Fieldlike and antidamping spin-orbit torques in as-grown and annealed Ta/CoFeB/MgO layers

Abstract: We present a comprehensive study of the current-induced spin-orbit torques in perpendicularly magnetized Ta/CoFeB/MgO layers. The samples were annealed in steps up to 300 degrees C and characterized using x-ray absorption spectroscopy, transmission electron microscopy, resistivity, and Hall effect measurements. By performing adiabatic harmonic Hall voltage measurements, we show that the transverse (field-like) and longitudinal (antidamping-like) spin-orbit torques are composed of constant and magnetization-dependent contributions, both of which vary strongly with annealing. Such variations correlate with changes of the saturation magnetization and magnetic anisotropy and are assigned to chemical and structural modifications of the layers. The relative variation of the constant and anisotropic torque terms as a function of annealing temperature is opposite for the field-like and antidamping torques. Measurements of the switching probability using sub-{\mu}s current pulses show that the critical current increases with the magnetic anisotropy of the layers, whereas the switching efficiency, measured as the ratio of magnetic anisotropy energy and pulse energy, decreases. The optimal annealing temperature to achieve maximum magnetic anisotropy, saturation magnetization, and switching efficiency is determined to be between 240 degrees and 270 degrees C.

Spin-Orbit Torques in Ta/CoFeB/MgO Trilayers

The paper presents a detailed investigation into the current-induced spin-orbit torques in perpendicularly magnetized Ta/CoFeB/MgO trilayers. The research explores how annealing affects the spin-orbit torque components in these layers, a process critical for enhancing applications in spintronics, particularly in magnetic random access memories.

Measurements and Findings

The research employed adiabatic harmonic Hall voltage measurements to examine the transverse (field-like) and longitudinal (antidamping-like) spin-orbit torques. The results revealed distinct changes in these torques with varying annealing temperatures, due to chemical and structural modifications of the layers. Notably, the study found that optimal annealing temperatures for achieving maximum magnetic properties and switching efficiency are between 240º and 270ºC.

Key numerical results include:
- The saturation magnetization and magnetic anisotropy increase significantly upon annealing up to 270ºC.
- The field-like torque components increase by 35% from as-grown to optimally annealed samples, while antidamping torque decreases by 40%.
- Switching probabilities and critical currents confirm that higher magnetic anisotropy demands more current for magnetization reversal.

Implications and Speculations

The paper elucidates the practical and theoretical implications of spin-orbit torque manipulation through annealing. It enhances the understanding of spintronic device optimization, supporting development in high-density data storage and efficient spintronic logic devices.

The findings suggest that future studies could delve deeper into the interplay between chemical modifications and torque behaviors, potentially examining other heavy metal and ferromagnetic combinations or nanostructuring techniques to further optimize spin-orbit torque effects.

Conclusion

The research advances our comprehension of spin-orbit torques in Ta/CoFeB/MgO layers, highlighting the sensitive dependence of these torques on heat-induced structural changes. The methodology and results provide a solid foundation for optimizing spintronic device performance in industry and academia alike—facilitating cutting-edge advancements in AI-driven technologies and memory storage solutions.