Spin-Torque Influence on the High-Frequency Magnetization Fluctuations in Magnetic Tunnel Junctions

Petit, Sébastien; Baraduc, C.; Thirion, C.; Ebels, U.; Liu, Y.; Li, M.; Wang, P.; Diény, B.

doi:10.1103/physrevlett.98.077203

Cited by 189 publications

(178 citation statements)

References 13 publications

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“…͑12͒ is written here with the most widely used sign convention contrary to our previous paper. 8 When the reference and free layers are in strictly parallel or antiparallel configuration, there is no spin-transfer torque effect on the equilibrium magnetization. However, spin-polarized electrons may exert a torque on the free layer fluctuating magnetization.…”

Section: B Magnetic Fluctuations In the Presence Of Spin Torquementioning

confidence: 99%

“…This observation led us therefore to suggest that spin-transfer torque reduces or enhances magnetization thermal fluctuations, depending on whether it tends to favor or disfavor the equilibrium magnetic configuration. 8 When spin-transfer torque tends to favor the parallel magnetic configuration, it is observed that the magnetic fluctuations are consistently quenched in the P state and enhanced in the AP state. Moreover, when spin-transfer torque tends to favor the antiparallel magnetic configuration, its effect on magnetic fluctuations is reversed.…”

Section: Influence Of Parallel Spin Torquementioning

confidence: 99%

“…Nevertheless, in the subcritical regime ͑i.e., at current density much below the critical current density for spin-torque switching͒ where there is no macroscopic signature of this effect, we have shown that spin-transfer torque influences the magnetization thermal fluctuations. 8 In this paper, we present a detailed analysis of this phenomenon. In Sec.…”

Section: Introductionmentioning

confidence: 99%

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Influence of spin-transfer torque on thermally activated ferromagnetic resonance excitations in magnetic tunnel junctions

et al. 2008

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Voltage noise measurements on magnetic tunnel junctions show that thermal fluctuations of the magnetization are either amplified or quenched by subcritical spin-transfer torque depending on the current direction. We present an analytical model that describes the dependence of thermally activated ferromagnetic resonance on bias current. The evolution of the peak amplitude and linewidth with the applied current is directly related to the longitudinal torque, whereas the shift of the resonance frequency is sensitive to the transverse torque. Both spin torque terms are independently extracted from the measured noise spectra. Our results support the general idea that it is more pertinent to describe spin torque in terms of voltage rather than current in magnetic tunnel junctions.

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Section: B Magnetic Fluctuations In the Presence Of Spin Torquementioning

confidence: 99%

Section: Influence Of Parallel Spin Torquementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Influence of spin-transfer torque on thermally activated ferromagnetic resonance excitations in magnetic tunnel junctions

et al. 2008

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“…2,3 Moreover, STT is utilized in MTJ nano-oscillators that generate signals in the GHz frequency range. [4][5][6] In order to optimize MTJ parameters, so that they can compete with existing memory and microwave technologies, it is necessary to fully understand STT. The spin-torque diode effect enables quantitative measurements of STT parameters.…”

Section: Introductionmentioning

confidence: 99%

Influence of MgO tunnel barrier thickness on spin-transfer ferromagnetic resonance and torque in magnetic tunnel junctions

et al. 2013

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Spin-transfer ferromagnetic resonance (ST-FMR) in symmetric magnetic tunnel junctions (MTJs) with a varied thickness of the MgO tunnel barrier (0.75 nm < tMgO < 1.05 nm) is studied using the spin-torque diode effect. The application of an RF current into nanosized MTJs generates a DC mixing voltage across the device when the frequency is in resonance with the resistance oscillations arising from the spin transfer torque. Magnetization precession in the free and reference layers of the MTJs is analyzed by comparing ST-FMR signals with macrospin and micromagnetic simulations. From ST-FMR spectra at different DC bias voltage, the in-plane and perpendicular torkances are derived. The experiments and free-electron model calculations show that the absolute torque values are independent of tunnel barrier thickness. The influence of coupling between the free and reference layer of the MTJs on the ST-FMR signals and the derived torkances are discussed.

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“…The dependence Eq. (1) has been verified by magneto-optical [25] and magnetoelectronic techniques [26]. We utilized the latter to verify the established effects of STT in the spin-valve nanopillars used in our study.…”

mentioning

confidence: 74%

Quantum Spin Torque

Zhang

2017

Physics

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We utilize a nanoscale magnetic spin-valve structure to demonstrate that current-induced magnetization fluctuations at cryogenic temperatures result predominantly from the quantum fluctuations enhanced by the spin transfer effect. The demonstrated spin transfer due to quantum magnetization fluctuations is distinguished from the previously established current-induced effects by a nonsmooth piecewise-linear dependence of the fluctuation intensity on current. It can be driven not only by the directional flows of spinpolarized electrons, but also by their thermal motion and by scattering of unpolarized electrons. This effect is expected to remain non-negligible even at room temperature, and entails a ubiquitous inelastic contribution to spin-polarizing properties of magnetic interfaces. DOI: 10.1103/PhysRevLett.119.257201 Spin transfer [1-3]-the transfer of angular momentum from spin-polarized electrical current to magnetic materials-has been extensively researched as an efficient mechanism for the electronic manipulation of nanomagnetic systems, advancing our understanding of nanomagnetism and electronic transport, and enabling the development of magnetoelectronic nanodevices [3][4][5][6][7][8][9][10][11][12][13][14][15]. This effect can be understood based on the argument of angular momentum conservation for spin-polarized electrons, scattered by a ferromagnet whose magnetization ⃗ M is not aligned with their polarization. The component of the electron spin transverse to ⃗ M becomes absorbed, exerting a spin transfer torque (STT) on the magnetization. In nanomagnetic devices such as spin valve nanopillars [ Fig. 1(a)], STT can enhance thermal fluctuations of magnetization [ Fig. 1(b)], resulting in its reversal [5,16] or auto-oscillation [6], which can be utilized in memory, microwave generation, and spin-wave logic [17,18].The approximation for the magnetization as a thermally fluctuating classical vector ⃗ M provides an excellent description for the quasiuniform magnetization dynamics [19]. However, for typical transition-metal ferromagnets, the frequencies f of the dynamical magnetization modes extend to ∼100 THz [19,20]. The modes with f > 6 THz are frozen out at room temperature (f > 70 GHz at T ¼ 3.4 K), and the effect of STT on them cannot be described in terms of the enhancement or suppression of thermal fluctuations. Such high-frequency modes are only now becoming experimentally accessible [21][22][23][24], and their role in spin transfer remains unexplored.Here, we introduce a frequency nonselective, magnetoelectronic approach allowing measurements of the effects of spin transfer on the magnetization fluctuations, not limited to quasiuniform modes. Our central result is that at low temperatures the current-dependent fluctuations arise predominantly from the quantum fluctuations enhanced by spin transfer; the quantum contribution remains non-negligible even at room temperature. The observed effect is analogous to the well-studied spontaneous emission of a photon by a two-level system, also caused by qu...

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Spin-Torque Influence on the High-Frequency Magnetization Fluctuations in Magnetic Tunnel Junctions

Cited by 189 publications

References 13 publications

Influence of spin-transfer torque on thermally activated ferromagnetic resonance excitations in magnetic tunnel junctions

Influence of spin-transfer torque on thermally activated ferromagnetic resonance excitations in magnetic tunnel junctions

Influence of MgO tunnel barrier thickness on spin-transfer ferromagnetic resonance and torque in magnetic tunnel junctions

Quantum Spin Torque

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