Searching atomic spin contrast on nickel oxide (001) by force microscopy

The 001 surface of NiO, an antiferromagnet at room temperature, was investigated under ultrahigh vacuum conditions with frequency modulation atomic force microscopy. The antiferromagnetic coupling between ions leads to a spin superstructure on 001 surfaces. Exchange interaction between the probe of a force microscope and the NiO 001 surface should allow us to image spin superstructures in real space. The surface was imaged with three different probing tips: nonmagnetic W tips, ferromagnetic Co tips, and antiferromagnetic NiO tips—and atomic resolution was achieved with all three of them in various distance regimes and in several channels. Atomic resolution is obtained with all tips, but evidence for spin contrast is lacking although oscillation amplitudes in the angstrom regime have been used, where optimal signal-to-noise ratio is expected.