Effect of the oxide layer on current-induced spin-orbit torques in Hf|CoFeB|MgO and Hf|CoFeB|TaOx structures

Akyol, Mustafa; Alzate, Juan G.; Yu, Guoqiang; Upadhyaya, Pramey; Wong, Kin; Ekicibil, Ahmet; Amiri, Pedram Khalili

doi:10.1063/1.4906352

Cited by 63 publications

(49 citation statements)

References 37 publications

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“…Remarkably, the second harmonic Hall voltage is negligible though we have eliminated the V ω signal interference during the measurements. [ 41 ] Thus we can attribute the total SOT almost to damping-like torque in our sample. [ 41 ] Thus we can attribute the total SOT almost to damping-like torque in our sample.…”

Section: Introductionmentioning

confidence: 61%

Strong Electrical Manipulation of Spin–Orbit Torque in Ferromagnetic Heterostructures

Yan

Wan

Zhou

et al. 2016

Adv Elect Materials

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metal (Pt, Ta, etc.) and/or the Rashba effect from the inversion asymmetry of HM/FM and FM/oxide interfaces both contribute to the spin-orbit torque and the effective switching fi eld. [16][17][18][19] Half a decade has already passed since the fi rst report of SOT in perpendicularly magnetized heterostructures. [ 20 ] Efforts are increasingly shifting not only to explore SOT in different systems, but also to its manipulation in practical devices. [21][22][23][24] At the same time, electric fi eld control of magnetization is of great interest in the area of spintronics for its rich physics and potential use in information technology due to its low energy consumption and compatibility with classic electronics. [25][26][27] Following the effective manipulation of magnetic order by electrical means in different systems, Liu et al. [ 28 ] proposed the concept of electrical control of SOT in Pt/Co/Al 2 O 3 heterostructures, but the efficiency is in a quite limited scale. Very recently, Fan et al. [ 29 ] utilized the Cr-doped topological insulator and successfully modulated the SOT by a factor of four using a gate voltage ( V G ) of 10 V at 1.9 K taking the ultralow Curie temperature ( T C ) of the magnetic topological insulator into account. Now the research interest is whether an elegant approach could significantly modulate the SOT in a nonvolatile manner at a practical temperature ( T ). We experimentally demonstrated the strong electrical control of SOT in perpendicularly magnetized Pt/Co/ HfO x heterostructures. Positive and negative V G enhance and reduce the critical current for magnetization switching respectively with the assistance of ionic liquid gating mainly through the modulation of damping-like spin-orbit effective fi elds and the concomitant effective spin Hall angle of Pt/Co. Results and DiscussionIn our Ta(2)/Pt(4)/Co(0.3)/HfO x (4) (unit in nanometers) heterostructures ( Figure 1 a), the bottom Ta layer acts as a seed layer to form a better Pt(111) orientation, and consequently induces a strong perpendicular magnetic anisotropy (PMA). Despite its high spin Hall angle, [ 9,30 ] the contribution of spin current from Ta to Co is negligible due to the short spin diffusion length of Pt and opposite sign of the spin Hall angle of Ta and Pt. [ 8,31 ] The capping HfO x layer, with a large permittivity, also enhances the PMA and protects the metal layers from erosion by ionic Electrical control of current-induced spin-orbit effects in magnets is supposed to reduce the power consumption in high-density memories to the utmost extent, but the effi cient control in metallic magnets at a practical temperature remains elusive. Here, the electrical manipulation of spin-orbit torque is investigated in perpendicularly magnetized Pt/Co/HfO x heterostructures in a nonvolatile manner using an ionic liquid gate. The switching current of magnetization can be reversibly tuned by a factor of two within a small gate voltage range of 1.5 V. The modulation of effective spin Hall angle and the corresponding damping-like torque...

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Section: Introductionmentioning

confidence: 61%

Strong Electrical Manipulation of Spin–Orbit Torque in Ferromagnetic Heterostructures

Yan

Wan

Zhou

et al. 2016

Adv Elect Materials

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“…However, to achieve high bit densities, perpendicular magnetization is required [7]. Switching of perpendicular magnetization by SOT has been widely investigated; when an in-plane charge current is passed through a material with high-spin-orbit coupling, such as a heavy-metal layer (Pt [1,3,8], Ta [9][10][11], W [12], and Hf [13,14]) or even a topological insulator [15], a spin current is generated, and it can apply torques on the adjacent ferromagnetic layer [3,8,[16][17][18]. However, deterministic switching of perpendicular magnetization driven by SOT requires an additional inversion symmetry breaking [19].…”

Section: Introductionmentioning

confidence: 99%

Joule Heating Effect on Field-Free Magnetization Switching by Spin-Orbit Torque in Exchange-Biased Systems

Lau

et al. 2017

Phys. Rev. Applied

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Switching of magnetization via spin-orbit torque provides an efficient alternative for nonvolatile memory and logic devices. However, to achieve deterministic switching of perpendicular magnetization, an external magnetic field collinear with the current is usually required, which makes these devices inappropriate for practical applications. In this work, we examine the current-induced magnetization switching in a perpendicularly magnetized exchange-biased Pt=CoFe=IrMn system. A magnetic field annealing technique is used to introduce in-plane exchange biases, which are quantitatively characterized. Under proper conditions, field-free current-driven switching is achieved. We study the Joule heating effect, and we show how it can decrease the in-plane exchange bias and degrade the field-free switching. Furthermore, we discuss that the exchange-bias training effect can have similar effects.

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“…7 Quantitatively, spin-orbit torques are characterized by the spin Hall angle (h H ), which is a measure of the ratio between spin current density (J s ) and charge current density (J c ). Different heavy metal/ferromagnet bilayers have been proposed as the source of spin-orbit torques, including Ta, 8 Hf, 9 Pt, 10 CuIr, 11 and W, 12,13 with W exhibiting the largest h H to date. Recent work on oxidized W has also revealed promising results.…”

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confidence: 99%

Temperature dependence of spin-orbit torques in W/CoFeB bilayers

Skowroński

Cecot

Kanak

et al. 2016

Applied Physics Letters

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We report on the temperature and layer thickness variation of spin-orbit torques in perpendicularly magnetized W/CoFeB bilayers. Harmonic Hall voltage measurements reveal dissimilar temperature evolutions of longitudinal and transverse effective magnetic field components. The transverse effective field changes sign at 250 K for a 2 nm thick W buffer layer, indicating a much stronger contribution from interface spin-orbit interactions compared to, for example, Ta. Transmission electron microscopy measurements reveal that considerable interface mixing between W and CoFeB is primarily responsible for this effect.

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Effect of the oxide layer on current-induced spin-orbit torques in Hf|CoFeB|MgO and Hf|CoFeB|TaOx structures

Cited by 63 publications

References 37 publications

Strong Electrical Manipulation of Spin–Orbit Torque in Ferromagnetic Heterostructures

Strong Electrical Manipulation of Spin–Orbit Torque in Ferromagnetic Heterostructures

Joule Heating Effect on Field-Free Magnetization Switching by Spin-Orbit Torque in Exchange-Biased Systems

Temperature dependence of spin-orbit torques in W/CoFeB bilayers

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