On-Off Intermittency in Randomly Driven Nonlinear Ferromagnetic Resonance

Abstract

Simple models of nonlinear ferromagnetic resonance are considered which describe perpendicular resonance and parallel pumping with the rf field amplitude changing randomly and chaotically in time. On-off intermittency is obtained from the numerical solution of the equations of motion for the spin-wave amplitudes when the mean value of the rf field amplitude exceeds the Suhl instability threshold. Possible experimental applications are discussed.

Simulations of Noise-Free Stochastic Resonance in Spin-Wave Chaos

“…Noise-free SR was first observed experimentally in chaotic ferromagnetic resonance (FMR) [5], and numerical simulations of the corresponding model were presented in Ref. [6].…”

“…The uniform mode driven by the rf field of frequency ω (close to its eigenfrequency ω0) decays into pairs of spin waves (SW) with opposite wave vectors and frequencies ωk ω/2, as soon as the rf field amplitude hT exceeds the threshold h. In our model the rf field amplitude is slowly modulated with a signal of frequency ω3 « ω, and only two SW pairs are included to interact with the uniform mode. The equations of motion for the weakly time-dependent complex amplitudes of the uniform mode α 0 and of the spin waves αl and α2 read [6] where n0,k, k = 1,2 are phenomenological damping parameters, Δω 0 = ω0 -ω, Δωk = ω -ω/2, δ0,k = n0,k+iΔω0,k, ε = hT/hTthr r, V0,k are the respective three-magnon coupling coefIicients and nth is the level of thermal excitation of SW. In (1) all detunings, dampings, and amplitudes are dimensionless and normalized to nιΡ, and the dot denotes the derivative with respect to rescaled time t' = n1t. '…”

“…s-1 and th 10 -1 0 at the liquid helium temperature [6]. Using the following parameters in our simulations: n0 = 1.25, n1 Ξ 1.0, n2 = 0.8, Δω0 = -1.5, Δω1 = 3.0, Δω2 = 2.62, |V02|/|V01| = 0.754 [8], the system (1) becomes chaotic for ε > 1.95.…”

“…In contrast to Ref. [6], where ε0 was used as a control parameter, here we chose the dc magnetic field. Its variation results in a detuning of the eigenfrequencies and corresponds in (1) to changes of Δω0 and Δωk.…”

“…3, 4 we have shown the influence of thermal excitation of SW: the extrema of the SNR or C1 curves are broadened and occur more distinctly. Thus, noise-free SR in experiments with on-off intermittency in SW dynamics will appear due to the combined effect of internal chaotic dynamics and weak thermal excitations of SW (the effect of th in other kinds of intermittency is not necessarily so large [6]). …”