Quantifying exchange forces of non-collinear magnetic structures on the atomic scale

Chiral magnets, e.g. magnetic skyrmions, are hot candidates for nano-scale magnetic storage. These magnetic structures are stabilized by an interplay between competing exchange interactions at the atomic-scale. So far, spin-polarized scanning tunneling microscopy (SP-STM) has achieved great success in investigating the magnetization of such structures [1], but faces a number of limitations in being able to directly detect the underlying exchange forces, as well as to delineate between structural and electronic contributions to the spin-polarized density of states. During the last decade, magnetic exchange force microscopy (MExFM) has shown its potential to resolve antiferromagnetic atomic-scale structures [2], but so far, this method has been scarcely applied to quantify magnetic exchange forces at the atomic scale.

To account for these shortcomings, we developed the combination of SP-STM and MExFM (for short SPEX) based on the tuning fork design. In my talk I will discuss how SPEX can contribute to understand non-collinear atomic-scale magnetism. We have recently used SPEX to resolve the nano-skyrmion lattice in a monolayer Fe/Ir(111) [3] as well as to independently determine the structural corrugation from the electronic and magnetic contributions for bi-layers of Fe/Ir(111) [4]. I will further show that SPEX can resolve the magnetic noncollinearity of the antiferromagnetic spin spiral in a monolayer Mn/W(110). Using distance-dependent spectroscopy together with first-principles calculations, we probe the interplay between different magnetic exchange interactions, i.e. antiferromagnetic and Zener-type ferromagnetic exchange mechanisms.

References:

[1] S. Heinze et al., Nat. Phys. 7, 713 (2011).

[2] U. Kaiser et al., Nature 446, 522 (2007).

[3] N. Hauptmann et al., Nano Lett. 17, 5660 (2017).

[4] N. Hauptmann et al, Phys. Rev. B 97, 100401(R) (2018).