Current-driven perpendicular magnetization switching in Ta/CoFeB/[TaOx or MgO/TaOx] films with lateral structural asymmetry

Yu, Guoqiang; Chang, Li‐Te; Akyol, Mustafa; Upadhyaya, Pramey; He, Congli; Li, Xiang; Wong, Kin; Amiri, Pedram Khalili; Wang, Kang L.

doi:10.1063/1.4895735

Cited by 84 publications

(45 citation statements)

References 20 publications

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“…This indicates that the two SOT contributions have different FM layer thickness-dependent trends and it is therefore possible that they can be tuned or optimized through interface and structural engineering in different ways. We also note that the maximum magnitude of |χ Wedged | ≈ 14Oe/10 11 A/m 2 for the wedged-deposited Pt/Co/MgO samples presented here is comparable to the reported values for Ta/CoFeB/MgO and Ta/CoFeB/TaO x systems [27,39]. However, current-induced switching in the absence of external field cannot be demonstrated with |I dc | 8 mA (corresponding to H z eff 40 Oe) due to the large coercivity (H c 100 Oe) of the present films.…”

supporting

confidence: 73%

“…Since the variation in Co thickness across the wedge is extremely small, we speculate that this effect might be related to the profile of local depinning field across the sample as evidenced by the global variation of coercive field H c along the wedgeddeposition axis (see Table I). This preferred nucleation on one edge of the device is drastically different from other reports [27,38,39] in which no observable asymmetric field-driven nucleation process is found. We believe that, although the existence of dH an /dy gradient-induced fieldlike SOT [27] cannot be completely ruled out, a major contribution of the measured χ Wedged originates from the asymmetric nature of nucleation/depinning process in these wedged-deposited Pt/Co/MgO devices.…”

contrasting

confidence: 53%

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Determination of spin torque efficiencies in heterostructures with perpendicular magnetic anisotropy

Pai¹,

Mann²,

Tan³

et al. 2016

Phys. Rev. B

317

304

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We report that by measuring a current-induced hysteresis loop shift versus in-plane bias magnetic field, the spin-Hall effect (SHE) contribution of the current-induced effective field per current density χ SHE can be estimated for Pt-and Ta-based magnetic heterostructures with perpendicular magnetic anisotropy. We apply this technique to a Pt-based sample with its ferromagnetic (FM) layer being wedged deposited and discover an extra effective field contribution χ Wedged due to the asymmetric nature of the deposited FM layer. We confirm the correlation between χ Wedged and the asymmetric depinning process in FM layer during magnetization switching by magneto-optical Kerr microscopy. These results indicate the possibility of engineering deterministic spin-orbit torque switching by controlling the symmetry of domain expansion through the materials growth process. DOI: 10.1103/PhysRevB.93.144409 Current-induced spin-orbit torque (SOT) has been shown to be an efficient way of manipulating the magnetization in heavy-metal/ferromagnet (HM/FM) heterostructures. Unlike conventional spin transfer torque [1,2] in which the source of spin angular momentum comes from a ferromagnetic polarizer layer, SOTs arise from either the bulklike spin-Hall effect (SHE) [3,4] of the nonmagnetic (NM) HM layer or Rashbatype spin-orbit interaction [5,6] at the interface. SOTs can be utilized to achieve efficient magnetization switching [7][8][9][10], ultrafast domain-wall (DW) motion [6,11,12], and microwave generation through magnetic oscillations [13,14] in spintronic device applications.SOTs are typically studied in magnetic heterostructures with perpendicular magnetic anisotropy (PMA), and in general both a Slonczewski-like and a field-like torque can be present. The Slonczewski-like torque is most relevant to magnetization switching: It manifests as an effective field H eff with an out-of-plane (easy-axis) component that can reverse the magnetization or drive DWs if a component of the magnetization lies along the current-flow direction. The most common measurement schemes used to quantify the Slonczewski-like SOT efficiency χ ≡ H eff /J e (effective field per unit current density J e ) include ferromagnetic resonance techniques [15][16][17], low-frequency harmonic voltage measurements using small ac currents [18][19][20], and analysis of current-induced DW motion in thin magnetic strips [11,12,21,22]. Current-induced SOT switching of PMA films under an in-plane bias field is another convenient means for determining the sign of χ ; however, a quantitative estimate of its magnitude is usually difficult to obtain in such measurements due to the complicated magnetization reversal process [23,24].In this paper we examine the role of domain nucleation and DW propagation in SOT-assisted magnetization switching in HM/FM bilayer systems with PMA. We show that the currentinduced shift of the out-of-plane hysteresis loop as a function of in-plane bias field can be well explained by a simple currentassisted DW propagation model. This simple mea...

