SPICE Workshop on Spin textures: Magnetism meets Plasmonics, July 23rd - 25th 2024
Kirsten von Bergmann
Complex magnetic order arises due to the competition of different magnetic interactions. Often the dominant interaction is the isotropic pair-wise exchange between neighboring atomic magnetic moments. With additional sizable contributions from the Dzyaloshinskii-Moriya-interaction or from the exchange between more distant neighbors any length-scale spin texture ranging from ferromagnetic to antiferromagnetic order can form. Spin-polarized scanning tunneling microscopy (SP-STM) is well suited to investigate complex magnetic order down to the atomic scale [1].
Recently we have investigated prototype antiferromagnetic states in hexagonal magnetic layers, ranging from collinear via coplanar to non-coplanar [1,2,3]. The formation of the magnetic ground state is governed by higher-order exchange interactions as they can favor either uniaxial states or multi-q states depending on their sign. In such systems we have experimentally observed a new type of antiferromagnetic domain wall with perpendicularly oriented nearest neighbor magnetic moments in its center [4] and more complex magnetic order where several domain walls meet. Higher-order magnetic interactions can also induce nanoscale two-dimensional nanoskyrmion lattices at zero magnetic field or stabilize their collinear mosaic state counterparts, reminiscent of nano-scale ferrimagnets [5]. The balance between these different magnetic interactions creates endless possibilities for complex magnetic order, either as magnetic ground state or at magnetic defects such as domain walls. Some of them give rise to topological orbital moments and are also expected to show an interesting response to currents.
[1] K. von Bergmann et al., J. Phys.: Cond. Mat. 26, 394002 (2014).
[2] J. Spethmann et al., Phys. Rev. Lett. 124, 227203 (2020).
[3] F. Nickel et al, Phys. Rev. B 108, L180411 (2023).
[4] J. Spethmann et al., Nature Commun. 12, 3488 (2021).
[5] M. Gutzeit et al., Nature Commun. 13, 5764 (2022).