall angle (SHA) was found to be as large as 18.83, which is the largest ever reported at room temperature (RT). Moreover, switching of a perpendicular CoFeB multilayer using SOT from the BixSe(1-x) has been observed with the lowest-ever switching current density reported in a bilayer system: 2.3 * 105 A/cm2 at RT. The giant SHA, smooth surface, ease of growth of the films on silicon substrate, successful growth and switching of a perpendicular CoFeB multilayer on BixSe(1-x) film opens a path for use of BixSe(1-x) topological insulator (TI) material as a spin-current generator in SOT-based memory and logic devices.

• The paper demonstrates that sputtered Bi_xSe(1-x) films yield a giant spin Hall angle of 18.83, driving efficient room-temperature magnetization switching.
• It employs a semiconductor-compatible magnetron sputtering method that produces smooth films suitable for large-scale wafer integration.
• The research reports a low switching current density of 2.3×10^5 A/cm², indicating reduced power consumption for future spintronic devices.

Evaluation of Spin-Orbit Torque in Topological Insulators for Magnetic Switching at Room Temperature

The paper presents an in-depth examination of spin-orbit torque (SOT) using topologically insulating materials, specifically those composed of Bi_xSe_(1-x), which exhibit remarkable efficiencies in terms of spin Hall effects at room temperature (RT). Historical interest in spin-orbit torque stems from its potential to reduce power consumption in spintronic devices, such as magnetic random-access memory (MRAM) and related spin-based logical applications. This research identifies giant spin Hall angles (SHA) and low switching current densities, placing these films as promising candidates for future SOT-based devices.

Key Contributions

The paper outlines several key contributions:

1. Material Synthesis via Magnetron Sputtering: The Bi_xSe_(1-x) films were deposited using a semiconductor-compatible magnetron sputtering process, demonstrating that industrial-scale compatibility is achievable. This process allows for the production of films with superb surface smoothness and large-scale wafer integration potential.
2. Room Temperature Giant SHA: The research identifies a substantial spin Hall angle (SHA) value of 18.83, which appears to be two orders of magnitude larger than typical heavy metals (HMs) and approximately one order of magnitude greater than other crystalline topological insulators. These results position the sputtered Bi_xSe_(1-x) as one of the most efficient spin-current sources currently reported.
3. Low Switching Current Density: The research reports an unprecedented low switching current density of 2.3 × 10^5 A/cm^2 for a CoFeB multilayer using Bi_xSe_(1-x) at room temperature. This density is notably lower than current densities observed with alternative SOT systems that rely on heavy metals, making Bi_xSe_(1-x) a promising material for reducing power consumption in real-world applications.

Experimental and Modeling Approaches

The research employed a dc planar Hall method to characterize the spin-orbit effects, analyzing multilayer heterostructures composed of Bi_xSe_(1-x) and CoFeB. The analysis also involved Slonczewski’s torque model and included assessments using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy dispersive X-ray spectroscopy (EDS) for structural verification of the film properties.

Implications and Future Work

From a practical perspective, the implications of this research are manifold. The ability to produce low switching current densities suggests significant advancements in energy efficiency and device longevity for future magnetic memories and spin-based processors. The ease of manufacturing these films using sputtering also enables widespread industrial adoption.

Future developments could explore optimization strategies for the Bi_xSe_(1-x) films to further maximize the spin Hall effect and overall efficiency of SOT systems. Additional research may investigate the integration of these materials into more complex device architectures, considering factors such as thermal stability and long-term reliability at consumer-scale operation conditions.

Theoretical Impact

Theoretically, the results challenge prevailing assumptions about the limitations of SOT efficiency using topological insulators, particularly at higher temperatures. The demonstrated large SHA suggests potential breakthroughs in understanding the SHE and Rashba effects in complex material systems. Researchers in the field may require a reevaluation of current theoretical models to accommodate these findings.

In conclusion, this paper presents notable advancements in spintronic device technologies, providing both new methodologies for material synthesis and key insights into the operational efficiencies at room temperature. This work opens avenues for future research into SOT-based devices and highlights the calculated potential for topological insulators to transform the landscape of low-power electronic devices.