Spin-orbit torques from interfacial spin-orbit coupling for various interfaces

Kim, Kyoung-Whan; Lee, Kyung Jin; Sinova, Jairo; Lee, Hyun–Woo; Stiles, Mark D.

doi:10.1103/physrevb.96.104438

Cited by 70 publications

(59 citation statements)

References 79 publications

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“…This further supports the scenario proposed in this work. From our model, it can be seen that the Rashba effect is able to induce both antidamping torque (longitudinal magnetic field) and field-like torque (transverse magnetic field) simultaneously, which is consistent with recent theoretical discussions [39][40][41][42][43][44] .…”

Section: Discussionsupporting

confidence: 91%

Tuning of current-induced effective magnetic field through Rashba effect engineering in hybrid multiferroic structures

et al. 2018

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Current-induced effective magnetic fields offer a new pathway through spin orbit interaction (SOI) to switch magnetization and have recently attracted great interest. In the conventional heavy metal/ferromagnetic metal/oxide (HM/FM/Oxide) structure, significant efforts have been made to study the role of the HM in determining effective magnetic fields. However, very little attention has been paid to the oxide layer and its interface with FM, where the Rashba effect may affect the effective field. In this report, we present a pathway to tune the effective magnetic field by engineering the Rashba effect in a hybrid multiferroic multilayer structure. A ferroelectric oxide of BaTiO 3 , whose polarizations either up or down are controlled by interface engineering, was introduced into the conventional SOI multilayer with the structure of BaTiO 3 /CoFeB/Pt. The current-induced effective magnetic fields increase by more than 200% when the ferroelectric polarization of BaTiO 3 changes from up to down. The changes in the effective magnetic field are mainly attributed to the different Rashba effective fields induced by the opposite ferroelectric polarizations. Our study offers a new path towards controlling the current-induced effective magnetic field and may pave the way for integrating other functional oxides into the spintronic devices.

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Section: Discussionsupporting

confidence: 91%

Tuning of current-induced effective magnetic field through Rashba effect engineering in hybrid multiferroic structures

et al. 2018

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“…In contrast, NEGF+ncDFT approach reviewed in this Chapter can handle arbitrary device geometry, such as spin-valves and MTJs exhibiting STT or bilayers of the type FM/spin-orbit-coupled-material which are made inhomogeneous by attachment to NM leads, at vanishing or finite applied bias voltage. In contrast to often employed 2D transport geometry [48,[51][52][53][54][55][56][57] for SOT theoretical analyses, we emphasize the importance of 3D transport geometry [117,126] to capture both the effects at the FM/spin-orbit-coupled-material interface and those further into the bulk of the FM layer. Finally, ultrathin FM layers employed in SOT experiments can hybridize strongly with the adjacent spin-orbit-coupled-material to acquire its SOC and the corresponding spin textures on all of the FM monolayers.…”

Section: Discussionmentioning

confidence: 97%

First-Principles Quantum Transport Modeling of Spin-Transfer and Spin-Orbit Torques in Magnetic Multilayers

