Engineering a Skyrmion Crystal in Ferromagnetic/Antiferromagnetic Bilayers Based on the Magnetic Frustration Mechanism

A magnetic skyrmion crystal (SkX), which is a topologically nontrivial swirling spin texture, has attracted attention as the origin of the emergent electromagnetic phenomena. One of the stabilization mechanisms of the SkX is the Dzyaloshinskii-Moriya (DM) interaction. Recently, other mechanisms to stabilize the SkX have been clarified, such as short-range competing exchange interactions [1] and effective long-range exchange interactions mediated by itinerant electrons [2]. These mechanisms without the DM interaction might give a keen insight to understand the origins of the SkXs discovered in centrosymmetric magnets, such as Gd2PdSi3 and GdRu2Si2 [3].

In the present study, we investigate another scenario to stabilize the SkX in a bilayer system without the DM interaction. Specifically, we consider a bilayer triangular lattice system with the ferromagnetic and antiferromagnetic layers. By performing the variational calculations and Monte Carlo simulations, we find that such a bilayer system can host the SkX under an external magnetic field and an easy-axis anisotropy depending on the strength of the interlayer exchange interaction. We also obtained the parameter conditions to stabilize the spiral state and the SkX with a finite-Q ordering vector in the strong coupling limit.

[1] T. Okubo et al., Phys. Rev. Lett. 108, 017206 (2012).

[2] S. Hayami et al., Phys. Rev. B 95, 224424 (2017).

[3] T. Kurumaji et al., Science 365, 914 (2019), N. D. Khanh et al., Nat. Nanotechnol. 15, 444 (2020).