Technique Images Magnets Using High Precision FMR

This article originally appeared at medGadget.com, part of the HCPLive network.

Researchers from Ohio State University just published a paper in Nature describing a new MRI technique that is capable of imaging the insides of micro-scale magnets, providing the highest ever resolution of magnetic fields. The technology, known as scanned probe ferromagnetic resonance imaging, promises the development of small scale biosensors that depend on tiny magnets to do their work.

From the article abstract:

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.

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