Abstract
Nonlinear magnetization dynamics is essential for the operation of numerous spintronic devices ranging from magnetic memory to spin torque microwave generators. Examples are microwave-assisted switching of magnetic structures and the generation of spin currents at low bias fields by high-amplitude ferromagnetic resonance. Here we use X-ray magnetic circular dichroism to determine the number density of excited magnons in magnetically soft Ni80Fe20 thin films. Our data show that the common model of nonlinear ferromagnetic resonance is not adequate for the description of the nonlinear behaviour in the low magnetic field limit. Here we derive a model of parametric spin-wave excitation, which correctly predicts nonlinear threshold amplitudes and decay rates at high and at low magnetic bias fields. In fact, a series of critical spin-wave modes with fast oscillations of the amplitude and phase is found, generalizing the theory of parametric spin-wave excitation to large modulation amplitudes.
Highlights
Nonlinear magnetization dynamics is essential for the operation of numerous spintronic devices ranging from magnetic memory to spin torque microwave generators
In the case of spin-wave excitations at ferromagnetic resonance (FMR) discussed in this study, the nonlinear spin-wave interaction depends on the amplitude of an external radio frequency (r.f.)-driving field and can be controlled
Large excitation amplitudes and nonlinear behaviour is essential in the switching process of the magnetization vector
Summary
Nonlinear magnetization dynamics is essential for the operation of numerous spintronic devices ranging from magnetic memory to spin torque microwave generators. Important is the understanding of spin transfer torque-driven nano-oscillators, which may function as radio frequency emitters or receivers Both phenomena inherently involve large excitation amplitudes (and precession angles) of the magnetization vector deep in the nonlinear regime[6,7,8,9,10,11,12]. Our measurements clearly show that the low-field nonlinear resonance behaviour cannot be described adequately using existing models for nonlinear magnetic resonance[15,16]. To understand these data we develop a novel model that generalizes existing theories of spin-wave turbulence. Pronounced fast oscillations of the amplitude and phase occur and dominate the nonlinear response
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