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 ${f}_{\mathrm{FMR}}$ and the lowest frequency of the magnon band ${f}_{\mathrm{min}}$ in narrow-shaped NiFe strips were electrically measured using the anisotropic-magnetoresistance effect. The comparison with a micromagnetic simulation shows that ${f}_{\mathrm{min}}$ of the magnon band can be controlled independent of ${f}_{\mathrm{FMR}}$ 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, ${f}_{\mathrm{FMR}}\ensuremath{-}{f}_{\mathrm{min}}$, 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.