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supporting

confidence: 73%

contrasting

confidence: 53%

Determination of spin torque efficiencies in heterostructures with perpendicular magnetic anisotropy

Pai¹,

Mann²,

Tan³

et al. 2016

Phys. Rev. B

317

304

View full text Add to dashboard Cite

show abstract

“…Field-free switching has been achieved by introducing a lateral structural asymmetry, where the thickness of one layer is changed laterally [10,19,20] or by inducing a tilt in the uniaxial anisotropy axis [21]. More recently, field-free switching was realized in the antiferromagnet and ferromagnet systems, where some form of in-plane exchange bias (EB) is used instead of an external field [22][23][24][25].…”

Section: Introductionmentioning

confidence: 99%

“…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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“…We chose the Co 40 Fe 40 B 20 (CoFeB) square nanomagnet grown on a ferroelectric (e.g., (011)-oriented Pb(Mg 1/3 Nb 2/3 ) 0.7 Ti 0.3 O 3 (PMN-PT)) single crystal as an example (see Fig. 1(a)) because CoFeB thin film is frequently applied in magnetic tunneling junctions (MTJs) [19][20][21][22] and the (011) PMN-PT single crystal can output giant anisotropic electrostrains. 23,24 Different from the previous preparation of the Ni/PMN-PT heterostructure, in this work, a magnetic field was applied during the growth process (see Fig.…”

mentioning

confidence: 99%

Electric-field-driven magnetization reversal in square-shaped nanomagnet-based multiferroic heterostructure

Ren

Wang

et al. 2015

Applied Physics Letters

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Articles you may be interested inSimultaneous imaging of the ferromagnetic and ferroelectric structure in multiferroic heterostructures APL Mat. 2, 076109 (2014); 10.1063/1.4890055Giant magneto-impedance effect in amorphous ferromagnetic wire with a weak helical anisotropy: Theory and experiment Based on phase field modeling and thermodynamic analysis, purely electric-field-driven magnetization reversal was shown to be possible in a multiferroic heterostructure of a square-shaped amorphous Co 40 Fe 40 B 20 nanomagnet on top of a ferroelectric layer through electrostrain. The reversal is made possible by engineering the mutual interactions among the built-in uniaxial magnetic anisotropy, the geometry-dependent magnetic configuration anisotropy, and the magnetoelastic anisotropy. Particularly, the incorporation of the built-in uniaxial anisotropy made it possible to reverse magnetization with one single unipolar electrostrain pulse, which is simpler than previous designs involving the use of bipolar electrostrains and may alleviate ferroelectric fatigue. Critical conditions for triggering the magnetization reversal are identified. V C 2015 AIP Publishing LLC.

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Current-driven perpendicular magnetization switching in Ta/CoFeB/[TaOx or MgO/TaOx] films with lateral structural asymmetry

Cited by 84 publications

References 20 publications

Determination of spin torque efficiencies in heterostructures with perpendicular magnetic anisotropy

Determination of spin torque efficiencies in heterostructures with perpendicular magnetic anisotropy

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

Electric-field-driven magnetization reversal in square-shaped nanomagnet-based multiferroic heterostructure

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