Energy‐Efficient Ultrafast SOT‐MRAMs Based on Low‐Resistivity Spin Hall Metal Au 0.25 Pt 0.75

Ralph

et al. 2020

Phys. Rev. Applied

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We experimentally investigate the origin of the two-magnon scattering (TMS) in heavy-metal (HM)/ferromagnet (FM)/oxide heterostructures (FM = Co, Ni 81 Fe 19 , or Fe 60 Co 20 B 20 ) by varying the materials located above and below the FM layers. We show that strong TMS in HM/FM/oxide systems arises primarily at the HM/FM interface and increases with the strength of interfacial spin-orbit coupling and magnetic roughness at this interface. TMS at the FM/oxide interface is relatively weak, even in systems where spin-orbit coupling at this interface generates strong interfacial magnetic anisotropy. We also suggest that the spin-current-induced excitation of non-uniform short-wavelength magnon at the HM/FM interface may function as a mechanism of spin memory loss for the spin-orbit torque exerted on the uniform mode.

Section: Influence Of Short-wavelength Magnons On Spin Torquesupporting

confidence: 77%

Origin of Strong Two-Magnon Scattering in Heavy-Metal/Ferromagnet/Oxide Heterostructures

Ralph

et al. 2020

Phys. Rev. Applied

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“…These results establish that the internal spin Hall ratio (θ SH ) in CoPt is very high. The negative sign of

ξ_{DL, ext}^{j}

of CoPt 24/Ti 0.8/FeCoB is somewhat surprising since all previous reports of θ SH for Pt‐based non‐ferromagnetic HMs, [ 4,20–23 ] including PtMn, [ 7 ] have given positive values. We speculate that the strong proximity effect, which has been calculated to result in a substantial exchange splitting for Pt, comparable to its SOC energy, [ 19 ] is responsible for the reversed sign and enhanced amplitude of θ SH for the CoPt.…”

Section: Resultsmentioning

confidence: 87%

“…Currently, exerting a nonzero damping-like spin-orbit torque (τ DL ) on a ferromagnet (FM) layer requires an external transversely polarized spin current from the bulk spin Hall effect (SHE) [1][2][3][4][5][6][7][8][9] of an adjacent spin-orbit layer, an interfacial spin-orbit effect at magnetic interfaces, [8,[10][11][12][13] or the anomalous Hall effect (AHE) [13] of an adjacent FM layer. Very recently, the generation of spinorbit torques (SOTs) via current flow inside FMs has become an emerging focus of spin-orbitronics.…”

Section: Introductionmentioning

confidence: 99%

Observation of Strong Bulk Damping‐Like Spin‐Orbit Torque in Chemically Disordered Ferromagnetic Single Layers

Zhang

Muller

et al. 2020

Adv Funct Materials

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Strong damping-like spin-orbit torque (τ DL) has great potential for enabling ultrafast energy-efficient magnetic memories, oscillators, and logic. So far, the reported τ DL exerted on a thin-film magnet must result from an externally generated spin current or from an internal non-equilibrium spin polarization in non-centrosymmetric GaMnAs single crystals. Here, for the first time a very strong, unexpected τ DL is demonstrated from current flow within ferromagnetic single layers of chemically disordered, face-centered-cubic CoPt. It is established here that the novel τ DL is a bulk effect, with the strength per unit current density increasing monotonically with the CoPt thickness, and is insensitive to the presence or absence of spin sinks at the CoPt surfaces. This τ DL most likely arises from a net transverse spin polarization associated with a strong spin Hall effect, while there is no detectable long-range asymmetry in the material. These results broaden the scope of spin-orbitronics and provide a novel avenue for developing single-layer-based spin-torque memory, oscillator, and logic technologies.

“…Spin‐orbit torques (SOTs) have attracted remarkable attention due to their potential for improving the efficiency of magnetic memory [ 1–5 ] and logic. [ 6 ] Most studies have examined cases in which the SOTs arise due to the exchange interaction of a magnetic layer with an externally generated spin current, for example, from an adjacent spin Hall metal [ 1–9 ] or topological surface states.…”

Section: Introductionmentioning

confidence: 99%

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

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.