Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spin polarization contrast observed in GaAs by force-detected nuclear
  magnetic resonance   We applied the recently developed technique of force-detected nuclear
magnetic resonance (NMR) to observe 71Ga, 69Ga, and 75As in GaAs. The nuclear
spin-lattice relaxation time is 21$\pm$5 min for 69Ga at $\sim 5$ K and 4.6
Tesla. We have exploited this long relaxation time to first create and then
observe spatially varying nuclear spin polarization within the sample,
demonstrating a new form of contrast for magnetic resonance force microscopy
(MRFM). Such nuclear spin contrast could be used to indirectly image electron
spin polarization in GaAs-based spintronic devices.

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The categories of this paper are: math
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The categories of this paper are: hep-th
5
The categories of this paper are: gr-qc
24
The categories of this paper are: dg-ga
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The categories of this paper are: math-ph
12
The categories of this paper are: nucl-th
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The categories of this paper are: q-bio
1
The categories of this paper are: cs
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The categories of this paper are: q-fin
9
The categories of this paper are: nlin
27
The categories of this paper are: comp-gas
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The categories of this paper are: mtrl-th
26
The categories of this paper are: bayes-an
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The categories of this paper are: hep-ex
13
The categories of this paper are: quant-ph
11
The categories of this paper are: hep-lat