Paramagnetic and ferromagnetic resonance imaging with a tip-on-cantilever magnetic resonance force microscope

Abstract

A magnetic resonance force microscope with a “tip-on-cantilever” configuration was used to compare imaging characteristics of paramagnetic and ferromagnetic samples. Three-dimensional electron paramagnetic resonance (EPR) imaging of diphenylpicrylhydrazil (DPPH) particles was accomplished by scanning the sample in two dimensions while stepping an external field. The EPR force map showed broad response reflecting the size and shape of the sample, allowing a three-dimensional real-space magnetization image to be successfully reconstructed. In contrast to the EPR case, ferromagnetic resonance imaging of a micron-scale yttrium iron garnet sample showed no significant line broadening despite the strong field gradient (∼10 G/μm). Two-dimensional force maps revealed spatial dependence of magnetostatic and magnetoelastic modes.

Advances in mechanical detection of magnetic resonance

“…47 Even the first demonstration of "magnet on tip" MRFM, though a remarkable development, employed a large enough magnetic tip that the gradient was not much larger than in early experiments. 48 By gluing magnets as small as 5 m to commercial silicon nitride cantilevers and operating the cantilevers within a few tens of nanometers of a surface, Bruland et al 49 were able to detect electron spin resonance using magnetic field gradients as large as 2.5ϫ 10 5 T / m. The sensitive slice in these experiments was only a nanometer thick, on the order of molecular dimensions. Remarkably, at a temperature of 77 K, Bruland et al achieved a magnetic moment sensitivity of ϳ200 e / ͱ Hz.…”

“…They concluded that the tip magnetic moment must be minimized and that the applied polarizing field must be highly uniform. 131,132 Magnet-on-tip cantilever detection of ESR was demonstrated by Wago et al 48 These experiments, though successful, indicated that operating the magnetic-tipped cantilever in high magnetic field also leads to a catastrophic increase in cantilever friction. This effect was not present in the magneton-cantilever ESR experiment of Bruland et al because the polarizing field was zero and the tip field was used to polarize the sample.…”

“…94,[96][97][98]100 The influence of the magnetic tip on the ferromagnetic resonances in these experiments has required careful analysis. 48,95,104,106 Variable-temperature ferromagnetic resonance measurements have recently been demonstrated. 107 Other potential applications of magnetic resonance force microscopy that have been explored experimentally include magnetic field mapping using ESR ͑Ref.…”

“…Ferromagnetic resonance can be registered as either a force 48,[91][92][93][94][95][96][97][98][99][100][101][102][103][104] or a torque 105 acting on a cantilever. New infor-mation about magnetic damping can be obtained by combining microwave susceptibility measurements, which probe transverse magnetization, with MRFM measurements, which probe longitudinal magnetization.…”

Nonclassical States of Light and Mechanics

“…following Ref. [48], where a Nickel sphere was attached to the cantilever, whose Q could then be changed by 3 orders of magnitude by applying a magnetic field.…”