Enhanced Spin-Orbit Torques in Rare-Earth 
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 Systems

Wong, Qi Ying; Murapaka, Chandrasekhar; Law, Wai Cheung; Gan, Wei Liang; Lim, Gerard Joseph

doi:10.1103/physrevapplied.11.024057

Cited by 26 publications

(16 citation statements)

References 57 publications

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“…The torque from the Rashba effect and SHE is namely the SOT comprising of a field-like torque and damping-like torque. Generally, the two torques are represented by the two corresponding effective fields, field-like term H F and damping-like term H D 3–7,9,10 .…”

Section: Introductionmentioning

confidence: 99%

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

Luo

Wong

et al. 2019

Sci Rep

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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.

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Section: Introductionmentioning

confidence: 99%

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

Luo

Wong

et al. 2019

Sci Rep

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“…Current induced spin-orbit torque (SOT) has attracted a remarkable amount of attention in the field of spintronics due to its ability to manipulate magnetization [1][2][3][4][5][6] . SOT based magnetic memory serves as an alternative for energy efficient memory as compared to spin transfer torque magnetic random-access memory (STT-MRAM) 7 .…”

mentioning

confidence: 99%

“…SOT based magnetic memory serves as an alternative for energy efficient memory as compared to spin transfer torque magnetic random-access memory (STT-MRAM) 7 . In a heavy-metal/ferromagnetic layer (HM/FM) system, the SOT is contributed by two well-known phenomena; the spin Hall effect (SHE) in HM 3,6,[8][9][10][11] and/or the Rashba-Edelstein effect at their interface [12][13][14] . In the former, a transverse spin current J S is generated from charge current J C passing through material of strong spin-orbit interaction and injected into the adjacent FM to exert an STT on the magnetization.…”

mentioning

confidence: 99%

Thermal behavior of spin-current generation in PtxCu1-x devices characterized through spin-torque ferromagnetic resonance

Wong

Law

Tan

et al. 2020

Sci Rep

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High temperature studies of spin Hall effect have often been neglected despite its profound significance in real-world devices. In this work, high temperature spin torque ferromagnetic resonance measurement was performed to evaluate the effects of temperature on the Gilbert damping and spin Hall efficiency of Pt x cu 1−x. When the temperature was varied from 300 K to 407 K, the Gilbert damping was relatively stable with a change of 4% at composition x = 66%. Alloying Pt and Cu improved the spin Hall efficiency of Pt 75 cu 25 /Co/Ta by 29% to a value of 0.31 ± 0.03 at 407 K. However, the critical switching current density is dependent on the ratio between the Gilbert damping and spin Hall efficiency and the smallest value was observed when x = 47%. It was found that at this concentration, the spin transparency was at its highest at 0.85 ± 0.09 hence indicating the importance of interfacial transparency for energy efficient devices at elevated temperature.

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“…The measurements were carried out in Ta 2 where the films were deposited with process steps similar to our previous report 62 Hence, the resultant direction of the diffused spin is aligned along the magnetisation direction of the FM layer after momentum transfer. Thus, the magnitude of the diffusing spin per unit volume, which is related to the magnitude of the SHE induced spin accumulation, can be written as sm in the harmonic Hall measurement, such that the total magnetisation becomes, + Ms mm .…”

Section: Resultsmentioning

confidence: 99%

Enhanced spin-orbit torque (SOT) and spin accumulation quantification in perpendicularly magnetised systems

Wong¹

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The ever increasing demand for high-speed data transfer and data processing have pushed the field of electronics toward spintronics, making the utilisation of electron spin in devices a reality. Spin-orbit torque (SOT) is a current-induced phenomenon which manipulates magnetisation via momentum transfer from accumulated spins at the heavy metal (HM)/ferromagnet (FM) interface. SOT strength is related to the anti-damping like (DL) and fieldlike (FL) effective fields. Due to its potential for faster switching and lower energy consumption, the pursuit of SOT physics becomes imperative. In this thesis, systematic investigations of SOT physics were carried out by evaluating the SOT effective fields, i.e. DL term and FL term, through a harmonic Hall measurement technique, in perpendicularly magnetised single FM (CoFeB) and multilayer (Co/Ni) structures. A combination of in-situ Kerr and harmonic measurement enabled the evaluation of the co-existing SOT fields while imaging the magnetisation behaviour during the measurement. Observation of dendritic-like domains indicates the influence of the interfacial Dzyaloshinskii Moriya interaction (DMI) at the CoFeB/Ta interface as affirmed by micromagnetic simulations. In the pursuit of alternative spin Hall materials, rare-earth metal Tb in Pt/[Co/Ni]2/Co/Tb multilayer structures with perpendicular magnetic anisotropy (PMA) have demonstrated enhanced SOT. Due to the large spin-orbit coupling in Tb, the effective damping like efficiency, eff DL  , is determined to be 0.55 for 9-nm Tb as compared to 0.18 eff DL  = for the reference Pt/[Co/Ni]2/Co/Ta stack. Enhanced magnetisation switching efficiency is observed with increasing Tb thickness affirming the sizable anti-damping torque responsible for deterministic switching. Furthermore, due to a more substantial interfacial coupling in Co/Tb interface than in Co/Ta interface, strong angular dependence of the dampinglike and field-like terms is present but diminishes with increasing Tb thickness. These results affirm that Tb plays a significant role in tuning the SOT efficiency in these structures as the increased Tb concentration leads to an enhancement of the effective spin Hall angle and switching efficiency. In a further investigation, an anomalous second harmonic Hall resistance was induced when a biasing current was applied to the structures. The analytical derivations and experimental results reveal an anomalous second Hall resistance originating from the spin accumulation. This measured anomalous second harmonic Hall resistance enables the adiabatic quantification of the spin accumulation in the structures. Spin accumulation ranges from ~3.0% in tTb = 5nm to ~6.6% in tTb = 8 nm, and ~1.3% in the reference stack of tTa = 5nm of the local magnetisation recorded when the total applied current density is 10 11 A/m 2 .

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Enhanced Spin-Orbit Torques in Rare-Earth Pt/[Co/Ni]2/Co/Tb Systems

Abstract: Enhanced spin-orbit torques in rare-earth Pt/[Co/Ni]2/Co/Tb systems. Physical Review Applied, 11(2), 024057-.

Cited by 26 publications

References 57 publications

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

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

Thermal behavior of spin-current generation in PtxCu1-x devices characterized through spin-torque ferromagnetic resonance

Enhanced spin-orbit torque (SOT) and spin accumulation quantification in perpendicularly magnetised systems

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