Exchange-torque-induced excitation of perpendicular standing spin waves in nanometer-thick YIG films

Qin, Huajun; Hämäläinen, Sampo J.; Dijken, Sebastiaan van

doi:10.1038/s41598-018-23933-y

Cited by 102 publications

(83 citation statements)

References 38 publications

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“…The latter generates a lattice-periodic dipolar field on the YIG magnetization with wave vectors = π where a is the nanowire period and = 2, 4, 6 … 32 . The perpendicular standing spin waves (PSSWs) 33,34 in films have mode numbers = 0, 1, 2, 3 …, but they are in the present thin film upshifted to above 35 GHz and can be disregarded.…”

mentioning

confidence: 89%

Excitation of unidirectional exchange spin waves by a nanoscale magnetic grating

et al. 2019

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Magnon spintronics is a prosperous field that promises beyond-CMOS technology based on elementary excitations of the magnetic order that act as information carriers for future computational architectures. Unidirectional propagation of spin waves is key to the realization of magnonic logic devices. However, previous efforts to enhance the Damon-Eshbach-type nonreciprocity did not realize (let alone control) purely unidirectional propagation. Here we experimentally demonstrate excitations of unidirectional exchange spin waves by a nanoscale magnetic grating consisting of Co nanowires fabricated on an ultrathin yttrium iron garnet film. We explain and model the nearly perfect unidirectional excitation by the chirality of the magneto-dipolar interactions between the Kittel mode of the nanowires and the exchange spin waves of the film. Reversal of the magnetic configurations of film and nanowire array from parallel to antiparallel changes the direction of the excited spin waves. Our results raise the prospect of a chiral magnonic logic without the need for fragile surface states.Spin waves (SWs) 1-6 can transport information in high-quality magnetic insulators such as yttrium iron garnet (YIG) 7-10 free of charge flow and with very low dissipation. Based on the interference and nonlinear interactions, the phase information of SWs 11-14 allows the design of wave-based logic circuits 15-17 for information transmission and processing with small environmental footprint. Surface SWs 18 are chiral, i.e. they propagate only in the direction of the outer product of magnetization direction and surface normal and, therefore, in opposite directions on the upper and lower film surfaces/interfaces. These "Damon-Eshbach" (DE) modes 18 are beneficial for magnonic logic devices 19 but exist only in thick magnetic films with sizable group velocities. As products of the dipolar magnetic interaction, in the case of thin films, they have small group velocities and are susceptible to surface roughness scattering. Previous efforts focused on magnetic metallic systems 20-28 with relative high dissipation. Short-wavelength spin waves 29-36 with dispersion governed by the exchange interactions, travel much faster at higher frequencies (Fig. 1d). However, pure exchange

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confidence: 89%

Excitation of unidirectional exchange spin waves by a nanoscale magnetic grating

et al. 2019

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“…Recently, it has been shown [20][21][22] that the weak interlayer exchange interaction between two magnetic materials can cause magnon-magnon coupling. However, the much stronger intrinsic exchange has not yet been leveraged for coupling phenomena.…”

Section: Arxiv:190304330v2 [Cond-matmtrl-sci] 23 Sep 2019mentioning

confidence: 99%

“…Antiferromagnets and ferrimagnets further host multiple magnon modes. Their coupling allows for coherent control and engineering of spin dynamics for applications in magnonics [16,17] and antiferromagnetic spintronics [18,19].Recently, it has been shown [20][21][22] that the weak interlayer exchange interaction between two magnetic materials can cause magnon-magnon coupling. However, the much stronger intrinsic exchange has not yet been leveraged for coupling phenomena.…”

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confidence: 99%

Exchange-Enhanced Ultrastrong Magnon-Magnon Coupling in a Compensated Ferrimagnet