Nikolić¹,

Dolui²,

Petrović³

et al. 2018

Handbook of Materials Modeling

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We review a unified approach for computing: (i) spin-transfer torque in magnetic trilayers like spin-valves and magnetic tunnel junction, where injected charge current flows perpendicularly to interfaces; and (ii) spin-orbit torque in magnetic bilayers of the type ferromagnet/spin-orbit-coupledmaterial, where injected charge current flows parallel to the interface. The experimentally explored and technologically relevant spin-orbit-coupled-materials include 5d heavy metals, topological insulators, Weyl semimetals and transition metal dichalcogenides. Our approach requires to construct the torque operator for a given Hamiltonian of the device and the steady-state nonequilibrium density matrix, where the latter is expressed in terms of the nonequilibrium Green's functions and split into three contributions. Tracing these contributions with the torque operator automatically yields field-like and damping-like components of spin-transfer torque or spin-orbit torque vector, which is particularly advantageous for spin-orbit torque where the direction of these components depends on the unknown-in-advance orientation of the current-driven nonequilibrium spin density in the presence of spin-orbit coupling. We provide illustrative examples by computing spin-transfer torque in a one-dimensional toy model of a magnetic tunnel junction and realistic Co/Cu/Co spin-valve, both of which are described by first-principles Hamiltonians obtained from noncollinear density functional theory calculations; as well as spin-orbit torque in a ferromagnetic layer described by a tight-binding Hamiltonian which includes spin-orbit proximity effect within ferromagnetic monolayers assumed to be generated by the adjacent monolayer transition metal dichalcogenide. In addition, we show how spin-orbit proximity effect, quantified by computing (via first-principles retarded Green's function) spectral functions and spin textures on monolayers of realistic ferromagnetic material like Co in contact with heavy metal or monolayer transition metal dichalcogenide, can be tailored to enhance the magnitude of spin-orbit torque. We also quantify errors made in the calculation of spin-transfer torque when using Hamiltonian from collinear density functional theory, with rigidly rotated magnetic moments to create noncollinear magnetization configurations, instead of proper (but computationally more expensive) self-consistent Hamiltonian obtained from noncollinear density functional theory. * bnikolic@udel.edu 1 For easy navigation, we provide a list of abbreviations used throughout the Chapter: 1D-Particle Current z y x Co Lead Co Lead Cu(a) (b) M free fixed M Co Pt θ θ M free MoS 2 Co M free θ (c) FIG. 2. Schematic view of: (a) FM/NM/FM trilayer for calculations of STT in spin-valves; (b) FM/HM bilayer for calculations of SOT in the presence of the spin Hall current along the z-axis generated by the HM layer; and (c) FM/monolayer-TMD for calculations of SOT in the absence of any spin Hall current. The semi-infinite FM layers in (a) are chosen as Co (0001), and t...

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“…Our findings suggest this hybridization-induced descendent state to be a possible candidate for the source that contributes to the experimentally observed large spin-transfer torque in TI-FM bilayers. While the spin-transfer torque in TI-based structures has attracted growing theoretical attention 6,26,27 , our model provides a starting point for theoretical studies on TI-FM heterostructures to take into account the lowest order effects from the FM layer. While the hybridization strength is material-dependent, our simple model provides a generic way to describe the hybridization effect for the experimentally relevant cases in which the Dirac interface state overlaps with many FM states.…”

Section: Discussionmentioning

confidence: 99%

Hybridization-induced interface states in a topological-insulator–ferromagnetic-metal heterostructure

2017

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Recent experiments demonstrating large spin-transfer torques in topological insulator (TI)-ferromagnetic metal (FM) bilayers have generated a great deal of excitement due to their potential applications in spintronics. The source of the observed spin-transfer torque, however, remains unclear. This is because the large charge transfer from the FM to TI layer would prevent the Dirac cone at the interface from being anywhere near the Fermi level to contribute to the observed spintransfer torque. Moreover, there is yet little understanding of the impact on the Dirac cone at the interface from the metallic bands overlapping in energy and momentum, where strong hybridization could take place. Here, we build a simple microscopic model and perform first-principles-based simulations for such a TI-FM heterostructure, considering the strong hybridization and charge transfer effects. We find that the original Dirac cone is destroyed by the hybridization as expected. Instead, we find a new interface state which we dub 'descendent state' to form near the Fermi level due to the strong hybridization with the FM states at the same momentum. Such a 'descendent state' carries a sizable weight of the original Dirac interface state, and thus inherits the localization at the interface and the same Rashba-type spin-momentum locking. We propose that the 'descendent state' may be an important source of the experimentally observed large spin-transfer torque in the TI-FM heterostructure.

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Spin-orbit torques from interfacial spin-orbit coupling for various interfaces

Cited by 70 publications

References 79 publications

Tuning of current-induced effective magnetic field through Rashba effect engineering in hybrid multiferroic structures

Tuning of current-induced effective magnetic field through Rashba effect engineering in hybrid multiferroic structures

First-Principles Quantum Transport Modeling of Spin-Transfer and Spin-Orbit Torques in Magnetic Multilayers

Hybridization-induced interface states in a topological-insulator–ferromagnetic-metal heterostructure

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