Magnetic-field gradient in nanostructures detected by nuclear spins

Based on standard nuclear magnetic resonance (NMR) technique, we have succeeded in observing local magnetic field produced by a micromagnet Ni₄₅Fe₅₅ (with 400 nm thickness), which was sputtered on an Al layer (with 20 nm thickness). By improving the sensitivity of our NMR spectrometer, we were able to clearly observe Al-NMR signals, which are confirmed to come from Al nuclei in the 20 nm layers. The analysis of the NMR spectra yielded the local magnetic field of +0.17 (-0.20) T, whose sign is consistent with the perpendicular (parallel) direction of the applied magnetic field to the sample. In addition, using finite element method, we have succeeded in reproducing both the value and the sign of the local magnetic field without any fitting parameters, which gave us the gradient of the local magnetic field as 0.38 Tesla/μm.