et al. 2019

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We experimentally study the spin dynamics in a gadolinium iron garnet single crystal using broadband ferromagnetic resonance. Close to the ferrimagnetic compensation temperature, we observe ultrastrong coupling of clockwise and counterclockwise magnon modes. The magnonmagnon coupling strength reaches almost 40% of the mode frequency and can be tuned by varying the direction of the external magnetic field. We theoretically explain the observed mode-coupling as arising from the broken rotational symmetry due to a weak magnetocrystalline anisotropy. The effect of this anisotropy is exchange-enhanced around the ferrimagnetic compensation point. arXiv:1903.04330v2 [cond-mat.mtrl-sci] 23 Sep 2019The strong and ultrastrong interaction of light and matter is foundational for circuit quantum electrodynamics [1][2][3]. The realizations of strong spin-photon [4][5][6] and magnonphoton [7][8][9][10][11][12] coupling have established magnetic systems as viable platforms for frequency up-conversion [13,14] and quantum state storage [15]. Antiferromagnets and ferrimagnets further host multiple magnon modes. Their coupling allows for coherent control and engineering of spin dynamics for applications in magnonics [16,17] and antiferromagnetic spintronics [18,19].Recently, it has been shown [20][21][22] that the weak interlayer exchange interaction between two magnetic materials can cause magnon-magnon coupling. However, the much stronger intrinsic exchange has not yet been leveraged for coupling phenomena. While the THz-frequency dynamics in antiferromagnets is challenging to address experimentally [23], the sublattice magnetizations in compensated ferrimagnets can be tuned to achieve GHzfrequency quasi-antiferromagnetic dynamics. Here, we report the experimental observation of ultrastrong exchange-enhanced magnon-magnon coupling in a compensated ferrimagnet with the coupling rate reaching up to 37% of the characteristic magnon frequency. We furthermore demonstrate that the coupling strength can be continuously tuned from the ultrastrong to the weak regime.We investigate spin dynamics, or equivalently the magnon modes, in a compensated, effectively two-sublattice ferrimagnet in the collinear state. Around its compensation temperature, this system can be viewed as a "quasi-antiferromagnet" due to its nearly identical sublattice magnetizations M A M B . Figure 1 schematically depicts the typical spatially uniform spin dynamics eigenmodes of the system [25]. Within the classical description, these become clockwise (cw) and counterclockwise (ccw) precessing modes which correspond to spin-down and spin-up magnons, respectively, in the quantum picture. The key physics underlying our experiments is the tunable exchange-enhanced coupling, and the concomitant hybridization, between theses two modes. The essential ingredients -mode coupling and exchange-enhancement -are both intuitively understood within the quantum picture as follows. First, due to their opposite spins, a spin-up magnon can only be coupled to its spin-down counterpart by ...

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“…To verify and refine our approach, we first calculated the expected convolved PSM spectrum for our reference sample by Equation . Calculating ν p via Equation does not provide a distribution of

I (ν)

. Using

d = 300 nm

, divided by the cosine of the angle of rotation around

{boldE}_{normali}

, and comparing preliminary results to the measured spectra (Figure a) allowed us to tune the peak shape via the use of a Gaussian signal window, Figure a.…”

Section: Resultsmentioning

confidence: 99%

“…Figure shows that their frequencies, for a given material and applied field, depend on p . Literature reports indicate that, typically, PSM intensities decay as

\propto p^{- 1 / 2}

, due to eddy current magnetic damping . Therefore, and based on the number of typically considered modes, we plotted

ν_{p = 10}

as the upper boundary for observable PSM, in Figure and in the presented results.…”

Section: Methodsmentioning

confidence: 99%

An Experiment‐Based Numerical Treatment of Spin Wave Modes in Periodically Porous Materials

Opdenbosch

Hukic-Markosian

Ott

et al. 2019

Physica Status Solidi (b)

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To determine a general correlation between structure and dynamic magnetic properties of porous materials, the frequencies of magnetic spin waves are studied by Brillouin light scattering from nickel inverse opals and backed up by micromagnetic simulations. Within the observed unit cell size regime between 400 and 800 nm, discrete thickness standing modes are found to change with unit cell size. By applying pair correlation functions of the inverse opal solid phase normal to the applied field to an equation for perpendicular standing modes, the directional and unit cell size‐dependent spectral intensities above the surface mode region can be traced. Thus, an accessible general approach for the prediction of standing spin waves in porous materials is obtained.

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Exchange-torque-induced excitation of perpendicular standing spin waves in nanometer-thick YIG films

Cited by 102 publications

References 38 publications

Excitation of unidirectional exchange spin waves by a nanoscale magnetic grating

Excitation of unidirectional exchange spin waves by a nanoscale magnetic grating

Exchange-Enhanced Ultrastrong Magnon-Magnon Coupling in a Compensated Ferrimagnet

An Experiment‐Based Numerical Treatment of Spin Wave Modes in Periodically Porous Materials

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