Spin-Orbit Torque Phenomena in Tungsten Thin Films

Spin–orbit torque (SOT) in tungsten thin films arises from the interplay between strong spin–orbit coupling in heavy‐metal layers and adjacent ferromagnetic materials. In its metastable A15 (β) phase, tungsten exhibits a large spin Hall effect, converting an in‐plane charge current into a transverse spin current. This spin current can exert torques on the magnetic moments of a neighbouring ferromagnetic layer, enabling efficient magnetisation switching without external magnetic fields. Control over film microstructure—through oxygen incorporation, impurity doping or precise phase engineering—directly influences resistivity, spin Hall angle and torque efficiency. Advances in deposition techniques and post‐growth treatments have made it possible to stabilise ultrathin β‐W films with tailored oxygen content, optimise interfacial properties and achieve deterministic switching at current densities compatible with semiconductor technologies. The global significance of these phenomena spans next‐generation non‐volatile memory, logic devices and neuromorphic computing, where low‐power, high‐speed magnetisation control is paramount.

Research from Nature Portfolio

Recent studies have demonstrated that controlled oxygen doping stabilises the β‐phase of tungsten, lowering its energy relative to the α‐phase and enhancing interfacial spin–orbit torques through increased spin Hall conductivity. Detailed experimental and theoretical analyses of the α‐to‐β transformation reveal how varying oxygen concentration drives local phase transitions, offering predictive control over film structure and resulting torque efficiencies. Foundational work has further shown that oxygen incorporation yields spin Hall angles approaching –0.5, irrespective of bulk resistivity changes, pointing to an interface‐dominated mechanism. Together, these investigations elucidate the atomic origins of large spin–orbit torques in β‐W and establish guidelines for tuning film composition to achieve robust, reproducible magnetisation switching.

Spin-Orbit Torque Phenomena in Tungsten Thin Films publication trend

The graph below shows the total number of articles in spin-orbit torque phenomena in tungsten thin films across all publications each year (not limited to Nature Index journals).

Technical terms

Spin–orbit torque (SOT): Torque on a ferromagnetic layer arising from spin currents generated by strong spin–orbit coupling in an adjacent non‐magnetic layer.

Spin Hall effect: Phenomenon in which a charge current in a heavy metal produces a transverse spin current due to spin–orbit coupling.

Spin Hall angle: Ratio of generated spin‐current density to applied charge‐current density, a measure of conversion efficiency.

β‐phase tungsten (β‐W): Metastable A15 crystal structure of tungsten with enhanced resistivity and large intrinsic spin Hall conductivity.

Rashba effect: Momentum‐dependent spin splitting in non‐centrosymmetric structures, contributing to field‐like spin–orbit torques.

References

1. Bulk Rashba‐Type Spin Splitting in Non‐Centrosymmetric Artificial Superlattices. Advanced Science (2023).
2. Highly Energy‐Efficient Spin‐Orbit‐Torque Magnetoresistive Memory with Amorphous W─Ta─B Alloys. Advanced Electronic Materials (2023).
3. Enhanced spin–orbit torques by oxygen incorporation in tungsten films. Nature Communications (2016).
4. Deterministic Current Induced Magnetic Switching Without External Field using Giant Spin Hall Effect of β-W. Scientific Reports (2018).
5. Unravelling oxygen driven α to β phase transformation in tungsten. Scientific Reports (2020).
6. Spin–orbit torque engineering in β-W/CoFeB heterostructures with W–Ta or W–V alloy layers between β-W and CoFeB. NPG Asia Materials (2021).