Spin torque dynamics with noise in magnetic nanosystems

Swiebodzinski, Jacek; Chudnovskiy, A. L.; Dunn, Tom; Kamenev, Alex

doi:10.1103/physrevb.82.144404

Cited by 24 publications

(41 citation statements)

References 38 publications

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“…21,22 The semiclassical part comes from treating the current electrons in STT as quantum scattering against the stochastic magnetization. [22][23][24][25] By contrast, quantum dynamics naturally produces all fluctuations. The source of fluctuation completely absent from the semiclassical approach is that arising from the entangled states between the control and the magnet.…”

Section: Basic Ingredients Of a Quantum Approachmentioning

confidence: 91%

A theory of quantum dynamics of a nanomagnet under excitation

Sham

2013

Spintronics VI

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A quantum treatment of magnetization dynamics of a nanomagnet between a thousand and a million spins may be needed as the magnet interacts with quantum control. The advantage of the all-quantum approach over the classical treatment of magnetization is the accounting for the correlation between the magnet and the control agent and the first-principles source of noise. This supplement to the conference talk will concentrate on an overview of the theory with a presentation of the basic ideas which could have wide applications and illustrations with some results. Details of applications to specific models are or will be published elsewhere. A clear concept of the structure of the ground and excited macrospin states as magnetization rotation states and magnons in the Bloch/Dyson sense gives rise to a consistent theory of the magnetization dynamics of a ferromagnet modeled by the Heisenberg Hamiltonian. An example of quantum control is the spin torque transfer, treated here as a sequence of scatterings of each current electron with the localized electrons of the ferromagnet, yields in each encounter a probability distribution of the magnetization recoil state correlated with each outgoing state of the electron. This picture provides a natural Monte Carlo process for simulation of the dynamics in which the probability is determined by quantum mechanics. The computed results of mean motion, noise and damping of the magnetization will be discussed.

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Section: Basic Ingredients Of a Quantum Approachmentioning

confidence: 91%

A theory of quantum dynamics of a nanomagnet under excitation

Sham

2013

Spintronics VI

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“…However, the thermal fluctuations cannot be ignored due to the nanometric size of STT devices, e.g., leading to mainly noise-induced switching at currents far less than the critical switching current without noise 20 switching at currents far less than the critical current in the absence of noise as well as introducing randomness into the precessional orbits which now exhibit energy-controlled diffusion. Thus the effect of the noise is generally to reduce the current-induced switching time.…”

Section: Below)mentioning

confidence: 99%

“…Thus the effect of the noise is generally to reduce the current-induced switching time. 20 To facilitate our discussion we first describe the archetypal schematic model of the STT effect.…”

Section: Below)mentioning

confidence: 99%

Spin-torque effects in thermally assisted magnetization reversal: Method of statistical moments

et al. 2013

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Thermal fluctuations of nanomagnets driven by spin-polarized currents are treated via the Landau-Lifshitz-Gilbert equation generalized to include both the random thermal noise field and the Slonczewski spin-transfer torque term. By averaging this stochastic (Langevin) equation over its realizations, the explicit infinite hierarchy of differential-recurrence relations for statistical moments (averaged spherical harmonics) is derived for arbitrary demagnetizing factors and magnetocrystalline anisotropy for the generic nanopillar model of a spin-torque device comprising two ferromagnetic strata representing the free and fixed layers and a nonmagnetic conducting spacer all sandwiched between two ohmic contacts. The influence of thermal fluctuations and spin-transfer torques on relevant switching characteristics, such as the stationary magnetization, the magnetization reversal time, etc., is calculated by solving the hierarchy for wide ranges of temperature, damping, external magnetic field, and spinpolarized current indicating new spin-torque effects in the thermally assisted magnetization reversal comprising several orders of magnitude. In particular, a pronounced dependence of the switching characteristics on the directions of the external magnetic field and the spin polarization exists.

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“…Therefore, the thermal fluctuations cannot be ignored. They lead to mainly noise-induced switching at currents far less than the critical switching current without noise as well as introducing randomness into the precessional orbits, which now exhibit energy-controlled diffusion [10]. Thus, the effect of the noise is generally to reduce the current-induced switching time.…”

Section: Introductionmentioning

confidence: 99%