Abstract
Voltage or electric field induced magnetization dynamics promises low power spintronics devices. For successful operation of some spintronics devices such as magnetic oscillators and magnetization switching devices a clear understanding of nonlinear magnetization dynamics is required. Here, we report a detailed experimental and micromagnetic simulation study about the effect of excitation power on voltage induced local magnetization dynamics in an ultrathin CoFeB film. Experimental results show that the resonance line-width and frequency remains constant, whereas cone angle of the magnetization precession increases linearly with square-root of excitation power below threshold value, known as linear excitation regime. Above threshold power, the dynamics enters into nonlinear regime where resonance line-width monotonically increases and resonance frequency monotonically decreases with increasing excitation power. Simulation results reveal that a strong nonlinear and incoherent magnetization dynamics are observed in our experiment above the threshold power which reduces dynamic magnetic signal by suppressing large cone angle of magnetization precession. Moreover, a significant transfer of spin angular momentum from uniform FMR mode to its degenerate spin waves outside of excitation area further restrict the cone angle of precession within only few degrees in our device. Our results will be very useful to develop all-voltage-controlled spintronics devices.
Highlights
The recent discovery of voltage-controlled magnetic anisotropy (VCMA) has a huge potential for the development of low power spintronics devices fully operated by voltage[1, 2]
The device with magnetic tunnel junctions (MTJ) structure consists of 3 nm top CoFeB layer and 1.4 nm bottom CoFeB layer separated by a 2 nm thick insulating MgO layer
Both CoFeB layers have perpendicular magnetic anisotropy (PMA) at the interface of CoFeB/MgO due to the hybridization of Fe-3d and O-2p orbitals[22, 23] and the magnitude of PMA strongly depends upon the thickness of ferromagnetic layer[24, 25]
Summary
We observe a deviation of Vpp from linear increment with Prf and deviation of θc from linear increment with Vrf above threshold value of Prf in experiment as well as in simulation results Note that this dynamic dephasing broadens resonance line-width. As the four magnon scattering process increases with the increase of Prf, we observed a monotonic increment of HWHM as a function of Vrf or Prf. In conclusion, we have shown a systematic transition from linear magnetization dynamics to nonlinear magnetization dynamics for local excitation of magnetization by experiment and micromagnetic simulation study. Simulations results demonstrate that the coherent and linear magnetization dynamics becomes incoherent and nonlinear above a certain threshold value of rf power This incoherent nonlinear dynamics significantly reduces dynamic signal i.e. cone angle of magnetization precession and increases resonance line-width. We think our study will be very useful for the development of all-voltage-controlled spin waves based logic devices
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