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

Abstract

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 spin-polarized 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.

an updated version

References in corpus (6)

• Thermal fluctuations of magnetic nanoparticles
• Generation linewidth of an auto-oscillator with a nonlinear frequency shift: Spin-torque nano-oscillator
• Spin-torque switching: Fokker-Planck rate calculation
• Lineshape distortion in a nonlinear auto-oscillator near generation threshold: Application to spin-torque nano-oscillators
• Thermally assisted spin transfer torque switching in synthetic free layers
• Spin-Transfer Torque Magnetization Reversal in Uniaxial Nanomagnets with Thermal Noise

Cited by in corpus (7)

• Reversal time of the magnetization of magnetic nanoparticles at very low damping
• Current dependence of spin torque switching rate based on Fokker-Planck approach
• Inertial dynamics and equilibrium correlation functions of magnetization at short times
• On a simple derivation of the very low damping escape rate for classical spins by modifying the method of Kramers
• Damping dependence of spin-torque effects in thermally assisted magnetization reversal
• Spin-transfer torque effects in the dynamic forced response of the magnetization of nanoscale ferromagnets in superimposed ac and dc bias fields in the presence of thermal agitation
• Switching probability of all-perpendicular spin valve nanopillars