Spin waves with large decay length and few 100 nm wavelengths in thin yttrium iron garnet grown at the wafer scale

Abstract

Using conventional coplanar waveguides (CPWs) we excited spin waves with a wavelength λ down to 310 nm in a 200 nm thin yttrium iron garnet film grown by liquid phase epitaxy. Spin-wave transmission was detected between CPWs that we separated by up to 2 mm. For magnetostatic surface spin waves we found a large nonreciprocity of 0.9 and a high group velocity v g of up to 5.4 km/s. The extracted decay length l d amounted to 0.86 mm. Small λ, high v g and large l d are key figures of merit when aiming at non-charged based signal transmission and logic devices with spin waves.Thin films of the insulating ferrimagnet yttrium iron garnet (YIG) have recently shown to exhibit small spin-wave (SW) damping [1][2][3][4][5][6][7] . A large decay length of up to 0.58 mm was reported for SWs in a 20 nm thick YIG film 3 . In Ref.3 , the films were grown by pulsed laser deposition (PLD) on small substrates of (111) gadolinium gallium garnet (GGG) with a lateral size of about 10 mm × 10 mm. Small damping is important for coherent nanomagnonics, low power consumption and devices such as magnonic holography memory, non-linear cellular networks and SW interferometers 3,[8][9][10][11] . Nonreciprocal characteristics of spin waves further enriches possible logic applications 12 . To scale substrate sizes up, PLD is however very challenging. Here, for instance, magnetron sputtering 13 and liquid phase epitaxy 7,14 are more suitable. Still, for decades, commercially available YIG films grown by liquid phase epitaxy (LPE) had a thickness of 1 µm and beyond 15 . Such thicknesses do not allow for application in nanomagnonics. Recently, a 500 nm thick LPE-grown film was explored with and without nanopatterning 16 . Parameters such as decay length l d , group velocity v g , and nonreciprocity parameter β were however not provided. Note that wafer bonding has already been explored to transfer LPE-grown YIG onto Si substrates to advance integrated photonics 17,18 . Such a route might be interesting for hybrid magnonic devices, and it is timely to explore in detail SW properties of thin YIG grown by LPE.We report on experiments performed on a commercially available YIG film ordered with a thickness t = 200 nm that was grown by LPE on a 3" GGG substrate 20 . Using coplanar waveguides (CPWs) we explored spin-wave propagation over broad frequency and magnetic field regimes. The smallest wavelength λ that we excited by the conventional CPWs amounted to 310 nm. This value is smaller than the wavelengths so far excited via microwave antenna in thin YIG with thicknesses ranging from 20 to 500 nm 3,6,16 . At the same time, we observe modes of higher order compared to earlier publications reporting spin-wave excitation in thin YIG 3,16,21 and thin ferromagnetic metals 22,23 using bare CPWs. The nonreciprocity is found to be pronounced with a parameter β of up to 0.9, much larger compared to 20 nm thick YIG 3 . For magnetostatic surface spin waves (MSSWs) we extract a decay length of 0.86 mm that is a factor of 1.5 larger compared to Ref. [3]. The resul...

Efficient wavelength conversion of exchange magnons below 100 nm by magnetic coplanar waveguides

“…With the help of phase-resolved BLS measurements ( Supplementary Fig. 5), we extracted the exchange constant and the effective magnetization of the thin YIG in sample 1: J = (2.7 ± 0.2) × 10 −7 erg cm −1 , and μ 0 M eff = (0.180 ± 0.002) T. The values were consistent with the values reported in the literature 27,34,49 . We used the experimentally determined values for the calculation of wavevectors.…”

“…We argue that the wavelength conversion based on mCPWs is very versatile and works in both insulting and metallic magnets, in nanoscopic ferromagnetic waveguides 45 and skyrmion-hosting materials 46 . The magnons with k max ¼ 62:4 rad μm −1 reported here possess wavelengths shorter than the minimum ones reported so far for nonmagnetic microwave waveguides 14,15,27 and signals are about three orders of magnitude larger (Fig. 6b).…”

“…Instead parametric pumping in the nonlinear regime has been utilized to obtain exchange magnons with k > 20 rad μm −116-18 . Concerning emission of such magnons in the linear regime, nonuniform spin textures [19][20][21][22] , magnetic interfaces 23,24 , and the magnonic grating coupler effect [25][26][27] have been explored. Magnons with λ ≈ 50 nm (k ≈ 120 rad μm −1 ) were induced in thin yttrium iron garnet (YIG) by means of a grating coupler consisting of a periodic lattice of parallel nanostripes 28 .…”

Low damping and microstructural perfection of sub-40nm-thin yttrium iron garnet films grown by liquid phase epitaxy

“…Since nucleation and crystal growth take place under almost thermodynamic equilibrium conditions, this guarantees high quality with respect to narrow absolute FMR linewidths and a small Gilbert damping coefficient [43][44][45] at the same time, making LPE comparable or superior to the other growth techniques. In addition, LPE allows YIG to be deposited in the required quality on 3-or 4-inch wafers [46]. This is important for possible applications mentioned above.…”

Co- and contra-directional vertical coupling between ferromagnetic layers with grating for short-wavelength spin wave generation

“…The possibility of miniaturization of spin-wave-based logic devices is dependent on the wavelength, thus the attention is focused on searching the ways of generation of short SWs. Several approaches has been recently reported: shortening the wavelength in a tapered waveguide [9], microwave-to-SW transducers based either on magnetic wires [10], nanostructure edges [11], diffraction gratings [12][13][14], coplanar waveguides [15] or anisotropy-modulated multiferroic heterostructures [16], transduction of acoustic waves into short SWs due to magneto-elastic coupling [17,18], and emitters based on current-driven oscillating pinned domain walls [19].…”