Long-lived frequency shifts observed in a magnetic resonance force microscope experiment following microwave irradiation of a nitroxide spin probe

Chen, Lei; Longenecker, Jonilyn G.; Moore, Eric W.; Marohn, John A.

doi:10.1063/1.4795018

Cited by 6 publications

(8 citation statements)

References 25 publications

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“…In a small spin ensemble, these random-sign, statistical "spin noise" fluctuations in magnetization greatly exceed the thermal equilibrium, Curie-law magnetization that one usually observes in a magnetic resonance experiment. Here we use dynamic nuclear polarization (DNP) to create Typeset by REVT E X arXiv:1601.07253v2 [cond-mat.mes-hall] 18 Feb 2016 hyperthermal nuclear spin magnetization in an MRFM experiment, with the goal of pushing the experiment out of the spin-noise limit.…”

Section: Introductionmentioning

confidence: 99%

“…MRFM experiment because of heating, and the optical nuclear polarization mechanism is restricted to semiconducting samples. Chen, Marohn, and coworkers observed a long-lived shift in the frequency of a magnettipped cantilever in an ESR-MRFM experiment carried out on a nitroxide-doped perdeuterated polystyrene film [18,19]. The size and buildup time of the frequency shift signal led them to hypothesize that it arose from a DNP enhancement of 2 H magnetization; they were unable to definitively prove this hypothesis, however, because they were not able to apply the radiowaves required to flip the 2 H nuclear spins.…”

Section: Introductionmentioning

confidence: 99%

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Dynamic nuclear polarization in a magnetic resonance force microscope experiment

Issac

Gleave

Nasr

et al. 2016

Phys. Chem. Chem. Phys.

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We report achieving enhanced nuclear magnetization in a magnetic resonance force microscope experiment at 0.6 tesla and 4.2 kelvin using the dynamic nuclear polarization (DNP) effect. In our experiments a microwire coplanar waveguide delivered radiowaves to excite nuclear spins and microwaves to excite electron spins in a 250 nm thick nitroxide-doped polystyrene sample. Both electron and proton spin resonance were observed as a change in the mechanical resonance frequency of a nearby cantilever having a micron-scale nickel tip. NMR signal, not observable from Curie-law magnetization at 0.6 T, became observable when microwave irradiation was applied to saturate the electron spins. The resulting NMR signal’s size, buildup time, dependence on microwave power, and dependence on irradiation frequency was consistent with a transfer of magnetization from electron spins to nuclear spins. Due to the presence of an inhomogenous magnetic field introduced by the cantilever’s magnetic tip, the electron spins in the sample were saturated in a microwave-resonant slice 10’s of nm thick. The spatial distribution of the nuclear polarization enhancement factor ε was mapped by varying the frequency of the applied radiowaves. The observed enhancement factor was zero for spins in the center of the resonant slice, was ε = +10 to +20 for spins proximal to the magnet, and was ε = −10 to −20 for spins distal to the magnet. We show that this bipolar nuclear magnetization profile is consistent with cross-effect DNP in a ~105 Tm−1 magnetic field gradient. Potential challenges associated with generating and using DNP-enhanced nuclear magnetization in a nanometer-resolution magnetic resonance imaging experiment are elucidated and discussed.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dynamic nuclear polarization in a magnetic resonance force microscope experiment

Issac

Gleave

Nasr

et al. 2016

Phys. Chem. Chem. Phys.

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“…With our new analysis we believe that it is possible that the reported long lived frequency shifts could be caused by nuclei polarized by interactions with these electron spins and that these electron spins are actually much shorter lived, as is reported for nitroxide-doped perdeuterated polystyrene films [19].…”

Section: Fig 3 (Color Online)mentioning

confidence: 75%

Spin-mediated dissipation and frequency shifts of a cantilever at milliKelvin temperatures

et al. 2015

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We measure the dissipation and frequency shift of a magnetically coupled cantilever in the vicinity of a silicon chip, down to 25 mK. The dissipation and frequency shift originates from the interaction with the unpaired electrons, associated with the dangling bonds in the native oxide layer of the silicon, which form a two-dimensional system of electron spins. We approach the sample with a 3.43 μm-diameter magnetic particle attached to an ultrasoft cantilever and measure the frequency shift and quality factor as a function of temperature and the distance. Using a recent theoretical analysis [J. M. de Voogd et al., arXiv:1508.07972] of the dynamics of a system consisting of a spin and a magnetic resonator, we are able to fit the data and extract the relaxation time T 1 = 0.39 ± 0.08 ms and spin density σ = 0.14 ± 0.01 spins per nm 2 . Our analysis shows that at temperatures 500 mK magnetic dissipation is an important source of noncontact friction.

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“…Plus, as the duration of a measurement increases, 1/f noise will increasingly become a limiting factor. T 1 times within the desired range for suitable proton samples are reported at low temperatures 24,38 . For very pure samples with long T 1 times, appropriate doping of the sample with impurities can be used to reduce the relaxation time 39 .…”

Section: Imaging Protonsmentioning

confidence: 94%

Feasibility of imaging using Boltzmann polarization in nuclear Magnetic Resonance Force Microscopy

de Wit,

Welker,

Wagenaar

et al. 2018

Preprint

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We report on Magnetic Resonance Force Microscopy measurements of the Boltzmann polarization of the nuclear spins in copper by detecting the frequency shift of a soft cantilever. We use the timedependent solution of the Bloch equations to derive a concise equation describing the effect of rf magnetic fields on both on-and off-resonant spins in high magnetic field gradients. We then apply this theory to saturation experiments performed on a 100 nm thick layer of copper, where we use the higher modes of the cantilever as source of the rf field. We demonstrate a detection volume sensitivity of only (40 nm) 3 , corresponding to about 1.6•10 4 polarized copper nuclear spins. We propose an experiment on protons where, with the appropriate technical improvements, frequencyshift based magnetic resonance imaging with a resolution better than (10 nm) 3 could be possible. Achieving this resolution would make imaging based on the Boltzmann polarization competitive with the more traditional stochastic spin-fluctuation based imaging, with the possibility to work at milliKelvin temperatures. II. METHODS A. Experimental setupWe improve on earlier measurements in our group on the nuclear spins in a copper sample. The setup and mea-

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Long-lived frequency shifts observed in a magnetic resonance force microscope experiment following microwave irradiation of a nitroxide spin probe

Cited by 6 publications

References 25 publications

Dynamic nuclear polarization in a magnetic resonance force microscope experiment

Dynamic nuclear polarization in a magnetic resonance force microscope experiment

Spin-mediated dissipation and frequency shifts of a cantilever at milliKelvin temperatures

Feasibility of imaging using Boltzmann polarization in nuclear Magnetic Resonance Force Microscopy

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