PROBING MAGNETIZATION DYNAMICS WITH NANOMETER SPATIAL RESOLUTION

Han-Jong Chia, Robert D. McMichael

 

In order for magnetic nanostructures to realize their potential in future devices such as bit patterned hard drives and magnetic random access memory (MRAM) it is vital that we understand their magnetization dynamics. Ferromagnetic resonance force microscopy (FMRFM) is a technique that combines the high spectral resolution of ferromagnetic resonance (FMR) and excellent spatial resolution of magnetic force microscopy (MFM) to probe magnetization dynamics of individual nanostructures with nanometer scale resolution. FMRFM derives its high spatial and spectral sensitivity through an ultrasensitive cantilever with a magnetic tip that responds to magnetic forces between the tip and sample.  A microwave waveguide excites the sample spins into precession and the resulting nonlinear change in static magnetization is detected by the cantilever. We have utilized a FMRFM to generate and detect localized spin wave modes in a Permalloy film with nanometer scale spatial resolution. The localized modes are the result of the strong dipolar field generated by the magnetic tip. Combining these results with micromagnetic modeling we show how FMRFM can be utilized to generate a 2-D map of magnetization dynamics within a magnetic nanostructure. In addition, we show measurements made on individual magnetic dots and stripes.