Ferromagnetic Resonance Imaging using a submicron localized spin wave mode*

Ferromagnetic Resonance Force Microscopy (FMRFM) is a highly sensitive spectroscopic tool for the study of nanoscale ferromagnets. Nanoscale imaging of buried or multi-component ferromagnetic systems requires a mechanism for defining the localized volume under study. Recently, we have discovered a new approach that employs the strong, nonuniform magnetic field of the micromagnetic probe tip aligned anti-parallel to magnetization in sample to localize FMR modes. The highest resolution obtained in our experiment is 200 nm with relatively large probe ($\sim $ 1.2 x 1.2 x 1.5 $\mu $m$^{3})$ and probe-sample separation ($\sim $ 1.3 $\mu $m), showing sub-surface scanning capability. We have imaged the non-uniform demagnetizing field of an individual 5 $\mu $m Permalloy disk and the variation of the internal magnetic field in the Permalloy film with high sensitivity ($\sim $ 1 Gauss/Hz$^{1/2})$ in the small volume $\sim $ 200 x 200 x 40 nm$^{3}$. Our method presents a technique for exploring nanoscale magnetism and spin dynamics in inhomogeneous magnetic fields.