Spin waves parametrically excited via three-magnon scattering in narrow NiFe strips

Three-magnon scattering can be used to evaluate the lowest frequency of the magnon band in a ferromagnet. Both the ferromagnetic-resonant (FMR) frequency fFMR and the lowest frequency of the magnon band fmin in narrow-shaped NiFe strips were electrically measured using the anisotropic-magnetoresistance effect. The comparison with a micromagnetic simulation shows that fmin of the magnon band can be controlled independent of fFMR by varying the width w and thickness t of the NiFe strip while maintaining a constant t/w ratio. In addition, we found that the frequency difference, fFMR-fmin, can be greatly increased in thicker NiFe strips. Our results show that narrow-shaped ferromagnets allow us to tune the magnon-band structures by varying their w and t. This ability is important for designing magnon circuits in integrated magnonic devices and for improving the quantitative study on the Bose-Einstein condensation of magnons.