Control of Spin–Orbit Torques by Interface Engineering in Topological Insulator Heterostructures (original) (raw)
Related papers
Physical Review Applied
Topological insulators demonstrate high charge-spin conversion efficiency due to their spin-momentum locking at the Dirac surface states. However, the surface states are sensitive to disruption caused by exchange coupling when interfaced with a ferromagnet. Here, we demonstrate the use of various nonmagnetic insertion layer materials, Ti, Cu, and Pt, at the Co/Bi-Sb(012) interface to preserve the topological surface state and promote spin-orbit-torque efficiency through the crystallinity control of Bi-Sb(012). For 20-nm-thick Bi-Sb, a spin Hall angle of up to 8.93 is observed with the use of a Pt insertion layer, while it is otherwise negligible for Co/Bi-Sb(012) interfaces. We further explore the enhancement of Bi-Sb(012) crystallinity with increasing Bi-Sb thickness, revealing a rapidly increasing spin-orbit-torque efficiency that gradually saturates above 30 nm. A clear correlation between spin-orbit-torque efficiency and Bi-Sb(012) crystalline size is identified using x-ray diffractometry, establishing the origin of the high spin-orbit efficiency to be the Bi-Sb(012) crystalline orientation. Our work demonstrates the spin-orbittorque origin in Bi-Sb experimentally and paves the way for the adaptation of topological insulators as a class of low-energy spin source material for spintronics applications.
Nature communications, 2017
Topological insulators with spin-momentum-locked topological surface states are expected to exhibit a giant spin-orbit torque in the topological insulator/ferromagnet systems. To date, the topological insulator spin-orbit torque-driven magnetization switching is solely reported in a Cr-doped topological insulator at 1.9 K. Here we directly show giant spin-orbit torque-driven magnetization switching in a Bi2Se3/NiFe heterostructure at room temperature captured using a magneto-optic Kerr effect microscope. We identify a large charge-to-spin conversion efficiency of ~1-1.75 in the thin Bi2Se3 films, where the topological surface states are dominant. In addition, we find the current density required for the magnetization switching is extremely low, ~6 × 10(5) A cm(-2), which is one to two orders of magnitude smaller than that with heavy metals. Our demonstration of room temperature magnetization switching of a conventional 3d ferromagnet using Bi2Se3 may lead to potential innovations in...
Large Spin Torque in Topological Insulator/Ferromagnetic Metal Bilayers
2013
Heterostructures utilizing topological insulators exhibit a remarkable spin-torque efficiency. However, the exact origin of the strong torque, in particular whether it stems from the spin-momentum locking of the topological surface states or rather from spin-Hall physics of the topological-insulator bulk remains unclear. Here, we explore a mechanism of spin-torque generation purely based on the topological surface states. We consider topological-insulator-based bilayers involving ferromagnetic metal (TI/FM) and magnetically doped topological insulators (TI/mdTI), respectively. By ascribing the key theoretical differences between the two setups to location and number of active surface states, we describe both setups within the same framework of spin diffusion of the non-equilibrium spin density of the topological surface states. For the TI/FM bilayer, we find large spin-torque efficiencies of roughly equal magnitude for both in-plane and out-of-plane spin torques. For the TI/mdTI bilayer, we elucidate the dominance of the spin-transfer-like torque. However, we cannot explain the orders of magnitude enhancement reported. Nevertheless, our model gives an intuitive picture of spin-torque generation in topological-insulator-based bilayers and provides theoretical constraints on spin-torque generation due to topological surface states.
Scientific reports, 2017
We investigate the thickness optimization for maximum current-induced spin-orbit torque (SOT) generated by topological surface states (TSS's) in a bilayer system comprising of a ferromagnetic layer coupled to a thin topological insulator (TI) film. We show that by reducing the TI thickness, two competing effects on the SOT are induced: (i) the torque strength is stronger as the bulk contribution is decreased; (ii) on the other hand, the torque strength becomes suppressed due to increasing hybridization of the surface states. The latter is attributed to the opposite helicities of the coupled TSS's. We theoretically model the interplay of these two effects and derive the optimal TI thickness to maximize the spin torque, which is estimated to be about 3-5 nm for typical Bi2Se3 films.
Spintronics Based on Topological Insulators
SPIN, 2016
Spintronics using topological insulators (TIs) as strong spin–orbit coupling (SOC) materials have emerged and shown rapid progress in the past few years. Different from traditional heavy metals, TIs exhibit very strong SOC and nontrivial topological surface states that originate in the bulk band topology order, which can provide very efficient means to manipulate adjacent magnetic materials when passing a charge current through them. In this paper, we review the recent progress in the TI-based magnetic spintronics research field. In particular, we focus on the spin–orbit torque (SOT)-induced magnetization switching in the magnetic TI structures, spin–torque ferromagnetic resonance (ST-FMR) measurements in the TI/ferromagnet structures, spin pumping and spin injection effects in the TI/magnet structures, as well as the electrical detection of the surface spin-polarized current in TIs. Finally, we discuss the challenges and opportunities in the TI-based spintronics field and its poten...
