Chiral magnets with topologically nontrivial spin order such as Skyrmions have generated enormous interest in both fundamental and applied sciences. We report broadband microwave spectroscopy performed on the insulating chiral ferrimagnet Cu2OSeO3. For the damping of magnetization dynamics we find a remarkably small Gilbert damping parameter of about 1 × 10 −4 at 5 K. This value is only a factor of 4 larger than the one reported for the best insulating ferrimagnet yttrium iron garnet. We detect a series of sharp resonances and attribute them to confined spin waves in the mm-sized samples. Considering the small damping, insulating chiral magnets turn out to be promising candidates when exploring non-collinear spin structures for high frequency applications. The development of future devices for microwave applications, spintronics and magnonics [1-3] requires materials with a low spin wave (magnon) damping. Insulating compounds are advantageous over metals for high-frequency applications as they avoid damping via spin wave scattering at free charge carriers and eddy currents [4,5]. Indeed, the ferrimagnetic insulator yttrium iron garnet (YIG) holds the benchmark with a Gilbert damping parameter α intr = 3 × 10 −5 at room temperature [6,7]. During the last years chiral magnets have attracted a lot of attention in fundamental research and stimulated new concepts for information technology [8,9]. This material class hosts non-collinear spin structures such as spin helices and Skyrmions below the critical temperature T c and critical field H c2 [10][11][12]. Additionally, Dzyaloshinskii-Moriya interaction (DMI) is present that induces both the Skyrmion lattice phase and nonreciprocal microwave characteristics [13]. Low damping magnets offering DMI would generate new prospects by particularly combining complex spin order with long-distance magnon transport in high-frequency applications and magnonics [14,15]. At low temperatures, they would further enrich the physics in magnonphoton cavities that call for materials with small α intr to achieve high-cooperative magnon-to-photon coupling in the quantum limit [16][17][18][19].In this work, we investigate the Gilbert damping in Cu 2 OSeO 3 , a prototypical insulator hosting Skyrmions [20][21][22][23]. This material is a local-moment ferrimagnet with T c = 58 K and magnetoelectric coupling [24] that gives rise to dichroism for microwaves [25][26][27]. The magnetization dynamics in Cu 2 OSeO 3 has already been explored [13,28,29]. A detailed investigation on the damping which is a key quality for magnonics and spintronics has not yet been presented however. To evaluate α intr we explore the field polarized state (FP) where the two spin sublattices attain the ferrimagnetic arrangement [21]. Using spectra obtained by two different coplanar waveguides (CPWs), we extract a minimum α intr =(9.9 ± 4.1)×10−5 at 5 K, i.e. only about four times higher than in YIG. We resolve numerous sharp resonances in our spectra and attribute them to modes that are confined modes across the macros...

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...

Using anisotropic magnetoresistance in a multi-probe configuration and local heating with a scanning laser, we investigate the magnetization reversal of individual permalloy (Py) and CoFeB nanotubes with spatial resolution. Nanocrystalline Py and amorphous CoFeB nanotubes are found to reverse via domain wall movement and chirality switching, respectively. Our experiments provide an understanding of the role of microstructure and magnetic anisotropy in the switching of ferromagnetic nanotubes at room temperature.

We performed broadband spin-wave spectroscopy on 200 nm thick yttrium iron garnet containing arrays of partially embedded magnetic nanodisks. Using integrated coplanar waveguides (CPWs), we studied the excitation and transmission of spin waves depending on the presence of nanomagnet arrays of different lateral extensions. By means of the grating coupler effect, we excited spin waves propagating in multiple lateral directions with wavelengths down to 111 nm. They exhibited group velocities of up to 1 km/s. Detection of such short-wavelength spin waves was possible only in symmetrically designed emitter/detector configurations, not with a bare CPW. We report spin waves propagating between grating couplers under oblique angles exhibiting a wave vector component parallel to the CPW. The effective propagation distance amounted to about 80 μm. Such transmission signals were not addressed before and substantiate the versatility of the grating coupler effect for implementing nanomagnonic circuits.