Florian Pielmeier, Franz J. Giessibl
The spin order of the nickel oxide (001) surface is resolved, employing non-contact atomic force microscopy at 4.4 K using bulk Fe- and SmCo-tips mounted on a qPlus sensor that oscillates at sub-50 pm amplitudes. The spin-dependent signal is weak using Fe-tips, but clearly visible in raw image data for SmCo-tips. We attribute this to the increased magnetocrystalline anisotropy energy of SmCo, which stabilizes the magnetic moment at the apex. Atomic force spectroscopy on the Ni up, Ni down and O lattice site reveals a magnitude of the exchange energy of merely 1 meV at the closest accessible distance with an exponential decay length of \lambda_exc = 18 pm.
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http://arxiv.org/abs/1304.6515
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