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Single-vortex pinning and penetration depth in superconducting<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">NdFeAsO</mml:mi><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">F</mml:mi><mml:mi>x</mml:mi></mml:msub></mml:math>
We use a magnetic force microscope (MFM) to investigate single-vortex pinning and penetration depth in NdFeAsO1−xFx, one of the highest-Tc iron-based superconductors. In fields up to 20 G, we observe a disordered vortex arrangement, implying that the pinning forces are stronger than the vortex-vortex interactions. We measure the typical force …