Using Magnetic Droplet Nucleation to Determine the Spin Torque Efficiency and Asymmetry in 
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:msub><mml:mi>Co</mml:mi><mml:mi>x</mml:mi></mml:msub><mml:msub><mml:mrow><mml:mi>(Ni,</mml:mi><mml:mi>Fe)</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:math>
 Thin Films

We demonstrate field and current controlled magnetodynamics in nanocontact spin-torque nano-oscillators (STNOs) based on orthogonal magnetic tunnel junctions (MTJs). We systematically analyze the microwave properties (frequency f , linewidth ∆f , power P , and frequency tunability df /dI) with their physical originsperpendicular magnetic anisotropy (PMA), damping-like and field-like spin transfer torque (STT), and voltage-controlled magnetic anisotropy (VCMA). These devices present several advantageous characteristics: high emission frequencies (f > 20 GHz), high frequency tunability (df /dI = 0.25 GHz/mA), and zero-field operation (f ∼ 4 GHz). Furthermore, a detailed investigation of f (H, I) reveals that df /dI is mostly governed by the large VCMA (287 fJ/(V·m)), while STT plays a negligible role. PACS numbers: Valid PACS appear here a) Correspondence to johan.akerman@physics.gu.se 1 arXiv:1907.10427v2 [physics.app-ph]

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“…For dc and microwave characterization, we used a custom-built 40 GHz probe station; the details of this setup can be found in Ref. [42].…”

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confidence: 99%

Magnetodynamics in orthogonal nanocontact spin-torque nano-oscillators based on magnetic tunnel junctions

Jiang

Ahlberg

Chung

et al. 2019

Applied Physics Letters

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“…The pseudo-potential energy density and field were introduced in Eqs. ( 16) and (17). The denominator of the spintorque field term can be written as an expansion in ν: To first order in ν, the term in parenthesis in Eq.…”

Section: Appendix A: Effective Field and Boundary Conditionsmentioning

confidence: 99%

“…After the first experimental evidence 8 and direct observation 9 of droplet solitons, multiple experiments have generated and studied magnetic droplet solitons and related structures over the past several years [10][11][12][13][14][15][16][17][18][19][20][21] . The usual experimen-tal situation leading to droplet soliton generation and decay occurs in a nanocontact spin torque oscillator (NC-STO), where two magnetic layers are separated by a nonmagnetic spacer; the top layer is known as the free layer and the bottom layer as the fixed (or polarizing) layer.…”

Section: Introductionmentioning

confidence: 99%

Thermal Activation Barriers for Creation and Annihilation of Magnetic Droplet Solitons in the Presence of Spin Transfer Torque

Chaves-O'Flynn,

Stein

2020

Preprint

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We study noise-induced creation and annihilation of magnetic droplet solitons in experimental parameter regions in which they are linearly stable against drift. Exploiting the rotational symmetry of the problem, we transform to the reference frame rotating with the droplet soliton and introduce an effective potential energy that accounts for the work done against spin-transfer torque to rotate the magnetization between two different orientations. We use this function to compute the activation barrier in both directions between the uniform magnetization state and the droplet soliton state for a variety of nanocontact radii and currents. We investigate droplet soliton structures with both zero and nonzero spin-torque asymmetry parameter. Our approach can be applied to estimate activation barriers for dynamical systems where non-gradient terms can be absorbed by changes of reference frames, and suggests a technique applicable to extended systems that may not be uniformly magnetized.

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“…This drift instability presents a significant challenge to the robust control of droplet solitons and the reliable operation of future spintronic devices. Due to growing interest in magnetic droplet solitons, experiments continue in spin torque nanocontacts [6,[9][10][11] and in spin Hall driven nanoconstrictions [12].…”

Section: Introductionmentioning

confidence: 99%

Stochastic ejection of nanocontact droplet solitons via drift instability

Moore

Hoefer

2019

Phys. Rev. B

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The magnetic droplet soliton is a large amplitude, coherently precessing wave state that exists in ferromagnetic thin films with perpendicular magnetic anisotropy. To effectively sustain a droplet, magnetic damping can be locally compensated in a nanocontact region that imparts spin-transfer torque; this has been successfully deployed in experiment to directly image the droplet and probe its dynamics electrically. However, theory predicts and experiments indicate the existence of a drift instability whereby the droplet is ejected from the spin-transfer-torque-active region and subsequently decays, an effect that may be enhanced or possibly induced by thermal fluctuations.Using soliton perturbation theory and large deviation theory, this work determines the soliton ejection rate and the most likely path an ejected soliton tracks in the presence of thermal fields.These results lead to an effective lower bound on the stability of magnetic droplet solitons in spintransfer torque nanocontact devices operating at finite temperature and point to ways in which droplets can be made more robust.

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Using Magnetic Droplet Nucleation to Determine the Spin Torque Efficiency and Asymmetry in Cox(Ni,Fe)1−x Thin Films

Cited by 8 publications

References 44 publications

Magnetodynamics in orthogonal nanocontact spin-torque nano-oscillators based on magnetic tunnel junctions

Magnetodynamics in orthogonal nanocontact spin-torque nano-oscillators based on magnetic tunnel junctions

Thermal Activation Barriers for Creation and Annihilation of Magnetic Droplet Solitons in the Presence of Spin Transfer Torque

Stochastic ejection of nanocontact droplet solitons via drift instability

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