Curvilinear nanomagnetism

Broken magnetic symmetry is a key aspect in condensed matter physics and in particular in magnetism. It results in the appearance of chiral effects, e.g. topological Hall effect [1] and non-collinear magnetic textures including chiral domain walls and skyrmions [2,3]. These magnetochiral effects originate from an antisymmetric exchange interaction, the intrinsic Dzaloshinskii-Moriya interaction (DMI). At present, tailoring of DMI is done rather conventionally by optimizing materials, either doping a bulk single crystal or adjusting interface properties of thin films and multilayers.
A viable alternative to the conventional material screening approach can be the exploration of the interplay between geometry and topology. In the emergent field of curvilinear magnetism chiral effects are associated to the geometrically broken inversion symmetries [4]. Those appear in curvilinear architectures of even conventional materials. There are numerous exciting theoretical predictions of exchange- and magnetostatically-driven curvature effects, which do not rely on any specific modification of the intrinsic magnetic properties, but allow to create non-collinear magnetic textures in a controlled manner by tailoring local curvatures and shapes [5,6]. Until now the predicted chiral effects due to curvatures remained a neat theoretical abstraction.
Here, I present the very first experimental confirmation of the existence of the curvature-induced chiral interaction with exchange origin in a conventional soft ferromagnetic material [7,8]. It is experimentally explored the theoretical predictions, that the magnetisation reversal of flat parabolic stripes shows a two step process. By measuring the domain wall depinning field, we established that it is linked to the exchange-induced DMI and scales with curvature, that is in line with the theoretical prediction. Furthermore, the exchange-induced DMI strength can be tuned by changing the local curvature at the apex of parabola.

[1] N. Nagaosa, et al., Nature Nanotech. 8, 899 (2013).
[2] U. K. Rößler, et al., Nature 442, 797 (2006).
[3] A. Fert, et al., Nature Rev. Mat. 2, 17031 (2017).
[4] Y. Gaididei, et al., Phys. Rev. Lett. 112, 257203 (2014).
[5] J. A. Otálora, et al., Phys. Rev. Lett. 117, 227203 (2016).
[6] V. P. Kravchuk, et al., Phys. Rev. Lett. 120, 067201 (2018).
[7] O. M. Volkov et al., Phys. Rev. Lett. 123, 077201 (2019).
[8] O. M. Volkov et al., Physica Status Solidi – Rapid Research Lett. 13, 1800309 (2019).