Giant Spin Hall Effect and Switching Induced by Spin-Transfer Torque in a $\mathrm{W}/{\mathrm{Co}}_{40}{\mathrm{Fe}}_{40}{\mathrm{B}}_{20}/\mathrm{MgO}$ Structure with Perpendicular Magnetic Anisotropy

Giant Spin Hall Effect and Switching Induced by Spin-Transfer Torque in a $W / {Co}_{40} {Fe}_{40} B_{20} / MgO$ Structure with Perpendicular Magnetic Anisotropy

Qiang Hao and Gang Xiao

Phys. Rev. Applied 3, 034009 – Published 26 March 2015

Abstract

We obtain robust perpendicular magnetic anisotropy in a $β − W / {Co}_{40} {Fe}_{40} B_{20} / MgO$ structure without the need of any insertion layer between W and ${Co}_{40} {Fe}_{40} B_{20}$ . This is achieved within a broad range of W thicknesses (3.0–9.0 nm), using a simple fabrication technique. We determine the spin Hall angle (0.40) and spin-diffusion length for the bulk $β$ form of tungsten with a large spin-orbit coupling. As a result of the giant spin Hall effect in $β − W$ and careful magnetic annealing, we significantly reduce the critical current density for the spin-transfer-torque-induced magnetic switching in ${Co}_{40} {Fe}_{40} B_{20}$ . The elemental $β − W$ is a superior candidate for magnetic memory and spin-logic applications.

Received 7 November 2014

DOI:https://doi.org/10.1103/PhysRevApplied.3.034009

Authors & Affiliations

Qiang Hao and Gang Xiao^*

Department of Physics, Brown University, Providence, Rhode Island 02912, USA

^*Gang_Xiao@Brown.edu

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 3, Iss. 3 — March 2015

Subject Areas

Reuse & Permissions

Access Options

Article Available via CHORUS

Download Accepted Manuscript

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
Sheet resistance ( $R_{□}$ ) of $(t) W / (1.0) {Co}_{40} {Fe}_{40} B_{20} / (1.6) MgO / (1.0) Ta$ (thickness in nanometers) multilayer stacks as a function of W thickness $t$ (2.5–9.0 nm). The solid line is the best fit to the data based on extracted resistivities of $ρ_{W} \approx 210 μ Ω cm$ and $ρ_{{Co}_{40} {Fe}_{40} B_{20}} \approx 80 μ Ω cm$ .
Reuse & Permissions
Figure 2
(a) A schematic of $W / {Co}_{40} {Fe}_{40} B_{20}$ bilayer in the Hall-bar configuration for magnetotransport measurement under an external magnetic field ( $B_{ext}$ ) and an excitation dc current ( $I$ ). $J_{C}$ is the charge current density in the W layer, and $J_{S}$ is the SHE converted spin current density into the ${Co}_{40} {Fe}_{40} B_{20}$ layer. (b) Anomalous Hall resistance versus cycling external magnetic field applied perpendicularly to the stacks of $(t) W / (1.0) {Co}_{40} {Fe}_{40} B_{20} / (1.6) MgO / (1.0) Ta$ ( $t$ : 3.0–9.0 nm). (c),(d) Current-induced magnetic-switching curves in the $(7.0) W / (1.0) {Co}_{40} {Fe}_{40} B_{20} / (1.6) MgO / (1.0) Ta$ sample, under either a positive ( $β = 0 °$ ) (c) or a negative ( $β = 180 °$ ) (d) external field $B_{ext}$ (0.2, 0.4, 0.7, 2.0 mT). From each switching curve, critical current ( $I_{C}$ ) can be obtained as shown.
Reuse & Permissions
Figure 3
(a) Normalized Hall resistance (i.e., $\sin θ$ ) as functions of nearly in-plane magnetic field $B_{ext}$ ( $β = 4 °$ ) under a positive or negative current ( $\pm 2 mA$ ). $θ$ is the angle between the magnetization vector $M$ and the $y$ axis. $B_{+} (θ)$ and $B_{-} (θ)$ are the magnetic fields required to rotate the $M$ to $θ$ corresponding to the positive and the negative current, respectively. (b) Linear relationships between $B_{+} (θ) - B_{-} (θ)$ and $1 / \sin (θ - β)$ under different excitation current (0.5–2 mA). The slope for each fitted straight line is the net spin-transfer torque per unit moment, $Δ τ_{ST}^{0}$ , between the positive and negative excitation current. (c) Spin-transfer torques ( $τ_{ST}^{0}$ ) per unit moment as functions of excitation currents for $(t) W / (1.0) {Co}_{40} {Fe}_{40} B_{20} / (1.6) MgO / (1.0) Ta$ ( $t$ : 3.0–9.0 nm). All the torques are linear in current and vanish as current approaches zero. Thicker W generates more torque per unit of current. (d) Magnetic-switching phase diagram of $(7.0) W / (1.0) {Co}_{40} {Fe}_{40} B_{20} / (1.6) MgO / (1.0) Ta$ , in the parameter space of $B_{ext}$ and critical current ( $I_{C}$ ) or critical current density ( $J_{C}$ ). The arrows ( $↑$ or $↓$ ) denote the directions of the $M$ vector in various regions. $I_{C}$ is the net current into the Hall bar, and $J_{C}$ is the corresponding current density only in the W layer. The lines connecting the data are guides to the eyes.
Reuse & Permissions
Figure 4
Spin Hall angles versus W thickness for $(t) W / (1.0) {Co}_{40} {Fe}_{40} B_{20} / (1.6) MgO / (1.0) Ta$ ( $t$ : 3.0–9.0 nm). The line represents theoretical fitting to the data assuming a finite spin-diffusion length in the $β − W$ film. For the bulk $β − W$ film, spin Hall angle is determined to be $0.40 \pm 0.03$ and spin-diffusion length is $3.5 \pm 0.3 nm$ at room temperature.
Reuse & Permissions

Physical Review Applied

Giant Spin Hall Effect and Switching Induced by Spin-Transfer Torque in a W/Co40Fe40B20/MgO Structure with Perpendicular Magnetic Anisotropy

Qiang Hao and Gang Xiao

Phys. Rev. Applied 3, 034009 – Published 26 March 2015

Abstract

Authors & Affiliations

Article Text (Subscription Required)

References (Subscription Required)

Issue

Subject Areas

Access Options

Authorization Required

Other Options

Download & Share

Images

Figure 1

Figure 2

Figure 3

Figure 4

Log In

Search

Article Lookup

Paste a citation or DOI

Enter a citation

Giant Spin Hall Effect and Switching Induced by Spin-Transfer Torque in a $W / {Co}_{40} {Fe}_{40} B_{20} / MgO$ Structure with Perpendicular Magnetic Anisotropy