A deeper understanding of the Dzyaloshinskii-Moriya interaction in magnetic multilayers

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 as well as at interfaces. We use Brillouin Light Scattering spectroscopy (BLS) to determine the DMI from the non-reciprocal frequency-shift of Damon-Eshbach 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 sample series to study different aspects of the DMI, examples are: 1.) A Cu/Co₉₀Fe₁₀ and a Pt/Co₉₀Fe₁₀ sample series were in-situ oxidized for different times and subsequently capped to prevent any further oxidation. Density functional theory (DFT) calculations have demonstrated that the hybridization and the associated charge transfer is important for DMI at oxide interfaces. We determined that the spectroscopic splitting factor g is correlated to the DMI. This is an indirect confirmation of the theory predictions. [2] 2.) We introduced a Cu dusting layer at the interface between CoFeB and Pt to disrupt the Heisenberg exchange directly at the interface. SQUID magnetometry shows that the Cu dusting layer reduces the proximity magnetization in the Pt as well. The proximity magnetization is a direct result of the exchange coupling and can be seen as a measure for its strength. 3.) So far, most work on DMI has been carried out for highly symmetric interfaces. Low symmetry systems can have anisotropic DMI. We prepared a Pt/Fe(110) sample and found that the DMI is anisotropic with the strongest DMI along the [001] direction, which coincides with the magnetic easy axis. We compared the results for the DMI with DFT calculations.

[1] H.T. Nembach et al., Nature Physics 11, 825 (2015)
[2] H.T. Nembach et al., arXiv:1906.08395