Propagation of Spin-Wave Packets in Individual Nanosized Yttrium Iron Garnet Magnonic Conduits

Abstract

Modern-days CMOS-based computation technology is reaching fundamental limitations which restrain further progress towards faster and more energy efficient devices [1]. A promising path to overcome these limitations is the emerging field of magnonics which utilizes spin waves for data transport and computation operations [2-5]. Many different devices have already been demonstrated on the macro-and microscale [2,4-12]. However, the feasibility of this technology essentially relies on the scalability to the nanoscale and a proof that coherent spin waves can propagate in these structures.Here, we present a study of the spin-wave dynamics in individual yttrium iron garnet (YIG) magnonic conduits with lateral dimensions down to 50 nm. Space and time resolved micro-focused Brillouin-Light-Scattering (BLS) spectroscopy is used to extract the exchange constant and directly measure the spin-wave decay length and group velocity. Thereby, the first experimental proof of propagating spin waves in individual nano-sized YIG conduits and the fundamental feasibility of a nano-scaled magnonics are demonstrated.State of the art investigations are typically performed in micron-sized structures [13][14][15] lacking the final push to the nanoscale and are often based on the so-called Damon-Eshbach (DE) geometry, since this geometry provides a high spin-wave group velocity [16]. However, large bias magnetic fields are required to achieve the corresponding magnetization state in nano-sized conduits. Therefore, using the Backward-Volume (BV) geometry is a necessity regarding any application of spin waves for data processing, since it corresponds to the natural self-magnetized state of such a conduit. Besides the propagation geometry, the choice of material is crucial as well. Being the material providing the lowest known spin-wave damping, yttrium iron garnet (YIG) is the naturally preferred material for magnonics. However, this comes at the cost of a complex crystallographic structure [17] featuring a unit cell size of 1.2376 nm [18], which opens up the question whether the material can be scaled down to the nanoscale while preserving its unique properties during this process.Here, a thin (111) YIG film with a thickness of = 44 nm is used, which is grown on top of a 500 µm thick (111) Gadolinium Gallium Garnet (GGG) substrate by Liquid Phase Epitaxy (LPE) [19]. A preliminary characterization by stripline Vector-Network-Analyzer ferromagnetic resonance (VNA-FMR) spectroscopy [20,21] is performed to obtain the fundamental magnetic properties. The measurement, shown in Supplementary Fig. S1, yields a saturation magnetization of s = (140.7 ± 2.8) kA m and a Gilbert damping parameter of = (1.75 ± 0.08) × 10 −4 . These values are common for high-quality YIG thin films [19]. Thereafter, the nanostructuring process is carried out by Figure 2| Measurement of the thermal spin-wave population and determined exchange constant. (a) Exemplary thermal BLS spectra in the absence of any microwave excitation for a = 1000 YIG waveguide. A field dependent ...

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

“…for a next-generation of computing circuits. The development of nanoscopic YIG waveguides and nanostructures is already underway and the first circuits are currently being fabricated [10,12,29]. With its scalability to large wafer diameters of up to 3 and 4 inches, LPE technology opens up an alternative way for efficient circuit manufacturing for a future YIG planar technology on a wafer scale.…”

“…A growing field of application for magnetic garnets is (i) magnonics, which deals with future potential devices for data transfer and processing using spin waves [1,[6][7][8][9]. The significant thickness reduction achieved today allows reducing the circuit sizes from classical millimeter dimensions [1] down to 50 nm [10][11][12]. Another important field is (ii) spintronics: By increasing the YIG surfaceto-volume ratio as much as possible (while keeping its magnetic properties), physical phenomena, such as the inverse spin Hall effect [13], spin-transfer torque [14], and the spin Seebeck effect [15] (generated by a spin angular momentum transfer at the interfaces between YIG and a nonmagnetic metallic conductor layer) become much more efficient [7,[16][17][18][19][20][21][22][23][24][25][26][27][28][29].…”

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

“… 17 However, their wavelengths are about twice the width of the CPW signal line, 18 restricting the accessible wave vector regime in both thin yttrium iron garnet (YIG) films 19 and along nanosized YIG magnon conduits. 20 To overcome this restriction and excite spin waves (SWs) with a wavelength λ much smaller than the size of the CPW is the subject of intense research. 21 Recently ultrashort SWs (magnons) were emitted by nanoscale spin textures which were irradiated by microwave fields.…”

A nonlinear magnonic nano-ring resonator

“…Here we study the single-mode nanoscale magnonic ring resonator using the critical coupling phenomenon and demonstrate its functionality analytically and by simulation, including linear and nonlinear operation regimes, as well as their anticipated applications. Despite the fact that this is a simulation, the recent progress in the realization of single-mode magnonic nano-conduits proves that the sizes chosen here can be realized based on the current nano-fabricating technology 33 .…”