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

TLDR

The study investigates current‑induced spin‑orbit torques in perpendicularly magnetized Ta/CoFeB/MgO layers. Samples were annealed up to 300 °C and characterized by XAS, TEM, resistivity, and Hall effect, while adiabatic harmonic Hall voltage measurements quantified the torques. Field‑like and antidamping spin‑orbit torques comprise constant and magnetization‑dependent components that vary strongly with annealing, correlating with changes in saturation magnetization and anisotropy; the optimal annealing temperature for maximum anisotropy, magnetization, and switching efficiency is 240–270 °C.

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.