Current-induced order parameter dynamics: Microscopic theory applied to<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">Co</mml:mi><mml:mo>∕</mml:mo><mml:mi mathvariant="normal">Cu</mml:mi><mml:mo>∕</mml:mo><mml:mi mathvariant="normal">Co</mml:mi></mml:mrow></mml:math>spin valves

Haney, Paul M.; Waldron, Derek; Duine, R. A.; Núñez, Álvaro S.; Guo, Hong; MacDonald, Allan H.

doi:10.1103/physrevb.76.024404

Cited by 56 publications

(27 citation statements)

References 41 publications

(30 reference statements)

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“…We present the details of the NEM scheme in Sec. III and verify the implementation for a spin valve system benchmarked in the literature; in the absence of SOC we can compare to STTs calculated using spin conservation [13,14]. In Sec.…”

Section: Introductionmentioning

confidence: 70%

“…where H ex (r) is the exchange field generated by the local magnetization M(r) [13,19,66]. Within linear response, m ne (r) is composed of contributions from propagating electronic states at the Fermi level.…”

Section: A Formalismmentioning

confidence: 99%

“…The effect of SOC is explicitly included in the Hamiltonian that is used to determine the current-induced nonequilibrium magnetization. The NEM scheme has been applied to calculate STT in spin valves [13], magnetic tunnel junctions [20], and ferromagnet/normal metal bilayers [21][22][23]. The other method is to consider the charge current pumped by a time varying magnetization.…”

Section: Introductionmentioning

confidence: 99%

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Spin-orbit-coupling induced torque in ballistic domain walls: Equivalence of charge-pumping and nonequilibrium magnetization formalisms

Yuan

Kelly

2016

Phys. Rev. B

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To study the effect of spin-orbit coupling (SOC) on spin-transfer torque in magnetic materials, we have implemented two theoretical formalisms that can accommodate SOC. Using the "charge-pumping" formalism, we find two contributions to the out-of-plane spin-transfer torque parameter β in ballistic Ni domain walls (DWs). For short DWs, the nonadiabatic reflection of conduction electrons caused by the rapid spatial variation of the exchange potential results in an out-of-plane torque that increases rapidly with decreasing DW length. For long DWs, the Fermi level conduction channel anisotropy that gives rise to an intrinsic DW resistance in the presence of SOC leads to a linear dependence of β on the DW length. To understand this counterintuitive divergence of β in the long DW limit, we use the "nonequilibrium magnetization" formalism to examine the spatially resolved spin-transfer torque. The SOC-induced out-of-plane torque in ballistic DWs is found to be quantitatively consistent with the values obtained using the charge-pumping calculations, indicating the equivalence of the two theoretical methods.

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Section: Introductionmentioning

confidence: 70%

Section: A Formalismmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Spin-orbit-coupling induced torque in ballistic domain walls: Equivalence of charge-pumping and nonequilibrium magnetization formalisms

Yuan

Kelly

2016

Phys. Rev. B

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“…We consider a steady-state formulation of the STT analogous to that described in Ref. [12]. The key points of our STT implementation PHYSICAL REVIEW B 95, 060403(R) (2017) FIG.…”

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confidence: 99%

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

et al. 2017

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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. DOI: 10.1103/PhysRevB.95.060403Antiferromagnetic (AF) materials are magnetically ordered compounds where two or more spin sublattices compensate each other, resulting in a vanishing macroscopic magnetization. As a consequence, an antiferromagnet does not produce stray field, and closely separated AF nanostructures are not magnetostatically coupled. In addition, the typical time scale for the dynamics of the antiferromagnetic order parameter, the Néel vector, is set by the AF resonance frequency, which is typically much larger than that of a ferromagnet, and may approach the THz range [1]. It is then not surprising that antiferromagnets have recently received considerable attention as a materials platform for magnetic data storage, logic, and high-frequency applications [2]. One limitation of the AF materials class is the fact that most antiferromagnets are insulators, while often spintronics devices require driving currents through the structure.Recently, metallic CuMnAs has been proposed as a good candidate for AF spintronics applications [3]. Tetragonal CuMnAs is antiferromagnetic at room temperature and can be grown epitaxially on GaP. Furthermore, it has been shown that one can manipulate the Néel vector of CuMnAs thin films by electric current pulses [4]. This is explained as the result of atomically staggered spin-orbit torques (SOTs), 1 which accompany the current flow in antiferromagnets where the global inversion symmetry is broken due to the presence of two spin sublattices forming inversion partners [5]. The reported Néel temperature of CuMnAs is (480 ± 5) K [6], while the lattice parameters of bulk tetragonal CuMnAs are a = b = 3.820Å and c = 6.318Å. According to density functional theory (DFT) calculations, CuMnAs in its AF ground state is metallic, but it has a rather low density of states at the Fermi level [3]. Here, we investigate whether such a unique AF metal can be used in standard magnetic tunnel junctions (MTJs) and demonstrate that these can be written by spin-transfer torques (STTs) and read by standard tunnel magnetoresistance (TMR). * stamenom@tcd.ie 1 These are also referred to ...

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“…In fact, to date only a few studies have attempted to analyze a MTJ on multiple scales [5,6]. At one side, significant effort has been devoted to develop more precise ab initio models of spin-transfer torque [7,8]. These typically rely on ballistic quantum transport theory, which is suitable for the spin-transport properties of MTJs formed by epitaxially grown thin layers with atomically sharp interfaces and very few defects, such as in Fe/MgO/Fe.…”

Section: Introductionmentioning

confidence: 99%

Multiscale modeling of current-induced switching in magnetic tunnel junctions using ab initio spin-transfer torques

2017

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There exists a significant challenge in developing efficient magnetic tunnel junctions with low write currents for nonvolatile memory devices. With the aim of analyzing potential materials for efficient current-operated magnetic junctions, we have developed a multi-scale methodology combining ab initio calculations of spin-transfer torque with large-scale time-dependent simulations using atomistic spin dynamics. In this work we introduce our multiscale approach, including a discussion on a number of possible schemes for mapping the ab initio spin torques into the spin dynamics. We demonstrate this methodology on a prototype Co/MgO/Co/Cu tunnel junction showing that the spin torques are primarily acting at the interface between the Co free layer and MgO. Using spin dynamics we then calculate the reversal switching times for the free layer and the critical voltages and currents required for such switching. Our work provides an efficient, accurate, and versatile framework for designing novel current-operated magnetic devices, where all the materials details are taken into account.

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Current-induced order parameter dynamics: Microscopic theory applied toCo∕Cu∕Cospin valves

Cited by 56 publications

References 41 publications

Spin-orbit-coupling induced torque in ballistic domain walls: Equivalence of charge-pumping and nonequilibrium magnetization formalisms

Spin-orbit-coupling induced torque in ballistic domain walls: Equivalence of charge-pumping and nonequilibrium magnetization formalisms

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

Multiscale modeling of current-induced switching in magnetic tunnel junctions using ab initio spin-transfer torques

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