Planar Hall Driven Torque in a Ferromagnet/Nonmagnet/Ferromagnet System

Safranski, Christopher; Xu, Jun-Wen; Kent, Andrew D.; Sun, J. Z.

doi:10.1103/physrevlett.124.197204

Cited by 32 publications

(11 citation statements)

References 39 publications

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“…[ 23 ] Since the angle‐dependent in‐plane HHVR technique is sensitive only to a SOT arising from a spin current that is transversely polarized and independent of the magnetization orientation, [ 13 ] the spin current associated with the detected bulk spin torque is most likely due to a bulk SHE. The anomalous Hall effect [ 24,25 ] and the planar Hall effect, [ 26,27 ] which can only generate spin current collinear with the magnetization, can be excluded as possible sources.…”

Section: Resultsmentioning

confidence: 99%

Unveiling the Mechanism of Bulk Spin‐Orbit Torques within Chemically Disordered Fe_xPt_1‐_x Single Layers

Zhu

Ralph

Buhrman

2021

Adv Funct Materials

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The recent discovery of spin‐orbit torques (SOTs) within magnetic single‐layers has attracted attention. However, it remains elusive as to how to understand and how to tune the SOTs. Here, utilizing the single layers of chemically disordered FexPt1‐x, the mechanism of the “unexpected” bulk SOTs is unveiled by studying their dependence on the introduction of a controlled vertical composition gradient and temperature. The bulk dampinglike SOT is found to arise from an imbalanced internal spin current that is transversely polarized and independent of the magnetization orientation. The torque can be strong only in the presence of a vertical composition gradient. The SOT efficiency per electric field is insensitive to temperature but changes sign upon reversal of the orientation of the composition gradient, which is analog to the strain behaviors. These characteristics suggest that the imbalanced internal spin current originates from a bulk spin Hall effect and that the associated inversion asymmetry that allows for a non‐zero net torque is most likely a strain non‐uniformity induced by the composition gradient. The fieldlike SOT is a relatively small bulk effect compared to the dampinglike SOT. This study points to the possibility of developing low‐power single‐layer SOT devices by strain engineering.

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Section: Resultsmentioning

confidence: 99%

Unveiling the Mechanism of Bulk Spin‐Orbit Torques within Chemically Disordered Fe_xPt_1‐_x Single Layers

Zhu

Ralph

Buhrman

2021

Adv Funct Materials

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“…Generation of spin current has been the focus of spintronics that aims at the development of energy-efficient and highspeed manipulation of magnetic memory [1][2][3][4][5] and logic [6]. Spin current can be generated by the spin Hall effect (SHE) [1,7,8], the topological surface states [9,10], the anomalous Hall effect [11,12], the planar Hall effect [13,14], spin Seebeck effect [15], spin pumping [16], or noncentrosymmetric crystals [17]. Recently, interfacial spinorbit coupling (ISOC) of a normal metal/ferromagnet (NM/FM) interface was also proposed to generate non-local spin current and thus dampinglike spin-orbit torque (SOT) [18][19][20][21][22].…”

mentioning

confidence: 99%

Absence of Significant Spin-Current Generation in Ti/Fe−Co−B Bilayers with Strong Interfacial Spin-Orbit Coupling

Zhu

Buhrman

2021

Phys. Rev. Applied

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We report a quantitative investigation of the absence/presence of spin current generation by interfacial spin-orbit coupling (ISOC) at a normal metal/ferromagnet (NM/FM) interface. Utilizing the Ti/FeCoB bilayers which are unique for the negligible spin Hall effect and strong tunable ISOC, we establish direct experimental evidence that there is no significant spin current generation at NM/FM interface via spin-orbit filtering effect or Rashba-Edelstein effect even when the ISOC is stronger than that of a typical Pt/FM interface and can promote strong perpendicular magnetic anisotropy. This result also suggests that 3d Ti has minimal orbital Hall effect.

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“…In recent studies, it has been predicted [70][71][72] and shown experimentally [73][74][75][76][77][78] that ferromagnetic materials can be sources of spin current produced by spin-orbit interactions. Unlike the spin-Hall effect in isotropic heavy-metal channel materials (such as Pt) where the polarization is set by geometry, in ferromagnetic materials it is further affected by the direction of the magnetization.…”

Section: Spin Current Sources: Advantages and Disadvantagesmentioning

confidence: 99%

A Perspective on Electrical Generation of Spin Current for Magnetic Random Access Memories

Safranski,

Sun,

Kent

2022

Preprint

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Spin currents are used to write information in magnetic random access memory (MRAM) devices by switching the magnetization direction of one of the ferromagnetic electrodes of a magnetic tunnel junction (MTJ) nanopillar. Different physical mechanisms of conversion of charge current to spin current can be used in 2-terminal and 3-terminal device geometries. In 2-terminal devices, charge-to-spin conversion occurs by spin filtering in the MTJ's ferromagnetic electrodes and present day MRAM devices operate near the theoretically expected maximum charge-to-spin conversion efficiency. In 3-terminal devices, spin-orbit interactions in a channel material can also be used to generate large spin currents. In this perspective article, we discuss charge-to-spin conversion processes that can satisfy the requirements of MRAM technology. We emphasize the need to develop channel materials with larger charge-to-spin conversion efficiency-that can equal or exceed that produced by spin filtering-and spin currents with a spin polarization component perpendicular to the channel interface. This would enable high-performance devices based on sub-20 nm diameter perpendicularly magnetized MTJ nanopillars without need of a symmetry breaking field. We also discuss MRAM characteristics essential for CMOS integration. Finally, we identify critical research needs for charge-to-spin conversion measurements and metrics that can be used to optimize device channel materials and interface properties prior to full MTJ nanopillar device fabrication and characterization.

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Planar Hall Driven Torque in a Ferromagnet/Nonmagnet/Ferromagnet System

Cited by 32 publications

References 39 publications

Unveiling the Mechanism of Bulk Spin‐Orbit Torques within Chemically Disordered Fe_xPt_1‐_x Single Layers

Unveiling the Mechanism of Bulk Spin‐Orbit Torques within Chemically Disordered Fe_xPt_1‐_x Single Layers

Absence of Significant Spin-Current Generation in Ti/Fe−Co−B Bilayers with Strong Interfacial Spin-Orbit Coupling

A Perspective on Electrical Generation of Spin Current for Magnetic Random Access Memories

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Planar Hall Driven Torque in a Ferromagnet/Nonmagnet/Ferromagnet System

Cited by 32 publications

References 39 publications

Unveiling the Mechanism of Bulk Spin‐Orbit Torques within Chemically Disordered FexPt1‐x Single Layers

Unveiling the Mechanism of Bulk Spin‐Orbit Torques within Chemically Disordered FexPt1‐x Single Layers

Absence of Significant Spin-Current Generation in Ti/Fe−Co−B Bilayers with Strong Interfacial Spin-Orbit Coupling

A Perspective on Electrical Generation of Spin Current for Magnetic Random Access Memories

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Product

Resources

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Unveiling the Mechanism of Bulk Spin‐Orbit Torques within Chemically Disordered Fe_xPt_1‐_x Single Layers

Unveiling the Mechanism of Bulk Spin‐Orbit Torques within Chemically Disordered Fe_xPt_1‐_x Single Layers