  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 hardly detectable with Fe-tips. In contrast, SmCo-tips
yield a height contrast of 1.35 pm for Ni ions with opposite spins. SmCo tips
even show a small height contrast on the O atoms of 0.5 pm within the 2x1 spin
unit cell, pointing to the observation of superexchange. 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.
