Direct Observation of Nuclear Spin Diffusion in Real Space

Eberhardt, Kai W.; Mouaziz, S; Boero, Giovanni; Brugger, Juergen; Meier, Beat H.

doi:10.1103/physrevlett.99.227603

Cited by 31 publications

(36 citation statements)

References 33 publications

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“…But the sensitivity of the persistent signal to tip-sample separation was larger than expected. Further understanding would require numerical simulations on a multi-scale model that can capture both the nanometer-scale quantum-mechanical interactions of out-of-equilibrium coupled electron and nuclear spins [22] in a large magnetic field gradient [15] and the diffusion of nuclear spins on the order of many microns [23]. While the most likely magnetization transfer mechanism is cross-effect DNP, it is worth keeping in mind that new DNP physics may be possible in the high magnetic field gradients present in an MRFM experiment.…”

Section: Resultsmentioning

confidence: 99%

Magnetic Resonance Force Microscopy Detected Long-Lived Spin Magnetization

et al. 2013

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Magnetic resonance force microscopy (MRFM), which combines magnetic resonance imaging with scanning probe microscopy together, is capable of performing ultra-sensitive detection of spin magnetization. In an attempt to observe dynamic nuclear polarization (DNP) in an MRFM experiment, which could possibly further improve its sensitivity towards a single proton spin, a film of perdeuterated polystyrene doped with a nitroxide electron-spin probe was prepared. A high-compliance cantilever with a 4 μm diameter magnetic tip was brought near the film at a temperature of 7.3 K and in a background magnetic field of ~0.6 T. The film was irradiated with 16.7 GHz microwaves while the resulting transient change in cantilever frequency was recorded in real time. In addition to observing the expected prompt change in cantilever frequency due to saturation of the nitroxide’s electron-spin magnetization, we observed a persistent cantilever frequency change. Based on its magnitude, lifetime, and field dependence, we tentatively attribute the persistent signal to polarized deuteron magnetization created via transfer of magnetization from electron spins. Further measurements of the persistent signal’s dependence on the cantilever amplitude and tip-sample separation are presented and explained by the cross-effect DNP mechanism in high magnetic field gradients.

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Section: Resultsmentioning

confidence: 99%

Magnetic Resonance Force Microscopy Detected Long-Lived Spin Magnetization

et al. 2013

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“…We have demonstrated chemical-shift imaging and its extension to two-dimensional spectroscopy using a magneticresonance force microscope. The spatial resolution, in this case about 2.0 mm in one dimension, can be significantly improved by reducing the size of the RF modulation during readout [26] and by using higher field gradients. [5] The experiments can be combined with Hadamard multiplexing schemes for the simultaneous acquisition of many slices in the spatial dimension, thus improving the signal-to-noise ratio.…”

Section: Methodsmentioning

confidence: 99%

One‐ and Two‐Dimensional NMR Spectroscopy with a Magnetic‐Resonance Force Microscope

et al. 2008

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Magnetic-resonance imaging (MRI) is a non-invasive method to generate three-dimensional images which have a high information content and is used in various fields, ranging from human medicine to material science. In microimaging, the spatial resolution of MRI can approach one micrometer in favorable systems.[1] Magnetic-resonance force microscopy (MRFM) [2][3][4] has opened an avenue for extending imaging to the nanometer range. Two-dimensional images mapping the spin density with 90 nm resolution have recently been obtained [5] and single-spin resolution, as reported for electrons, [6] can be envisioned. As with MRI, the MRFM method is not limited to the three spatial dimensions. Spectroscopic dimensions can be added, providing detailed chemical and structural information at the atomic level. Such experiments are routinely performed in clinical MRI and are denoted as MR spectroscopic imaging (MRSI) or chemical-shift imaging (CSI). [7] Spectral information, for example, from dipolar and quadrupolar interactions, has been used in MRFM experiments, in particular for generating new image contrast. [8][9][10] The most important interaction-the chemical shift-however, has not been employed in MRFM, because of the difficulty of combining high spatial with high spectral resolution. Mechanical detection of chemical shifts, without spatial resolution, has been demonstrated on millimeter-sized samples [11,12] with a setup where the field gradient vanishes at the sample position.MRFM provides an image of the objects spin density by using the spatial variation of the resonance frequency in a magnetic field gradient, in full analogy to MRI. In contrast to MRI, the magnetization is detected mechanically with a micromechanical cantilever that measures the force on the spin magnetic moment in a magnetic field gradient. Spatial resolution and detection sensitivity can be significantly improved over inductively detected MRI, [13] but the permanent presence of a gradient complicates spectroscopy. This problem is particularly true for chemical-shift spectroscopy, because the interaction has the same symmetry properties as the interaction with the magnetic field (gradient). In principle, it is conceivable to extract chemical-shift information in a gradient by recording zero-quantum spectra. [14] Other, related methods have also been discussed; [15,16] all of them, however, have limitations and the full information content of a regular NMR spectrum is not reproduced.An alternative approach, presented herein, is to temporarily move away the gradient source during the experiment (see Figure 1). The spectroscopic information can then be collected in a nearly homogeneous field. We shall demonstrate below that this method allows for chemical-shift imaging.

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“…2. The monotonic decrease of the background relaxation rate with increasing magnetic field is well described by simulations if we choose the (field independent) radius δ = 0.86 nm and D = 400 nm directions, respectively [28], and to the recently measured diffusion constant D = 620±70 nm 2 /sec in the same crystal by making use of magnetic resonance force microscopy [29].…”

Section: F Relaxation Ratesmentioning

confidence: 99%