First-principles spin-transfer torque in $\mathrm{CuMnAs}|\mathrm{GaP}|\mathrm{CuMnAs}$ junctions

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First-principles spin-transfer torque in $CuMnAs | GaP | CuMnAs$ junctions

Maria Stamenova, Razie Mohebbi, Jamileh Seyed-Yazdi, Ivan Rungger, and Stefano Sanvito

Phys. Rev. B 95, 060403(R) – Published 7 February 2017

Abstract

We demonstrate that an all-antiferromagnetic tunnel junction with current perpendicular to the plane geometry can be used as an efficient spintronic device with potential high-frequency operation. By using state-of-the-art density functional theory combined with quantum transport, we show that the Néel vector of the electrodes can be manipulated by spin-transfer torque. This is staggered over the two different magnetic sublattices and can generate dynamics and switching. At the same time the different magnetization states of the junction can be read by standard tunneling magnetoresistance. Calculations are performed for $CuMnAs | GaP | CuMnAs$ junctions with different surface terminations between the antiferromagnetic CuMnAs electrodes and the insulating GaP spacer. We find that the torque remains staggered regardless of the termination, while the magnetoresistance depends on the microscopic details of the interface.

Received 29 November 2016
Revised 13 January 2017

DOI:https://doi.org/10.1103/PhysRevB.95.060403

Physics Subject Headings (PhySH)

Ballistic transport Magnetic interactions Magnetoresistance Magnetotransport Spin transfer torque Spintronics

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Maria Stamenova^1,*, Razie Mohebbi², Jamileh Seyed-Yazdi², Ivan Rungger³, and Stefano Sanvito¹

¹School of Physics, AMBER and CRANN Institute, Trinity College, Dublin 2, Ireland
²Department of Physics, Vali-e-Asr University of Rafsanjan, Rafsanjan, Iran
³National Physical Laboratory, Teddington TW11 0LW, United Kingdom

^*stamenom@tcd.ie

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Vol. 95, Iss. 6 — 1 February 2017

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Figure 1
Atomistic depictions of the two $CuMnAs | GaP | CuMnAs$ junctions studied, differing by their spacer terminations: (a) Ga-terminated structure (labeled as GPG) and (b) P-terminated structure (PGP). The position of the central atomic layer is marked by “C” and the labels “L” and “R” stand for the left- and right-hand-side half of the junction. (c) and (d) show diagrams of the two spin configurations considered, the arrows indicating the direction of the spin of all Mn atoms in a corresponding vertical layer above. We define a parallel (P) and antiparallel (AP) spin state of the junction, respectively, based on the orientation of the two innermost Mn planes (i.e., in the AP case the R-lead order parameter is rotated by $180^{\circ}$ with respect to the P state). The coordinate system is chosen such that the $z$ axis is along the transport direction, while the Néel vectors of the leads lie in the $(x − y)$ plane and the spin quantization axis is along $y$ .
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Figure 2
Ground state observables atomically projected along the $z$ direction in each of the two junctions for the $90^{\circ}$ alignment of the lead order parameters: (a) The $x$ and $y$ components of the local spin moments and (b), (c) the spin-transfer torkance per unit area (for both junctions $A = 14.59$ $Å^{2})$ for GPG and PGP, respectively. The torkance is also converted to torque per current in units of $μ_{B} / e$ using the corresponding Fermi-level transmission coefficients [7] computed for the $90^{\circ}$ alignment $t_{F} = 2.4 \times 10^{- 4}$ for GPG and $t_{F} = 6.7 \times 10^{- 4}$ for PGP.
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Figure 3
Electronic and transport properties of the two junctions in the P state: (a), (b) The PDOS of atoms in the $(C \to R)$ half of the junction. The atom indexes are the same as in Fig. 2. Note that the black curves correspond to the atom (P or Ga) in the very center of the junctions. (c) and (d) show the spectrum of the total transmission in both the P and AP state, while in (e) and (f) the TMR is defined as $TMR = (t_{P} - t_{AP}) / (t_{P} + t_{AP})$ .
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Figure 4
Contour plots in the two-dimensional $(k_{x}, k_{y})$ BZ orthogonal to the transport direction for various transport quantities. (a) depicts the total number of open channels in the CuMnAs leads; (b) and (c) show the Fermi-level transmission $t (k_{x}, k_{y})$ (top panels) and the spin-polarized transmission $Tr [\hat{t} (E_{F}) {\hat{σ}}^{z}]$ (bottom panels) in the P and AP state and for the PGP and GPG junction, respectively.
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Figure 5
(a), (b) Fermi-level spin PDOS as a function of atom position in one of the two partitions $[(C \to L)$ or $(C \to R)]$ for the P and AP spin state of each junction. In (c) and (d) the cumulative spin PDOS is shown, integrated from the center of the junction in all cases. The symbol legend is in (d).
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Physical Review B

covering condensed matter and materials physics

First-principles spin-transfer torque in $CuMnAs | GaP | CuMnAs$ junctions

Maria Stamenova, Razie Mohebbi, Jamileh Seyed-Yazdi, Ivan Rungger, and Stefano Sanvito

Phys. Rev. B 95, 060403(R) – Published 7 February 2017

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Physical Review B

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First-principles spin-transfer torque in CuMnAs|GaP|CuMnAs junctions

Maria Stamenova, Razie Mohebbi, Jamileh Seyed-Yazdi, Ivan Rungger, and Stefano Sanvito

Phys. Rev. B 95, 060403(R) – Published 7 February 2017

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First-principles spin-transfer torque in $CuMnAs | GaP | CuMnAs$ junctions