Magnetic fluctuation and reversal by current-induced spin-orbit torques in heavy metal/ferromagnet heterostructure

Abstract

The structure utilizing a heavy metal/ferromagnetic heterojunction induces spin polarization due to the spin Hall effect when current flows through the heavy metal layer. The resulting spin current transfers spin-orbit torque to the ferromagnet, leading to the phenomenon such as spin wave excitation or magnetic reversal. We confirmed the amplification of magnetic fluctuations in a nanostructure, Ta(1)/Pt(10)/Pt1-xCox(5)/Al2O3(5),co-deposited with Permalloy and cobalt through Brillouin light scattering (BLS) system. Although direct measurements of the auto-oscillation state could not be obtained due to resolution limitations, we indirectly observed that the critical current was reduced by 27.3% from the analysis of the BLS spectrum when Co was co-deposited compared to the case where only Permalloy was deposited. Current-induced field-free magnetic reversal using spin–orbit torque was conducted in heavy metals/ferromagnetic heterstructures. The ferromagnetic layer was designed as a [Co/Pt] multilayer structure to control perpendicular magnetic anisotropy of free layer instead of single ferromagnetic layer. Additionally, by exploiting the interlayer exchange interaction between a copper insertion layer and a ferromagnetic layer with in-plane magnetic anisotropy. the symmetry of the structure was broken, enabling magnetization reversal without the need for an external magnetic field. We confirm magnetic reversal electrically by anomalous Hall measurement in Hall bar pattern.This approach provides a simple method to optimize the efficiency of magnetization reversal in studies which utilize interlayer exchange interaction as symmetry-breaking component.