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

TL;DR

This study demonstrates the use of frequency modulation atomic force microscopy to image and analyze spin superstructures on NiO (001) surfaces, revealing weak spin contrast detectable mainly in Fourier space.

Contribution

It provides experimental evidence of atomic-scale spin contrast on NiO surfaces using various AFM tips, highlighting the conditions for optimal magnetic imaging.

Findings

Atomic resolution achieved with different AFM tips.

Weak spin contrast observed primarily in Fourier space.

Optimal imaging conditions identified with NiO tips and specific oscillation amplitudes.

Abstract

The (001) surface of NiO, an antiferromagnet at room temperature, was investigated under ultra-high vacuum conditions with frequency modulation atomic force microscopy (FM-AFM). 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 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. Evidence for spin contrast was obtained in experiments that utilize NiO tips and oscillation amplitudes in the \AA-regime, where optimal signal-to-noise ratio is expected. The spin contrast is weaker than expected and only visible in Fourier space images.