We utilize ferromagnetic resonance force microscopy (FMRFM) to generate and detect multiple localized spin wave modes with spatial dimensions less than 100 nm in ferromagnetic thin films. Localized spin waves are a potentially powerful tool for imaging local magnetic properties within ferromagnetic nanostructures. We generate localized spin waves by positioning a 1 μm soft magnetic tip in close proximity to an in-plane magnetized Ni80Fe20 (Permalloy) thin film. The dipole field of the tip generates a field well in the film directly below the tip, where spin waves may propagate while being excluded from the extended film. Our experimental results indicate detection of multiple spin wave modes as well as the extended film . A 1-D WKB approximation and micromagnetic modeling were used to interpret the FMRFM spectra. While the WKB approach yields only a qualitative understanding of the trapped modes, micromagnetic modeling of the shape and field- dependence of the spectra are in close agreement with our experimental results. In addition, we use micromagnetic modeling to generate two dimensional spatial maps of the localized spin wave modes. Fitting the lowest frequency spin wave mode to a Gaussian yields dimensions of 45.2 ± 0.3 nm in the applied field direction.
Citation: Physical Review Letters
Pub Type: Journals
nanomagnetics, magnetization dynamics, ferromangetic resonance, magnetic force microscopy