Efficient Excitation of Perpendicular Standing Spin-Waves in Undulating CoFeB Films

We report on efficient excitation of perpendicular standing spin-waves (PSSWs) in undulating CoFeB films. PSSWs are exchange dominated spin-waves and have been observed through non-uniform excitation of spin-waves across a ferromagnetic (FM) layer film, and current methods have proven to be inefficient, resulting in weak excitations. We achieve efficient coupling to PSSWs by creating periodic undulations in 100 nm thick CoFeB. The S₁₁ parameter was measured using coplanar waveguides and a network analyzer. An additional mode, not present in flat control samples, was observed for undulating CoFeB films. We attributed this mode to PSSWs being excited due to the non-uniform excitation of spin-waves across the thickness of the FM film. The dispersion relations for Magnetostatic surface spin-waves (MSSW) and PSSWs were used to fit the measured curves and determine key material and excitation parameters such as the exchange constant. Simulations were also used to visualize the dynamics of the oscillations in the CoFeB film. Efficient excitation of such exchange coupled spin-waves can help realize spintronic applications where exchange coupled magnetic oscillations are critical. These undulating structures also provide a simple method to measure the exchange constant for thin FM films.