Nanoscale scanning probe ferromagnetic resonance imaging using localized modes

Abstract

The discovery of new phenomena in layered and nanostructured magnetic devices is driving rapid growth in nanomagnetics research. Resulting applications such as giant magnetoresistive field sensors and spin torque devices are fuelling advances in information and communications technology, magnetoelectronic sensing and biomedicine. There is an urgent need for high-resolution magnetic-imaging tools capable of characterizing these complex, often buried, nanoscale structures. Conventional ferromagnetic resonance (FMR) provides quantitative information about ferromagnetic materials and interacting multicomponent magnetic structures with spectroscopic precision and can distinguish components of complex bulk samples through their distinctive spectroscopic features. However, it lacks the sensitivity to probe nanoscale volumes and has no imaging capabilities. Here we demonstrate FMR imaging through spin-wave localization. Although the strong interactions in a ferromagnet favour the excitation of extended collective modes, we show that the intense, spatially confined magnetic field of the micromagnetic probe tip used in FMR force microscopy can be used to localize the FMR mode immediately beneath the probe. We demonstrate FMR modes localized within volumes having 200 nm lateral dimensions, and improvements of the approach may allow these dimensions to be decreased to tens of nanometres. Our study shows that this approach is capable of providing the microscopic detail required for the characterization of ferromagnets used in fields ranging from spintronics to biomagnetism. This method is applicable to buried and surface magnets, and, being a resonance technique, measures local internal fields and other magnetic properties with spectroscopic precision.

Spectroscopy and Imaging of Edge Modes in Permalloy Nanodisks

“…2. In contrast to some of the previous work [33][34][35][36] where the spin waves in the films were localized by the strong tip fields, this tip has a much weaker stay field due to its small size and no tip-localized modes have been observed. The tip is typically lifted 50 nm off of the sample surface.…”

“…X-ray microscopy based on magnetic circular dichroism also provides dynamic magnetic imaging [18][19][20] with resolution as fine as 25 nm. [18] In parallel, ferromagnetic resonance force microscopy (FMRFM) [21][22][23][24] has been developed and proven to be a useful tool for various areas in magnetic dynamics, such as spin wave dynamics in confined structures [22,[25][26][27][28][29][30], spin-transfer torque device dynamics [31], defect detection in an array [32], and spin wave localization [33][34][35][36]. With spin waves localized by the stray field from the FMRFM tip, a resolution of 200 nm has been reported [33].…”

Engineering the Spectrum of Dipole Field-Localized Spin-Wave Modes to Enable Spin-Torque Antidamping

“…Comparison of ST-FMR spectra in the case of the larger, 5 µm, Ni particle on the 3 µm × 3 µm strip and 3 µm × 6 µm strip, shown in Fig 2(a) and (b) with those from the bare 3 µm-width strip (in the figure inset) reveals an additional peak on the higher field side as expected for localized modes [12][13][14]. We performed micromagnetic modeling [12,[25][26][27] Fig.…”

“…Localized spin wave modes, confined by the strongly inhomogeneous dipole magnetic field of a nearby scanned micromagnet, have been demonstrated in ferromagnetic resonance force microscopy (FMRFM) for both imaging and studies of magnetization dynamics at * hammel@physics.osu.edu the nanoscale [12][13][14]. Using magnetic field-localization to define the eigen-modes of a spin-Hall oscillator offers a new approach to the study of spin-Hall torque physics, and multi-mode interactions.…”

Nonlinear ferromagnetic resonance shift in submicron Permalloy ellipses

“…The spectra are measured using ferromagnetic resonance force microscopy (FMRFM) [14][15][16][17][18][19][20] , which has a number of advantages for these measurements. First, FMRFM has the ability to measure single structures.…”