Mona Bhukta1, Takaaki Dohi1, Maria-A. Syskaki1,2, Robert Frömter1, and
Mathias Kläui1
1 Institute of Physics, Johannes Gutenberg University Mainz, 55099 Mainz,
Germany
2 Singulus Technologies AG, Hanauer Landstrasse 107, 63796 Kahl am Main,
Germany
Magnetic skyrmions1 are twisted spin configurations, which can be stabilized by various interactions like the Dzyaloshinskii-Moriya interaction2,3, frustrated exchange, dipolar coupling, etc. However, skyrmions shows a non-zero skyrmion Hall angle when driven by current in a ferromagnetic (FM) material due to their topological nature4, which is detrimental for applications. In synthetic antiferromagnets (SAFs), two FM layers are coupled antiferromagnetically via the RKKY interaction, which cancels out the effect of the gyrotropic force on the skyrmion (as Q = 0), and hence skyrmions in both layers move as a composite structure without showing a skyrmion Hall effect. Recent observations of skyrmions in SAFs have opened the possibility for using skyrmions as a candidate for logic operations, data storage devices etc5. Here, we investigate different, more exotic spin textures in a SAF consisting of (CoFeB/Ir/CoFeB)n by using scanning electron microscopy with polarization analysis (SEMPA). SEMPA is a powerful surface-sensitive imaging technique that uses the spinpolarized secondary electrons emitted from a magnetic material and gives a twodimensional (2D) vector map of the in-plane magnetization. In this way, the chiral character of out-of-plane magnetized spin textures becomes accessible6. The unique feature of SEMPA is especially effective on SAFs, enabling us to investigate the formation of topological spin textures even in a “fully” compensated composition. We report high-resolved vortex- anti-vortex pairs in the SAF that are stable at zero magnetic fields and room temperature. Micromagnetic simulations of the investigated SAF stacks have been carried out to understand the way of stabilization for these exotic spin textures as well as to explore the possible emergence of three-dimensional (3D) spin structures in the SAF multilayer system.
References
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[2] I. Dzyaloshinskii, J. Phys. Chem. Solids 4, 241 (1958).
[3] T. Moriya, Phys. Rev. 120, 91 (1960).
[4] K. Litzius et al., Nat. Phys. 13, 170 (2017).
[5] T. Dohi et al., Nat. Commun. 10, 5153 (2019).
[6] B. Seng et al., Adv. Funct. Mater 31, 2102307 (2021)