Optimization of Spin-Wave Propagation with Enhanced Group Velocities by Exchange-Coupled Ferrimagnet-Ferromagnet Bilayers

Abstract

We report broadband spectroscopy and numerical analysis by which we explore propagating spin waves in a magnetic bilayer consisting of a 23 nm thick permalloy film deposited on 130 nm thick Y 3 Fe 5 O 12 . In the bilayer, we observe a characteristic mode that exhibits a considerably larger group velocity at small in-plane magnetic field than both the magnetostatic and perpendicular standing spin waves. Using the finite element method, we confirm the observations by simulating the mode profiles and dispersion relations. They illustrate the hybridization of spin wave modes due to exchange coupling at the interface. The high-speed propagating mode found in the bilayer can be utilized to configure multi-frequency spin wave channels enhancing the performance of spin wave based logic devices.I.

Coherent Spin Pumping in a Strongly Coupled Magnon-Magnon Hybrid System

“…In spintronics, exchange-induced magnetic excitations, called spin waves, or magnons [3,4], are good candidates because information can be encoded by both the amplitude and the phase of spin waves. For example, the interference of coherent spin waves can be engineered for spin wave logic operations [5][6][7]; the coherent interaction of spin-torque oscillators leads to mutual synchronization [8][9][10][11][12][13], which can be applied in artificial neural networks [14,15]; and the coherent coupling between magnons and microwave cavities [16][17][18][19][20][21][22] opens up new opportunities for magnon-based quantum information science [23,24].Recently, strong coupling between two magnonic systems has been observed [25][26][27], which allows excitations of forbidden spin wave modes and high group velocity of propagating spin waves [28,29]. The coupling is dominated by the exchange interaction at the interface of the magnetic bilayers, providing a new pathway to coherently transfer magnon excitations between two magnetic systems possessing distinctive properties: from conductor to insulator, from uniform to nonuniform mode and from high-damping to low-damping systems.…”

“…The second question is particularly important for optimizing the coherence of spin wave transfer in hybrid systems. Furthermore, any parasitic effect on the incoherent spin current from the conduction band is well-removed [34-36] by using magnetic insulators such as yttrium iron garnet (Y 3 Fe 5 O 12 , YIG) [29,37,38], which facilitates the study of spin pumping coherency.In this work, we study YIG/permalloy (Ni 80 Fe 20 , Py) bilayers with varying Py thicknesses. By using a much thinner YIG film compared with previous work [25,27], we define well-separated perpendicular standing spin wave (PSSW) modes in YIG and create an avoided crossing much larger than the linewidths, allowing us to study the linewidth evolution of the two individual hybrid modes.…”

“…The second question is particularly important for optimizing the coherence of spin wave transfer in hybrid systems. Furthermore, any parasitic effect on the incoherent spin current from the conduction band is well-removed [34][35][36] by using magnetic insulators such as yttrium iron garnet (Y 3 Fe 5 O 12 , YIG) [29,37,38], which facilitates the study of spin pumping coherency.…”

Nanoimaging of Ultrashort Magnon Emission by Ferromagnetic Grating Couplers at GHz Frequencies

“…Pronounced excitations of PSSWs were recently reported for heterostructures consisting of a ferromagnetic layer and a YIG film. 36 − 38 To compare transmission amplitudes, we show in Figure 2 c Mag(S21) obtained on sample2 (black line) at 11 mT and Mag(S21) of a reference sample (green line) with CPWs without GCs (details and field-depended spectra are displayed in Figure S3 ). For sample2, 1 G and 2 G peaks are clearly visible.…”

Resonant subwavelength control of the phase of spin waves reflected from a Gires–Tournois interferometer

“…2 d,g) have lower group velocity and shorter wavelengths. It is worth noting that the wavelengths of SWs in separated layers do not depend on the direction of propagation, while the dynamic dipolar coupling between SW modes in both layers combined with the nonreciprocal nature of surface SW modes introduces asymmetry 23 – 25 . For nm the coupling is still very weak and at the frequency of 11 GHz, which is used in further analysis and marked with the white horizontal line in Fig.…”