2021
In a topological insulator (TI)/magnetic insulator (MI) hetero-structure, large spin-orbit coupling of the TI and inversion symmetry breaking at the interface could foster non-planar spin textures such as skyrmions at the interface. This is observed as topological Hall effect in a conventional Hall set-up. While this effect has been observed at the interface of TI/MI, where MI beholds perpendicular magnetic anisotropy, non-trivial spin-textures that develop in interfacial MI with inplane magnetic anisotropy is under-reported. In this work, we study Bi2Te3/EuS hetero-structure using planar Hall effect (PHE). We observe planar topological Hall and spontaneous planar Hall features that are characteristic of non-trivial in-plane spin textures at the interface. We find that the latter is minimum when the current and magnetic field directions are aligned parallel, and maximum when they are aligned perpendicularly within the sample plane, which maybe attributed to the underlying planar ani...
Interfacial reactions at Fe/topological insulator spin contacts
Journal of vacuum science and technology. B, Nanotechnology & microelectronics : materials, processing, measurement, & phenomena : JVST B, 2017
The authors study the composition and abruptness of the interfacial layers that form during deposition and patterning of a ferromagnet, Fe on a topological insulator (TI), Bi2Se3, Bi2Te3, and SiOx/Bi2Te3. Such structures are potentially useful for spintronics. Cross-sectional transmission electron microscopy, including interfacial elemental mapping, confirms that Fe reacts with Bi2Se3 near room temperature, forming an abrupt 5 nm thick FeSe0.92 single crystalline binary phase, predominantly (001) oriented, with lattice fringe spacing of 0.55 nm. In contrast, Fe/Bi2Te3 forms a polycrystalline Fe/TI interfacial alloy that can be prevented by the addition of an evaporated SiOx separating Fe from the TI.
Nature Materials, 2014
Here we demonstrate experimentally the magnetization switching through giant SOT induced by an in-plane current in a chromium-doped TI bilayer heterostructure. The critical current density required for switching is below 8.9 × 10 4 A cm −2 at 1.9 K. Moreover, the SOT is calibrated by measuring the e ective spin-orbit field using second-harmonic methods. The e ective field to current ratio and the spin-Hall angle tangent are almost three orders of magnitude larger than those reported for HMFHs. The giant SOT and e cient current-induced magnetization switching exhibited by the bilayer heterostructure may lead to innovative spintronics applications such as ultralow power dissipation memory and logic devices. R ecently, heavy metals (for example, Pt, Ta) with strong SOC have been used to generate spin currents by passing an in-plane charge current to control the magnetization dynamics in an adjacent ferromagnet layer (for example, Co, CoFeB; refs 1-12). Such spin currents, arising from either the spin-Hall effect 1-3,13,14 within the heavy metals or the Rashba effect at the interfaces 7-10,14-20 , can apply efficient spin torques to the ferromagnet, and result in current-induced magnetization manipulation 2,6,7,9-12 and even switching 1,3,8 . Although the underlying mechanisms of the SOTs are still debated 1,4,14 , the ability to manipulate magnetic moments with lateral current has shown promising applications in miniaturized magnetic memory and logic devices, and more appropriate material/structure to generate these SOTs still deserves further investigation. Besides heavy metals, TIs (refs 21-23), in which the SOC is large enough to invert the band structure 24 , are expected to be the most promising candidates to exploit the SOTs when coupled to magnetic moments . In addition, the recently demonstrated magnetism in magnetically doped TIs (for example, Cr-doped TIs; refs 28-34) makes it accessible to study the SOTs in the TI/magnetic-TI bilayer heterostructures . Here, we demonstrate the magnetization switching by in-plane current injection into epitaxial TI/Crdoped TI bilayer films. Using the second-harmonic analysis 4,5 of the anomalous Hall effect (AHE) resistance, we calibrate the effective spin-orbit field arising from the SOT. Most importantly, we find that the effective field to current ratio, as well as the spin-Hall angle tangent, is nearly three orders of magnitude larger than those reported in HMFHs so far. This giant SOT, together with the current-induced switching behaviour, suggests that magnetically doped TI heterostructures could potentially be the materials/structures to generate SOTs with efficiency beyond today's HMFHs.
APL Materials, 2021
Topological insulator (TI) based heterostructure is a prospective candidate for ultrahigh spin-to-charge conversion efficiency due to its unique surface states. We investigate the spin-to-charge conversion in (Bi,Sb)2Te3 (BST)/CoFeB, BST/Ru/CoFeB, and BST/Ti/CoFeB by spin pumping measurement. We find that the inverse Edelstein effect length (λIEE) increases by 60% with a Ru insertion while remains constant with a Ti insertion. This can be potentially explained by the protection of BST surface states due to the high electronegativity of Ru. Such enhancement is independent of the insertion layer thickness once the thickness of Ru is larger than 0.5 nm, and this result suggests that λIEE is very sensitive to the TI interface. In addition, an effectively perpendicular magnetic anisotropy field and additional magnetic damping are observed in the BST/CoFeB sample, which comes from the interfacial spin–orbit coupling between the BST and the CoFeB. Our work provides a method to enhance λIEE...