The impact of morphology and hybridization on the Dzyaloshinskii-Moryia Interaction

The Dzyaloshinskii-Moriya interaction (DMI) gives rise to chiral magnetic structures, which include chiral spin chains and skyrmions. DMI requires broken inversion symmetry and can exist in the bulk of a material as well as at interfaces. We used Brillouin light scattering spectroscopy to determine the DMI strength from the non-reciprocal frequency-shift of spin waves [1]. In order to gain deeper insight into the underlying physics of DMI and explore ways on how to tune the DMI through interface modifications, we prepared multiple samples to study different aspects of the DMI [2], [3], [4]. Specifically, Cu/Co₉₀Fe₁₀, Pt/Co₉₀Fe₁₀ and Co₉₀Fe₁₀/Ta(t) series were in-situ oxidized for different times and subsequently capped to prevent further oxidation. Density functional theory (DFT) calculations have demonstrated that 2p-3d and 3d-5d hybridization and the associated charge transfer is important for DMI. We determined that the spectroscopic splitting factor g is correlated to the DMI in the Cu/Co₉₀Fe₁₀ and Pt/Co₉₀Fe₁₀ oxide sample series. This is an indirect confirmation of the DFT predictions. We introduced a Cu dusting layer at a CoFeB/Pt interface to modify the Heisenberg exchange locally. SQUID magnetometry shows that the Cu layer reduces the proximity magnetization in the Pt as well, which can be seen as a measure for the strength of the exchange coupling. This demonstrates the correlation between the exchange directly at the interface and the DMI. Finally, we irradiated CoFeB/Pt samples with He⁺ to modify the interface morphology and measured an increase of 20 % for the DMI before it decreases for the highest fluences.
Reference: [1] H. Nembach et al., Nature Physics 11, 825 (2015), [2] H. T. Nembach et al., Physical Review B 101, 020409(R) (2020), [3] M. Arora et al., Phys. Rev. B 101, 054421 (2020), [4] H.T. Nembach et al., arXiv:2008.06762