Efficient Excitation of High-Frequency Exchange-Dominated Spin Waves in Periodic Ferromagnetic Structures

Abstract

Spin waves are of great interest as an emerging solution for computing beyond the limitations of scaled transistor technology. In such applications, the frequency of the spin waves is important as it affects the overall frequency performance of the resulting devices. In conventional ferromagnetic thin films, the magnetization dynamics in ferromagnetic resonance (FMR) and spin-waves are limited by the saturation magnetization of the ferromagnetic (FM) material and the external bias field. High-frequency applications would require high external magnetic fields which limit the practicality in a realistic device. One solution is to couple microwave excitations to perpendicular standing spin-waves (PSSWs) which can enable higher oscillation frequencies. However, efficient coupling to these modes remains a challenge since it requires an excitation that is non-uniform across the FM material thickness and current methods have proven to be inefficient, resulting in weak excitations. Here, we show that by creating periodic undulations in a 100 nm thick Co 40 Fe 40 B 20 layer, high-frequency PSSWs (>20 GHz) can be efficiently excited using micrometer sized transducers at bias fields below 100 Oe which absorb nearly 10% of the input RF power. Efficient excitation of such spin-waves at low fields may enable high

Modified dispersion law for spin waves coupled to a superconductor

“…Note that while exchangedominated spin waves are the most promising for applications owing to a wide range of its high eigen frequencies, these are the hardest to excite due to a sub-micro scale of their typical wavelengths. Operation with exchange-dominated spin waves requires either precise nanotechnology [23][24][25] or more sophisticated approaches. 26,27 The dispersion relation of a ferromagnetic system can be studied numerically using micromagnetic simulations 18,19 as demonstrated in Refs.…”

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

“…Symmetrical pinning only induces odd PSSW modes, whereas both odd and even modes should be detected if the magnetization is pinned at one of the interfaces. Most work on PSSWs has focussed on metallic ferromagnetic materials such as Co/Py 19 , Py 18 , 23 , 24 , 26 , and CoFeB 27 , 28 . In YIG, Klingler et al .…”

“…used PSSWs to extract the exchange constant 25 and Navabi et al . demonstrated the excitation of a 1st order PSSW mode in a 100-nm-thick YIG film on top of an undulating substrate 28 .…”

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

“…Conventional micro-structured microwave antennas allow one to transfer on the order of 1 rad/µm but, if integrated to a planar film, are known to excite PSSW only weakly [11]. Recently, undulation of a CoFeB film was shown to allow for efficient PSSW excitation within the same film [12]. For planar YIG, it was reported that top layers of either Co [13] or Co 40 Fe 40 B 20 [14] enhanced PSSW amplitudes considerably.…”