Quantitative characterization of spin-orbit torques in Pt/Co/Pt/Co/Ta/BTO heterostructures due to the magnetization azimuthal angle dependence

Engel, Christian; Goolaup, S.; Luo, Feilong; Lew, Wen Siang

doi:10.1103/physrevb.96.054407

Cited by 11 publications

(12 citation statements)

References 46 publications

(85 reference statements)

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“…The anisotropy field as a function of the azimuthal angle can be seen in Fig. 60 (a) [44]. We noted, that the magnitude of B ϕ H in Fig.…”

Section: B2 Angular Dependence Of Anisotropy Fieldmentioning

confidence: 89%

“…A Keithley 6221 AC current source and a 7265 Dual Phase DSP lock-in amplifier were used for harmonic Hall voltage measurement. The AC frequency was set to 309 Hz at room temperature for all our measurements which ensures an adiabatical change of magnetization vector which is usually in the GHz range [44].…”

Section: Methodsmentioning

confidence: 99%

“…The experimental evaluation is carried out for the BTO sample. This chapter has been reproduced from published article in Physical Review B [44].…”

Section: A G N E T I Z At I O N a N G U L A R D E P E N D E N C E Omentioning

confidence: 99%

“…The only difference lies in the coefficient which can be converted as explained elsewhere and usually just shifts the results by a factor of ∼ 10 to lower current densities for SOT effect [99]. This chapter has been published in IEEE Transactions on Magnetics [44].…”

Section: E F F E C T O F G E O M E T R I C a L M O D U L At I O N Omentioning

confidence: 99%

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Current-induced spin-orbit torque effective fields in multilayer structures with perpendicular magnetic anisotropy

Engel¹

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“…The anisotropy field as a function of the azimuthal angle can be seen in Fig. 60 (a) [44]. We noted, that the magnitude of B ϕ H in Fig.…”

Section: B2 Angular Dependence Of Anisotropy Fieldmentioning

confidence: 89%

Section: Methodsmentioning

confidence: 99%

“…The experimental evaluation is carried out for the BTO sample. This chapter has been reproduced from published article in Physical Review B [44].…”

Section: A G N E T I Z At I O N a N G U L A R D E P E N D E N C E Omentioning

confidence: 99%

Section: E F F E C T O F G E O M E T R I C a L M O D U L At I O N Omentioning

confidence: 99%

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Current-induced spin-orbit torque effective fields in multilayer structures with perpendicular magnetic anisotropy

Engel¹

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“…Angular dependence of the SOT fields was conducted to determine its relation with the azimuthal angle,  = H between current direction and the magnetisation in Tb-based PMA samples similar to the barium titanate, BaTiO3 (BTO) samples166 . The V  and 2 V  were measured at different azimuthal angle values, with magnetisation set to be in the z orientation for all measurements.…”

mentioning

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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Spin Reflection-Induced Field-Free Magnetization Switching in Perpendicularly Magnetized MgO/Pt/Co Heterostructures

Jin

Lim

Poh

et al. 2022

ACS Appl. Mater. Interfaces

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Field-free magnetization switching is critical towards practical, integrated spin-orbit torque (SOT)-driven magnetic random-access memory with perpendicular magnetic anisotropy. Our work proposes a technique to modulate the spin reflection and spin density of states within a heavy-metal Pt through interfacing with a dielectric MgO layer. We demonstrate tunability of the effective out-of-plane spin torque acting on the ferromagnetic Co layer, enabling current-induced SOT magnetization switching without the assistance of an external magnetic field. The influence of the MgO layer thickness on effective SOT efficiency shows saturation at 4 nm, while up to 80% of field-free magnetization switching ratio is achieved with the MgO between 5 and 8 nm. We analyze and attribute the complex interaction to spin reflection at the dielectric/heavy metal interface and spin scattering within the dielectric medium due to interfacial electric fields. Further, through substituting the dielectric with Ti or Pt, we confirm that the MgO layer is indeed responsible for the observed field-free magnetization switching mechanism.

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Quantitative characterization of spin-orbit torques in Pt/Co/Pt/Co/Ta/BTO heterostructures due to the magnetization azimuthal angle dependence

Cited by 11 publications

References 46 publications

Current-induced spin-orbit torque effective fields in multilayer structures with perpendicular magnetic anisotropy

Current-induced spin-orbit torque effective fields in multilayer structures with perpendicular magnetic anisotropy

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

Spin Reflection-Induced Field-Free Magnetization Switching in Perpendicularly Magnetized MgO/Pt/Co Heterostructures

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