Dependence of spin-orbit torque effective fields on magnetization uniformity in Ta/Co/Pt structure

Feilong Luo,Sihua Li,Qi Ying Wong,Wen Siang Lew,Funan Tan,Gerard Joseph Lim,Xuan Wang

doi:10.1038/s41598-019-47125-4

Feilong Luo, Sihua Li + Show 5 more

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https://doi.org/10.1038/s41598-019-47125-4

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Abstract

The spin-orbit torque (SOT) effective fields, namely field-like and damping-like terms, depend on the thicknesses of heavy metal (HM) and ferromagnetic metal (FM) layers, in a stack comprising of HM/FM/HM or oxide. In this work, we report on the dependence of the SOT effective fields on the magnetization uniformity in the wires comprising of Ta/Co/Pt layer structure. SOT dependence on magnetization uniformity dependence was investigated by concurrent variation of the magnetization uniformity in Co layer and characterization of the SOT effective fields in each wire which excludes the layer thickness dependence influences. Our experimental results reveal that the field-like term decreases while the damping-like term increases with increasing Co magnetization uniformity. The magnetization uniformity influence on the effective fields is attributed to the spin Hall effect, which contributes to the SOT.

Highlights

The control of magnetization switching in magnetic structures by an electric current is crucial for the development of spintronics devices[1]
X is used to apply in the expression of the second harmonic Hall resistance R2ndHall which is: R2nd Hall where HD and HF are the damping-like term and field-like term, respectively, RAHE and RPHE are the amplitudes of anomalous Hall effect and planar Hall effect resistances, and H⊥ is the effective field orientating the magnetization in the film plane
Our measurement results show that the spin-orbit torque (SOT) effective fields depend on the magnetization uniformity in Ta/Co/Pt structure

Summary

Experiments and Discussion

Harmonic Hall resistance measurement technique, which has been reported earlier[20], were employed to characterize the SOT effective fields. The thermal gradient contributes to the measured second harmonic Hall resistances which were used to calculate the SOT effective fields[13]. The magnetization uniformity is equivalent to magnetization amplitude M for the magnetic wire This magnetization amplitude can be characterized with respect to the applied longitudinal field by measuring R1st Hall, thereby obtaining the RPHE. The field-like term decreases with respect to the magnetization magnitude while the damping-like term increases in each sample. The transverse spin accumulation induces two effective fields: bmr and amf × mr, where mr and mf are unit vectors of the local magnetization of the reference layer and the free layer, respectively. HF decreases and HD increases with respect to the magnetization, respectively, as the term hje/eMstF is a constant for each sample

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