Spin wave Brillouin measurements in FeCo with a virtually imaged phased array spectrometer.

We demonstrate for what we believe to be the first time the efficient acquisition of spin wave Brillouin spectra with a virtually imaged phase array-based spectrometer and an etalon-based notch filter. Thermally excited magnons in a 5 nm epitaxially grown single-crystalline Fe₇₅Co₂₅ film are detectable within 100 ms and a signal-to-noise ratio greater than 100 is achieved in 10 seconds with a spectral resolution of 0.45 GHz and a pump power of 23 mW. The dependence of the Brillouin shift on the externally applied magnetic field is characterized for fields ranging from 29 to 370 mT, and the effective magnetization is estimated to be 1.6 ± 0.1 MA/m. A 2D map of the spatial variation of the Brillouin shift obtained in a non-uniform magnetic field demonstrates the suitability of virtually imaged phase array-based instrumentation for imaging spin wave propagation in magnonic devices.