Giant nonlinear self-phase modulation of large-amplitude spin waves in microscopic YIG waveguides

Abstract

Nonlinear self-phase modulation is a universal phenomenon responsible, for example, for the formation of propagating dynamic solitons. It has been reported for waves of different physical nature. However its direct experimental observation for spin waves has been challenging. Here we show that exceptionally strong phase modulation can be achieved for spin waves in microscopic waveguides fabricated from nanometer-thick films of magnetic insulator, which support propagation of spin waves with large amplitudes corresponding to angles of magnetization precession exceeding 10°. At these amplitudes, the nonstationary nonlinear dynamic response of the spin system causes an extreme broadening of the spectrum of spin-wave pulses resulting in a strong spatial variation of the spin-wave wavelength and a temporal variation of the spin-wave phase across the pulse. Our findings demonstrate great complexity of nonlinear wave processes in microscopic magnetic structures and importance of their understanding for technical applications of spin waves in integrated devices.

Deeply nonlinear excitation of self-normalised exchange spin waves

“…We attribute the limitations of the observed nonlinear frequency shift in the previous studies to the onset of spin-wave instabilities caused by the interaction between different width/thickness modes in macro/micro-scale waveguides [32,33,41,42]. However, the width/thickness modes in our nanoscale waveguides are well separated due to the strong contribution of exchange energy that shifts the frequency of the higher-order width/thickness modes by several gigahertz.…”

“…This huge nonlinear frequency shift is two orders of magnitude larger than the frequency shift of tens of MHz noticed in previous studies [32,33,41]. Very recently, Merbouche et al reported the self-phase modulated propagation of FVSWs in a 1 m wide YIG waveguide with a precession angle around 12° and a 100 MHz nonlinear frequency shift [42].…”

Deeply nonlinear excitation of self-normalized short spin waves

“…Very recently, Merbouche et al. ( 42 ) reported the self-phase modulated propagation of FVSWs in a 1-μm-wide YIG waveguide with a precession angle around 12° and a 100 MHz nonlinear frequency shift. We attribute the limitations of the observed nonlinear frequency shift in the previous studies to the onset of spin-wave instabilities caused by the interaction between different width/thickness modes in macro-/micro-scale waveguides ( 32 , 33 , 41 , 42 ).…”

“…Very recently, Merbouche et al (42) reported the self-phase modulated propagation of FVSWs in a 1μm-wide YIG waveguide with a precession angle around 12°and a 100 MHz nonlinear frequency shift. We attribute the limitations of the observed nonlinear frequency shift in the previous studies to the onset of spin-wave instabilities caused by the interaction between different width/thickness modes in macro-/micro-scale waveguides (32,33,41,42). However, the width/thickness modes in our nanoscale waveguides are well separated due to the strong contribution of exchange energy that shifts the frequency of the higher-order width/thickness modes by several gigahertz.…”

Phase-resolved optical characterization of nanoscale spin waves

“…With the use of a different type of the spin-wave source it should be possible to detect spin waves with sub-100 nm wavelengths. Also, with the presented technique other types of BLS exper-iments, such as time-resolved measurements [42] can be easily performed on nanoscale spin waves. These results show that Mie-enhanced BLS microscopy is relevant and highly versatile tool for nanoscale magnonics research.…”