Nontrivial spatial dependence of the spin torques in 
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 FePt-based tunneling junctions

Galante, Mario; Ellis, Matthew O. A.; Sanvito, Stefano

doi:10.1103/physrevb.99.014401

Cited by 5 publications

(7 citation statements)

References 27 publications

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“…This is completely different from the oscillations in L1 0 ferromagnets, which remain commensurate to the lattice. 22 The oscillations we observe here have identical periods and are approximately in anti-phase on the two magnetic sublattices. The in-plane STTk on the Mn II -sublattice is nearly twice as large as that on the Mn I sublattice.…”

Section: Linear Response Sttsupporting

confidence: 52%

Spin transfer torque in Mn$_3$Ga-based ferrimagnetic tunnel junctions from first principles

Stamenova,

Stamenov,

Mahfouzi

et al. 2020

Preprint

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We report on first principles calculations of spin-transfer torque (STT) in epitaxial magnetic tunnel junctions (MTJs) based on ferrimagnetic tetragonal Mn3Ga electrodes, both as analyser in a Fe/MgO stack, and also in an analogous stack with Mn3Ga electrode (instead of Fe) as polariser. Solving the ballistic transport problem (NEFG+DFT) for the non-equilibrium spin density in a scattering region extended to over 7.6 nm into the Mn3Ga electrode, we find long-range spatial oscillations of the STT decaying on a length scale of a few tens of Angströms, both in the linear response regime and for finite bias. The oscillatory behavior of the STT in Mn3Ga is robust against variations in the stack geometry (e.g. the barrier thickness and the interface spacing) and the applied bias voltage, which may affect the phase and the amplitude of the spacial oscillation, but the high (carrier) frequency mode is only responsive to variations in the longitudinal lattice constant of Mn3Ga (for fixed in-plane geometry) without being commensurate with the lattice. Our interpretation of the long range STT oscillations is based on the bulk electronic structure of Mn3Ga, taking also into account the spin-filtering properties of the MgO barrier. Comparison to a fully Mn3Gabased stack shows similar STT oscillations but a significant enhancement of the TMR effect at the Fermi level and the STT at the interface due to resonant tunneling. From the calculated energy dependence of the spin-polarised transmissions at 0 V, we anticipate asymmetric or symmetric TMR as a function of the applied bias voltage for the Fe-based and the all-Mn3Ga stacks, respectively, which also both exhibit a sign change below ±1 V. In the latter, symmetric, case we expect a TMR peak at zero, which is larger for the thinner barriers because of spin-polarised resonant tunneling.

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Section: Linear Response Sttsupporting

confidence: 52%

Spin transfer torque in Mn$_3$Ga-based ferrimagnetic tunnel junctions from first principles

Stamenova,

Stamenov,

Mahfouzi

et al. 2020

Preprint

Self Cite

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“…Finally, the longitudinal energy [panel (c)] shows an increase with temperature for both the Fe and Pt moments but on a much larger scale in Pt. Again, we attribute this behavior The solid lines show a fit using equation (12). With increasing temperature the resonance field drops and so does the magnitude of the background white noise.…”

Section: Resultsmentioning

confidence: 79%

“…At high frequency, away from the resonance peak, the spectral profile is flat, in agreement with the white noise approximation of stochastic micromagnetic models 27 . The lines in figure 7 show a fit to the data obtained by using equation (12) with resonance frequency, Gilbert damping and the pre-factor taken as fitting parameters. As shown in figure 7 the function fits the data well but due to the large damping used (λ = 0.1) the signal-to-noise ratio is poor, giving a large data scatter for the Gilbert damping.…”

Section: Resultsmentioning

confidence: 99%

“…However, Mryasov's model has the limitation that it does not directly simulate the Pt moments. Thus in non-equilibrium situations, such as those produced by the alternating spin-transfer torques observed in FePt tunnel junctions 12 or excitations by a laser 13 , the full details of the dynamics cannot be modeled.…”

Section: Introductionmentioning

confidence: 99%

“…(Color online) Fourier transform of the m x correlation function at 10 K, 300 K and 550 K. The solid lines show a fit using equation(12). With increasing temperature the resonance field drops and so does the magnitude of the background white noise.…”

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confidence: 99%

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Role of longitudinal fluctuations in L10 FePt

2019

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L1 0 FePt is a technologically important material for a range of novel data storage applications. In the ordered FePt structure the normally non-magnetic Pt ion acquires a magnetic moment, which depends on the local field originating from the neighboring Fe atoms. In this work a model of FePt is constructed, where the induced Pt moment is simulated by using combined longitudinal and rotational spin dynamics. The model is parameterized to include a linear variation of the moment with the exchange field, so that at the Pt site the magnetic moment depends on the Fe ordering. The Curie temperature of FePt is calculated and agrees well with similar models that incorporate the Pt dynamics through an effective Fe-only Hamiltonian. By computing the dynamic correlation function the anisotropy field and the Gilbert damping are extracted over a range of temperatures. The anisotropy exhibits a power-law dependence with temperature with exponent n ≈ 2.1. This agrees well with what observed experimentally and it is obtained without including a two-ion anisotropy term as in other approaches. Our work shows that incorporating longitudinal fluctuations into spin dynamics calculations is crucial for understanding the properties of materials with induced moments. arXiv:2001.03074v1 [cond-mat.mtrl-sci] 9 Jan 2020

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Spin-transfer and spin-orbit torques in the Landau–Lifshitz–Gilbert equation

Meo

Cronshaw²,

Jenkins³

et al. 2022

J. Phys.: Condens. Matter

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Dynamic simulations of spin-transfer and spin-orbit torques are increasingly important for a wide range of spintronic devices including magnetic random access memory, spin-torque nano-oscillators and electrical switching of antiferromagnets. Here we present a computationally efﬁcient method for the implementation of spin-transfer and spin-orbit torques within the Landau-Lifshitz-Gilbert equation used in micromagnetic and atomistic simulations. We consolidate and simplify the varying terminology of different kinds of torques into a physical action and physical origin that clearly shows the common action of spin torques while separating their different physical origins. Our formalism introduces the spin torque as an effective magnetic ﬁeld, greatly simplifying the numerical implementation and aiding the interpretation of results. The strength of the effective spin torque ﬁeld uniﬁes the action of the spin torque and subsumes the details of experimental effects such as interface resistance and spin Hall angle into a simple transferable number between numerical simulations. We present a series of numerical tests demonstrating the mechanics of generalised spin torques in a range of spin-tronic devices. This revised approach to modelling spin-torque effects in numerical simulations enables faster simulations and a more direct way of interpreting the results, and thus it is also suitable to be used in direct comparisons with experimental measurements or in a modelling tool that takes experimental values as input.

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Nontrivial spatial dependence of the spin torques in L10 FePt-based tunneling junctions

Cited by 5 publications

References 27 publications

Spin transfer torque in Mn$_3$Ga-based ferrimagnetic tunnel junctions from first principles

Spin transfer torque in Mn$_3$Ga-based ferrimagnetic tunnel junctions from first principles

Role of longitudinal fluctuations in L10 FePt

Spin-transfer and spin-orbit torques in the Landau–Lifshitz–Gilbert equation

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