Spin-contrast in non-contact SFM on oxide surfaces: Theoretical modelling of NiO(001) surface

Low-temperature non-contact scanning force microscopy (NC-SFM) is now being used to try and measure the exchange force with metal tips on magnetic oxide surfaces. This demanding test of NC-SFM has yet to prove successful and therefore it is important to use a theoretical model to predict the magnitude and range of the exchange force, and the best way to measure it. In this study, a simple model of a spin-polarized tip has been used to measure the difference in interaction over opposite spin Ni ions in an ab initio simulation of the NiO(001) surface. The contribution of the exchange force and the role of ion instabilities in the tip-surface interaction are calculated, and used as an example to predict whether spin-contrast over ions should be observable in NC-SFM experiments and how best to achieve this.